The Yukon Ecosystem and Landscape Classification · PDF fileThe Yukon Ecosystem and Landscape Classification (ELC) ... We also discuss factors that influence ecosystems at the macroclimate,

The Yukon Ecosystem and Landscape Classification (ELC) Framework:

Overview and Concepts

February 22, 2011

INTERIM DRAFT for REVIEW

Prepared by Nadele Flynn and Shawn Francis with assistance of Yukon ELC Working Group

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Yukon ELC Framework – Interim Draft for Review February 22, 2011

PREFACE

This Draft Yukon ELC Framework document is intended for discussion and review by Yukon land and resource managers. It provides an overview of the major concepts and components of the Yukon ELC Framework, describes how the different components integrate, and terminology used. A companion technical document will be developed at a future date describing detailed ecosystem classification and mapping methods and conventions. ACKNOWLEDGEMENTS Yukon has a long history of ELC-related activities, including vegetation, forest cover, surficial geology and bedrock geology mapping. The current concepts for the Yukon ELC Framework evolved over a period of approximately ten years. Key individuals in territorial and federal government departments realized the potential and need for such a system to sustainably manage Yukon ecosystems and biological diversity. The funding and opportunities created by these individuals provided opportunities for ELC projects to occur, leading to advances in ELC concepts and awareness. Progress made to date has only been possible through the dedicated and valuable support and input of many different people, groups and practitioners. The following individuals have made significant contributions to the development of the Yukon ELC Framework:

• John Meikle, Kwanlin Dun First Nation, Whitehorse • John Grods, Makonis Consulting, Kelowna • Karen McKenna, Cryogeographic Consulting, Whitehorse • Val Loewen, Habitat Coordinator, Yukon Environment • Nancy Steffen, formerly Applied Ecosystem Management Ltd., Whitehorse • Fritz Mueller and Ian Church, formerly Environment Directorate, Indian and

Northern Affairs Canada, Whitehorse • Silvatech Consulting Group, Salmon Arm

This document is currently under review by the Ecological and Landscape Classification – Technical Working Group.

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SUMMARY

Yukon’s diversity of ecological communities reflect a macro-and micro climatic regime that is intertwined with the influence of glacial history, topography and soil development, that endure over time. A climatic approach to classifying ecological communities occurring on enduring sites relies on vegetation communities as a reliable diagnostic tool for classification at all levels of the hierarchy. Yukon’s climatically-based Ecological and Landscape Classification (ELC) framework can facilitate: mapped distribution and abundance of ecosystems, monitoring for change over time, assess ecosystem productivity and ability to recover after disturbance. This report provides an overview of major components and ecological concepts of Yukon’s ELC Framework. Previous interim framework documents, workshop outcomes, and the advice of ecosystem mapping specialists are integrated into this document. Section 1 provides a background and premise for ecosystem classification in Yukon, including relevance to management and planning. Guiding principles developed over prior ELC workshops and previous framework papers are also presented. Section 2 defines ecosystems and ecosystem and landscape classification and describes components of the ecological classification including how ecosystem classifications are mapped. We also discuss factors that influence ecosystems at the macroclimate, microclimate and enduring site level. Section 3 describes the Yukon Ecosystem Classification framework and methods for classifying ecosystems within a bioclimate framework using reference sites that are defined as zonal. The report concludes with a list of cited references, a table of potential terrain descriptors for ecosystem labels (Appendix 1) and an expanded discussion of zonal concepts (Appendix II).

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TABLE OF CONTENTS

Preface................................................................................................................................. 2 Summary ............................................................................................................................. 3 Table of Contents................................................................................................................ 4 List of Tables ...................................................................................................................... 5 List of Figures ..................................................................................................................... 6 1. Introduction................................................................................................................. 7

1.1 Guiding Principles .............................................................................................. 8 2. Ecosystem Components .............................................................................................. 8

2.1 Ecosystem Classification .................................................................................... 9 2.2 Ecosystem Mapping............................................................................................ 9 2.3 Factors Influencing Ecosystems ....................................................................... 10

2.3.1 Climate...................................................................................................... 10 2.3.2 Soil and Topography................................................................................. 13 2.3.3 Disturbance ............................................................................................... 15

3. Yukon ELC Framework............................................................................................ 16 3.1 Vegetation Classification .................................................................................. 19 3.2 Bioclimate Classification .................................................................................. 20

3.2.1 Zonal Concepts ......................................................................................... 20 3.2.2 Bioclimate Region .................................................................................... 22 3.2.3 Bioclimate Zone........................................................................................ 22 3.2.4 Bioclimate Subzone .................................................................................. 22 3.2.5 Bioclimate Subzone Variant ..................................................................... 23

3.3 Local and Broad Ecological Classification....................................................... 23 3.3.1 Local Ecosystems...................................................................................... 23 3.3.2 Broad Ecosystems..................................................................................... 31 3.3.3 Ecosystem Phase....................................................................................... 32 3.3.4 Naming Conventions ................................................................................ 35

4. References................................................................................................................. 37 Appendix 1 – Potential Terrain Descriptors for Ecosystem Labels.................................. 40 Appendix II – Concept of zonal........................................................................................ 42

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LIST OF TABLES

Table 1. Nested relationship between Yukon ELC Framework components, showing conceptual ecosites and broad ecosystems for the Alpine bioclimate zone of South-central Mountains and Plateau bioclimate region. .............................. 17

Table 2. Provisional bioclimate regions of Yukon. ......................................................... 24

Table 3. Provisional bioclimate zones of Yukon. ............................................................ 26

Table 4. Broad ecosystem classes for the boreal (BOL and BOH) and taiga (TAW and TAS) bioclimate zones of Yukon. Similar tables would be created for Alpine and Subalpine bioclimate zones. .................................................................... 32

Table 5. Ecosite phase vegetation structural stage descriptors (BC Ministry of Forests LMH 25, Describing Terrestrial Ecosystems in the Field. 1998).................. 34

Table 6. Provisional seral stages used for describing Yukon forest ecosite phases. ....... 35

Table 7 Broad ecosystem naming conventions for the boreal (BOL and BOH) and Taiga (TAW and TAS) bioclimate zones of Yukon. *Similar tables would be created for Alpine, Subalpine bioclimate zones............................................. 36

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LIST OF FIGURES

Figure 1 Conceptual model showing the integration of climate, terrain, soil and vegetation into an ecosystem unit. ................................................................... 7

Figure 2 Derived climate normals for Yukon. Mean annual temperature (2a) and mean annual precipitation (2b). Source: Climate Data for Western North America, USDA Forest Service, Rocky Mountain Research Station, http://forest.moscowfsl.wsu.edu/climate/current/ .......................................... 12

Figure 3 Distribution of major soil types (orders) in the Yukon. Adapted from White et al. (1992) (Smith 2004) .................................................................................. 13

Figure 4 Continuous, extensive discontinuous and sporadic discontinuous permafrost zones. Numbers indicate locations of ground temperature profiles in another figure. (Burn 2004)......................................................................................... 14

Figure 5. Nested relationship between the classification systems that integrate into the Yukon Ecological and Landscape Classification........................................... 18

Figure 6. Provisional bioclimate regions of Yukon representing macroclimatic patterns in Yukon............................................................................................................. 25

Figure 7 Provisional bioclimate zones (Tundra, Alpine, Subalpine, Boreal High, Boreal Low, Shrub Taiga and Wooded Taiga) with provisional bioclimate regions superimposed. Bioclimate zones have not been delineated within the white areas of the map. ............................................................................................ 27

Figure 8. Example of a toposequence for organizing ecosites within a bioclimate subzone........................................................................................................... 29

Figure 9. Example of edatopic grid from Ecosites of Northern Alberta (Beckingham and Archibald 1996). ............................................................................................ 30

Figure 10. Suggested process for identifying broad ecosystems. .................................... 31

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1. INTRODUCTION

Describing and mapping Yukon’s ecological diversity is an important undertaking that benefits all resource management activities. Ecosystems arise out of the spatial and temporal interaction between abiotic and biotic factors at multiple scales. Ecosystem classification and mapping refers to an integrated approach to land survey in which areas or units of land are classified and mapped according to their ecological similarity (Rowe 1979). The aims of ecosystem classification and mapping are to provide primary information on the biological and physical characteristics of various landscape components in order to facilitate a range of interpretations and assist in sustainable management (Rowe and Sheard 1981).

The Yukon ELC Framework proposes a classification system that describes ‘ecosystems’ through the integration of soils/surficial geology, terrain, vegetation and climate patterns at regional, broad and local scales. This integration is shown conceptually in Figure 1. The classification system is based on principles developed in other jurisdictions, but has been modified to fulfill the guiding principles established for Yukon. The Yukon ELC Framework also distinguishes the related but independent processes of classification and mapping. A classification includes the criteria for distinguishing classes within a particular level of a given hierarchy; it does not deal with how to map those classes.

Figure 1 Conceptual model showing the integration of climate, terrain, soil and vegetation into an ecosystem unit. This report describes the major components, ecological concepts and terminology of the Yukon ELC Framework. Drawing on a variety of sources, this document attempts to integrate interim ELC framework documentation, previous workshop outcomes, and the advice of ecosystem mapping specialists. This document is not intended to be a methodology guidebook; it provides a general overview of the Yukon ELC Framework. A separate technical document, prepared at a future date, will describe detailed ecosystem classification and mapping methods.

Ecosystem Unit

Climate Terrain

Vegetation Soil

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1.1 GUIDING PRINCIPLES

The guiding principles for the Yukon ELC Framework were developed with input from many different Yukon land and resource management agencies. The Yukon ELC Framework has been designed with consideration of the following criteria. The Yukon ELC Framework should:

• be based on valid ecological principles and methods;

• be developed through the use of existing data, knowledge and expertise;

• be cost-effective to develop, implement and maintain;

• be designed for mapping applications;

• provide an integrated classification and mapping system that provides adequate information for most Yukon land and resource management activities;

• be applied at both regional and local (site-level) scales;

• describe both forested and non-forested ecosystems (including wetlands), and be able to incorporate future aquatic and/or riparian classification systems as they are developed;

• at the local scale, describe both the current and vegetation potential of a site;

• be adaptable and flexible to incorporate new information and technologies as they become available; and,

• integrate and be consistent with national and international ELC systems, to the extent possible.

