10 Years of Conservation Science on the Zumwalt Prairie

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10 YEARS OF CONSERVATION SCIENCE ON THE ZUMWALT PRAIRIE

What Have We Learned?

Geographically isolated and comprised mostly of private lands, scant scientific information exists regarding the soils, vegetation, wildlife and ecology of the Zumwalt Prairie. Science is at the core of the Nature Conservancy’s conservation approach and soon after the Conservancy acquired the Zumwalt Prairie Preserve in 2000, the organization recognized the need to support scientific inquiry into the prairie’s ecology and how human actions such as livestock grazing, fire, and invasive species affect it. Beginning with a study of the prairie’s raptor populations in 2003, the Conservancy has collaborated with universities and agencies for over ten years in its quest to find answers to key conservation questions. Over 10 published papers, dozens of reports and presentations have resulted in these efforts, broadening our knowledge of the biodiversity and ecological processes of the Zumwalt and informing stewardship and other conservation actions. Conservancy staff also serve on technical advisory groups, review boards, and in other roles to promote scientific inquiry and communication of information to landowners and other stakeholders. Short summaries of findings resulting from Zumwalt Science efforts are summarized below. For more information contact Rob Taylor ([email protected]). Many of the reports, lists, and publications cited here can be found on the Conservation Gateway at: https://www.conservationgateway.org/ConservationByGeography/NorthAmerica/UnitedStates/oregon/grasslands/zumwalt

BIODIVERSITY

While no formal “bio blitz” has ever been undertaken on the Zumwalt Prairie, various inventory, monitoring and research projects have contributed to our understanding of the biodiversity that inhabits this extraordinary grassland ecosystem.

 A total of 491 vascular plant species belonging to 69 families have been documented on the Zumwalt Prairie, the majority of these from the Zumwalt Prairie and Clear Lake Ridge Preserves. The aster family (Asteraceae) and grass family (Poaceae) are the most prolific, having 74 and 73 species, respectively. Other common families are the snapdragons (Scrophulariaceae), sedges (Cyperaceae), roses (Rosaceae), peas (Fabaceae), mustards (Brassicaceae), carnations (Caryophyllaceae), lilies (Liliaceae), rushes (Juncaceae), and buckwheats (Polygonaceae). Twenty-five families are represented by just a single species. Forbs (310 species) and grasses (72 species) are the most common growth forms. Over 40 species of sedges/rushes and shrubs are found. Trees species are few, with only 15 species documented to date.

The majority of species (385) on the Zumwalt Prairie are native. Of these 144 range across much of North America while 192 are found throughout the west. Pacific northwest endemics constitute a total of 48 species of which just 1, Wallowa needlegrass (Achatherum wallowensis), occurs only in eastern Oregon. Of the 106 exotic species, 72 are forbs and 30 are grasses. The Zumwalt herbarium contains specimens of over half of the documented species (271).

 A diversity of non-vascular plants have also been documented on the Zumwalt Prairie with 50 lichen species documented to date, 15 of which are soil lichens (Anonymous 2010), including the newly described vagrant lichen Aspicilia rogeri (Sohrabi et al. 2011).

 Both research and monitoring efforts have revealed a rich diversity of insect and other invertebrate life on the Zumwalt Prairie. Visits to the Prairie by prominent lepidopterists such as Cliff Ferris and Dana Ross have elucidated many butterfly and moth species. To date, 54 species have been documented which includes 21 brush-footed butterflies (Nymhphalidae), 14 gossamer-winged butterflies (Lycaenidae), 8 skippers (Herperiidae), 6 whites (Pieridae), and 5 swallowtails (Papilionidae) (Jansen 2008). A research project investigating the role of cattle grazing on invertebrates has provided us with detailed information on the bee species which inhabit the prairie which (Kimoto 2011, Rao et al. 2011, Kimoto et al. 2012a, Kimoto et al. 2012b). At last count 94 species and 117 morphospecies have been documented (Kimoto et al. 2012a). Macro- invertebrate sampling on Camp Ck and Pine Ck has helped in understanding the diversity of aquatic insects, worms, crustaceans, and molloscs with 91 species documented to date (Wooster and DeBano 2011). 1

