The observation of long-term changes in managed grassland plant community composition creates an opportunity for collaboration of proper techniques and a better understanding of the resilience of these vital communities to future change. Grazing by large herbivores can have an immense impact on natural plant communities and has been extensively studied. Traditionally, the use of grazing exclosures has been a useful tool for land managers in both comparing the effects of grazing on natural communities and allowing plant communities the time to recover after grazing. Here we have explored the similarities and differences in vegetation structure utilizing historical grazed and un-grazed vegetation coverage data (1931 – 2014) from 31 grazing exclosures, obtained from British Columbia’s Ministry of Forests, Lands, and Natural Resources, across a 300 km range in the Interior British Columbia, Canada grassland ecosystem. Non-metric, multidimensional scaling (NMS) was performed on species cover for each grazed and un-grazed transect at each site and sampling period in order to observe both the direction and trajectory of change over time. Species richness and diversity was analyzed and compared across regions as well as between grazed and un-grazed communities to observe and variability that may contribute to the magnitude in changes in trajectory.
Results/Conclusions
Results of this research show that grazing removal leads to greater variability in diversity among sites depending on what scale of time is being observed. On average, species richness along ungrazed transects increased by an average of 0.3 species and 0.4 species in grazed areas, with the higher latitude sites showing some of the greatest change in species composition in the ungrazed areas when looking at results of the NMS. Shannon diversity indices for grazed (2.0) and ungrazed (1.8) areas show that over longer time periods the effects of grazing balance out. However, on a shorter time scale, there is much more fluctuation in this variability, with Shannon diversity being 2.2 in ungrazed and 1.7 grazed on sites sampled under a 20-year period. Although high fluctuations exist with variable timing between sampling we see that a pattern exists that can illicit further study of the effects of changes in grazing regimes and landscape differences that can influence the recovery. 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.