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HomeMy WebLinkAboutAddenda - RFP - P982 BOBCAT RIDGE TRAIL DESIGN AND CONSTRUCTONChapter 3. Vegetation Resources In this chapter we describe the various plant and vegetation resources found at Bobcat Ridge. This includes a discussion of plant communities, rare plants, and system factors including ecological processes that give rise to the vegetation composition and distribution within the natural area. In the summer of 2004, the Colorado Natural Heritage Program (CNHP) was contracted to conduct a biological survey of Bobcat Ridge Natural Area for the purpose of identifying native plant communities and ecosystems present that are of conservation concern. Much of the following section is adapted from their report (Doyle 2004). Plant Communities and Ecosystems Ecosystems are defined as dynamic assemblages of plant and animal communities that occur together on the landscape. They are unified by similar ecological processes such as climate moderated by elevation, natural disturbance processes and/or underlying abiotic factors and gradients such as bedrock geology and hydrology. Native plant communities at Bobcat Ridge Natural Area occur within five ecosystems as shown in Figure 3.1 and Table 3.1. There is one wetland ecosystem: Lower Montane Riparian Woodland; and four upland ecosystems: Ponderosa Pine Woodland, Ponderosa Pine Savanna, Lower Montane-Foothills Shrubland, and Foothills Grassland. In each of these ecosystems several native plant community associations occur. Rare communities within these ecosystems are listed in Table 3.2. The Ponderosa Pine Woodland ecosystem is located at the highest elevations on the slopes and high points along Green Ridge in the western part of the property. This area was severely altered by the Bobcat Gulch wildfire in 2000 that burned 1,000 acres of forest within Bobcat Ridge Natural Area. At lower elevations on the east- and south-facing slopes of Green Ridge, the Ponderosa Pine Woodland grades into the Ponderosa Pine Savanna, a mosaic of shrubs, grasses and scattered trees. The valley between Green Ridge and the hogbacks to the east has remnants of a Foothills Grassland ecosystem. The majority of this ecosystem has been converted to agricultural land use or has been degraded by grazing. The Lower Montane-Foothills Shrubland ecosystem is found on the sandstone hogbacks that run along the east side of Bobcat Ridge. The Lower Montane Riparian Woodland ecosystem is located along stream drainages, some of which have intermittent surface flow. Figure 3.1. Map of plant communities and ecosystems at Bobcat Ridge. Table 3.1. Rare plant communities at Bobcat Ridge Natural Area Upland Plant Ecosystems Rare Plant Communities CNHP State Ranking Ponderosa Pine Woodland Pinus ponderosa/Leucopoa kingii Ponderosa pine/spike fescue Vulnerable Ponderosa Pine Savanna Pinus ponderosa/ Cercocarpus montanus/ Andropogon gerardii P. pine/mountain mahogany/big blue stem Imperiled * Lower Montane-Foothills Shrubland Cercocarpus montanus/ Stipa scribneri Mountain mahogany/scribner needlegrass Vulnerable* Cercocarpus montanus/ Stipa neomexicana Mountain mahogany/New Mexico feathergrass Imperiled/vulnerable* Foothills Grassland Stipa comata/Bouteloua gracilis Needle-and-thread/blue gramma Imperiled/vulnerable Riparian Plant Ecosystems Lower Montane Riparian Woodland Populus angustifolia /Prunus virginiana Narrow-leaved cotoonwood/American plum Critically imperiled *Plant community was found to be intact and cover a significant enough area to be considered an element occurrence by the CNHP. See the 2004 Inventory of Larimer County by the Colorado Natural Heritage Program for more details. Woodland and Savanna Woodland and Savannas occupy about 70% of the land area at Bobcat Ridge Natural Area. The Bobcat Gulch Fire of 2000 burned approximately two-thirds of the forested area on the property. The forest consists mostly of ponderosa pine (Pinus ponderosa) with some Rocky Mountain maple (Acer glabrum). The burned area contains a mix of well-established native grasses and patches dominated by various weedy species (Figure 3.2). In the areas with an open canopy (savannas), a large part of the understory consists of cheatgrass (Bromus tectorum). However, pockets of mountain mahogany (Cercocarpus montanus) and big bluestem (Andropogon gerardii) in the understory of ponderosa pine comprise a plant community ranked as globally imperiled