Silene spaldingii wats. in the channeled scablands of Eastern Washington: demography, monitoring protocol, community characteristics, and habitat modeling

Tiana Linell Luke

Federally threatened Silene spaldingii (Spalding's catchfly), a perennial geophyte, occurs primarily on pristine grasslands and occasionally in shrub steppe and open ponderosa pine forests of the interior Northwest. Much of the species' habitat was lost to agricultural development or degraded by invasive species. The demography of approximately 1000 Silene spaldingii plants on 10 sites monitored by the Bureau of Land Management for 17 years were assessed for population trends using ANOVA. Total plant numbers (p=0.449) and reproductive plants (p=0.534) were stable. Mean stem height (p<0.001) and mean number of reproductive structures per plant (p<0.001) decreased over time. These characteristics were regressed against local precipitation and temperature data. Mean stem height and mean number of reproductive structures were positively associated with precipitation. The stable total plant and reproductive plant counts could be considered hopeful, although an increasing population is preferred. Decreases in fecundity and photosynthetic area could lead to future population declines. Climate models predict that future precipitation will decrease in eastern Washington, potentially exacerbating decreasing mean stem height and reproductive structures. Other factors that could influence these characteristics include mechanical disturbance, resource competition from invasive species, or inbreeding. Using recommendations from the Silene Technical Team (2012), a new v monitoring protocol was developed and implemented for the Spokane District Bureau of Land Management. Seventy monitoring sites were randomly selected from 1083 known locations and 56 met requirements for monitoring. Data collected twice during the growing season included phenological and plant community measures. Initial results from 2012 indicate that this protocol will accurately measure progress towards recovery and represent the channeled scabland population of Silene spaldingii on BLM lands. Future data can be compared to other populations using comparable methods to better assess the species range-wide. Early evidence suggests a negative correlation between rosette plant numbers and exotic species in the plant community. A habitat model was attempted but available data proved too coarsely scaled for the microhabitat preferences of the species. These results support concerns about the future of Silene spaldingii in the channeled scablands and management changes may be needed to improve prospects for the species' recovery in this habitat.

Silene spaldingii wats. in the channeled scablands of Eastern Washington: demography, monitoring protocol, community characteristics, and habitat modeling

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