53 Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA. PLANT COMMUNITIES ASSOCIATED WITH THE RARE, PALEOENDEMIC OAK, QUERCUS TOMENTELLA ON SANTA CRUZ AND SANTA ROSA ISLANDS, CALIFORNIA Laura Kindsvater Save the Redwoods League 114 Sansome St. #1200 San Francisco, CA 94104 [email protected]ABSTRACT: Descriptive statistics and canonical correspondence analysis were used with vegetation plot data to discover more about plant communities and environmental factors associated with Quercus tomentella on Santa Rosa and Santa Cruz Islands. In comparisons with existing data on Santa Rosa Island, plots with Q. tomentella shared the most species in common with closed-cone pine forest, mixed island woodland, Torrey pine woodland, and mixed chaparral communities. These communities probably covered a much larger acreage on the islands 200 years ago, before intensive grazing. Of the 162 taxa of higher plants that were associated with Q. tomentella in this study, 124 are native. Twenty-four native taxa were found in groves near to those sites that have suffered severe soil erosion, and some of these may be useful for planting in groves in need of restoration, in order to help trap and build plant litter and topsoil. Ten moderately to highly invasive taxa were found in Q. tomentella groves, and these may be contributing to low regeneration in Q. tomentella because of their tendency to reduce and deplete soil moisture. KEY WORDS: California Channel Islands, island oak, woodland, Quercus tomentella, restoration, chaparral, Canonical Correspondence Analysis INTRODUCTION California's Channel Islands are home to a rich diversity of plants. About 1,788 plant species, subspecies, and varieties grow on the islands (compared to more than 5,800 native species in the state as a whole; Raven 1967, Hickman 1993). As urbanized southern California is one of the world's hotspots for biodiversity, the lightly populated islands are an important refuge for rare and native plant species. Restoration managers working on the islands are faced with a difficult challenge: how to restore an ecosystem without a clear picture of what the pre-European or optimal conditions for a rare and native species might be. Reference sites have become, arguably, non-existent. Non-native grazers and browsers (including sheep, goats, pigs, cattle, deer, elk, and others) introduced to the islands within the last 150 years have caused soil erosion and greatly changed the distribution and prevalence of native vegetation (Junak et al. 1995, Peart et al. 1994, Van Vuren and Coblentz 1987, Baber 1982, Hobbs 1980, Hochberg et al. 1980). Records and maps of what the plant communities were like 150-200 years ago are vague (for example, a map published in 1886 lists only two plant communities on Santa Rosa: "cactus" and "oak brush"; United States Coast Survey 1886). In the absence of detailed records or good reference sites, where can restoration managers turn for information? How do they know where a certain species was in the past? In addition, because ecosystems have changed so dramatically, it may be impossible to restore the land to past conditions. This is a question of much debate between land managers and ecologists: should we be trying to restore the past? Or, should we aim to restore to some set of optimal conditions that are different than the past, in which rare species can thrive?
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
PLANT COMMUNITIES ASSOCIATED WITH THE RARE, PALEOENDEMIC OAK,
QUERCUS TOMENTELLA ON SANTA CRUZ AND SANTA ROSA ISLANDS, CALIFORNIA
ABSTRACT: Descriptive statistics and canonical correspondence analysis were used with vegetation
plot data to discover more about plant communities and environmental factors associated with Quercus
tomentella on Santa Rosa and Santa Cruz Islands. In comparisons with existing data on Santa Rosa Island, plots with Q. tomentella shared the most species in common with closed-cone pine forest, mixed
island woodland, Torrey pine woodland, and mixed chaparral communities. These communities probably
covered a much larger acreage on the islands 200 years ago, before intensive grazing. Of the 162 taxa of
higher plants that were associated with Q. tomentella in this study, 124 are native. Twenty-four native taxa were found in groves near to those sites that have suffered severe soil erosion, and some of these may
be useful for planting in groves in need of restoration, in order to help trap and build plant litter and
topsoil. Ten moderately to highly invasive taxa were found in Q. tomentella groves, and these may be contributing to low regeneration in Q. tomentella because of their tendency to reduce and deplete soil
moisture.