by the Colorado Natural Heritage Program. Ponderosa Pine Woodland The Ponderosa Pine Woodland ecosystem is the most common found in the foothills and montane elevations (6,000-9,000 feet) along the Front Range. Ponderosa pine grows on warm dry slopes, is intolerant of shade, and grows well in full sun from bare mineral soil. These trees are the dominant species on dry slopes, but they are interspersed with Douglas fir (Pseudotsuga menziesii) on moister, north-facing slopes. Historically, these ecosystems likely sustained frequent, low intensity fires and sporadic catastrophic (i.e. stand-replacing) burns (Huckaby et al. 2003, Shinneman and Baker 1997). Figure 3.2. Burned area of Woodland at Bobcat Ridge. The Bobcat Gulch Fire was one such catastrophic, large natural disturbance in the Ponderosa Pine Woodland ecosystem on Bobcat Ridge Natural Area. Most of the trees in this ecosystem were killed by the severe crown fire, even in usually protected steep drainages and north-facing slopes. A site visit made on August 13, 2004 with US Forest Service researcher Laurie Huckaby revealed that widespread surface fire had occurred at least two times at Bobcat Ridge during the last 200 years. The majority of tree mortality occurred in what is likely a single stand of ponderosa pine dating to the early 1900’s. This suggests that, historically, the current Ponderosa Pine Woodland was more characteristically a Ponderosa Pine Savanna. Unusual climatic events (perhaps an extended wet period) likely promoted the regeneration and growth of ponderosa pine across Bobcat Ridge into a more closed-canopy forest condition. In the 2000 fire, much of the understory was consumed or lost to erosion following denudation. Understory regeneration may have been suppressed by emergence of early successional weeds (e.g. mullein (Verbascum thapsus)) or plants from post-fire seeding measures undertaken by the US Forest Service. Aerial seeding of the area included species such as slender wheatgrass (Elymus trachycaulus), sandberg bluegrass (Poa secunda), milk vetch (Astragulus spp.), mountain brome (Bromus marginatus), mountain muhly (Muhlenbergia montana), Arizona fescue (Festuca arizonica), and Parry’s oats (Danthonia parryi). Only small vestiges of what was likely present prior to the fire are recognizable. Ponderosa pine and spike fescue (Leucopoa kingii) occupy several ridgetops at higher elevations. Spike fescue is considered an indicator of late successional forest stands within this ecosystem (Tirmenstein 1987). Pockets of spike fescue have survived on several ridgetops and slopes at the outer edges of the fire at the north end of the property. These areas are currently threatened by the invasion of cheatgrass, especially notable as monotypic circles around trees that burned. It is difficult to assess whether spike fescue occurred on adjacent ridges to the south in the severely burned area. Otherwise, the Ponderosa Pine Woodland ecosystem can be seen to have a typical species composition, with Geyer’s sedge (Carex geyeri) locally abundant in areas of the understory where it is not out-competed by cheatgrass. North-facing slopes are co-dominated by ponderosa pine and Douglas fir forming relatively dense, closed canopy forests. No ponderosa pine seedlings were noted in the severe burn area during the 2004 inventory. However, seedlings were seen in the less severely burned areas. Ponderosa pine seed germination is reduced by moisture stress, such as that from the drought conditions that have persisted since the fire. Competing vegetation also decreases germination (Burns and Honkala 1990). Future fire management at Bobcat Ridge is being addressed as part of the comprehensive restoration plan (prescribed fire). Wildfire operations falls under the jurisdiction of the Loveland Rural Fire District. All wildfires at Bobcat Ridge will be suppressed. Conservation Target Ponderosa Pine Woodland Objectives Allow natural regenerative processes to restore portions of the forest while aggressively controlling invasive weeds and undertaking proactive restoration efforts to reduce erosion and enhance the native character. Natural Processes/ Functions/ Interactions High frequency – mixed severity fire is the dominant ecological process. Threats & Stresses (Source of Stress)  High intensity rainstorms leading to severe erosion.  Introduction and establishment of weeds, especially cheatgrass.  