2. ECOSYSTEM COMPONENTS

The broad meaning of the term “ecosystem” is any natural system in which biotic and abiotic components interact, and which can exist at any spatial scale (Ponomarenko and Alvo 2001). Several popular definitions include:

• “a self-regulating association of living plants, animals and their non-living physical and chemical environment”;

• “the sum of the plant community, animal community and environment in a particular region or habitat”; and

• “any community of interacting organisms, including their physical and chemical environment, energy fluxes, and the types, amounts and cycles of nutrients in the various habitats within the system”.

While definition of scale and ecological process differ slightly, the concept of integration between biotic and abiotic components is central to all definitions.

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For the purposes of ecosystem classification, ecosystems are characterized in the Yukon ELC Framework by:

“An observable unit of the landscape with relatively uniform vegetation (a plant community) occurring on relatively uniform soil conditions”.

Ecosystems may be scale independent but the concept of “observable at meaningful management and mapping scales” is central to the definition used in the Yukon ELC Framework. Within this definition, no size or scale is inferred.

2.1 ECOSYSTEM CLASSIFICATION

Ponomarenko and Alvo (2001) in Perspectives on Developing a Canadian Classification of Ecological Communities describe the scientific discipline of classification as an “element-based classification” that places different species into different groups based on well-defined criteria. Classification is also the process of using an orderly, well-defined process or criteria to “classify” or place different elements into various “classes”. A class is defined by criteria that separate it from other classes; the name of the class usually reflects the name features of the criteria (e.g. coniferous forest). Elements or elementary units (units for short), are the classes of the lowest hierarchical level in a classification. Describing all potential elements is the major goal of classification. We will continue to use the term class and element/unit when referring to the ecological classification system described in this document. An excellent summary about the history of ecosystem classification and mapping in Canada is provided by Ponomarenko and Alvo (2001).

2.2 ECOSYSTEM MAPPING

Ecosystem mapping, within the context of this paper, is the process of applying methods and guidelines to make classification classes spatially explicit. An ecosystem map may combine one or several classifications together usually, but not always, adhering to one level of the classification(s). The map legend, which tells the reader what is being mapped, is not equivalent to the corresponding classification (Ponomarenko and Alvo 2001). The map legend is only a snapshot of the classification at one level and only those classes that can be mapped at a given scale and area. Approaches to ecosystem mapping, at any map scale, can be split into two groups: predictive modelling and direct interpretation. A modelling approach to ecosystem mapping relies on combining existing abiotic and biotic map layers and information in such a way that ecosystem classes can be predicted within an acceptable degree of accuracy. An interpretive approach relies on expert-driven interpretation of remotely-sensed imagery (usually low altitude aerial photography) to delineate and identify ecosystem classes. There are pros and cons and typical situations where one approach may yield better end-results than the other in terms of cost and spatial/classification accuracy. Ecosystem mapping is not described further in this paper but ensuring that

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classes are mappable is an underlying criterion of the Yukon ELC Framework classification.

2.3 FACTORS INFLUENCING ECOSYSTEMS

Climate and enduring features are important components of Yukon’s ELC framework. Climate, soils, topography, and disturbances shape the development of landforms and associated ecosystems to produce recognizable and repeatable vegetation patterns through space and time. Each of these factors and their significance to ecological processes are discussed below in general and within a Yukon context. Please refer to Ecoregions of Yukon (Smith et al. 2004) for detailed descriptions of Yukon’s climate, physiography, geology, soils and hydrology—much of the text below is adapted from this source.

2.3.1 Climate

Climate is the cumulative long-term effect of weather or, in other words, the distribution of heat and moisture (temperature and precipitation). A macroclimate is the climate of a relatively large geographic area. Macroclimates are influenced by physiography, elevation and latitude. Microclimates are localized climatic patterns of heat and moisture that are different from the surrounding area. Examples of factors that drive the formation of microclimates are proximity to large bodies of water, topographic changes in slope or aspect, or valley systems that experience temperature inversions. Below we discuss factors that result in patterns of temperature and precipitation at both macro- and microclimate scales in Yukon.

Temperature patterns Temperature and precipitation are driven by elevation, latitude, and orographic barriers resulting in characteristic macro- and microclimatic patterns throughout Yukon. Compared to the precipitation regime, Yukon’s temperature regime is complex due to the wide range of elevation and latitude interrelationship (Figure 2a,b). Mean annual temperatures in Yukon are influenced by both elevation and latitude. Temperature normally decreases with increasing elevation at a rate of 6oC per 1,000m. This change, known as the lapse rate, is the major factor that determines the distribution of bioclimate zones in mountainous areas. “The Yukon lies between latitudes 60°N and 70°N. At these latitudes, the hours of possible sunshine in the southern Yukon range from 19 hours per day on June 21 to less than 6 hours per day on December 21.” “The angle of the sun above the horizon is lower over the Yukon than in southern Canada, therefore, the solar energy available to the Yukon averages only 60% of that of extreme southern Canada. When microclimates are being evaluated, it should be recognized that slopes facing to the east, south or west are more perpendicular to the sun’s rays and therefore absorb more of the sun’s heat.” (Wahl 2004) With increasing latitude and distance from the Pacific Ocean, temperatures decrease by approximately 5 to 10oC for every 500 to 1,000 km of distance travelled northward. With

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the exception of some very localized areas along the Yukon – British Columbia border, all areas of Yukon have mean annual temperatures below 0oC (Figure 2a). The valley systems around Whitehorse, Teslin and the Haines Road are, on average, the warmest areas of Yukon. (Wahl 2004) Mountainous areas experience seasonal microclimates in the winter as days shorten. “Cold air will develop over all surfaces, although on mountain slopes this air, being relatively heavy, will slide into the valley bottoms. The result is a reversal of the normal lapse rate, known as an inversion. Air temperature, instead of being cooler with increased elevation, will remain isothermal through a vertical portion of the atmosphere or, in some cases; the temperature will actually rise with increased elevation. In addition, inversions may be caused at lower elevations by very cold air masses from the Arctic. This arctic inversion is generally in place over the Yukon from late October to early March and is at its extreme in January.” “These inversions can be temporarily destroyed by strong winds mixing the warm air from above into the colder valley floors. This occurs most frequently over the southwestern Yukon.” (Wahl 2004).

Precipitation patterns The relationship between orographic barriers, elevation and precipitation patterns is strong (Burn 2004). The main source of moisture for Yukon is the Pacific Ocean. In a typical storm system, southerly winds force air masses to rise over the St. Elias and Coast Mountains of southwest Yukon. Most of the moisture is precipitated on southern and western slopes of this mountain barrier (Figure 2b). The air then descends and dries, resulting in a rain shadow over the Kluane and Southern Lakes regions. This pattern is then repeated, to a lesser degree, in the Pelly and Cassiar mountains of southeast Yukon. The Mackenzie and Selwyn mountains of central and eastern Yukon also act as further orographic barriers.

“Generally, precipitation increases with elevation with a maximum near 2,000 m asl. A review of Yukon data comparing precipitation amounts with elevation, allows a crude approximation of an increase of 8% for every 100-m increase of elevation, up to a maximum at 1,500 to 2,000 m asl and then a slow decrease with increased elevations.” (Wahl 2004)

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2a) 2b) Figure 2 Derived climate normals for Yukon. Mean annual temperature (2a) and mean annual precipitation (2b). Source: Climate Data for Western North America, USDA Forest Service, Rocky Mountain Research Station, http://forest.moscowfsl.wsu.edu/climate/current/

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2.3.2 Soil and Topography

Soils (including permafrost as a special case) are influenced by climatic patterns albeit at different time scales and well as geologic history. Topography in turn influences soil development and macro- to microclimates. Compared to day to day changes in weather and successional changes in vegetation through disturbance, soil and topography are relatively stable and enduring features through time. Site types (soil and topography) that represent enduring features when combined with macro and micro climates are powerful ecosystem drivers.

Soils “Soils form at the earth’s surface as the result of interactions between climate, geologic parent material, time, relief and living organisms. Soils in the Yukon have formed under a cold, semi-arid to moist subarctic climate on a range of geologic materials. The result is that most Yukon soils are only mildly chemically weathered, and many contain near-surface permafrost. Because much, but not all, of the territory has been glaciated in the past, some soils have formed directly over local bedrock, whereas others have formed in glacial debris of mixed lithology. In mountainous terrain, soils form on a range of slope debris, called colluvium, and are subject to ongoing mass wasting and erosion.” (Smith 2004) “Within the Canadian System of Soil Classification, the most common soil orders in the Yukon are the Brunisols - mildly weathered forest soils, the Regosols - unweathered alluvial and slope deposits, and the Cryosols - soils underlain by near-surface permafrost. Each of these “soil orders” is associated with a specific environment created by the soilforming factors.” (Smith 2004) Major soil types in Yukon are shown in Figure 3.

Figure 3 Distribution of major soil types (orders) in the Yukon. Adapted from White et al. (1992) (Smith 2004)

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“Parent materials, combined with local and regional climate patterns (temperature, precipitation) have influence on soils formation. For example, areas dominated by soils formed under a semi-arid climate on calcareous glacial parent materials tend to be alkaline and belong to the Eutric Brunisol great group of soils (Ruby Ranges, Yukon Southern Lakes and Yukon Plateau-Central ecoregions). Milder summer temperatures, higher precipitation and finer-textured parent materials result in soils containing subsurface clay accumulations. These belong to the Grey Luvisol great group of soils. (e.g valleys and basins of the Liard Basin and Hyland Highland). Where parent materials are coarse textured, Eutric Brunisols are formed.” (Smith 2004)

Permafrost “Permafrost is defined as ground that remains at or below 0°C for two or more years. Continuous permafrost covers the Taiga Ecozone of northern Yukon. Figure 4 shows areas of continuous, extensive discontinuous and sporadic discontinuous areas of Yukon. Permafrost occurs in all of the Yukon’s ecoregions, but its thickness and the proportion of ground it underlies increases northwards. All terrain, except rivers and lakes, is underlain by perennially frozen ground in the northern Yukon, but the scattered permafrost of the southern Yukon is found under less than 25% of the ground surface. Permafrost terrain comprises a seasonally thawed active layer, underlain by perennially frozen ground. The active layer is the layer of ground above the permafrost that thaws in the summer and freezes in the winter.” (Burn 2004)

Figure 4 Continuous, extensive discontinuous and sporadic discontinuous permafrost zones. Numbers indicate locations of ground temperature profiles in another figure. (Burn 2004)

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“Permafrost derives its ecological significance from cold ground temperatures within the active layer, and the influence of a relatively impermeable frost table on drainage. Moisture- and frost-tolerant species, such as black spruce and mosses, are often associated with permafrost, while deciduous forests usually grow in drier, permafrost-free soil. The relations between vegetation and permafrost are illustrated by the sequence of vegetation succession that commonly follows forest fire. Ground warming and thickening of the active layer in years shortly after fire improves drainage and allows the establishment of species suited to dry soils, especially pine. However, as a surface organic horizon redevelops, the active layer thins, segregated ice persists at the base of the active layer, and drainage is impeded, leading to replacement of this vegetation by moisture-tolerant species, such as spruce.” (Burn 2004)

Topography “The Yukon is part of the Canadian Cordillera, the system of mountain ranges that run generally in a north–south direction from the U.S. border to the Beaufort Sea. The complex topography of rugged mountains, plateaus, lowlands and valleys is a result of deposition, volcanic activity, deformation and plate movement along the western margins of the North American craton, extensively modified by glaciation, erosion and weathering.

