B4WarmED forest warming experiment: The effects of increased temperature and drought on boreal tree species leaf size and shape.

Background/Question/Methods

The impacts of climate change have the potential to transform the forests of Minnesota, where the boreal and temperate biomes converge. One scenario suggests that future climate patterns will include higher global temperature and longer periods of extreme drought. This study seeks to understand whether increased plant temperature and rainfall manipulation affect leaf size and shape.  Analyzing leaf size and shape, in particular leaf length, width, and SLA of red maple, sugar maple, red oak, bur oak, paper birch, quaking aspen and buckthorn may help us to understand the potential effects of this changing climate on the leaf growth of these respective species. We tested this at the Boreal Forest Warming at an Ecotone in Danger (B4WarmED) project which is a manipulative open-air warming experiment that uses infrared heat lamps and soil cables to heat continuously through the growing season.  Here we present results showing potential alternation of the leaf size and shape associated with +1.7°C and +3.4°C warming and rainfall removal on seven broadleaf tree species at the Hubachek Wilderness Research Center near Ely, Minnesota. During June, July, and August of 2012 we measured the size, shape and mass of leaves throughout the crown, between the treatments.

Results/Conclusions

Analysis of data revealed there was no overall effect on leaf size and shape, however species’ responses varied. For example, red oak, quaking aspen, and buckthorn developed larger leaves, especially in +1.7°C while compared to ambient, while red maple and sugar maple developed smaller leaves. Furthermore, rainfall manipulation appeared to have various effects on leaf development, showing a positive effect on the leaf sizes of red maple and paper birch, while red oak, quaking aspen and buckthorn developed smaller leaves. This suggests that while warming and rainfall manipulation may not have an overall effect on leaf size and shape, on a species level there may be notable responses to a warmer, drier climate. These results can provide a glimpse into leaf dynamics of Minnesota forests if climate change creates hotter and drier summers.