Additional high intensity wildfires due to unnatural surface fuel buildup (invasion of cheatgrass together with downed woody material). Strategy/Action  Stabilize eroding soils.  Prevent the introduction and spread of invasive weeds.  Develop prescribed fire management plan to reduce probability of high intensity surface fires; contain the spread should one ignite.  Enhance wildlife habitat Measure of Success Successful mitigation of eroded areas. Reduced area of invasive species. Conservation Plan  Complete a site restoration plan.  Inventory severe erosion locations and implement management measures to reduce soil loss.  Aggressively control invasive species. Monitor routinely to detect new invasions.  Prevent further catastrophic fire from post-fire fuel buildups.  Determine historic range of variability of forest density and disturbance regime.  Create patches of meadows to attract native browsers.  Determine utilization of burned area by woodpeckers, flickers, nuthatch and similar species for cavity nesting, feeding, etc.  Monitor re-establishment of ponderosa pine seedlings. Ponderosa Pine Savanna The Ponderosa Pine Savanna ecosystem consists of widely spaced ponderosa pine trees with grassland parks or shrublands. It occurs at relatively lower elevations and on somewhat rockier substrates, making this ecosystem moderately drier than the Ponderosa Pine Woodland ecosystem. The main plants associated with this ecosystem are ponderosa pine, mountain mahogany and big bluestem. This plant association is found at the ecotone between forests on higher slopes and grasslands in valley bottoms, combining elements of each. Unique in this association is the presence of big bluestem, a species that abundantly occurs in the tallgrass prairie of the Plains states to the east, but is much less common in the Foothills. Patches of big bluestem are scattered throughout the savanna approximately between 5,960 and 6,440 feet on the east-facing slopes of Green Ridge. At higher elevations in this range, this association tends to occur on more south-facing aspects. Much of the savanna sustained low intensity surface fire during 2000. Some trees were torched and shrubs and grasses were top-killed by the fire. Mountain mahogany is resprouting from root bases and several native grasses are abundant. Big bluestem, like many native grasses, is well-adapted to fire (Uchytil 1988). There is an abundance of fringed sage (Artemisia frigida) following the 2000 fire. This species and certain other early successional colonizers (e.g. mullein) will likely decrease in abundance over time. However, cheatgrass is abundant and dominant in many areas and may persist and expand if not addressed. Conservation Target Ponderosa Pine Savanna Objectives Enhance habitat value and native character through restoration efforts designed to eradicate weeds and maintain the system through periodic natural disturbance. Natural Processes/ Functions/ Interactions Seasonal grazing and periodic fire and drought are natural processes that sustain native grasslands. A June 2004 wildfire on 10 acres of grassland and woodland resulted in the conversion of non-native ground cover to native grasses and forbs. Threats & Stresses (Source of Stress)  Invasion by non-native like cheatgrass and Canada thistle.  Lack of natural disturbance. Strategy/Action  Locate remnant grassland patches to determine restoration targets including species diversity and abundance.  Use a combination of targeted cool-season and dormant season grazing, prescribed fire, and enhancement seeding to convert non-native areas to native. Measure of Success Reduced areas of non native species and increase of native species, specifically the ponderosa pine, mountain mahogany, big bluestem plant community. Conservation Plan  Complete a site restoration plan.  Monitor vegetation recovery from the 2004 burn; implement early season prescribed burning if area continues to demonstrate native plant recovery.  Use prescriptive grazing to reduce cool season, non native species like cheatgrass.  Introduce small scale prescribed burns to reduce the abundance of widespread non-native species.  