KEY WORDS: California Channel Islands, island oak, woodland, Quercus tomentella, restoration,
chaparral, Canonical Correspondence Analysis
INTRODUCTION
California's Channel Islands are home to a rich diversity of plants. About 1,788 plant species, subspecies,
and varieties grow on the islands (compared to more than 5,800 native species in the state as a whole; Raven 1967, Hickman 1993). As urbanized southern California is one of the world's hotspots for
biodiversity, the lightly populated islands are an important refuge for rare and native plant species.
Restoration managers working on the islands are faced with a difficult challenge: how to restore an
ecosystem without a clear picture of what the pre-European or optimal conditions for a rare and native species might be. Reference sites have become, arguably, non-existent. Non-native grazers and browsers
(including sheep, goats, pigs, cattle, deer, elk, and others) introduced to the islands within the last 150
years have caused soil erosion and greatly changed the distribution and prevalence of native vegetation (Junak et al. 1995, Peart et al. 1994, Van Vuren and Coblentz 1987, Baber 1982, Hobbs 1980, Hochberg
et al. 1980).
Records and maps of what the plant communities were like 150-200 years ago are vague (for example, a
map published in 1886 lists only two plant communities on Santa Rosa: "cactus" and "oak brush"; United
States Coast Survey 1886). In the absence of detailed records or good reference sites, where can
restoration managers turn for information? How do they know where a certain species was in the past? In addition, because ecosystems have changed so dramatically, it may be impossible to restore the land to
past conditions. This is a question of much debate between land managers and ecologists: should we be
trying to restore the past? Or, should we aim to restore to some set of optimal conditions that are different than the past, in which rare species can thrive?
54
Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Island oak (Quercus tomentella) is the rarest of all of California's oak species, and is restricted in its
present-day natural distribution to six islands off the coast of California (Pavlik et al. 1991). It is one of many island species of special concern in need of recovery. Many of its stands in Channel Islands
National Park are not currently recruiting to the seedling and/or sapling stage, a problem not limited to the
islands. Most white oak species in California are suffering from poor regeneration, for reasons that are not
completely understood (Brooks and Merenlender 2001). As the number of non-native grazers and browsers has been greatly reduced on the islands over the past 20 years, and because there are a few
stands where regeneration of island oak has resumed within the last decade or more, island oak may also
offer some insight to scientists working to conserve and restore oak woodlands on mainland California. Gophers and ground squirrels, which significantly limit oak seedling establishment and survival on the
mainland (Tyler et al. 2002), are absent on Santa Cruz and Santa Rosa islands, which may help to reduce
the complexity of the regeneration puzzle.
To inform a plan for recovery of island oak, I have researched its current and potential habitats. The
objectives of this paper are to analyze the habitat of island oak, Quercus tomentella, on Santa Rosa and
Santa Cruz Islands with regard to the species and range of environmental conditions associated with it, and compare its plant assemblages with that of other communities found on these islands. In addition, I
have examined soil conditions (Kindsvater 2006a), and constructed a GIS model based upon associated
environmental parameters identified as a result of fieldwork (Kindsvater 2006c). This knowledge will inform restoration and conservation protocols for the oak and its environs.
This study examines the diversity of species associated with island oak, how consistently these species are found in island oak stands, and which native species are most closely associated with island oak stands
suffering most extensive erosion. Introduced and potentially invasive species associated with island oak
stands were also catalogued. It was hypothesized that Q. tomentella’s distribution might have been
significantly limited by the availability of water, and expected that plant species associated with Q. tomentella would be more similar to those in riparian communities than those in chaparral.
Previous research has shown that Quercus tomentella grows in a variety of plant communities. On Santa Cruz Island, it is found in oak woodland, pine forest, riparian woodland, and chaparral communities
(Junak et al. 1995). On Santa Rosa Island, it forms island oak woodland, and grows in mixed oak
woodland, and closed-cone pine communities (Clark et al. 1990); it has also been observed growing as a
shrub in chaparral on very rocky locations.
METHODS
This study utilizes field data collected during mid-April to mid-May of 2003 and 2004 in 23 large
rectangular plots, ranging from 200 to 225 m2 in size. The plots were located in 11 sites: five on Santa
Rosa Island and six on Santa Cruz Island. Plot locations were chosen to include all geologic substrates, topographic positions, and general vegetation types in which Q. tomentella is known to grow on these two
islands.