 The Zumwalt Prairie and adjacent canyons provides habitat for many bird species having a variety of life histories. Initial surveys by Frank Conley provide a backbone of valuable knowledge of these species while additional inventory work (Taylor and VanCantfort 2003) and the efforts of many visitors and volunteers continue to add to our knowledge of Zumwalt bird life. To date 188 species have been documented (Anonymous 2008) of which songbirds (order: Passeriformes) comprise, by far the richest group (93 species). Raptors are another well-represented group with 7 hawks (3 accipiters, 4 buteos), both bald and golden eagles, northern harrier, osprey, and 4 falcons documented. Surprisingly, 20 duck species, have been documented attesting to the importance that artificial water sources now play in attracting waterfowl during the spring and fall migration seasons. Many of the birds of the Zumwalt Prairie migrate there in the summer to breed (79 species) while 66 species are resident. Five species of raptor (1 hawk, 3 falcons, and bald eagle) and 8 species of songbirds regularly use the Zumwalt primarily during the winter months, most migrating there from there more northern breeding grounds while some species, such as snowy owl, occasionally wander to the prairie sometimes remaining for the winter.

 Little work has been done to document the mammal diversity of the Zumwalt Prairie and what is known primarily comes from casual observation of mid-size and large mammals and inference from range maps and other accounts. Forty-seven species of mammals are thought to occur on the Zumwalt Prairie which include 16 rodents (Rodentia), 12 carnivores (Carnivora), 9 bats (Chiroptera), 5 species of hooved mammal (Artiodactlya), 3 rabbits/hares, and 2 shrews (Insectivora) (Trask and Taylor 2012). Investigations into small mammals would be helpful in corroborating existing information.

 The generally arid landscape of the Zumwalt Prairie is reflected in the paucity of reptiles and amphibians species found there. Of the 7 reptile species, 5 are snakes. Three frog and toad species and a single salamander (Ambystoma macrodactlyum) are known (Taylor 2008). Limited work has been done to date to document herptile biodiversity of the area and it is likely that additional efforts, especially if focused on canyon areas adjacent to the prairie, would reveal additional snake and lizard species.

SOILS AND PLANTS

Investigations by the Conservancy and others have expanded our knowledge of the soils and certain plant species of conservation concern on the Zumwalt Prairie. In some cases this information has allowed land managers to adjust management to accommodate the conservation of these species and for others it has raised questions which compel future research.

 Soils on the Zumwalt prairie are dominated by silt-loam soils and influenced greatly by windborne loess (Schmalz 2007). The fine grain heterogeneity of vegetation on the Zumwalt Prairie, evidenced by dramatic changes in plant communities from one location to another just a few meters distant, is a consequence of soil heterogeneity, slope, and aspect (Schmalz 2011). This diversity of soils drives patterns of plant diversity, contributing to the high richness of grass and forb species (Darambazar et al. 2007).

 Several years of mapping and monitoring efforts by Conservancy staff have documented the largest known population of the federally-listed wildflower Spalding’s catchfly (Silene spaldingii) (Taylor et al. 2008, Jansen and Taylor 2009b, 2010d, Schmalz and Taylor 2011c). This population is currently estimated at 50-60,000 individuals on the Zumwalt Prairie Preserve (Schmalz and Taylor 2011c) while Clear Lake Ridge is estimated to have a population of approximately 4,000 (Youtie 1990, Schmalz and Taylor 2011b). The health of the Spalding’s catchfly population, however, is not known and research by Conservancy staff suggest that this species may produce an insufficient amount of seed to maintain the population over time (Taylor et al. 2012b). One possible cause for the low reproductive rates is lack of pollination services by bumble bees, which have been shown to be the primary pollinator of this species (Tubbesing et al. in press) and which may be sensitive to cattle grazing (Kimoto et al. 2012b). Predation by moth larvae is another possible cause (Taylor and DeBano 2012). Cattle do not appear to forage extensively on Spalding’s catchfly, at least during the early summer when the plant is emerging (Cullen and Taylor 2010).

