Dwarf woolly-heads, specific populations, COSEWIC assessment status report: chapter 8
Limiting Factors and Threats
Climate change may present a significant threat to the species by reducing the frequency of flooding in suitable sites. This could increase mortality within soil seed banks while at the same time decreasing the size and frequency of seed bank inputs. The impacts of climate change may be exacerbated by the species’ weak powers of dispersal, which will likely restrict colonization of sites that may become more suitable for the species.
Southern Mountain Population
The Southern Mountain Population is particularly vulnerable because the small area of occupancy and scarcity of suitable habitat leave it prone to extirpation. The most obvious threats are posed by altered hydrological regimes or changes in patterns of livestock grazing. Changes in vegetation cover around the area would alter snow accumulation, the capture and release of water and transpiration losses. Such changes may occur as a result of various influences including timber harvesting and fire. Changes in the timing and intensity of grazing may directly or indirectly impact the hydrological regime, favour the accumulation of thatch which would stifle germination, shift the competitive balance towards perennial species, or directly damage plants through trampling during the early growing season. Invasive species are unlikely to have a significant impact on Psilocarphus brevissimus unless there are changes in hydrology or grazing. The use of herbicides to control invasive weeds on rangelands, transmission rights-of-way and highway verges (all of which occur near or adjacent to one or more of the sub-populations) may also eliminate the population. All-terrain-vehicle use, an increasingly popular form of recreation in the region, may threaten the population by churning up soil, altering hydrology or directly impacting plants. The habitat occupied by P. brevissimus presently lies within the Agricultural Land Reserve (ALR), designed to protect agricultural land from other forms of development. Key areas within the ALR have been deleted over the past decade in order to allow development in the vicinity of towns and cities. Given the proximity of the sub-populations to Princeton (less than 10 km away) and the scenic nature of the grasslands where they occur (near the dramatic breaks of the Similkameen Valley), it may become a candidate for deletion from the ALR for purposes of development. Housing sales have trended upwards in the last 12-18 months in the Princeton area in tandem with markets in the Okanagan Valley (Fabri, pers. comm., 2003). A wide range of agricultural practices (even topsoil stripping) are permitted within the ALR (Provincial Agricultural Land Commission 2003) and even without deletion from the ALR, changes in use may eliminate the critical habitat.
Prairie Population
Douglas et al. (2000) cite habitat destruction associated with agricultural development and oil and gas exploration as the primary threats to populations of this species in the prairies. Some of the sites lie within an area intensively developed for agriculture while others may be at less risk because soil and climatic factors discourage intensification of agricultural activities.
Significant amounts of habitat of sixteen of the sites have been directly damaged by pipeline development (Rintoul pers. comm. 2005). Several other populations, while lying just outside a pipeline rights-of-way, may be impacted by changes in hydrology associated with pipeline development and maintenance.
As with the Southern Mountain Population, range management practices and weed control measures present a threat to many of the sub-populations.
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