Once desired condition is achieved, reintroduce periodic natural disturbance processes (i.e. grazing, fire). Shrubland The hogback area at Bobcat Ridge is covered in shrubs with exposed cliff faces and comprises about 5% of the area (Figure 3.3). Shrublands are also found in the transition between woodlands and grasslands on the west side of the valley. Shrubs across the site are mostly native and include mountain mahogany, rabbitbrush (Chrysothamnus viscidiflorus), three-leaf sumac (Rhus trilobata), and plum thickets (Prunus americana). Lower Montane-Foothills Shrubland The Lower Montane-Foothills Shrubland ecosystem occupies the sandstone hogback that extends along the east side of the property. The expression of this ecosystem on Bobcat Ridge Natural Area is a mosaic of mountain mahogany with Scribner needlegrass (Stipa scribneri) and New Mexico feathergrass (Stipa neomexicana). Shrublands with New Mexico feathergrass form sizable patches within the more common Scribner needlegrass at this site. Native grasses are diverse and dominant in the understory beneath mountain mahogany, including Indian ricegrass (Achnatherum hymenoides), purple threeawn (Aristida purpurea), side-oats grama (Bouteloua curtipendula), blue grama (Bouteloua gracilis) and sand dropseed (Sporobolus cryptandrus). The rare Bell’s twinpod (Physaria bellii) occurs throughout this shrubland ecosystem. Cheatgrass is problematic within this extensive stretch of habitat. It is creeping up from the pasture and hayfields below as well as colonizing patches at higher elevations just below the cliffs where rocks have fallen from the eroding bluffs causing localized disturbance. Conservation Target Foothills Shrubland Objectives Enhance habitat value and native character by restoration of native plant understory (grasses and forbs) through aggressive weed control. Natural Processes/ Functions/ Interactions Grazing, drought and fire historically interacted to form the shrubland and its grassland understory. While the shrub communitiy is intact, the understory has been severely altered by non-native cheatgrass. Threats & Stresses (Source of Stress)  Non prescriptive grazing.  Weed invasion. Strategy/Action  Use grazing to help eliminate cheatgrass problems.  Aggressive weed control. Measure of Success Increase in percent coverage and in diversity of understory native species. Conservation Plan  Complete a restoration plan.  Target early spring cattle grazing to eliminate non native and Figure 3.3. Shrubland on hogback ridge. invasive species such as cheatgrass and Canada thistle.  Use of herbicides and other methods must not impact the native shrubs.  Attempt to control cheatgrass with fall herbicide treatments of 2 oz/acre application of Plateau.  Once established, routine grazing or periodic fire may be used to maintain disturbance regime and health of the ecosystem. Grasslands and Croplands Grasslands and croplands comprise about 25% of the acreage at Bobcat Ridge Natural Area. The valley portion of Bobcat Ridge harbors a mix of native grassland remnants and areas that have been modified by agricultural practices. Alfalfa (Medicago sativa) and wheat have been actively cropped for decades; perhaps a century or more. Today, many of the fields are irrigated with NCWCD water allowing the ranchers (who lease water rights) to complete an average of two rotations of hay per year. Much of the grassland and cropland area is threatened by undesirable species such as smooth brome (Bromus inermis), Canada thistle (Cirsium canadensis) and cheatgrass. Montane grasslands interspersed with ponderosa pine in the area of Mahoney Park were once in crop production, which has reverted to cheatgrass and will require aggressive weed control (Figure 3.4). Foothills Grassland The Foothills Grassland ecosystem occupies the deeper soils over siltstone and fine-grained sandstones in the valley bottom of Bobcat Ridge Natural Area (Figure 3.5). It is also found in Mahoney Park. The Foothills Grassland is one of the most severely altered ecosystems in the Southern Rocky Mountains ecoregion (Rondeau 2001). Prior to conversion to agriculture and construction of the canal, the valley was probably fully occupied by a mix of mid- and tallgrass plants, remnants of which are now relegated to shrubland, mountain parks and edges of the ponderosa pine forest. Patches of this ecosystem Figure 3.4. Montane grassland in Mahoney Park. Figure 3.5. Foothills grassland in valley bottom. still exist in the valley on rocky knolls that were likely too difficult to plow. The deeper soils of the swales and rolling hills were plowed and planted in hay crops and pasture grasses like crested wheatgrass (Agropyron cristatum), quackgrass (Elytrigia repens), and alfalfa. The remnant patches of native species