 Though it lacks federal or state protection, the Wallowa rice (Achnatherum wallowaensis) is a rare plant limited to approximately 30 populations in eastern Oregon and considered “imperiled” due to its limited occurrence and for the

threat that cattle grazing poses in those areas (Maze and Robson 1996, NatureServe 2012). Inventory efforts conducted by the Conservancy reveal that this species is common throughout the ridges of Clear Lake Ridge Preserve (249 point locations to date) and has been found in three areas of the Zumwalt Prairie Preserve (TNC, unpublished data). Little is known of the ecology of this species and how human actions may affect it.

 The effects that various intensities of cattle grazing has on prairie soils was investigated as part of an experiment conducted by Oregon State University and the Conservancy (Kennedy et al. 2011). This study (hereafter referred to as the “Grazing Food Web” study; see section on Cattle Grazing and Wild Ungulate Herbivory) found that soil compaction increased and litter decreased under higher cattle stocking rates with implications for long-term range sustainability (Schmalz 2011, Schmalz et al. In press).

 Long- term monitoring of prairie vegetation on the Zumwalt Prairie Preserve suggests unplowed and unburned areas have experienced a decrease in native perennial grasses while native perennial forbs increased. The invasive annual grass Ventenata also increased at many sites (Taylor and Schmalz 2012). Continued research and monitoring is critical in evaluating whether these trends continue and in determining causes.

 Aspen (Populus tremuloides) and deciduous shrub communities on the Zumwalt Prairie Preserve are heavily browsed and may be declining in abundance. A study conducted by Conservancy staff on the age structure and recruitment of aspen showed that the majority of mature aspen on the preserve were initiated from 1960 – 1970 and that since that time recruitment has been minimal, except where wild ungulate resistant exclosures have been built (Taylor and Arends 2011). Recruitment of serviceberry (Amelanchier alnifolia) and hawthorn (Crataegus douglasii) show similar patterns except that recruitment declines were experienced more recently, i.e., after 1970. Studies of the effects of browse on aspen and shrub communities suggest that elk and deer currently account for the bulk of over-browsing (Taylor and Arends 2011; see also "Cattle Grazing and Wild Ungulate Herbivory", Taylor 2012b).

 Many areas of the Zumwalt Prairie that were once plowed for the growing of grains and other crops but were later abandoned and re-seeded with non-native grass species. Decades after abandonment these areas are still dominated by exotic species though some native species have re-colonized these areas remain low in native species abundance and richness (Bartuszevige et al. 2012, Taylor and Schmalz 2012). Restoration of old field areas has been identified as one way of abating the threat of invasive species and improving conditions for native biodiversity (Elseroad et al. 2008). Methods for restoring old field areas while maintaining existing ecological values have been investigated (Taylor et al. In press). Based on this research a pilot project for improving the condition of two old fields on the Zumwalt Prairie Preserve was initiated in 2010 using grazing, fire, and seeding with native species (Taylor et al. 2012a). Although this work is still in ongoing, monitoring indicates that good progress is being made towards the goals of decreasing exotic dominance and increasing native species abundance.

WILDLIFE BIG AND SMALL

As grasslands throughout the Pacific Northwest have been destroyed, there are few areas where wildlife that depend on these ecosystems can find refuge. The Zumwalt Prairie provides habitat for thousands of species of mammals, birds, reptiles, arthropods. With the reintroduction of Columbian sharp-tailed grouse (Tympanuchus phasianellus columbianus) in the early 1990s and the recent return of gray wolves (Canis lupus) to the area, only one native species, the grizzly bear (Ursos arctos horribilis) is absent.

