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ESTIMATING WILDLIFE HABITAT TRENDS ON 1 Estimating Wildlife Habitat Trends on Agricultural Ecosystems in the United States Stephen J. Brady 1 and Curtis H. Flather 2 1US Department

Jan 25, 2020

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  • ESTIMATING WILDLIFE HABITAT TRENDS ON AGRICULTURAL ECOSYSTEMS IN THE UNITED STATES

    Stephen J. Brady1 and Curtis H. Flather2

    -- Plenary Session 2 --

    Ecosystem/Habitats Impacted by Agricultural Activities

    Tuesday 6 November 2001

    Paper presented to the:

    OECD Expert Meeting on Agri-Biodiversity Indicators 5-8 November 2001 Zürich, Switzerland

    1 US Department of Agriculture, Natural Resources Conservation Service. Natural Resources Research Center, 2150 Centre Ave.,Ft. Collins, Colorado 80526-1891, United States.

    2 US Department of Agriculture, Forest Service Natural Resources Research Center, 2150 Centre Ave., Ft. Collins, Colorado 80526-1891, United States.

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    Estimating Wildlife Habitat Trends on Agricultural Ecosystems in the United States

    Stephen J. Brady1 and Curtis H. Flather 2

    1US Department of Agriculture, Natural Resources Conservation Service 2US Department of Agriculture, Forest Service

    1&2 Natural Resources Research Center, 2150 Centre Ave., Ft. Collins, Colorado 80526-1891

    Abstract Recent trends (1992 – 1997) in wildlife habitat on agricultural and grazed ecosystems are reviewed using data from the 1997 National Resources Inventory. Land use changes, the losses and gains of wetlands, and reasons for wetland losses are described. Ecological indices describing spatial pattern and fragmentation of cropland and rangeland habitats are discussed, and geographically explicit summary statistics are presented for the United States. The effect of the Department of Agriculture’s Conservation Reserve Program is described as an example of a multi-purpose habitat intervention scheme. Because land resource planners need estimates of habitat quantity and condition, the concept of wildlife habitat management as a secondary use of agricultural lands is reviewed. The uses and limitations of ecological indicators and habitat matrices, including statistical estimates of precision and the need to establish relationships between habitat-based indicators and direct measures of biodiversity, are also discussed.

    Keywords: Agri-environmental indicators, National Resources Inventory, wildlife habitat, United States.

    Introduction The kind, amount, and distribution of life supporting elements on the landscape collectively determine the quality of habitat useful to wildlife. Each species has unique requirements with regard to these various elements. Our knowledge of these requirements for most species is very limited while for a few species our understanding of their habitat needs is better. Species response to management of habitats exhibits great variability over scales of both time and space. While our ability to measure ecological pattern continues to improve there is much to be learned about ecological processes and functions. Although scientists continue to make models of ecological systems there remains a substantial amount of unexplained variance in the explanatory power of those models. Habitat management is therefore a combination of both science and art. Aldo Leopold (1966: p. 177-178) provided an interesting description: “There is much confusion between land and country. Land is the place where corn, gullies, and mortgages grow. Country is the personality of the land, the collective harmony of its soil, life, and weather. ….Poor land may be rich country and vice versa. Only economists mistake physical opulence for riches. Country may be rich despite a conspicuous poverty of physical endowment, and its quality may not be obvious at first glance, nor at all times…. It [wildlife] often represents the difference between rich country and mere land.” All land can be considered habitat, but its quality varies from extreme poverty to abundance.

    The task at hand is a challenging one, again as per Leopold (1933:p. 124): “When the game manager asks himself whether a give piece of land is suitable for a given species of game, he must realize that he is asking no simple question, but rather he is facing one of the great enigmas of animate nature. An answer good enough for practical purposes is usually easy to get by the simple process of noting whether the species is there and ready, or whether it occurs as ‘similar’ range nearby. But let him not be cocksure about what is ‘similar’, for this involves the deeper questions of why a species occurs in one place and not

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    in another, which is probably the same as why it persists at all. No living man can answer that question fully in even one single instance.”

