COS 74-2
Plant community responses to abiotic conditions within variably aged grazing exclosures in British Columbia, Canada
The effects of climate induced plant community composition change are still relatively misunderstood in managed grassland plant communities. Traditionally, the use of long term grazing exclosures has been a useful tool for land managers in both comparing the effects of grazing on natural communities as well as allowing plant communities the time to recover after intensive grazing and can improve their ability to act against the negative effects of climate change on a changing plant community by having the best possible understanding of these systems. With this research we wanted to explore the similarities and differences in vegetation structure under different climatically driven conditions utilizing historical vegetation coverage data (1959 – 2007) from approximately 30 grazing exclosures, obtained from British Columbia’s Ministry of Forests, Lands, and Natural Resources, across a 300 km range in the Interior British Columbia grassland ecosystem. This data was then analyzed in conjunction with several climate (temperature and precipitation) measures to determine floristic similarities and differences over time and among geographically varying sites.
Results/Conclusions
All exclosures responded to climate similarly within a smaller geographic range (10’s of kilometers), while coarser scale relationships were less apparent (between regions). Principal Component Analysis (PCA) utilizing the 180 available climate indices showed a strong association with temperature, with axis 1 explaining over 40% of the variability in the data and indices related to moisture increasing this explanation to nearly 60%. Climate variables were then reduced to 10 distinct monthly temperature and precipitation indicators based on the first two axes. These reduced climate indices combined with reduced vegetation cover (53 total species which represents >10% average coverage to reduce noise) were then ordinated using Redundancy Analysis (RDA). RDA showed that only 41% of species coverage can be explained by climate variables used, which indicates that species composition change within these communities is not necessarily driven by these temperature and precipitation indicators, but that species and communities most likely react as individuals, likely based on other conditions. By combining appropriate climatic variables and plant coverage with a knowledge of individual species ecology, seral stage as well as utilizing grazed and ungrazed conditions we will greatly enhance our ability to forecast possible impacts on managed and unmanaged communities.