Vegetation was sampled using the Braun-Blanquet relevé method (Mueller-Dombois and Ellenberg 1974). Each plant species and its approximate cover within seven cover classes were recorded: a single
occurrence of a plant, < 1% cover, 1 - 5% cover, 6 - 25% cover, 26 - 50% cover, 51 - 75% cover, or >
75% cover. Each tree was included in a maximum of one plot, although some plots were less than 0.5 km apart from each other. Nomenclature for vascular plants follows Junak et al. (1995).
The ideal plot size needed to capture species diversity was determined by beginning with a small plot (1 m
2) and then repeatedly doubling the plot’s area and measuring the incremental increase in number of
species. As long as the increase in number of species met or exceeded 10%, the size of the plot was
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
increased. The increase in number of species dropped below 10% at about 200 m2, which is similar to the
optimal plot size for forests in general, given by Mueller-Dombois and Ellenberg (200 - 500 m2 for tree
stratum and 50 - 200 m2 for undergrowth vegetation only; 1974). The objective was to capture as many
species as possible, while limiting the sampling to a homogeneous plant community (Mueller-Dombois
and Ellenberg 1974). Both closed-canopy and partial canopy woodlands were included in the study.
Geologic substrates sampled on Santa Cruz Island included Santa Cruz Island volcanics (Diablo Peak
member), Santa Cruz Island schist, Monterey shale, and the Blanca formation. Geologic substrates
sampled on Santa Rosa Island included the Beechers Bay formation, Rincon formation, and Santa Rosa Island volcanics (basaltic volcaniclastic rocks). Some of these geologic substrates are also found on the
mainland (e.g. Monterey shale).
For each plot, the following environmental data was collected: slope, aspect, elevation, amount of shelter
from the wind (using a scale from 0 to 10, with 10 being maximum shelter), an estimate of the percent of
bare ground and percent exposed rock, topographic position, percent of surface covered by litter, average
depth of litter, and GPS coordinates of the plot’s corners. The number of strata in the vegetation was recorded, as well as which stratum was dominant, and an estimate of the height of the trees.
Soil samples were collected in both 2003 and 2004 and used to calculate each site’s bulk density and soil color (Kindsvater 2006a). Each soil sample collected in 2003 was also tested for its texture (as percent
sand, silt, and clay) and cation exchange capacity. Each sample collected in 2004 was tested for its soil
texture, total nitrogen, total carbon, total phosphorus, exchangeable potassium, and pH by the University of California Agriculture and Natural Resources Analytical Laboratory.
All vegetation and environmental data were entered into the Turboveg database (Hennekens and
Schaminee 2001). Canonical correspondence analysis was used in the ordination program PC-ORD to examine the relationships between each plot’s plant species and its environment.
RESULTS
Species associated with Quercus tomentella and their overlap with other plant communities
All of the vascular plants found to be associated with Q. tomentella on Santa Rosa Island (SRI) and Santa Cruz Island (SCI) in this study are listed in Appendix 1. The following taxa were found in more than half
of this study’s plant community plots: Baccharis pilularis, Bromus diandrus, Galium aparine,
Gnaphalium spp., Hypochaeris glabra, Silene gallica, Sonchus oleraceus, and Stellaria media. Most of these are non-native, weedy species that occur in open grassland or partly shaded woodland. The only
natives among them are Baccharis pilularis and Gnaphalium spp.
Species growing in an intermediate number of plots (i.e., 25-50% constancy) included: Achillea
Lotus dendroideus var. dendroideus, Marah sp., Mimulus flemingii, Pentagramma triangularis,
Polypodium californicum, Pterostegia drymarioides, Quercus pacifica, Senecio vulgaris, and Vulpia myuros. Of these taxa, 79 percent are native. Only the following are non-native: Avena barbata, Senecio
vulgaris, and Vulpia myuros.
Other native species were found in five (22%), four (17%), or three (13%) plots. Species found in five
plots include: Chenopodium californicum, Clarkia epilobioides, Lessingia filaginifolia var. filaginifolia,
Melica imperfecta, Mimulus longiflorus, Sanicula arguta, and Trifolium willdenovii. Species found in four plots include: Carex globosa, Dryopteris arguta, Dudleya sp., Eriogonum arborescens, Hieracium
Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Uropappus lindleyi. Species found in three plots include: Adiantum jordanii, Agoseris grandiflora,
confertiflorum, Eucrypta chrysanthemifolia var. chrysanthemifolia, Filago californica, Luzula comosa,
Ranunculus californicus, Rhus integrifolia, and Toxicodendron diversilobum.
