Acclimation and adaptation of deciduous tree seedlings to a warmer, wetter climate

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 among species and a general northward shift is their distribution.  Model predictions can be used to generate field studies that study the underlying mechanisms that may drive ecosystems changes.  We undertook a field study that simulates predicted changes in climate in a regenerating forest in central Pennsylvania.  The overarching objective of this study is to determine if species’ morphological or physiological responses to altered climatic conditions will facilitate changes in the competitive success of deciduous tree seedlings. Measurements of seedling response to climate manipulations were collected in a 2-factor design of increased temperature (~2°C) and precipitation (~20%).  Each plot is 2X2m and N=4 for the four combinations of treatments: ambient, heated, irrigated, and heated+irrigated.  A minimum of 10 seeds from 11 species were planted in each plot and monitored for morphological, as well as, physiological responses to the imposed treatments.

Results/Conclusions

Significant changes in growth and photosynthesis have occurred for most species in response to 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 significantly higher above-ground growth in 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.  Fraxinus americana had higher levels of net photosynthesis on all three imposed climate treatments in comparison to the ambient conditions. All four northern Quercus species showed higher net photosynthesis levels on the heated+irrigated treatments, while the southern Quercus stellata had higher net photosynthesis in the heated treatment. Based on these results, the imposed temperature and precipitation treatments are differentially affecting the morphology and physiology of newly germinated deciduous tree species.    Further study is needed to determine the impact that these treatments will have on the competitive success of these species and how potential morphological and physiological changes can be applied to predict species responses to climate change.