The physiography of the territory varies from the gently sloping Yukon Coastal Lowland along the Beaufort Sea in the north to the ice-covered Icefield Ranges in the southwest. Between these two extremes are extensive plateaus, lowlands and numerous mountain ranges.” (McKenna and Smith 2004)

The character of relief, combined with climate and surficial geology influences, and is predictable to an extent, soil types and drainage patterns. At locals-scale topography will influence surficial geology, for example colluvial veneers that thicken downslope into aprons of organic debris (Bond, Fuller, Jackson, and Roots 2004). Certain vegetation communities may be restricted to specific arrangements of topography and climate, for example grasslands are restricted to steep, dry, south-facing slopes along the Yukon and Pelly rivers on moraine, colluvium, and glaciofluvial material (McKenna et al. 2004).

2.3.3 Disturbance

Disturbances in the boreal region that shape vegetation include: fire, insect-outbreak, windthrow, avalanches, and slides (often due to thawing permafrost). These disturbances can set back the seral stage of vegetation communities and in some circumstance such as in avalanche shoots that maintain vegetation in an early successional stage. A region’s physiography, climate and vegetation combine to characteristize the fire-cycle. Fire can also alter species composition in forest stands, as earlier seral stages may include species not dominate in the later, mature stages (McKenna et al. 2004). As a vegetated landscape goes through fires periodically over centuries a mosaic of vegetation at various stages of succession emerge, affecting succession (seral) patterns and vegetation structure.

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In areas that have underlying permafrost, fire can warm the active permafrost layer resulting in a drier post-fire state allowing species suited to dry soils to establish (Burn 2004). If the active layer drops to a depth of below 2m, soils are technically classified as Brunisols rather than Cryosols (Yukon Ecoregions Working Group 2004). The Yukon Ecoregions Working Group (2004) reported that in the Peel River Plateau and Fort McPherson Plain ecoregions retrogressive thaw flow slides are common where ground ice has been exposed in glaciolacustrine deposits by forest fires, debris flows and regressive erosion thus reshaping the landscape entirely. Further in middle and upper slope positions forest fires may affect the thermal regime so much that frozen water is released, possibly triggering further disturbances if the slope slumps. (Yukon Ecoregions Working Group 2004)

3. YUKON ELC FRAMEWORK

The Yukon ELC Framework considers and accounts for factors that influence ecosystem distribution by combining a climatic and site-level classification, while maintaining a geographic link to regional landscapes. The Yukon ELC Framework integrates existing climatic classification approaches of the British Columbia Biogeoclimatic Ecosystem Classification (Pojar et al. 1987; Meidinger and Pojar 1991), vegetation classification of the Canadian - National Vegetation Classification, and ecosite classification concepts of Alberta (Beckingham and Archibald 1996; Beckingham et al. 1996a) and Saskatchewan (Beckingham et al. 1996b). Where required, these classification approaches have been modified to better reflect the Yukon ecological setting and guiding principles established for the Yukon ELC Framework. Table 1 and Figure 5 illustrate the major components and linkages of the Yukon ELC Framework. Yukon’s ELC framework groups ecosystems at four levels of integration: regional, broad, local and phase. At the regional scale, the primary factor influencing vegetation potential is considered to be climate. The Yukon ELC Framework therefore has an initial focus on bioclimate classification, or climate conditions that influence vegetation potential and ecosystem distribution. Bioclimate regions provide a geographic link to Yukon landscapes, while bioclimate zones, bioclimate subzones and bioclimate subzone variants describe increasingly more specific climate conditions that influence vegetation potential and productivity. In the Yukon ELC Framework, both local and broad level ecosystems are classified based on a phytotopological approach where climate, vegetation, soils and landscape position are considered. At the broad-level, the landscape is classified into units that organize broad vegetation communities, terrain type (soils and topography) within bioclimatic zones. Vegetation communities are classified by physiognomic structure; identified through combinations of dominant and diagnostic growth forms that reflect global macroclimatic factors as modified by altitude, seasonality of precipitation, substrates, and hydrologic conditions. Ecosites are organized along a toposequence of landscape positions, and within an edatopic grid to describe relative soil moisture and nutrient conditions. A reference ecosite based on zonal concepts, provides the link between regional climate and vegetation potential; each bioclimate subzone is characterized by a

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reference ecosite. Local or Ecosite and broad ecosystem classifications have been designed with full consideration of mapping applications.

At the phase level of integration (both broad and local), ecosystems are classified according to either seral stage or structural stage. The phase component of the framework recognizes the current vegetation community development stage of a particular broad ecosystem or ecosite unit.

In order to arrange ecosystems at the four levels of integration (regional, broad, local and phase), the ELC combines three classifications: vegetation, climate (bioclimate), and landscape position (site). Table 1 and Figure 5 illustrate the nested relationship between the three classifications systems that integrate into the Yukon Ecological and Landscape Classification.

The Yukon ELC Framework emphasis on climatic control of ecosystem distribution results in a different approach to ELC than the physiographic focus of the National Ecological Framework. The existing National Ecological Framework terrestrial ecozones and ecoregions of Yukon (Smith et al. 2004) is not a formal part of the Yukon ELC Framework, but they will continue to be used in national reporting and other management applications. Ecoregions and ecodistricts can inform provisional boundaries to define macroclimate patterns as will be discuss later in this section. Development, refinement and continued maintenance of Yukon’s Ecoregion Framework will be the focus of another report, to be produced at a later date. Table 1. Nested relationship between Yukon ELC Framework components, showing conceptual ecosites and broad ecosystems for the Alpine bioclimate zone of South-central Mountains and Plateau bioclimate region. Yukon ELC component Description Bioclimate Region South-central Mountains and Plateau Bioclimate Zone Alpine Bioclimate Subzone Alpine, South-central Mountains and Plateau

Bioclimate Subzone Variant Alpine, Southern Lakes, Coast Mountains variant

Broad Ecosystem Sparsely Vegetated

Dwarf Shrub

Moist Conifer Forest

Ecosite Bedrock Talus Crowberry Dwarf-willow Heath

Krummoltz Fir-Bog Birch

Phase SS=1 SS=1 SS=3a SS=3a SS=3a SS=6

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Figure 5. Nested relationship between the classification systems that integrate into the Yukon Ecological and Landscape Classification

Site Classification

Ecosite Broad Ecosystem

Ecosite Phase Phase

Bioclimate Classification

Bioclimate Subzone

Bioclimate Variant

Bioclimate Region

Bioclimate Zone

Reference Site, Ecological Equivalence and Mature

Concepts

Predominant vegetation condition reflecting macro-climate (7 Zones - ALP, SUB, BOH, BOL, TAS, TAW, TUN)

Canadian National Vegetation Classification

Formation class

Formation subclass

Formation

Alliance

Association

Sub-association

Reference Site and Mature Concepts at Formational

Level

Yukon Ecological and Landscape Classification

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3.1 VEGETATION CLASSIFICATION

Vegetation classification is an important diagnostic tool for ELC because vegetation is readily observed and described, and differences in vegetation reflect climatic, site and successional relationships. Vegetation (successional and non-successional) of mature1 ecosystems is emphasized in ELC as it is considered to be the best integrator of the combined influence of the environmental factors affecting a site.

The Canadian National Vegetation Classification system or C-NVC (Canadian National Vegetation Working Group 2011) and described in Ponomarenko and Alvo (2001) is a floristically-driven vegetation classification system. In C-NVC, vegetation units are determined by grouping plot data and then comparing the resulting units in a series of vegetation tables. C-NVC hierarchically classifies vegetation communities at a scale and level of detail appropriate for describing the vegetation component of both local and broad scale ecological classification.

The outcome is a hierarchy of vegetation units with “Formation Class” being the most general where physiognomy plays a predominant role. At meso-scale both floristics and physiognomy play a significant role. At the lower scale alliance, association and subassociation are divided entirely by floristics. Plant associations are the basic unit of the vegetation classification hierarchy and integrate well into an elemental (lowest) level of the ELC hierarchy. At the lowest level the definition of vegetation association class adopted by C-NVC is derived from the Ecological Society of America's guidelines document for the USNVC. The formal definition is as follows: “A vegetation classification unit defined on the basis of a characteristic range of species composition, diagnostic species occurrence, habitat conditions and physiognomy.” (Ecological Society of America, Vegetation Classification Panel 2004). Within C-NVC this is interpreted as a plant community type with consistency of overstorey dominance and floristic composition, as well as having a clearly interpretable ecological context as expressed by diagnostic indicator species within a defined physiognomy (e.g. closed forest vs. ecological woodland) or structure (Baldwin 2007).

Plant associations contain ecosystems from several climates; it can be somewhat variable in its environmental conditions. The plant associations may also include several ecosites that occur on ecologically equivalent sites due to compensating effects of climate, landscape position and soil characteristics.