 Insect pollinators play an essential ecological role in grasslands with many species dependent on them for reproduction. In the Zumwalt Prairie grasslands, isolated aspen stands may play an important role in maintaining pollinator abundance and diversity (Gonzales et al. in press). The Zumwalt Prairie harbors the only known large population of the once common western bumblebee (Bombus occidentalis), a species of emerging conservation concern, in the Pacific Northwest (Rao et al. 2011).

 The effects that various intensities of cattle grazing has on bumblebees and other pollinating insects were investigated as part of an experiment conducted by Oregon State University and the Conservancy (Kennedy et al. 2011). This study (hereafter referred to as the “Grazing Food Web” study), found that bumblebee (Bombus spp.) abundance and diversity declined at higher cattle stocking rates while other species, such as digger bees (Andrena spp.) appeared to benefit (Kimoto et al. 2012b).

 The hawks of the Zumwalt Prairie were first investigated by Cottrell (1981) and popularized in her book The Prairie Keepers (Houle 1996). Since then, a follow-up investigation has examined whether the high numbers of hawks observed by Cottrell are being maintained and preliminary results suggest that numbers are stable, though long-term shifts in vegetation, particularly declines in aspen (Populus tremuloides), may lead to future declines in some species such as ferruginous hawk (Buteo regalis) (Kennedy et al. In review).

 Grasshopper sparrows (Ammodramus savannarum) are one species which appears to have increased on the Zumwalt Prairie Preserve. Very low abundances of this species were documented in 2001 (Hohmann 2001) and 2003 (Taylor and VanCantfort 2003) while the bird has been more commonly observed in since 2007 (Johnson et al. 2011). This change may be a reflection of changes in livestock grazing on the Preserve, specifically, lower grazing levels and increased structure of herbaceous vegetation.

 Grassland songbirds are declining throughout North America making the Zumwalt Prairie a vital area for their conservation. An investigation into the abundance and nesting performance of songbirds in both native and exotic dominated areas revealed that vegetation structure rather than species composition is likely most important in providing habitat for these species (Kennedy et al. 2009) although less common species, such as grasshopper sparrow could not be assessed by this study.

 The effects that cattle grazing have on grassland songbirds was also investigated as part of the Grazing Food Web study. Key findings were that Savannah sparrows (Passerculus sandwichensis) decreased in number at the high stocking rate while horned lark (Eremophila alpestris) tended to increase. Grasshopper sparrows did not nest in any of the high grazing treatment areas (Johnson et al. 2011). Specific causes of nest failure were also investigated. Though removal of vegetation by livestock is thought to decrease overall cover thereby increasing the chances that predators will discover and depredate nests, this was not supported by the study, perhaps because the primary predators of nests were not avian but small mammals and snakes (Johnson et al. in press). Cattle trampling was not common (< 1%) but did occur more frequently in moderate to high stocking rate treatments.

 Columbian sharp-tailed grouse were once abundant on the Zumwalt Prairie but were extirpated in the 1940s (Hansen et al. 2005). Restoration of this species began in 1992 with the re-introduction of sharp-tails at Clear Lake Ridge Preserve (Snyder 2001). The headwaters of Pine Creek and Camp Creek have been identified as having the best potential for sharp-tailed grouse in Oregon (D. Budeau, ODFW, pers. comm.) and the Conservancy has undertaken studies to assess the suitability of this area for the species (Joseph 2012). These studies indicate that suitable habitat likely exists and the feasibility of efforts to translocate birds to the area is currently being evaluated.

STREAMS AND FISHES

The Zumwalt Prairie lies at the headwaters of several stream systems which provide important habitat for aquatic and riparian species and influence water quality downstream where anadromous fishes spawn.