have a vastly different composition dominated by blue grama, needle-and-thread (Stipa comata), sand dropseed, and fringed sage. Other diverse forbs also occur. These patches of native species are not without weeds like cheatgrass, but native species are dominant. Conservation Target Foothills Grassland Objective Enhance habitat value and native character through restoration efforts designed to eradicate weeds and convert hay crop and pasture grasses to native grasses. Natural Processes/ Functions/ Interactions Seasonal grazing, periodic fire and drought are natural processes that sustain native grasslands. Threats & Stresses (Source of Stress)  Active haying operations/ a century of agriculture.  Non-native and invasive species like cheatgrass and Canada thistle.  Lack of natural disturbances. Strategy/Action  Locate remnant grassland patches to determine restoration targets including species diversity and abundance.  Use a combination of targeted cool-season and dormant season grazing, prescribed fire and enhancement seeding to convert non-native areas to native. Measure of Success Increase in percent of area converted from pasture to native grasses Conservation Plan  Complete site restoration plan  Aggressive management action will be required to convert agricultural areas for feeding cattle to native grasses more compatible with wildlife values.  Using remnant grassland patches as a target, a combination of grazing, prescribed fire and enhancement seeding will be used.  It is possible that multiple restoration treatments might be used on an experimental basis to determine the most effective means to achieve the grassland restoration.  Cease most crop agriculture activities with one exception: the 18 acre alfalfa pasture where the grasshopper sparrows are nesting. Delay first cutting of alfalfa until mid August to accommodate fledging and foraging.  Target cool-season or dormant-season grazing to reduce cool- season no-native species like cheatgrass.  Introduce small-scale prescribed burns to reduce abundance of widespread non-native species.  Once desired conditions are attained, proactively manage to mimic natural disturbances. Riparian/Wetlands Riparian areas and wetlands comprise only 1% of the land area on Bobcat Ridge Natural Area. As in most places in the west, wet areas are extremely valuable to native plants and wildlife. Riparian and wetland areas on Bobcat Ridge predominately occupy hillside drainages and seeps that support diverse plant communities and the wildlife that depend on them. There are no known year-round springs on the valley sections; however, three springs exist on the mountain section. Brooks Canyon has a small ephemeral spring feeding the creek that runs out to County Road 27(Figure 3.6). In this narrow canyon, a mature cottonwood gallery consisting of three species of native cottonwoods combines with an understory of native plants to comprise one of the highest quality habitats on the natural area. Hillside drainages also support communities of rare butterflies. Two artificial ponds were created on the site by small dams. These block and drain the water into stock tanks. One is at the eastern edge of Mahoney Park just north of the Powerline Road. Wetland plants such as Nebraska sedge (Carex nebrascensis), spikerush (Eleocharis spp.) and duckweed (Lemna spp.) are growing at the edge of this pond. The second, larger pond is between Powerline Road and the North Road further downhill and to the east. Lower Montane Riparian Woodland The Lower Montane Riparian Woodland ecosystem occupies the immediate area adjacent to stream drainages throughout Bobcat Ridge Natural Area. Skunkbush sumac, willows (Salix spp.) and cherries (Prunus spp.) are common at the higher elevations coming down from Green Ridge. Where there is sufficient water flow at lower elevations, narrow-leaved cottonwoods (Populus angustifolia) emerge in the draws. This ecosystem is best expressed along Brooks Creek, an ephemeral stream, as it flows through the canyon and cliffs that form a break in the hogback chain on the east side of the property. Stately cottonwood galleries consisting of three species: plains (Populus deltoides), lanceleaf (P. x acuminata) and narrowleaf (P. lanceolatum), line a good portion of this stream reach. Chokecherry (Prunus virginiana) and American plum (P. americana) form shrub groves in the understory. The herbaceous layer throughout the various drainages on Bobcat