Seed bank and existing plant community mismatch: Potential impacts on climate change induced species range shifts

Background/Question/Methods

Plants species can respond to climate change by shifting distributions into new suitable habitat, but plants can only “migrate” into new areas through propagation. Long distance seed dispersal is an important mechanism that enables a plant species to track the fast pace of predicted climate change. Upon seed arrival, conditions may be temporarily unsuitable for germination. A seed bank may buffer unsuitable periods and thus contribute to successful long-distance establishment. However, we know little about the importance of seed banks in supporting range expansion. Big sagebrush (Artemisia tridentata) covers a significant portion of the western United States and can only regenerate via seed. Our goal was to enhance understanding of the potential for migration in big sagebrush plant communities under future climate change, specifically by quantifying how the seed bank reflects the established plant community at sites adjacent to the leading edge of the big sagebrush distribution. At three sites, we sampled species composition and big sagebrush cover and density as well as the seed bank for a greenhouse emergence study. We used Bray-Curtis dissimilarity percentages to compare seed bank composition to aboveground composition within sites as well as compare species composition in the aboveground and seed bank across sites. 

Results/Conclusions

We found 44 species in our study; of those, 28 were represented in the established plant community and 31 in the seed bank, but only 17 were shared between both. This resulted in less than a 30% similarity between the seed bank and the aboveground vegetation. The seed bank was dominated by annual species (~70% of total number of seedlings that emerged) whereas the extant vegetation was dominated by big sagebrush and C₃ perennial grasses (20% and 16% respectively). Furthermore, of 4698 seedlings that emerged only 29 were big sagebrush, indicating that sagebrush has a short-lived seed bank. A mismatch in composition between the seed bank and extant vegetation underscores the potential for change in the composition of these communities under future climate conditions. These results highlight that plant communities dominated by dispersal limited, long-lived species, such as big sagebrush, with little presence in the seed bank are at risk of declining populations because of a lack of means to track climate change into areas that are becoming more climatically suitable.