Description
Background: The Pryor Mountain Wilderness Study Area (PMWSA) in south-central Montana encompasses an elevational range from 4000 to 9000 ft in elevation. Vegetation varies from arid shrublands, woodlands and semi-arid grasslands at lower and middle elevations to subalpine forest and grassland at higher elevations (DeVelice and Lesica 1993). Terrain is relatively gentle at the highest and lowest elevations but steep and rugged throughout much of the middle elevations. Most of the research on the effects of the wild horses in the Pryor range has been conducted on the gentle terrain occurring in the subalpine grasslands or the desert grasslands at the base of the mountains. However, the sparsely vegetated, steep slopes found throughout much of the wild horse range are expected to be more susceptible to degradation, especially following disturbance. Effects of wild horse grazing on this steep terrain have not been determined. Pryor Mountain bladderpod (Lesquerella lesicii =Physaria lesicii) is a short-lived perennial in the Mustard Family (Brassicaceae) that is known to occur only in the Pryor Mountains of Montana (Rollins 1995, Oâ¿¿Kane 2010). Pryor Mountain bladderpod is known from three areas on the Pryor Mountain Wild Horse Range in sparsely vegetated soil of grasslands and mountain mahogany and juniper woodlands (Lesica 1995). The largest known population occurs on Sykes Mountain, in an area that is disturbed by horse trampling. The other two, smaller populations are in less disturbed sites at higher elevation (Lesica 1995). Pryor Mountain bladderpod is listed as a species of concern by the Montana Natural Heritage Program and highly threatened by The Montana Interagency Plant Threats Assessment Committee. The effects of ungulates, both native and domestic, on the vegetation of semi-arid grasslands are numerous. Grazing removes vegetation, thereby reducing litter and changing competitive balances (Biondini et al. 1998, Milchunas et al. 1998, Olff and Ritchie 1998). Grazing concentrates nutrients and alters cycling (Schuman et al. 1999). In addition to the effects of grazing are the effects of trampling. Trampling may cause erosion directly (DeLucca et al. 1998, Wilson and Seney 1994) or by destroying biotic crusts (Cole 1990, Memmott et al. 1998). Trampling adversely affects vegetation (Cole 1995, Cole and Spildie 1998, Weaver and Dale 1978), in some cases threatening rare species (Maschinski et al. 1997, Thomas and Willson 1992). Trampling by horses can have severe impacts on vegetation (Cole and Spildie 1998, Weaver and Dale 1978), but the effects of horse trampling on Pryor Mountain bladderpod are not known. In Missouri, high levels of trampling by humans reduced the survival of Missouri bladderpod (Lesquerella filiformis; Thomas and Potter 1992). Idaho bladderpod (Lesquerella carinata) has been shown to be positively associated with and survive better under bunchgrasses than in the open in stressful habitats (Greenlee and Callaway 1996). Results of their study suggest that Idaho bladderpod would suffer from the loss of bunch grasses that might occur with severe trampling. A similar interaction may occur at the Sykes Ridge site where Pryor Mountain bladderpod appeared to be most common beneath shrubs or bunchgrasses (Lesica 1995). On the other hand, Pryor Mountain bladderpod occurs in habitats with 50-80% bare ground, suggesting that it may be a poor competitor favored by ample bare soil. Many other species of Lesquerella and other members of the Brassicaceae also have a ruderal life history (Rollins and Shaw 1973, Rollins 1993). Such ruderal species are often favored by intermediate levels of disturbance (Bowles et al. 1990, Huston 1994, Parsons and Browne 1982). The effects of trampling on vegetation have usually been assessed on level ground although they are expected to be more severe on steep slopes (Summer 1986). Project Objectives: To determine the effects of different levels of horse trampling on steep terrain in semi-arid habitats and on Pryor Mountain bladderpod in particular. Results of this study will assist managers to determine wild horse herd sizes and pasture rotations compatible with maintaining habitat quality in the Pryor Mountains. In addition, permanent transects will be established in order to determine long-term trends in the abundance of Pryor Mountain Bladderpod, which is listed on the BLM MT/DKs sensitive species list, IM MT-2014-067. Public Benefit: The results of this research proposal would augment other inventory and monitoring studies and help land managers determine the Appropriate Management Level (AML) for wild horses inhabiting the Range.