    Land use is the principal factor determining the base level of abundance of indigenous species. In most cases land use has a greater impact on species abundance than does the management of land (e.g., application of practices for agricultural production or soil and water conservation). Agriculture affects habitat directly through converting natural habitats to cultivation, grazing, or other manipulation and the associated repeated disturbances that accompany those conversions. Agriculture indirectly affects wildlife habitat through water management practices for irrigation and drainage, soil erosion and sedimentation, and elevated nutrient and pollutant discharges into the environment. The direct effects of land use conversions on habitat are more easily measured than are the indirect effects. While the use of land is relatively easy to document, assessing its quality (productive, economic, habitat, etc.) is more challenging.

    Most indicators of agriculture’s affect on habitat reflect habitat patterns across the landscape. Those patterns and the biological diversity associated with them are the cumulative result of many ecological processes operating over time. It is much easier to describe the resulting patterns than it is to quantify the processes. Natural systems are inherently variable, and this variability is expressed both spatially and temporally. Because wildlife populations are the result of many processes operating together, the quantity and quality of habitat are just two of the indicators affecting the distribution and abundance of wildlife. Population density is often an inaccurate estimator of habitat quality (Van Horne 1983) and some population fluctuations are not related to habitat but may be the result of catastrophic weather conditions, disease, or overexploitation (Schamberger 1988). Habitat indicators may be useful for comparing between alternative agricultural land management scenarios for regional or national program planning and related purposes. However, they must be designed so that they may be tested against empirically derived wildlife population estimates. Ideally they will be designed as falsifiable hypotheses.

    Testing of habitat indicators should be done with multiple measures of biological diversity to properly reflect the complexity of natural systems. This is a problem because extant data sources representing many species are usually not available. Where data are available for a class of organisms, such as birds, the measures of diversity within that class should include statistical estimates of species richness as well as equitability or dominance. One should examine population responses by the very abundant species, very rare species, and those in between. Tests of habitat indicators for community diversity should accompany tests of habitat indicators for favored species (e.g., ring-necked pheasants, Phasianus colchicus, or gray partridge, Perdix perdix).

    The National Resources Inventory Much of the data in the succeeding pages is the result of analyses of the 1997 National Resources Inventory (NRI, Natural Resources Conservation Service 2000). The NRI is an inventory of soil, water, land cover/uses and related resources on the nonfederal lands of the U.S. It is a stratified random sample of over 800,000 points that has been repeated at 5-year intervals since 1982. The purpose is to obtain statistically reliable estimates of the conservation treatment of the nonfederal lands for use by the U.S. Department of Agriculture, Congress, policy makers, and others in evaluating national programs and policies pertaining to agriculture, land use and natural resources occurring on nonfederal lands. In the following pages NRI data are displayed by Farm Resource Regions and by hydrologic units. The Farm Resource Regions are defined primarily for economic analyses by the Economics Research Service, U.S. Department of Agriculture. The hydrologic units represent the boundaries of large watersheds defined by the U.S. Geological Survey. This scale represents the 4-digit hydrologic unit scale although hydrologic units can be aggregated or divided from this scale for other purposes. It should be noted that neither of these categories are “ecological regions” although as progress is made we will move toward ecological regions as an analysis framework.

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    Land Use Seventy-nine percent of the land in the United States is in nonfederal ownership. Land in federal ownership consists primarily of forests, rangelands, and parks. Some federally owned rangeland is used by private individuals to graze livestock on an annual fee basis. However most agricultural production occurs on nonfederal land. Major land uses in the United States for 1997 (Natural Resources Conservation Service, 2000) are rangeland (20.9%), forest (20.9%), federal (20.7%), cropland (19.4%), pasture (6.2%), urban, built-up and roads (5.0%), Conservation Reserve Program (CRP, 1.7%), and miscellaneous (water bodies, mined land, barren, etc., 5.2%). Rangeland is land used by grazing animals where the management consists of manipulating the vegetation primarily by adjusting

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