Contrary to my hypothesis, plant species associated with Q. tomentella were not more similar to those in
riparian communities than those in chaparral. Only 64% of all species found in riparian woodland and
26% of species in riparian herbaceous vegetation on Santa Rosa Island (Clark et al. 1990) were also found in the Q. tomentella sites, while 74% of all species found in mixed chaparral matched Q. tomentella sites
(Table 1). Three vegetation types had even higher percent similarity on Santa Rosa Island: 79% in mixed
woodland, 87% in closed-cone pine forest, and 76% of all species in Torrey pine forest.
Percent matching species were less for all other habitats: 60% in coastal sage scrub 57% in both grassland
and caliche scrub, 55% in Baccharis scrub, 48% in lupine scrub, 29% in coastal bluff scrub, and 40% and
20% in coastal marsh and coastal dune scrub, respectively (all non-native).
Table 1. Percent of species in Santa Rosa Island plant communities associated with Quercus tomentella.
Vegetation Community % associated
species SRI Closed-Cone Pine Forest 87%
SRI Mixed Woodland 79%
SRI Torrey Pine Forest 76%
SRI Mixed Chaparral 74%
SRI Riparian Woodland 64%
SRI Coastal Sage Scrub 60%
SRI Caliche Scrub 57%
SRI Grassland 57%
SRI Baccharis Scrub 55%
SRI Lupine Scrub 48% SRI Coastal Marsh 40%
SRI Coastal Bluff Scrub 29%
SRI Riparian Herbaceous Vegetation 26%
SRI Coastal Dune Scrub 20%
Canonical correspondence analysis between species and environmental variables
Canonical correspondence analysis of the multivariate relationships between species associated with Q.
tomentella and environmental factors produced no statistically significant results, however, they show some general trends that might become more apparent if more data were collected (Kindsvater 2006b).
The lack of statistical significance could be due to the small number and diversity of plots; the plots
included the diversity of all known types of geology and plant communities in which Q. tomentella is
currently known (mixed woodland, chaparral, closed-cone pine forest, and Q. tomentella woodland).
DISCUSSION: IMPLICATIONS FOR RESTORATION
On Santa Rosa Island, several Q. tomentella groves have suffered severe soil erosion (along Burma Road
in the vicinity of Soledad Peak, and facing the back side of Black Mountain near Pecho Peak), which
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
could be attributed to overgrazing by cattle, elk, and deer introduced to the island. Pig rooting could also
have contributed to this problem. Smith thought that these groves had become denuded of topsoil “probably due to a combination of fog drip and some form of allelopathy” and remarked that he had been
told that cattle had rarely gathered there (1976). Regardless of whether allelopathy or severe grazing has
happened in these groves, soil tests show that the remaining soil is highly acidic, with pH as low as 3.3,
and that soil compaction is higher than in groves in which regeneration is currently occurring (Kindsvater 2006a). In addition, these groves are in extremely windy locations, so leaf litter is swept away by the
wind. There is currently no understory vegetation (Figure 1).
Figure 1. Island oak groves near Soledad Peak on Santa Rosa Island, soil erosion
has been so severe that no topsoil remains.
To begin rebuilding topsoil, it would be helpful to plant native plant species in the understory and in the open areas between island oak trees, which could both produce organic matter and help to trap and retain
it. Park staff constructed coco-fiber swales at the Soledad Peak groves in 2006 in order to begin re-
building topsoil, and surrounded the groves with fencing to keep out elk and deer. Near these swales, where small pockets of moisture from fog drip are common, small herbaceous plants such as Lupinus
bicolor have begun to colonize the site. These volunteers could be supplemented with plantings in the
future.
On the periphery and nearby vicinity of the Soledad Peak groves, there are a few native species present,
and several likely candidate species for planting emerge because they are adapted to the site: Baccharis
pilularis ssp. consanguinea, Nassella pulchra, N. cernua, and N. lepida (Chaney 2004), as well as Bromus carinatus, Calandrinia ciliata, Gnaphalium purpureum, Lasthenia californica, Layia
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
platyglossa, Lupinus bicolor, and Sanicula arguta. Other good candidates might be species that are
successfully growing in the nearby (but less eroded) groves (Kindsvater 2006a), as well as species that are well adapted to nutrient poor, extremely acidic soils (McEachern pers. comm. 2004).