 In 2003 the National Riparian Service Team (NRST) conducted a survey of Camp Creek on the Zumwalt Prairie Preserve and found that conditions were impaired in several areas due to channelization, impoundments, and past heavy livestock grazing (National Riparian Service Team 2002). Follow-up work by the Conservancy mapped over 100 head cuts on upper Camp Creek (McClure and Taylor 2004, Jansen et al. 2007). Based on the recommendations of the NRST report, a restoration project was executed on the Zumwalt Prairie Preserve in 2011 in which some impoundments were removed and channels re-engineered. 4

 Camp Creek is an important stream for spawning steelhead (Oncorhynchus mykiss) and the Oregon Department of Fish and Wildlife has monitored spawning activity across approximately 6 miles of its lower reach since 1965. During that time the total number of redds counted have fluctuated considerably, ranging from 1 to 108 (mean 35 ± 29 SD). No trends in redd counts are apparent from the data and both local (stream conditions) and regional factors (dams, ocean survivorship) make interpretation difficult.

 In 2006, the Conservancy partnered with Dave Wooster and Sandy Debano of Oregon State University to conduct an assessment of the condition of Camp Creek on the Zumwalt Prairie Preserve using macro-invertebrates as indicators. This survey found that the stream had low taxonomic richness, few sensitive taxa (e.g., stoneflies of the order Plecoptera), was dominated by taxa tolerant of high sediment levels and water temperatures (i.e., midges of the subfamily Orthcladiinae), and low functional diversity (Wooster and DeBano 2006). The following year, this effort was expanded to include Pine Creek which was found to have slightly lower water quality (Wooster and DeBano 2007). One of the goals of this sampling was to document stream conditions prior to restoration activities planned for Camp Creek, thus allowing for evaluation management actions, specifically reductions in cattle grazing along streams and a planned stream restoration project on Camp Creek. A final year of pre-restoration sampling was performed on Camp Creek in 2008 which confirmed the overall characteristics of the macro-invertebrate communities and variability between sites (Wooster and DeBano 2008). In 2011, the first year of post-restoration sampling was conducted for Camp Ck and a second year of sampling for Pine Ck (Wooster and DeBano 2011). While the 2011 data still mostly reflected poor water quality on both Camp and Pine Ck, sensitive taxon richness was higher on Camp Ck in 2011 (13 taxa vs 7-8 in previous years), potentially indicating a trend towards improved conditions. Specific goals for macroinvertebrate indicators do not currently exist for Camp and Pine Ck, the creation of which could improve the Conservancy’s ability to manage streams on the Zumwalt Prairie Preserve and ensure that management is having the desired effect of improving the condition of these streams.

 Where livestock have been excluded from streams and riparian areas on the Zumwalt Prairie Preserve, recovery of herbaceous vegetation has been observed (Dingeldein and Taylor 2009, 2010) while shrub vegetation appears mostly unchanged.

FIRE

Like nearly all grasslands of the western U.S., the plants, animals, and ecosystems have experienced and adapted to naturally-ignited fires for thousands of years. Indigenous people likely influenced the fire cycle – using it to increase the abundance of game animals and plant foods –after arriving in the area 10,000 or so years ago. The fire cycle changed dramatically after Euro-American settlement as wildfires were suppressed and extensive grazing by domestic livestock reduced fuels necessary to carry fire. The consequences of this are not well understood but may include increased grass dominance, reduced forb cover and reduced abundance of fire-tolerant species such as snowberry (Symphoricarpus albus). The Conservancy aims to restore the fire cycle of the Zumwalt Prairie, however, fire-adapted exotic plant species and other factors make it prudent to evaluate fire’s effects so as to avoid serious negative ecological consequences that may result from re-introduction of fire.

 Initial investigations into fire’s effects on the Zumwalt Prairie suggest that fire does not cause harmful effects in otherwise intact prairie sites. In 2003 Louis Provencher and Bob Unnasch initiated a study of the effects of fire and grazing on the Zumwalt Prairie Preserve. Though data from baseline (pre-treatment) monitoring were lost by the primary investigators, the design of this study (16 plots arranged in a full factor, randomized block design) make it possible to draw some conclusions on fire’s effects using post-treatment data collected in 2008 and 2010. Fire significantly reduced foliar cover of exotic perennial forbs, litter, and standing dead plant material and increased bare ground. Total basal plant cover and basal cover of perennial native bunchgrasses and annual exotic grasses were also lower in burned plots (Taylor and Schmalz 2012).  Increases in conifer cover on the Zumwalt Prairie have occurred over the last 75-100 years (Getz et al. 2005, Bartuszevige et al. 2012) and a study of conifer age structure determined that 88% of the trees established in 1970 or later (Taylor 2012a). Lack of stumps or other evidence of timber harvests suggest that lack of fire, perhaps combined with effects of heavy livestock grazing, is likely responsible for this profound increase in conifer abundance. 5