Ridge Natural Area is strongly dominated by weedy perennials with very little of the native flora expected in undisturbed riparian corridors. Canada thistle and smooth brome are the biggest threats. Smooth brome is strongly dominant along Brooks Creek. In some places within the Front Range foothills this is a result of planting. However, altered hydrology (usually a lowered water table) Figure 3.6. Riparian area in canyon through hogback ridge. combined with heavy grazing pressure, compromises the competitive edge of native species and allows smooth brome to invade from adjacent pastures (Carsey et al. 2003). There are numerous drainages that run from west to east providing water to this community. The riparian corridor in the Brook’s Canyon drainage may also be fed by an irrigation outlet. This needs to be further investigated to determine the source of the water. Stock water tanks located in the upper reaches of these drainages back-up water cutting off the natural supply to the drainage area below. These require further investigation. Restoration of the hydrology will need to occur parallel with aggressive weed control. Of particular concern is Dalmatian toadflax (Linaria dalmatica) which was observed during the site inventory. Cattle grazing in these areas add additional pressure on this ecosystem which, due to weed content, has already lost some resiliency. For this reason it is recommend that cattle grazing be carefully managed in the lower elevation riparian corridors. Conservation Target Lower Montane Riparian Woodland Objectives Maintain and enhance vegetative quality of this natural community through restoration of natural hydrology and weed eradication. Natural Processes/ Functions/ Interactions Hydrology is the sustaining function in this ecosystem. Threats & Stresses (Source of Stress)  Non-native and invasive species (Canada thistle and smooth brome)  Inappropriate cattle grazing  Compromised hydrology such as stopped drainages and water tanks Strategy/Action  Pursue aggressive control of Canada thistle and smooth brome.  Identify the source of the hydrology and restore natural flows.  Carefully manage cattle grazing in this community. Measure of Success Improved quality of the vegetation condition. Conservation Plan  Complete restoration plan.  Pursue aggressive weed control of Canada thistle and smooth brome.  Monitor for invasion of Dalmation toadflax and eradicate.  Investigate the source of the water for Brook’s Canyon and restore hydrology.  Evaluate impact of stock tanks and possibility of restoring natural water flow to lower elevation riparian areas.  Carefully manage cattle grazing from riparian areas throughout site; use wildlife friendly fencing.  Explore other opportunities to restructure the pasture layout within the landscape. Bell’s twinpod (Physaria bellii) Bell’s twinpod, a globally imperiled plant, grows at Bobcat Ridge Natural Area (Figure 3.7 and for locations see Figure 3.1). This small, yellow-flowered mustard occurs on sparsely vegetated red sandstone outcrops of the Fountain and Ingleside Formations found on the western slopes of the hogbacks. The Fountain Formation consists of red and minor gray, coarse-grained sandstone with lenses and layers of siltstone and fine-grained sandstone and the Ingleside Formation is comprised of red calcareous fine- to medium-grained, well-sorted, cross-bedded sandstone (Braddock et al 1970). Bell’s twinpod is known only from the foothills of the Front Range of Colorado (Larimer, Boulder, and Jefferson counties) and has been documented primarily on the limestone and shale of the Niobrara Formation. Recent work has verified that this rare plant also occurs on the Fountain and Ingleside Formations. Other nearby properties with outcrops of these formations that support Bell’s twinpod populations include Devil’s Backbone Open Space, and Horsetooth Mountain Park. The dominant community on the hogbacks is mountain mahogany shrubland with a variety of native grasses. Bell’s twinpod is most abundant where the vegetation is sparse at the top of the slope and in ephemeral drainage channels. The meadows at the base of the slopes are dominated by non-native grasses including smooth brome and cheatgrass. These non-native grasses occupy the lower portions of the hogback slope, likely decreasing the potential habitat for Bell’s twinpod. Conservation Target Bell’s Twinpod Objectives Maintain and enhance existing population. Enhance conditions that perpetuate this species. Natural Processes/ Functions/ Interactions Plant is most abundant where vegetation is sparse at the top of hogback slopes and in ephemeral drainage channels. Figure 3.7. Bell’s twinpod (Physaria bellii) (left) and habitat (right) - hogbacks of red sandstone of the Ingleside Formation. Colorado Natural Heritage Program photos by Georgia Doyle Threats & Stresses (Source of Stress)  Non-native and invasive species like cheatgrass, smooth brome, and Canada thistle.  