The eroded grove near Pecho Peak differs from the Burma Road groves in that it is growing in soils
derived from Santa Rosa Island volcanics (rather than the Monterey shale or Rincon formation, which are sedimentary substrates). On the periphery of the Pecho Peak grove, these native species are present:
ovatum, Stephanomeria virgata, Solanum douglasii, Trifolium willdenovii, Baccharis pilularis, and Lupinus bicolor. Some of these may be suitable for planting among the eroded groves; additional research
to determine which can survive nutrient poor, highly acidic soils would also be helpful.
Introduced species that were in many of this study’s 23 plots included Avena barbata (nine plots),
Bromus diandrus (definitely in 10 plots, with the possibility of being in eight additional plots),
media (12 plots). Of these species, both Avena barbata and Bromus diandrus received a Moderate ranking from the California Invasive Plant Council, signifying that they “have substantial and apparent –
but generally not severe – ecological impacts on physical processes, plant and animal communities, and
vegetation structure” (California Invasive Plant Council website 2009). Research by Doria Gordon, Kevin Rice, J. M. Welker, and others has shown that Bromus diandrus (as well as other annual grasses and
forbs) can have a significant negative impact on Quercus douglasii (blue oak) seedling growth and
survival by dramatically reducing soil moisture (Gordon and Rice 2000; Momen et al 1994; Gordon and
Rice 1993; Gordon et al 1991; Gordon et al 1989). It is is likely that this is also true for Quercus tomentella’s seedling growth and survival.
Bromus madritensis subsp. rubens was also present in some Q. tomentella plots and has received a High ranking from the California Invasive Plant Council; it is thought to have severe ecological impacts.
According to the Council’s website, the rationale for this is that Bromus madritensis subsp. rubens
increases fuel continuity and flammability, and by contributing to removal of shrub cover, alters microhabitat characteristics and soil nutrient cycling and distribution. This grass may also reduce vigor,
fecundity, and species diversity of native annual plant communities, and may hybridize with both alien
and native Bromus species and become more invasive (California Invasive Plant Council website 2009).
Other introduced species that were present in a small number of Quercus tomentella plots and that
received a Moderate ranking from the California Invasive Plant Council website included Brassica nigra,
glomerata, Hirshfeldia incana, Hordeum murinum, and Vulpia myuros all have the potential to spread
rapidly (California Invasive Plant Council website 2009). Erechtites glomerata is of particular concern. It was first collected in 1989 on Santa Cruz Island and is noted in Junak et al 1995 as scarce at present but
spreading. It is among the most serious pests in the Channel Islands; it spread rapidly in an established
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
grassland on San Miguel Island, displacing native grasses and forbs, and did not require any disturbance
prior to this event. Its rapid rate of spread may be caused by its ability to establish facultative mycorrhizal relationships. Seeds disperse by wind and are thought to have blown from San Miguel to Santa Barbara
Island (California Invasive Plant Council website 2009).
CONCLUSION
In combination with other negative factors such as: soil erosion; herbivory, trampling, and rooting by
non-native grazers and browsers; and possibly climate change and/or drought, competition with non-native annual species for water could be a significant limiting factor in Quercus tomentella’s
regeneration. This seems particularly likely on Santa Rosa Island, where many Q. tomentella groves are
isolated, small stands surrounded by a sea of non-native annual grassland.
The low constancy of natives throughout the plots in this study could mean: (1) that Q. tomentella plant
communities have lost some of the species that were formerly associated with them in recent times, in
some or all of the stands; (2) that modern-day Q. tomentella inhabits a variety of different plant communities, with diverse assemblages; or (3) Q. tomentella plant communities on Santa Rosa Island
may differ significantly from Q. tomentella plant communities on Santa Cruz Island (McEachern pers.
comm. 2004). Based on observations made during fieldwork and my general knowledge of the species, I suggest that all three of these are probably true. The first hypothesis is difficult to impossible to test. The
second is correct, given that Q. tomentella has been found in mixed woodland, chaparral, pine forest,
riparian woodland, and pure Q. tomentella forest and that these plant communities have already been shown by other researchers (Clark et al. 1990; Junak et al. 1995) to have characteristic plant species
consistently associated with them. GIS models depicting Q. tomentella potential habitat for Santa Rosa
and Santa Cruz Island also show a large degree of overlap with chaparral, closed cone pine, Torrey pine,
and mixed oak woodland (Kindsvater 2006c). In the new edition of the Manual of California Vegetation, Q. tomentella will likely be considered a “special element” of other vegetation types, since it is found in
more than one vegetation type, but is not consistently present in any of them (John Sawyer pers. comm.