INVASIVE SPECIES

Invasive species were ranked one of the top three threats affecting conservation on the Zumwalt Prairie (Shephard and Taylor 2009, Nichols et al. 2010). Various plant inventory and monitoring efforts have been conducted to better our understanding of which invasive species are present on the preserve and where they occur on Conservancy-owned lands, focusing on those species ranked as highest priority by the Wallowa County Weed Board (Taylor et al. 2006, Taylor et al. 2007, Taylor and Jansen 2008, Jansen and Taylor 2009c, a, 2010c, b, Schmalz and Taylor 2011e, d, a). In addition, studies have been done to assess the abundance of these priority weed species (e.g., number of plants) and whether management interventions (e.g., herbicides) are effective in reducing threats associated with these species. Some key findings of this work include:

 Eleven priority invasive forb species had at least one occurrence on the Zumwalt Prairie and/or Clear Lake Ridge Preserve in 2012, these included: common bugloss (Anchusa officinalis), scotch cottonthistle (Onopordum acanthium),. rush skeletonweed (Chondrilla juncea), whitetop (Lepidium draba), meadow hawkweed (Hieraceum pratense), yellow starthistle (Centaurea solstitialis), sulfur cinquefoil (Potentilla recta). puncture vine (Tribulus terrestris), spotted knapweed (Centaurea maculosa), common crupina (Crupina vulgaris) and myrtle spurge (Euphorbia myrsinites).

 Invasive grass species include several annual brome species (Bromus spp., e.g., cheatgrass [Bromus tectorum]), Ventenata (Ventenata dubia), and dense silkybent (Apera interrupta). Long-term monitoring suggests that the Ventenata is increasing in unplowed, un-burned native prairie sites, more than doubling from 2006 to 2011 (Taylor and Schmalz 2012). Moreover, this increase may have been at the expense of native bunchgrass species.

 As of 2011, sulfur cinquefoil (50-100,000 plants) was estimated to infest 253 ha of lands on the Zumwalt Praire Preserve; on Clear Lake Ridge a population of approximately 25,000 plants infested 159 ha (Schmalz and Taylor 2011d, e). When left untreated, sulfur cinquefoil increased in abundance compared to sites where chemical herbicides were used (Jansen and Taylor 2009c). Populations of this invasive plant have been declined in recent years in the main infestation areas on the Zumwalt Prairie Preserve, presumably as a consequence of herbicide treatment (Tella et al. 2004, Schmalz and Taylor 2011e, Jones 2013) whereas trends on Clear Lake Ridge are uncertain (Schmalz and Taylor 2011d). What is not clear is whether this plant continues to spread from its main infestation areas; new patches have been discovered over time but whether these are truly “new” or the result of increased, cumulative survey effort is not clear (Schmalz and Taylor 2011e). Long-term vegetation monitoring plots suggest that herbicide treatments targeting sulfur cinquefoil may cause reductions in native grass and forb species (Taylor and Schmalz 2012).

 Meadow hawkweed is an invasive forb species that is a top priority for control and for which herbicide treatments have been conducted most years since 2003. Monitoring of this species from 2006-2011 indicates that while earlier control efforts were not effective (Jansen and Taylor 2009a) despite studies showing that Transline® , the herbicide used, did reduce hawkweed abundance at the small plot scale (Taylor et al. 2004) . Redoubling of control efforts since that time has reduced the abundance of this weed in main infestation areas (Schmalz and Taylor 2011a). It is still unclear whether this plant continues to spread from its main infestation areas; new patches have been discovered over time but whether these are truly “new” or the result of increased, cumulative survey effort (Schmalz and Taylor 2011a). Long-term vegetation monitoring plots suggest that herbicide treatments targeting meadow hawkweed may result in increases in native and exotic perennial grass species (Taylor and Schmalz 2012).

