Seedling physiological responses to increased temperature and precipitation in a northeastern deciduous forest

Background/Question/Methods

Global circulation models have predicted warmer and wetter conditions throughout the northeastern United States, and the potential impact of these climate changes on forest ecosystems could be dramatic.  Existing regression and gap models have predicted differential success rates and a general northward shift for all species.  Forest management and harvesting provide opportunities for forest community composition to change dramatically and can facilitate species migration northward.  Field studies can test model predictions and develop an understanding of the underlying mechanisms which may drive ecosystems changes.  These studies can provide better understanding of several key factors; including acclimation and species interactions, which can be applied to improve predictions species and community responses to environmental changes. The objective of this study is to determine if species and community responses to altered climatic conditions will facilitate changes forest succession and composition in the future.

The study will take place in a harvested forest area in central Pennsylvania.  Data will be collected from 20 plots in a 2-factor study of increased temperature (~2°C) and precipitation (~20%).  Each plot contains 2 - 2X2m halves and N=4 for the four combinations of treatments: control, heated, irrigated, heated+irrigated, and unmanipulated “extra”.  This study involves investigation of changes in of seedling morphology and physiology as well as changes in altered early successional vegetation communities.  To study seedling response, minimum of 10 seeds from 11 species are planted in each plot and monitored for morphological, as well as, physiological responses to the imposed treatments.  Changes in early successional vegetation dynamics will be studied by observing differences in the naturally occurring post-harvest communities of our treated plots.  

Results/Conclusions

Significant observable changes in growth and photosynthesis have occurred for most species as a result of the imposed climate manipulation treatments.  When compared to the ambient treatment, both Acer rubrum and Fraxinus americana showed an increase in above-ground growth on the heated+irrigated treatments, while Quercus rubra and Quercus velutina showed significant increased trends in above-ground growth on the heated treatment.  As expected, drought tolerant species Quercus prinus and Quercus stellata, had higher net photosynthetic rates on the heated treatments when compared to those grown on the ambient treatment.  Based on these results, the imposed climate treatments are affecting the morphology and physiology of newly germinated deciduous seedling and further study is needed to determine the impact that these treatments will have on the competitive success of these species.