1 Note that the concept of mature is a relative one. An ecosite may trend towards a particular successional trajectory after disturbance. When these systems have “matured” that is to have become relatively stable is quite relative. The timeline to ‘maturity’ will vary from ecosite to ecosite. Typically however sites that trend towards a treed systems mature in 70-90 years, whereas grasslands may reach maturity after a decade after fire and will remain in that vegetation class for decades without disturbance.

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3.2 BIOCLIMATE CLASSIFICATION

The bioclimate classification of the Yukon ELC Framework identifies areas with similar climate conditions that influence vegetation potential and ecosystem distribution.2 The term bioclimate zone is adopted, in part, from Holland (1976), who originally used the approach to map biophysical features of Jasper and Banff National Parks in Alberta. The bioclimate classification is based on long-term climate normals of mean annual temperature and precipitation. Meidinger and Pojar (1991) however recognized that using climatic data is likely not adequate alone to classify and map bioclimates: “Because climatic data are scant or lacking in many areas and climatic analysis alone will not produce a practical ecosystem classification, a reliable functional link between climate and ecosystems is needed… the concept of zonal [sic] ecosystem provides this link” (Meidinger and Pojar, 1991). Thus the geographic extent of bioclimatic units in the ELC system is inferred from the distribution of mature plant communities on reference sites that are defined as zonal. Reference sites are those that best reflect the regional climate and are least influenced by the local topography and/or soil properties (i.e moisture or ice-content).The hierarchical levels of the bioclimate classification, from broad to most detailed, are bioclimate region, bioclimate zone, bioclimate subzone and bioclimate subzone variant. Zonal concepts and bioclimate hierarchy is described below.

3.2.1 Zonal Concepts3

“The concept of zonal is fundamental to ecosystem classification in both forested and non-forested ecosystem units. Zonal ecosystem units represent the average of all influencing conditions on the landscape – climatic, physiographic and topographic. Only by understanding the characteristics of zonal, can the characteristics of the other edaphic ecosystems in the suite for the bioclimate subzone be recognized. The zonal ecosystem unit lies at the center of the suite and all other ecosystem units are distinguished in reference to it. For every bioclimate subzone, it is important to first become familiar with the zonal site characteristics by making a mental imprint of it, in order to then recognize the shifts to other ecosystem units. Zonal also establishes the geographic boundaries of the bioclimate subzone, since the plant community on the zonal site will change as you cross into a new bioclimate subzone.” (Jones et al. 2007).

In British Columbia, where Biogeoclimatic Ecosystem Classification (BEC) zonal concepts were developed, the criteria for a ‘zonal site’ were easily met in forested biogeoclimatic subzones. In Yukon the definition of ‘reference site’ may need to be modified in order to apply it within a Yukon context (i.e permafrost-influence subzones as in northern Yukon). In Yukon’s ELC framework we refer to “zonal sites” as “reference sites”.

2 The bioclimate concept is a fundamental component of the British Columbia Biogeoclimatic Ecosystem Classification System (Meidinger and Pojar 1991), which recognizes broadly defined Biogeoclimatic Zones, Subzones and Variants. 3 This section was largely extracted from Jones et al. “Chapter 4. Principles of Ecosystem Classification for the Yukon” In Yukon’s Ecological Land Classification and Mapping Program: Concepts Towards a Strategic Plan, 28-31. Silvatech Group, 2007.

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The reference site is that which best reflects the mesoclimate or regional climate of an area. The integrated influence of climate on the vegetation, soil, and other ecosystem components is most strongly expressed in those ecosystems least influenced by local relief or by physical and chemical properties of soil parent materials. Such ecosystems have the following characteristics:

1. middle slope position on the meso-slope in mountainous terrain; upper slope position in subdued terrain;

2. slope position, gradient, aspect, and location that does not result in a strong modification of climate (e.g., frost pocket, snow drift area, steep south or north aspect);

3. gentle to moderate (5-30%) slope; in dry or cold climates, on slopes to less than 5%; in wet climates, on slopes up to 50%; and

4. soils that have: (a) a moderately deep to deep (50-100+ cm) rooting zone, (b) no restricting horizon within the rooting zone, (c) loamy texture with coarse fragment content less than 50% by volume, and (d) free drainage.

5. For continuous permafrost regions in which the active ice layer is 30-50cm deep, zonal occurs on the soils with average drainage conditions (i.e. morainal deposits) over the permafrost.

In reference sites, “the biogeochemical cycles and energy exchange pathways of reference ecosystems are more or less independent of local relief and soil parent material, and are in equilibrium with the regional climate. Other ecosystems in a given area are influenced more strongly by local physiography and the physical and chemical properties of soil parent materials. They can be drier, wetter, richer, or poorer than zonal ecosystems; and overall they do not provide as clear a reflection of the regional climate.” (Meidinger and Pojar, 1991)” (Jones et al. 2007)

“When the vegetation composition changes notably on reference sites, this marks the location of a change in bioclimatic subzones. Within a bioclimatic area, a suite of repeating edaphic and reference ecosystem units will occur as predictable patterns on the landscape. When the ecosystems no longer follow the patterns, the bioclimatic area has changed. Since the reference ecosystem unit is reflective of only the climatic influences and not topographic or soil influences, its distribution is used to determine the geographical extent of the bioclimatic units (Meidinger and Pojar, 1991).” (Jones et al. 2007)

“Reference ecosystem units are not necessarily the most common ecosystems in a bioclimate subzone. In keeping with the description above, some mountainous areas may have relatively few areas that are flat to moderate slopes with loamy soils. There may in fact be more north and south slopes, but these will not likely represent the reference ecosystem units due to greater topographical influences. That said, however, the boundary of the change between reference and the submesic ecosystem units on the steeper slopes, varies with each bioclimate subzone depending on the climatic influences.

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In wetter bioclimate subzones, such as coastal mountains, the reference ecosystem unit extends upwards on both north and south slopes, due to the lack of strong solar insolation (drying and heating by the sun). How far that reference ecosystem extends upward across other landscape positions or on other parent materials, establishes the range of site conditions for reference in that bioclimate subzone. A new ecosystem unit is defined when there are significant changes to the site characteristics reflected in the understory vegetation community.” (Jones et al. 2007)

The concept of zonal relies upon the identification of the reference ecosystem unit, the suite of edaphic ecosystem units around it, and the geographic range of this suite denoted as the bioclimatic subzone.

3.2.2 Bioclimate Region

Bioclimate regions represent areas of broad, relatively homogeneous climatic conditions. The location and orientation of major mountain ranges and plateaus, interacting with territorial-scale weather patterns, create distinct regional climates throughout Yukon. Provisional bioclimate regions are listed in Table 2 and shown in Figure 6 . In some cases, bioclimate regions generally correspond to Yukon ecoregions (Smith et al. 2004), but in other situations there may be limited correlation.

3.2.3 Bioclimate Zone

Bioclimate zones are areas with similar climate conditions that influence vegetation potential. Each bioclimate zone is characterized by the predominant vegetation community on reference sites where regional climate is the primary controlling factor of vegetation potential and ecosystem distribution, and other influences such as soils and terrain are secondary.

Bioclimate zones result primarily from changes in elevation and/or latitude. Within each bioclimate region, a bioclimate zone has a characteristic range in elevation and corresponding temperature and precipitation conditions. In mountainous areas, bioclimate zone boundaries are visible as relatively abrupt changes in general vegetation communities or species, and are organized along a gradient of elevation. In lower elevation or rolling terrain, bioclimate zone boundaries may be subtle and transitional. With increasing latitude, the elevational boundary between two bioclimate zones is generally lower. Seven provisional general bioclimate zones are currently recognized in Yukon (Table 3). Figure 7 shows the arrangement of provisional bioclimate zones within the provisional bioclimate regions of Yukon. The boreal bioclimate zones of southern and central Yukon are in a more advanced stage of development and understanding than the Taiga bioclimate zones of northern Yukon—future revisions should be expected.

3.2.4 Bioclimate Subzone

Bioclimate subzones have characteristic vegetation communities occurring on reference sites. Bioclimate subzones have been provisionally identified through the integration of

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bioclimate regions and bioclimate zones (Figure 7). Bioclimate subzone differences, as expressed by different plant communities on reference sites, results from geographic differences in temperature and precipitation regimes. For example, within the boreal low bioclimate zone, which covers portions of southern Yukon, there are notable climate differences between the Kluane area of southwest Yukon, the Southern Lakes area of south central Yukon, and the Liard Basin of southeast Yukon. While the boreal low bioclimate zone is similar between these three areas, each may be slightly cooler, warmer, wetter or drier, relative to the other, resulting in differences in reference vegetation communities and productivity. Bioclimate subzones describe these climatic differences.

The climate link between bioclimate conditions and local-level ecosystems (ecosites) is expressed through the concept of a reference ecosite. A reference ecosite represents the average vegetation and soil conditions that characterize a bioclimate subzone within a specified bioclimate region. A change in reference ecosite conditions marks the boundary between bioclimate subzones.

3.2.5 Bioclimate Subzone Variant

Bioclimate subzone variants are special conditions within bioclimate subzones. At this stage in the development of the Yukon ELC Framework, bioclimate subzone variants are conceptual, but could be used to account for special climate conditions, or differences in permafrost, glacial history or physiography, within a bioclimate subzone. The Yukon ELC Framework will place initial emphasis on bioclimate zone and subzone classification and mapping.

3.3 LOCAL AND BROAD ECOLOGICAL CLASSIFICATION

The Yukon ELC Framework describes both broad and local, or site-level ecosystems. Broad ecosystems are applicable at scales smaller than 1:50,000. Local-level ecosystems are termed ecosites and represent the elemental classification unit of the Yukon ELC Framework. Ecosite phase describes the current vegetation structural or seral stage of the ecosite. Each is described below.

3.3.1 Local Ecosystems

An ecosite represents the local, or site-level, classification unit of the Yukon ELC Framework. Ecosites are the fundamental classification unit (element) for local ecosystems; they are intended for use and mapping at scales of 1:50,000 or larger. Ecosites are classified based on a phytotopological approach that considers climate and site (terrain, soils, landforms) and vegetation combined, with initial emphasis on relatively stable and enduring landscape position and terrain features.