 While initially is was believed that certain weed species (meadow hawkweed, yellow starthistle) could be eradicated from the Zumwalt Prairie Preserve (Guse and Shephard 2004), it is now acknowledged that this will not be possible due to the widespread extent of these species and persistent seed banks (Nichols et al. 2010). This illustrates the importance of discovering new invasive species as quickly as possible when populations are small enough to allow for eradication.

CATTLE GRAZING AND WILD UNGULATE HERBIVORY

Livestock grazing, if not managed very carefully, has been shown to degrade many ecosystems (Dormaar and Willms 1998, Jones 2000), especially those that have not evolved with an abundance of large, native, ruminants (Mack and Thompson 1982, but see also Burkhardt 1996). The aim of the Conservancy is to discover and promote grazing practices that are compatible with the conservation of biodiversity while still allowing for livestock production which would sustain the local economy and discourage subdivision of the large ranches on which it is conducted. Two formal studies of cattle grazing’s effects on the Zumwalt prairie have been conducted to date. One, a study of the effects of different stocking rates (basically, the number of cattle in a pasture) on the grassland food web. This study, known as the Grazing-Food Web Study, investigated how different stocking rates affected soils, vegetation, insects (including pollinators and butterflies), songbirds, as well the performance (e.g., weight gain) of the cattle themselves (Kennedy et al. 2011). Some key results of this research are listed below. See also sections on Soils and Plants and Wildlife Big and Small.

 Soil compaction increased and other factors associated with hydrological function were affected by stocking rate suggesting that higher levels of grazing could reduce soil fertility and increase erosion (Schmalz 2011, Schmalz et al. In press). Soil compaction may also affect certain animal species such as ground-nesting bees (Kimoto et al. 2012b).

 Vegetative structure was affected by stocking rate with more heavily stocked areas having less structure and cover for bird species (Johnson 2011, Johnson et al. 2011).

 Songbird species had similar densities and nesting success across areas where no cattle grazed and areas grazed at low to moderate stocking rates. At the highest stocking rates, however, certain species such as Savannah sparrows were found in lower numbers while grasshopper sparrows avoided these areas when choosing nest sites (Johnson et al. 2011).

 Some insect taxa were sensitive to grazing and unlike birds, effects tended to be linear with no clearly identifiable threshold. Bumblebees showed the strongest negative response to higher grazing; both abundance and species richness declined with higher stocking rates in early summer (Kimoto 2011, Kimoto et al. 2012b). Sweat bees (Lasioglossum spp.) and mason bees (Osmia spp.) also tended to decrease while soil-nesting ground digger bees (Adrena spp.) appeared to benefit from higher grazing, possibly because the more compacted soils in these areas provided better nest sites.

 The effects of cattle grazing on other insect species is currently being analyzed. Preliminary data suggest that abundance of spiders (an important food source for grassland songbirds) and adult butterflies (Order: Lepidoptera) were lower in the high stocking rate treatments.

 While no evidence was found that higher stocking rates resulted in decreased body condition or lower weight gains, or diet quality, cattle foraging efficiency and preference for non-native grasses was lower in the higher stocking rate treatments (Wyffels 2009) . This suggests that cattle in the higher stocking rate treatments were spending less time eating and more time searching for preferred foods. Over time this might have led to decreased performance.

A study of the effects of fire and cattle grazing was initiated in 2003 by Provencher and Unnasch (see section on Fire). Analysis of post-treatment data collected in 2008 and 2010 reveal the following regarding the effects of grazing (Taylor and Schmalz 2012).

 Grazed plots had lower total live plant foliar cover, lower native perennial forb cover (both foliar and basal) and lower amounts of litter than ungrazed plots.