Effects of cattle grazing on this species are not understood. Strategy/Action  Aggressive weed control around known occurrences.  Remove cattle grazing from and enhance Bell’s Twinpod habitat.  Maintain and enhance population of Bell’s Twinpod. Measure of Success Self-sustaining population with successful recruitment. Conservation Plan  Control weeds aggressively around known occurrences to reduce the threats from non native and invasive species like cheatgrass, smooth brome, and Canada thistle.  Maintain the ephemeral drainages.  Limit cattle grazing in these areas until it can be determined what effect grazing has on the species.  Monitor populations every 3-5 years and provide periodic updates to CNHP’s element occurrence tracking system. Weed Management Weed management at Bobcat Ridge Natural Area will follow current City of Fort Collins Natural Areas Program Vegetation Management Guidelines. This includes an integrated pest management approach to noxious and invasive plant species. In accordance with the Colorado Noxious Weed Act, plants will be managed as specified by their placement in one of three categories on the Colorado Noxious Weed List. Plants in category “A” are managed for eradication, category “B” plants are managed to contain the spread of infestations, and “C” category plants are managed where deemed appropriate by county weed districts. No species from category “A” occur at Bobcat Ridge Natural Area. Monitoring for these species is a priority and will continue on an ongoing basis. If any species from category “A” are found at Bobcat Ridge, management objectives and strategies will orient toward eradication. In addition to the species listed below, the Natural Areas Program will monitor and manage smooth brome and crack willow as undesirable species. Colorado Noxious Weeds found on Bobcat Ridge Category “B” species Category “C” species Bull thistle Cirsium vulgare Common mullein Verbascum thapsus Canada thistle Cirsium arvense Cheatgrass Bromus tectorum Dalmatian toadflax Linaria dalmatica Field bindweed Convolvulus arvensis Leafy spurge Euphorbia esula Common burdock Arctium minus Musk thistle Carduus nutans Scotch thistle Onopordum acanthium Chapter References Braddock, W.A., R.H. Calvert, S.J. Gawarecki, and P. Nutalaya. 1970. Geologic Map of the Masonville Quadrangle, Larimer County, Colorado. 1:24,000. GQ-832. U.S. Geological Survey, Washington, D.C. Burns, Russell M., and Barbara H. Honkala, tech. coords. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 p. Carsey, K., G. Kittel, K. Decker, D. J. Cooper, and D. Culver. 2003. Field guide to the wetland and riparian plant associations of Colorado. Fort Collins, CO: Colorado Natural Heritage Program. Doyle, Georgia, Stephanie Neid, and Renee Rondeau. 2004. Bobcat Ridge Natural Area Invetory: Preliminary Results of Larimer County Inventory. Fort Collins, CO: Colorado Natural Heritage Program. Huckaby, L.S., M.R. Kaufmann, P.J. Fornwalt, J.M. Stoker, and C. Dennis. 2003. Identification and ecology of old ponderosa pine trees in the Colorado Front Range. Gen. Tech. Rep. RMRS-GTR-110. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 47pp. Rondeau, R.J. 2001. Ecoecosystem viability specifications for Southern Rocky Mountain ecoregion. Colorado Natural Heritage Program. Fort Collins, CO. (Available at http://www.cnhp.colostate.edu/reports.html). Shinneman, D.J. and W.L. Baker. 1997. Nonequilibrium dynamics between catastrophic disturbances and old-growth forests in ponderosa pine landscapes of the Black Hills. Conservation Biology 11(6): 1276-1288. Tirmenstein, D.A. 1987. Leucopoa kingii. In: Fire Effects Information Ecosystem, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Available: http://www.fs.fed.us/database/feis/ [2004, August 13]. Uchytil, Ronald J. 1988. Andropogon gerardii var. gerardii. In: Fire Effects Information Ecosystem, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2004, August 13].