Climate The climate relationship between ecosites and different geographic areas of Yukon is described by the bioclimate classification at the subzone level. Reference ecosites represent site and vegetation conditions that characterize a bioclimate subzone; they are representative of the regional climate and are not strongly influenced by topographic or

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edaphic extremes. Reference ecosites provide a reliable climate link between site-level vegetation conditions and bioclimate subzones. Distribution of the reference ecosite and its characteristic vegetation association determines the overall spatial extent of the bioclimate subzone. A change in the vegetation association of a reference ecosite determines the spatial boundary between bioclimate subzones. Table 2. Provisional bioclimate regions of Yukon.

No Bioclimate Region Description

1 Yukon North Slope Coldest and driest area of Yukon – arctic tundra

2 Northern Mountains and Plateau

Old Crow, Eagle Plain, Richardson Moutains

3 Ogilvie Mountains and Plateau

Weather systems from the Gulf of Alaska drop most of their moisture before they reach the slopes of this region, but some moisture reaches this area in systems moving eastward through Alaska. The result is moderate precipitation, coming predominantly as rain in the summer. Because of its northern latitude, temperatures are fairly low, but are not as extreme as in the lowlands of Northern Mountains and Plateau to the north (Ecoregions Working Group, 2004)

4 Mackenzie Mountains Mackenzie and Selwyn Mountains. Strong orographic effect

5 Interior Plateau Mayo, Pelly Crossing, Ross River and Faro. Cooler and wetter than South central.

6 Klondike Plateau Dawson area. Colder than South central and Mayo area.

7 Southeast Mountains and Plateau

Southeast Yukon, including Cassiar Mountains, Liard Basin and Hyland Plateau. Similar temps as South central but wetter. (Muskwa Plateau is likely an exception)

8 Kluane and Ruby Ranges

The Ruby ranges, in the rain shadow of the St. Elias Mountains, contains some of the coldest and driest areas of Yukon’s boreal forest.

9 South-central Mountains and Plateau

Southern Lakes, Whitehorse, Teslin. Low elevations of south-central region are dry but warmer than Kluane. High elevations (Coast Mountains) are wet. Also included are Pelly Mountains

10 St. Elias Mountains

The St. Elias Mountains are the highest mountain range in Canada. Located on the Pacific Ocean, this area receives over 2m of precipitation annually. Most of the area is covered in glaciers or sparsely vegetated alpine.

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Figure 6. Provisional bioclimate regions of Yukon representing macroclimatic patterns in Yukon

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Table 3. Provisional bioclimate zones of Yukon. Bioclimate Zone Code Description Boreal Bioclimate Zones (Southern Yukon)

Boreal Low BOL

Continuously forested areas at low to middle elevations, below the BOH of all mountain valley and plateau ecoregions of southern and central Yukon. Landscapes are generally wide valleys. Winters are long and cold, with short, cool and dry summers. Forests are generally mixedwood (lodgepole pine, white spruce and aspen) with moderately developed understories. Wetlands are common.

Boreal High BOH

Middle to upper elevations of forested areas in all mountain valley and plateau ecoregions of southern and central Yukon. Found above the BOL in large valleys. Characterized by steep slopes in southern mountainous ecoregions and gentle rolling plateaus in the central ecoregions. Summers are brief, cool and moist, with long cold winters. Forests are dominated by white spruce, lodgepole pine, and subalpine fir.

Subalpine SUB

Sparsely forested areas at moderate to higher elevations on steep slopes above the BOH (or BOL). Subalpine areas form a transitional zone between forested Boreal and the higher elevation non-forested, Alpine bioclimate zones. Open canopy conifer forests (tree cover < 20%) and tall shrub communities are characteristic vegetation conditions. Subalpine fir is the predominant tree species. Winters are long and cold, while summers are short, cool and moist.

Taiga and Tundra Bioclimate Zones (Northern Yukon)

Taiga Wooded TAW

Coniferous or mixedwood forested areas with an open canopy in northern Yukon. Taiga Wooded generally occurs in valley bottoms and lower slopes of mountain valleys, or on plateaus and plains. Slope position, aspect and the distribution and depth of permafrost are major influences on vegetation distribution and dynamics. In steep terrain, active slope processes (rock slides, slumps, talus cones) play a major role in the distribution of forests.

Taiga Shrub TAS

High elevation Taiga Shrub replaces the term ‘Subalpine’ in northern Yukon. These areas are tall or low shrub-dominated, with sparse or sporadic tree cover. Taiga Shrub generally occurs at high elevations in northern mountain systems. However, the distribution of Taiga Shrub in some areas of northern Yukon appears to be influenced by arctic weather systems (e.g., along the eastern foothill slopes of the Richardson Mountains); this situation may require a different bioclimate zone designation similar to BOH and BOL.

Tundra TUN High latitude areas in northern Yukon above the arctic tree line. Dwarf shrubs, tussock tundra, herb/cryptograms and low-growing and scattered krummholtz trees are the predominant vegetation condition.

Alpine Bioclimate Zone (all of Yukon)

Alpine ALP High elevations associated with mountainous conditions throughout Yukon. Dwarf shrubs, herb/cryptograms and low-growing and scattered krummholtz trees are the predominant vegetation condition. In very high elevation areas, bare rock, colluvium or ice/snow may be the dominant conditions.

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Figure 7 Provisional bioclimate zones (Tundra, Alpine, Subalpine, Boreal High, Boreal Low, Shrub Taiga and Wooded Taiga) with provisional bioclimate regions superimposed. Bioclimate zones have not been delineated within the white areas of the map.

Toposequence

Within a bioclimate subzone, ecosites are organized along a topographic gradient and occur in relatively predictable locations across the landscape (Figure 8). This topographic gradient, or profile, is known as a toposequence. Toposequences can also illustrate how some ecosites may not just be associated with certain landscape positions, but also surface materials (a rock outcrop hill crest is different than a morainal hill crest). Understanding the relationship between landscape position and where ecosites may occur is a key concept of classifying and mapping ecosites in the Yukon ELC Framework. Toposequences and their corresponding ecosites will be developed for each bioclimate subregion of Yukon.

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Along with the toposequence, an edatopic grid is used to organized ecosites along a gradient of soil moisture and nutrient conditions (Figure 9). On the edaptopic grid, all ecosites are described in relation to the reference ecosite, with other ecosites being drier, wetter, more nutrient poor, etc., in comparison to the reference ecosite. In Figure 9, the reference ecosite would be ‘Ecosite d – low-bush cranberry’, with a medium soil nutrient regime and a mesic soil moisture regime. Within the toposequence, the reference ecosite generally occupies the relatively level, mesic site location, or average condition. The edatopic grid is described below.

Edatopic Grid The Edatopic grid describes the relative soil moisture and nutrient regime of an ecosite in comparison to other ecosites, grading from wet to dry, and from nutrient poor to nutrient rich (Figure 9). Different ecosites are characterized by a range of soil moisture and nutrient conditions, and can be organized along these gradients through the use of the edatopic grid. The edatopic grid allows users to understand relative relationships between different ecosites, and how the ecosites are likely organized along a landscape toposequence, such as shown in Figure 8. Some ecosites are limited in their distribution to specific environmental conditions, represented by the very wet, dry or nutrient poor ranges of the edatopic grid. Other ecosites may occur over broader range of topographic and edaphic conditions, as some soil, slope or aspect conditions may compensate for other environmental factors resulting in ecological equivalence.

Vegetation Classification For many users, vegetation is the most obvious visual component of ecosystem classification. Vegetation communities are reflective of the local climate and underlying site conditions, and so may be reliable indicators of ecosites. Indicator plant species, usually found in the understory, often provide the most reliable criteria to classify ecosites in the field. In the Yukon ELC Framework, plant associations described by the Canadian National Vegetation Classification (C-NVC) are used to classify and describe the vegetation component of ecosites. C-NVC plant associations are combined with the toposequence and edatopic grid concepts described above, and interpreted within the bioclimate classification, to classify ecosites. Ecosites are characterized by the ‘mature’ potential vegetation condition that is expected to occur on a site. In forested ecosystems, mature is generally considered to be greater than 80-years since the last stand initiating disturbance event. Some C-NVC plant associations are young seral or structural stages of mature vegetation, but can be organized and understood within the context of the more enduring features of the ecosite classification (soil conditions and landscape position). Seral and structural stages are described at the ecosite phase level.

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Toes of slopes

Midslopes

Upperslopes

North South

Rock &Shallow soils

Colluvium

Ridges& Hills

Mid-slopestreams

Permafrost Variations

Undula

tions

Rockoutcrops

Stream benches

Streams

Morainal tills

Wetlands& Lakes Rivers

Organics

Flat to

gentl

e slop

es

Lacu

strine

benc

hes

Glaciof

luvial

terrac

esKam

es

Fluvial

benc

hes

Kettles

BogsSwampsFensMarsh

Permafrost VariationsGullies

Lacustrine, Fluvial, Morainal

Toes of slopes Crest

20

03

03

40

10

04

04

10

06

02

06

12 0112

25

10

01 09 11

4033

31

2430

41 34

Within a bioclimate subzone, ecosites are organized based on landscape position, or along a toposequence. Along this toposequence, characteristic ecosites occur in predictable locations, based on slope, aspect, parent material, and soil moisture and nutrient conditions. The reference ecosite occurs in the relatively level, moderately drained position.

Figure 8. Example of a toposequence for organizing ecosites within a bioclimate subzone.

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Figure 9. Example of edatopic grid from Ecosites of Northern Alberta (Beckingham and Archibald 1996).

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3.3.2 Broad Ecosystems

The broad ecosystem classification is intended to provide basic ecosystem information for regional land-use planning, wildlife management and environmental assessment. This level of the Yukon ELC Framework combines broad classes of vegetation types (formation level of C-NVC), generalized landscape types, and bioclimate zones or subzones. Broad ecosystems are designed to be mappable at a scale of 1:50,000 to 1:250,000. The broad ecosystem classification system is strongly linked to mapping considerations that can rapidly provide Yukon resource managers with useful products for large geographic areas. Broad ecosystems are typically identified using predictive methods (predictive ecosystem mapping—PEM) through the use of GIS, remotely sensed imagery and DEM analysis. Figure 10 shows the method for identifying broad ecosystems.