2008).
In comparing Santa Rosa to Santa Cruz, I suggest that the communities differ somewhat both in terms of
which species are present, and in the relative abundance of the different communities. For example, on
Santa Rosa Island’s Black Mountain, Q. tomentella’s largest populations are thickly forested stands, of 100 percent canopy cover. Yet, on Santa Cruz’s Diablo Peak and Alta 2, Q. tomentella’s largest
populations have less than 100 percent cover, making them more savanna than forest; the individual trees
have large patches of grassland in between. The associated species on Black Mountain are somewhat different than those on Diablo Peak and Alta 2. The idea that plant communities on Santa Rosa are
somewhat different than those on Santa Cruz Island is worthy of more study (a larger amount of data,
from more sampling sites, stratified across plant communities would be needed). It would also be very interesting to see how vegetation types associated with Q. tomentella on these two islands compare to
other islands.
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GTR-184, Albany CA.
United States Coast Survey. 1886. Topography of Santa Rosa Island, Santa Barbara Channel, Coast of
California. Register No. 1325. U.S. National Archives, Washington, DC. Van Vuren, D. and B. Coblentz. 1987. Some ecological effects of feral sheep on Santa Cruz Island,
California. Biological Conservation 41:253-268.
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
APPENDIX 1: 162 HIGHER PLANT TAXA ASSOCIATED WITH QUERCUS TOMENTELLA ON SANTA ROSA AND
SANTA CRUZ ISLANDS
Scientific name Common name Endemicity Introduced? Cal-IPC
Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Scientific name Common name Endemicity Introduced? Cal-IPC
Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Scientific name Common name Endemicity Introduced? Cal-IPC
Nuttall's island bedstraw 3 r (plot 13), + (plot 18)
Galium porrigens climbing bedstraw + (plot 11)
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Scientific name Common name Endemicity Introduced? Cal-IPC
Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Scientific name Common name Endemicity Introduced? Cal-IPC
rating
Cover classes for each plot
Lotus dendroideus var.
dendroideus
island deerweed 3 + (plot 1), 1 (plot 3), r (plot 4), + (plot 5), 1 (plot
Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Scientific name Common name Endemicity Introduced? Cal-IPC
rating
Cover classes for each plot
Prunus ilicifolia subsp.
lyonii
island or Catalina cherry 2 (plot 13), + (plot 14), + (plot 17)
Silybum marianum milk thistle X Limited + (plot 15)
Sisymbrium officinale hedge mustard X + (plot 3), r (plot 15), + (plot 16)
Solanum clokeyi island nightshade 3 1 (plot 16)
Solidago californica California goldenrod + (plot 7)
Sonchus asper prickly sow thistle X Eval No
List
+ (plot 9), r (plot 21), r (plot 22), r (plot 23)
Sonchus oleraceus common sow thistle X r (plot 1), r (plot 3), r (plot 6), + (plot 7), + (plot 9),
+ (plot 11), + (plot 12), + (plot 13), r (plot 14), r
(plot 15), + (plot 16), + (plot 17), + (plot 21) Sonchus species sow thistle r (plot 2), r (plot 5), + (plot 9)
Spergula arvensis var.
arvensis
stickwort or starwort X + (plot 9)
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Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA.
Scientific name Common name Endemicity Introduced? Cal-IPC
rating
Cover classes for each plot
Stachys bullata hedge nettle or wood mint r (plot 14), 2 (plot 16), 1 (plot 17), + (plot 23)
Stebbinoseris heterocarpa + (plot 7)
Stellaria media common chickweed X 1 (plot 1), + (plot 2), + (plot 5), 1 (plot 6), 1 (plot
Endemicity: 1 = Endemic to Santa Rosa Island; 2 = Endemic to Santa Cruz Island; 3 = Endemic to multiple California islands.
Introduced species: X = introduced; ? = not known whether introduced or native.
Cover classes: r = single individual; + = less than one percent cover; 1 = one to five percent cover; 2 = six to 25 percent cover; 3 = 26 to 50 percent cover; 4 = 51 to 75 percent cover; 5 = 76 to 100 percent cover.