 Grazed plots had higher amounts of bare ground.

 The abundance of exotic grass species (exotic brome grasses and Ventenata) did not differ between the grazed and ungrazed plots.

Cattle on the Zumwalt Prairie Preserve are managed according to a management plan (Freeman 2008). Two of the criteria used in grazing management is forage utilization and stubble height(Coulloudon et al. 1999) and since 2006 these parameters have been

7 measured using a variety of techniques on the Preserve, though not all parameters have been measured in all years. Some lessons learned from this work include:

 Measuring actual forage utilization at a proper scale is actually very difficult to do and stubble height measures may not provide good proxies for residual forage (Bauer and Taylor 2003). Measures of utilization, using the height-weight, can significantly underestimate actual utilization, especially when data are collected weeks or months after the grazing period has concluded (Jansen and Taylor 2010a; TNC, unpublished data). Measures of forage utilization using height-weight also suffer from significant variability between observers (TNC, unpublished data).

 Measuring utilization accurately depends on the ability to accurately measure the amount (i.e., dry weight) of vegetation before and after cattle graze (Smith et al. 2007). Traditionally, this requires that vegetation be clipped and weighed in grazed and un-grazed areas (e.g., paired plots) but the time required makes this unfeasible at the landscape scale. Several methods for estimating standing crop through other means have been evaluated , including use of the “Robel pole” (Robel et al. 1970) and digital photography (Limb et al. 2007). Unfortunately, none of these methods have been shown to provide accurate measures (Damiran et al. 2006; TNC, unpublished data). The lack of a technique to accurately assess livestock utilization at large scales continues to be an impediment in the Conservancy’s goal understanding grazing patterns and in developing sustainable grazing methods.

When the numbers of wild ungulates exceed an areas capacity to support them they can damage important natural resources. Studies conducted by Conservancy staff have shown that excessive herbivory by elk and/or deer currently limit the growth and reproduction of aspen and deciduous shrub communities on the Zumwalt Prairie Preserve.

 Data by ODFW indicate that elk (Cervus elaphus) numbers on the Zumwalt Prairie increased substantially in the past 15 years, from approximately 300 individuals (average 1970-1999) to over 1500 in recent years (average 2000-2011). Since 2005 numbers have averaged over 2000 head (ODFW unpublished data). Mule deer numbers for the Chesnimnus unit, within with the Zumwalt Prairie lies, have remained fairly stable during that time.

 An inventory of browse levels on the Zumwalt Prairie Preserve conducted in 2010 showed that of the 65 sites surveyed, only 1 (within an elk and deer resistant fence) had low to moderate levels of browse while 87% of sites experienced “intense browse” which restricted growth of all aspen and shrubs observed (Taylor and Arends 2011).

 Browse monitoring conducted by the Conservancy from 2010 through 2012 indicated that consistently high browse levels occurred in areas where cattle and wild ungulates grazed and also in areas where cattle were excluded. The only sites where browse levels allowed for growth of aspen and shrubs were those within elk/deer resistant fences suggesting that wild ungulates rather than cattle were the primary browse agents on the Zumwalt Prairie Preserve (Taylor 2012b). Recovery of aspen stands where elk and deer resistant fencing has been demonstrated using repeat photography (Dingeldein and Taylor 2011) though not all aspen stands appear to regenerate and the cause of this is not known.

REFERENCES

Anonymous. 2008. Zumwalt Prairie Bird List. The Nature Conservancy, Enterprise, OR.

Anonymous. 2010. Zumwalt Prairie Lichen List. The Nature Conservancy, Enterprise, OR.

Bartuszevige, A. M., P. L. Kennedy, and R. V. Taylor. 2012. Sixty-seven years of landscape change in the last, large, remnant of the Pacific Northwest Bunchgrass prairie. Natural Areas Journal 32:166-170.

Bauer, J. and R. V. Taylor. 2003. Pilot Studies of Herbaceous Removal in Zumwalt Prairie Preserve Pastures. The Nature Conservancy, Enterprise, OR.

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