Figure 10. Suggested process for identifying broad ecosystems. Broad ecosystems are identified by combining landscape position and generalized vegetation conditions (Table 4). Five relative soil moisture classes are recognized, based primarily on landscape position and/or slope curvature – dry, mesic, moist, wet and fluvial. Generalized vegetation classes are based on the physiognomic level (i.e., formation level) of the C-NVC classification system.4 The terms upland, lowland and riparian are used to organize broad ecosystems into ecological groups (Table 4). Dry, mesic and moist sites are considered upland, while wet sites are lowland. Riparian is used to describe fluvial landscape positions, or those areas influenced by active flooding, erosion and deposition. In addition to the broad ecosystem class, terrain descriptors can be added to the ecosystem label for additional ecological information, if required (see Appendix 1). While a standard suite of broad ecosystems exists for all of Yukon, combining the bioclimate zone or subzone with the broad ecosystem classification is critical to their ecological interpretation. When broad ecosystems are interpreted within a given bioclimate zone or subzone, they can be described with more certainty and within a narrower range of species/ecological conditions. For example, without knowledge of the 4 Utilizing the formation-level classes of the C-NVC maintains consistency with the land cover legend used for the EOSD project which is, in turn, based on the National Forest Inventory classification.

Bioclimate Region

Bioclimate Zone Broad

Ecosystem Grouped to formation (upper) levels of C-

NVC and generalized landscape types

Ecosites

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bioclimate zone or subzone, there is no way of knowing what understory plant species may be associated with a moist conifer forest. Interpreting broad ecosystems within the context of bioclimate zones or subzones provides the linkage between the ecosite and broad ecosystem classifications, as shown earlier in Table 1. As with ecosites, broad ecosystems can be correlated to neighbouring jurisdictions using reference tables. Table 4. Broad ecosystem classes for the boreal (BOL and BOH) and taiga (TAW and TAS) bioclimate zones of Yukon. Similar tables would be created for Alpine and Subalpine bioclimate zones.

Landscape Type

Relative Moisture Regime

C-NVC Formation

Broad Ecosystem Class

DRY (hill and ridge crests, very steep slopes, shallow soils and rock outcrops)

Herb, Shrub, Deciduous, Mixedwood, Conifer

Upland Dry

MESIC (reference sites, slightly dry to slightly moist, gentle slopes, glaciofluvial terraces)


Upland Mesic

Upland

MOIST (toes of slopes, depressions, seepages, stream edges)


Upland Moist

Lowland WET Horsetail Flats, Swamp forests, bog forests, bog woodlands,

Wetland – Herb, Forested, Shrub

Lowland Wet

Riparian Fluvial (large river benches with active flooding, deposition and erosion)


Riparian

3.3.3 Ecosystem Phase

3.3.3.1 Ecosite Phase

Vegetation, in particular forest vegetation, is dynamic in that vegetation structure and composition change over time following disturbances such as wildfire or forest harvesting. Identifying relatively stable ecosites, and then having a method to describe the current vegetation condition, is therefore required. Ecosite phase describes the current vegetation condition on relatively stable ecosites. Both structural and seral stage is considered, with greater emphasis placed on structural stage characteristics.

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Structural Stage The structural stage of vegetation refers to its composition, height and similar structural characteristics. Ecosite structural stage modifiers are important attributes for wildlife habitat modeling. In the Yukon ELC Framework, ecosite structural stage descriptions generally follow the terms and methods of BC Ministry of Environment, Lands and Parks and BC Ministry of Forests LMH 25, Describing Terrestrial Ecosystems in the Field (1998) (Table 5). In some cases, height classes and other vegetation attributes have been modified to better reflect boreal and taiga environments.

Seral Stage The term succession is the process by which a plant community on the same site undergoes a series of changes which begin with colonization of the ground after a disturbance by shade intolerant species, followed by incursions of shade tolerant species, eventually replaced by shade tolerant species as shown in (Kimmins 1997). Seral stages represent the different stages of plant succession, and attempt to describe where the current vegetation community may be organized chronologically along a successional pathway. Some boreal forest communities, such as lodgepole pine on dry sites, do not undergo significant post-disturbance community change. Theoretically, seral stages may apply to all plant communities but they are best understood in forest ecosystems. However, understanding the potential vegetation of ecosites in a fire patterned landscape such as Yukon can be challenging. This situation was an important consideration for placing initial emphasis on relatively stable, enduring features for the ecosite classification. The seral stage classification of the Yukon ELC Framework is not well developed. Currently, more emphasis should be placed on structural stage. A provisional seral stage classification for Yukon forest ecosystems is shown in Table 6.

3.3.3.2 Broad Ecosystem Phase

Broad ecosystem phase is described more generally than ecosite phase. Given the generalized nature of C-NVC formation-level vegetation descriptions, detailed structural stage descriptors are generally not possible to identify. Therefore, only the four seral stages identified for ecosites in Table 6 are utilized. In general, for upland broad ecosystems, ES corresponds to herbaceous (recent burn), MS is deciduous-dominated (forest or shrub), and LS and ST are recognizable by coniferous-dominated forest cover, but may not be able to be differentiated. Broad ecosystem phase concepts are most applicable to upland ecosystems in boreal and taiga bioclimate zones, where forests are the dominant vegetation and fire disturbances are common. Sites where fire disturbances generally do not occur, such as alpine areas, are considered relatively stable and non-successional.

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Table 5. Ecosite phase vegetation structural stage descriptors (BC Ministry of Forests LMH 25, Describing Terrestrial Ecosystems in the Field. 1998).

Structural Stage Description 1 – Sparse / bryoid

Initial stages of primary and secondary succession; bryophytes and lichens often dominant; time since disturbance < 20 years for normal forest succession, may be prolonged (50–100+ years) where there is little or no soil development (bedrock, boulder fields); total shru. b and herb cover < 20%; total tree cover < 10%. 1a – Sparse. less than 10% vegetation cover. 1b – Bryoid. bryophyte and lichen-dominated communities (> 50% of total vegetation cover)

2 – Herb Early successional stage or herb communities maintained by environmental conditions or disturbance (e.g., snow fields, avalanche tracks, wetlands, flooding, grasslands, intensive grazing, intense fire damage); dominated by herbs (forbs, graminoids, ferns); some invading or residual shrubs and trees may be present; tree cover < 10%, shrubs < 20% or < 33% of total cover, herb-layer cover > 20%, or > 33% of total cover; time since disturbance < 20 years for normal forest succession; many non-forested communities are perpetually maintained in this stage. 2a – Forb-dominated 2b – Graminoid-dominated 2c – Aquatic 2d – Dwarf shrub-dominated

3 – Shrub 3a – Low Shrub - dominated by shrubby vegetation < 2 m tall; seedlings and advance regeneration may be abundant; time since disturbance < 20 years for normal forest succession; may be perpetuated indefinitely by environmental conditions or disturbance; 3b – Tall Shrub - – dominated by shrubby vegetation that is 2–10 m tall; seedlings and advance regeneration may be abundant; time since disturbance < 40 years for normal forest succession; may be perpetuated indefinitely.

4 – Pole Pole/Sapling - Trees > 10 m tall, typically densely stocked, have overtopped shrub and herb layers; younger stands are vigorous (usually > 10–15 years old); older stagnated stands (up to 100 years old) are also included; self-thinning and vertical structure not yet evident in the canopy – this often occurs by age 30 in vigorous broadleaf stands, which are generally younger than coniferous stands at the same structural stage; time since disturbance < 40 years for normal forest succession; up to 100+ years for dense (5000 – 15000+ stems per ha) stagnant stands.

5 – Young forest Young Forest - Self-thinning has become evident and the forest canopy has begun to differentiate into distinct layers (dominant, main canopy, and overtopped); vigorous growth and a more open stand than in the PS stage; begins as early as age 30 and extends to 50–80 years; time since disturbance generally 40–80 years, depending on tree species and ecological conditions.

6 – Mature forest Mature Forest - Trees established after the last disturbance have matured; a second cycle of shade-tolerant trees may have become established; understories become well developed as the canopy opens up; time since disturbance generally 80– 140 years

7 – Old forest Old Forest - Old, structurally complex stands comprised mainly of shade-tolerant and regenerating tree species, although older seral and long-lived trees from a disturbance such as fire may still dominate the upper canopy; snags and coarse woody debris in all stages of decomposition and patchy understories typical; understories may include tree species uncommon in the canopy, because of inherent limitations of these species under the given conditions; time since disturbance generally > 140 years

8 – Remnant forest

Remnant Forest - stand has undergone natural thinning, gaps have been created, well-developed understorey and a more or less continuous age and height class distribution, although a gap may exist between the older or upper class and the next class. Some remnants of the earlier stand may remain, but they should not have any effect on the density or structure of the stand. Removal of a tree would not cause a significant response in the growth rate of or tree community composition.

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Table 6. Provisional seral stages used for describing Yukon forest ecosite phases. Seral Stage Description

ES = Early Seral Deciduous-dominated shrub and forest canopy; few or no coniferous trees in canopy.

MS = Mid Seral Evenly mixed deciduous and coniferous trees in canopy; may include early (pine) and late-successional (spruce) conifer species.

LS = Late Seral Early-successional species (pine) in conifer-dominated canopy; includes pine post-fire regeneration with few or no deciduous tree species present.

ST = Stable Late-successional species (spruce and fir) in conifer-dominated canopy; may have a minor component of deciduous trees in canopy.

3.3.4 Naming Conventions

3.3.4.1 Ecosites

Regardless of the bioclimate zone or subzone they occur within, ecosites are referenced by a two letter numeric code. A standard suite of ecosystems can potentially occur in all bioclimate conditions, but will not always occur. A single ecosite classification describes the ecological diversity of each bioclimate zone or subzone; separate classifications are not created for each physiognomic vegetation class (e.g., forest, grasslands, shrub, tundra, etc.) In this ‘blocked’ system, as one moves from one bioclimate subzone to another, the ecosite numbers would be similar5.

• 01 reserved for the reference ecosite • 02 – 19 reserved for upland ecosites • 20 – 29 reserved for riparian ecosites • 30 – 39 reserved for wetland ecosites • 40 – 49 reserved for aquatic features (both lotic and lentic)

Within a bioclimate subzone, ecosites are organized based on landscape position, or along a Toposequence (refer back to Figure 8). Along this toposequence, characteristic ecosites occur in predictable locations, based on slope, aspect, parent material, and soil moisture and nutrient conditions. The reference ecosite occurs in the relatively level, moderately drained position. An additional standardized name based on vegetation associations (with diagnostic indicator plant species) or site conditions is also identified for each ecosite (e.g., 01-white spruce/feathermoss, 20-gravel bar, 30-rich fen, etc.).

