A climate warming of 2–7°C by the end of this century will impact the likelihood of seed germination and the rate of successful seedling establishment for many tree species. Here we investigate the reproductive success of sugar maple (Acer saccharum Marshall.), a widely distributed hardwood tree species found across northeastern North America. Sugar maple makes an ideal candidate to test the influence of climate warming as it possesses a restricted temperature range to ensure successful reproduction. We hypothesized that seed origin affects germination due to the species’ local adaptation to temperature. We tested this experimentally by investigating the effect of the average and the variance of temperature on seed germination from seven different seed sources representing the current species range. Second, we evaluated the current regenerative capacity of the species to germinate and survive beyond its northern distribution by conducting a large scale transplant study using the same seed sources. Seeds were transplanted to sites within, at, and beyond the current northern species limit, where we assessed the effects of seed source, local demographics, and climate on early seedling establishment and survival.
Results/Conclusions
Our results showed that seeds from the northern range had the highest germination percentage, while the southern range had the lowest. Seed germination was also highest when constant temperatures were ≤5°C, where at warmer temperatures germination percentages greatly declined. We find that a climate warming of up to +5°C would severely reduce germination of seeds from the southern range. However, under a more pronounced warming of 7°C, seeds from all provenances will have poor germination. In the field, sugar maple germination and establishment was much higher within its distribution than those transplanted at the species limit or beyond, however, survival rates were comparable. Interestingly, establishment on all sites investigated increased with a latitudinal shift northward in seed origin, where seeds from southernmost origins were less likely to establish. Ultimately, we find that sugar maple holds the capacity to successfully establish and survive way beyond its current range limit on a diversity of seed beds, however, recruitment rates should be expected to lag severely behind its climatic niche under predicted climate warming.