5 The direction we received in previous workshops (2008) was not to order them sequentially, but give them standard blocks. This way as ecosites come and go, you don’t have to re-organize the entire system.

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The ecosystem naming convention can be simplified into an ecosystem unit, its seral stage, and its structural stage (primarily for forested ecosites). Alternatively, ecosites can be described using only the name and structural stage. Some examples are:

• 01 MS (4): reference site with a pole/sapling forest stand that is mid-seral and is

therefore composed of mixed deciduous and conifer trees; • 03 LS (3a): dry crest site with a low shrub but late seral forest – such as a hill top

of pure pine regeneration following a fire; • 04 ST (6): submesic glaciofluvial site with a mature stand – such as an

Glacioflucial Terrace (FgT) flat dominated by pine and a few aspen trees; • 10 (3a): stable (non-successional) low shrub-dominated ecosite; or • 30 (2c): rich fen, predominantly aquatic conditions

3.3.4.2 Broad Ecosystems

Broad ecosystems are identified by a 3-digit number in a blocked manner similar to ecosites. Certain blocks are reserved for different classes, organized by bioclimate zone, landscape position (upland, lowland and fluvial), moisture regime, and vegetation formation, reflecting broad ecosystem phase. A proposed naming convention is given in Table 7. Table 7 Broad ecosystem naming conventions for the boreal (BOL and BOH) and Taiga

(TAW and TAS) bioclimate zones of Yukon. *Similar tables would be created for Alpine, Subalpine bioclimate zones.

100 – Low-middle elevation broad ecosystems (BOL, BOH, TAW, TAS)

200 – High elevation broad ecosystems (ALP, SUB)*

101 – Exposed/rock 102 – Anthropogenic (settlement, agriculture, minesite, etc)

Upland Dry 110 – Upland Dry 111 – Upland Dry Herb (early seral) 112 – Upland Dry Shrub /Deciduous Forest (mid seral) 113 – Upland Dry Mixedwood Forest (late seral) 114 – Upland Dry Conifer Forest (stable)

Upland Mesic 120 – Upland Mesic 121 – Upland Mesic Herb (early seral) 122 – Upland Mesic Shrub /Deciduous Forest (mid seral) 123 – Upland Mesic Mixedwood Forest (late seral) 124 – Upland Mesic Conifer Forest (stable)

Upland Moist 130 – Upland Moist 131 – Upland Moist Herb (early seral) 132 – Upland Moist Shrub /Deciduous Forest (mid seral) 133 – Upland Moist Mixedwood Forest (late seral) 134 – Upland Moist Conifer Forest (stable)

Lowland Wet 140 – Lowland Wet: Wetland classes (fen, bog, swamp, marsh) 150 – Riparian Fluvial

201 – Exposed/rock 202 – Anthropogenic (settlement, agriculture, minesite, etc)

210 – Upland Dry

220 – Upland Mesic (reference site)

230 – Upland Moist

240 – Lowland Wet (if exists) 250 – Riparian Fluvial (if exists)

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4. REFERENCES

B.C. Ministry of Environment. 1998a. Field Manual for Describing Terrestrial Ecosystems – LMH #25 (DTEIF). Ministry of Environment, Lands and Parks, and the Ministry of Forests – Research Branch, Victoria, BC.

B.C. Ministry of Environment. 1988b. Terrain Classification System for British Columbia – MoE Manual 10. Ministry of Environment, Victoria, BC.

Baldwin, K. 2007. “Boreal Forests and Woodlands: a national approach to classification Canadian National Vegetation Classification” Source Unknown. Powerpoint presentation May 2007. Accessed on December, 2010 [http://arcticportal.org/uploads/Da/6l/Da6lnanBdluNJO0GAwSDow/BALDWIN-Boreal-Forests-and-Woodlands.pdf]

Beckingham, J.D., Archibald, J.H. 1996. Field guide to ecosites of northern Alberta. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre. Special Report 5.

Beckingham, J.D., Corns, I.G.W., Archibald, J.H. 1996a. Field guide to ecosites of west-central Alberta. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre. Special Report 9.

Beckingham, J.D., Nielsen, D.G., and Futoransky, V.A. 1996b. Field guide to ecosites of the mid-boreal ecoregions of Saskatchewan. Canadian Forestry Service, Northern Forestry Centre. Special Report 6.

Bond, J., Fuller, E., Jackson, L., and Roots, C. 2004. Surficial Geology. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 27-31.

Burn, C., 2004. Permafrost. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 32-35.

Canadian National Vegetation Classification Working Group [online April 2011] 2011. Canadian National Vegetation Classification. Sault Ste. Marie, ON, Canada. http://cnvc-cnvc.ca. System Requirements: Adobe Acrobat Reader v. 7.0 or higher.

Ecological Society of America, Vegetation Classification Panel. 2004. Guidelines for describing associations and alliances of the U.S. National Vegetation Classification. v. 4.0. [Available online: http:// vegbank.org/vegdocs/panel/NVC_guidelines_v4.pdf, Accessed February 21, 2011]

Holland, W.D. 1976. Biophysical Land Classifcation of Banff and Jasper National Parks. In: Ecological (Biophysical) Land Classifcation in Canada, Proceedings of the First Meeting, 25-28 May, Petawawa, Ont.

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Jones, C.F., Albricht, R.C., Rosie, R., and McKenna, K. 2008 “Chapter 4. Principles of Ecosystem Classification for theYukon” In Yukon’s Ecological Land Classification and Mapping Program: Concepts Towards a Strategic Plan , 28-31. Prepared by Silvatech Consulting Group for Yukon Department of Environment and Yukon Department of Energy, Mines and Resources, Whitehorse, Yukon.

Kimmins, J.P. 1997. Forest Ecology – A Foundation for Sustainable Management 2nd Edition. Prentice Hall, Upper Saddle River, New Jersey. 596 pp

McKenna, K. and Smith, S. 2004. Physiography. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 8-10.

McKenna, K. Smith, S. and Bennett, B. 2004. Surficial Geology. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 39-42.

Meidinger, D.V. and Pojar, J. (compilers and editors). 1991. Ecosystems of British Columbia. Special Report Series 6. British Columbia Ministry of Forests, Victoria, British Columbia.

Pojar, J., Klinka, K., and Meidinger, D.V. 1987. Biogeoclimatic ecosystem classification in British Columbia. Forest Ecology and Management 22: 119-154.

Ponomarenko, S., R. Alvo. 2001. Perspective on developing a Canadian classification of ecological communities. Information Report ST-X018E. Science Branch, Canadian Forest Service, Ottawa. 50pp.

Rowe, J.S. 1979. Revised working paper on methodology/philosophy of ecological land classification. In Proceedings of 2nd Meeting of Canadian Committee on Ecological Land Classification. pp. 23-30.

Rowe, J.S. and Sheard, J.W. 1981. Ecological land classification: a survey approach. Environmental Management 5: 451-464.

Smith, C.A.S., J.C. Meikle, C.F. Roots (Editors). 2004. Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes. Agriculture and Agri-Food Canada, PARC Technical Bulletin No.04-01, Summerland, British Columbia, 313 pp.

Smith, S., 2004. Soils. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 35-38.

Wahl, H. 2004. Climate. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 19-23.

White, M.P., Smith, C.A.S., Kroetsch, D. and McKenna, K.M., 1992. Soil landscapes of Yukon. Agriculture and Agri-Food Canada (database and map at 1:1,000,000 scale).

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Yukon Ecoregions Working Group, 2004. Yukon Coastal Plain. In: Ecoregions of the Yukon Territory: Biophysical properties of Yukon landscapes, C.A.S. Smith, J.C. Meikle and C.F. Roots (eds.), Agriculture and Agri-Food Canada, PARC Technical Bulletin No. 04-01, Summerland, British Columbia, p. 63-72.

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APPENDIX 1 – POTENTIAL TERRAIN DESCRIPTORS FOR ECOSYSTEM LABELS

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(Codes taken from the BC Terrain Mapping Standards, 1998) To be modified by YSGC legend Surface Material Codes Surface Expression Codes Geomorphological Process Codes

A Anthro-pogenic

Artificial or human modified material

a Moderate slope Unidirectional surface; > 15° to < 26°

A Avalanches Terrain modified by snow avalanches

C Colluvium Products of mass wastage

b Blanket A mantle of unconsolidated materials; > 1 m thick

B Braiding Diverging/converging channels; unvegetated bars

D Weathered bedrock

In situ, decomposed bedrock

c Cone(s) A cone or segment of a cone; > 15°

C Cryoturbation Materials modified by frost heaving and churning

E Eolian Materials deposited by wind action

d Depression(s) A lower area surrounded by a higher terrain

D Deflation Removal of sand and silt by wind action

F Fluvial River deposits f Fan(s) A segment of a cone; up to 15°

E Channeled Channel formation by meltwater FG

Glaciofluvial Ice contact fluvial material

h Hummock(s) Hillocks and hollows, irregular in plan; 15–35°

F Slow mass Slow downslope movement of masses of cohesive or non-cohesive material

I Ice Permanent snow, glaciers and icefields

j Gentle slope Unidirectional surface; > 3° and < 15°

H Kettle Depressions in surficial material resulting from the melting of buried partially buried glacier ice

L Lacustrine Lake sediments; includes wave deposits

k Moderately steep

Unidirectional surface; > 26° and < 35 slope

I Irregular channel

A single, clearly defined main channel displaying irregular turns and bends

LG

Glacio-lacustrine

Ice contact lacustrine material

m Rolling Elongate hillocks; 3–15°; parallel forms in plan view

J Anastomosing channel

A channel zone where channels diverge and converge around many vegetated islands

M Morainal Material deposited directly by glaciers

p Plain Unidirectional surface; up to 3°

K Karst Processes associated with the solution of carbonates

O Organic Accumulation/decay of vegetative matter

r Ridge(s) Elongate hillocks; 15–35°; parallel forms in plan view

L Surface seepage Zones of active seepage often found along the base of slope positions

R Bedrock Outcrops/rocks covered by less than 10 cm of soil

s Steep slope Steep slopes; > 35° M Meandering channels

Channels characterized by a regular pattern of bends with uniformed amplitude and wave length

U Undifferentiated

Layered sequence; three materials or more

t Terrace(s) Step-like topography N Nivation Erosion beneath and along the margin of snow patches

V Volcanic Unconsolidated pyroclastic sediments

P Piping Subterranean erosion by flowing water

W Marine Marine sediments; includes wave deposits

R Rapid mass movement

Rapid downslope movement of dry, moist, or saturated debris

WG

Glaciomarine Ice contact marine S Solifluction Slow downslope movement of saturated overburden across a frozen or otherwise impermeable substrate

U Inundation Seasonally under water because of high water table

V Gully erosion Parallel/subparallel ravines caused by running water

W Washing Modification by wave action X Permafrost Processes controlled by the

presence of permafrost

Z Periglacial processes

Solifluction, cryoturbation, and nivation processes occurring within a single unit

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APPENDIX II – CONCEPT OF ZONAL

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Concept of zonal6 “The concept of zonal is fundamental to ecosystem classification in both forested and non-forested ecosystem units. Zonal ecosystem units represent the average of all influencing conditions on the landscape – climatic, physiographic and topographic. Only by understanding the characteristics of zonal, can the characteristics of the other edaphic ecosystems in the suite for the bioclimate subzone be recognized. The zonal ecosystem unit lies at the center of the suite and all other ecosystem units are distinguished in reference to it. For every bioclimate subzone, it is important to first become familiar with the zonal site characteristics by making a mental imprint of it, in order to then recognize the shifts to other ecosystem units. Zonal also establishes the geographic boundaries of the bioclimate subzone, since the plant community on the zonal site will change as you cross into a new bioclimate subzone.” (Jones et al. 2007)

In British Columbia, where Biogeoclimate Ecosystem Classification (BEC) zonal concepts originally developed, the criteria for a “zonal” site could be met for forested biogeoclimate subzones. In Yukon the definition of ‘zonal’ may need to be modified in order to apply it within a Yukon context (i.e non-forested subzones as in northern Yukon). In order to distinguish Yukon’s ELC zonal concept from that used in BEC, we refer to “zonal sites” as “reference sites” to avoid confusion.

“Reference ecosystem units reflect the climatic and physiographic influences at the site level; as such, it is a ground-up approach. Reference site series represent the average conditions in terms of climate, soil texture, soil moisture, and soil nutrients; “sites on which the moisture conditions experienced by plants are primarily under the control of the local climate” (Kimmins, 1997). The influences of climate at the local level include precipitation duration and type, cold air draws, frost valleys, windward and leeward slopes, rain-shadow valleys, and so on, which are not accurately recorded using weather stations. However, it is possible to see these climatic patterns reflected in the plant communities of the reference ecosystem units. “Because climatic data are scant or lacking in many areas and climatic analysis alone will not produce a practical ecosystem classification, a reliable functional link between climate and ecosystems is needed… the concept of zonal ecosystem provides this link” (Meidinger and Pojar, 1991).

The zonal ecosystem is that which best reflects the mesoclimate or regional climate of an area. The integrated influence of climate on the vegetation, soil, and other ecosystem components is most strongly expressed in those ecosystems least influenced by local relief or by physical and chemical properties of soil parent materials. Such ecosystems have the following characteristics:

1. middle slope position on the meso-slope in mountainous terrain; upper slope position in subdued terrain;

6 This section was largely extracted from Jones et al. “Chapter 4. Principles of Ecosystem Classification for the Yukon” In Yukon’s Ecological Land Classification and Mapping Program: Concepts Towards a Strategic Plan, 28-31. Silvatech Group, 2007.

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2. slope position, gradient, aspect, and location that does not result in a strong modification of climate (e.g., frost pocket, snow drift area, steep south or north aspect);

3. gentle to moderate (5-30%) slope; in dry or cold climates, on slopes to less than 5%; in wet climates, on slopes up to 50%; and

4. soils that have: (a) a moderately deep to deep (50-100+ cm) rooting zone, (b) no restricting horizon within the rooting zone, (c) loamy texture with coarse fragment content less than 50% by volume, and (d) free drainage.

5. [For continuous permafrost regions in which the active ice layer is 30-50cm deep, zonal occurs on the soils with average drainage conditions (i.e. morainal deposits) over the permafrost.]

Hence, the biogeochemical cycles and energy exchange pathways of reference ecosystems are more or less independent of local relief and soil parent material, and are in equilibrium with the regional climate.

Other ecosystems in a given area are influenced more strongly by local physiography and the physical and chemical properties of soil parent materials. They can be drier, wetter, richer, or poorer than zonal ecosystems; and overall they do not provide as clear a reflection of the regional climate.” (Meidinger and Pojar, 1991)

Edaphic ecosystem units are those drier and wetter than reference. Xeric sites are drier than expected with the local precipitation due to rapid drainage from steep slopes, thin soils over bedrock, coarse-textured soils that don’t hold moisture, or crest positions that shed water quickly but receive no up-slope soil moisture (Kimmins, 1997). Hygric sites have good-to-moderate soil drainage, but receive abundant water and nutrients from up-slope terrain. Hydric sites have poor soil drainage due to a high clay and organic materials content, and receive abundant soil water from up-slope areas resulting in saturated soils for much of the year (Kimmins, 1997). The dry edaphic ecosystem units are found on upper slopes, crests, ridge tops, shallow soils, rock outcrops, or on glaciofluvial parent materials. The moist edaphic ecosystem units are found on toes of slopes, seepage sites, draws, gullies, stream edges, or on fluvial and alluvial parent materials. The wet edaphic ecosystem units are found on depressions, lake benches, wetland benches, or on lacustrine parent materials.

When the vegetation composition changes notably on reference sites, this marks the location of a change in bioclimate subzones. Within a bioclimate area, a suite of repeating edaphic and reference ecosystem units will occur as predictable patterns on the landscape. When the ecosystems no longer follow the patterns, the bioclimate area has changed. Since the reference ecosystem unit is reflective of only the climatic influences and not topographic or soil influences, its distribution is used to determine the geographical extent of the bioclimate units (Meidinger and Pojar, 1991). “On xeric, hygric, and hydric sites, soil conditions dominate, and the vegetation does not accurately reflect the regional climage. Only on the mesic site does the vegetation and soil truly

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indicate the climate of the area. Consequently, the geographical extent of a zone or subzone is defined by the composition and structure of the vegetation and the nature of the soil on the mesic site” (Kimmins, 1997).

The concept of zonal leads to the identification of the reference ecosystem unit, the suite of edaphic ecosystem units around it, and the geographic range of this suite denoted as the bioclimate subzone.

Reference ecosystem units are not necessarily the most common ecosystems in a bioclimate subzone. In keeping with the description above, some mountainous areas may have relatively few areas that are flat to moderate slopes with loamy soils. There may in fact be more north and south slopes, but these will not likely represent the reference ecosystem units due to greater topographical influences. That said, however, the boundary of the change between reference and the submesic ecosystem units on the steeper slopes, varies with each bioclimate subzone depending on the climatic influences. In wetter bioclimate subzones, such as coastal mountains, the reference ecosystem unit extends upwards on both north and south slopes, due to the lack of strong solar insolation (drying and heating by the sun). How far that reference ecosystem extends upward across other landscape positions or on other parent materials, establishes the range of site conditions for reference in that bioclimate subzone. A new ecosystem unit is defined when there are significant changes to the site characteristics reflected in the understory vegetation community.

Ecosystem units are best identified by their understory plant compositions. The combination of understory plants (shrubs, herbs and mosses/lichens) reflect the site conditions of local climate, soil moisture and nutrients, parent materials, and topographic position. The understory plants are more susceptible to small changes in these site conditions since their roots are shallower and more confined. As the site conditions become undesirable, they drop out of the community. Trees on the other hand, are able to overcome small changes in site conditions since their roots extend further and deeper, and their physical size enables them to compensate for lack or excess in site conditions. As a result, the same trees may exist on a wide range of ecosystem units. Typically, though, the growth rates of these trees vary with the site conditions. On optimal sites, the trees grow at their most vigorous rate and to their greatest size. On less than optimal sites, either drier or wetter, the trees grow more poorly. The vigour of the trees can be used as an indicator of the ecosystem unit through the assessment of core samples. However, this is not practical means of determining the quality of the site. It is easier and more effective to assess the understory plants.

In this regard, non-forested ecosystems that span the full range of site conditions can be identified in the same way, using the same principles and techniques. The site conditions that indicate the mesic ecosystems in forest stands are the same site conditions that indicate the mesic ecosystems in shrublands, grasslands, alpine and tundra. Wetlands, however, do not follow the reference concept since represent the ecosystems in the hydric soil moisture classes and instead include other influencing factors such as water pH.

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When the phytotopology ecosystem classification systems began to be developed in Canada, ecologists acknowledged the difficulty of assessing the understory plants in seral stage stands. The abundance of plants varies considerably with the age of the stand and its successional stage. The solution for creating a solid classification system was to describe the ecosystem units as they exist in their climax state. This facilitated the sorting and classifying of ecosystems into a simpler classification system. The description of the seral stage versions of the ecosystem units was intended to come at a later date, pending funding and resources. One such example is the field guide for the “Hardwood-dominated Ecosystems in the SBSdk and ICHmc2 of the Prince Rupert Forest Region” (Williams, et.al, 2001). Regardless, the classification systems were sufficient to assist foresters and ecologists without seral descriptions, due to the emphasis on many site variables that lead to the determination of the ecosystem unit. Where one variable (e.g. vegetation) is confusing, the other variables take on greater emphasis.

This is how users of the ecosystem classification can identify the units on the ground as well as during mapping, regardless of the seral stage of the stand; this is how an ecosystem classification system can be developed independent of the seral stage, yet still provide a description of the plant community in each of the seral stages.” (Jones et al. 2007)

The Yukon Ecosystem and Landscape Classification · PDF fileThe Yukon Ecosystem and Landscape Classification (ELC) ... We also discuss factors that influence ecosystems at the macroclimate,

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