COS 4-7
Environmental controls of seedling growth under experimental warming
As the climate warms tree growth rates are expected to increase; however, depending on species thermal limits and the prevailing environment, climate change can induce positive or negative effects on plant growth. Future composition and ecosystem function will be directly related to the species most responsive to future climate. Understanding this responsiveness is the best way to successfully manage the impacts of environmental change on forest communities. In 2008, a manipulative warming experiment was implemented in North Carolina and Massachusetts to determine seedling responses to changing climatic conditions. The experiment utilizes a factorial design for warming (control, ambient, +3-5°C), and two light levels (gap and understory) for a total of 48 plots. A Bayesian state-space model was constructed to quantify both the magnitude and timing of environmental variables on seedling growth, revealing how environmental sensitivity will shift the competitive balance between species.
Results/Conclusions
Warming treatments do not consistently increase growth rates. Instead, seedlings interact with environmental factors in a more complicated way. For instance, tulip poplar growth is positively correlated to the length of the previous year’s growing season for the first two months after leaf-out. After that growing season no longer influences growth. Instead, current soil moisture (negative correlation) and temperature (positive correlation) have the strongest influence on growth. In general, growth rates are positively correlated with warmer temperatures with only two species, planted near their southern range limit, having a negative response to elevated temperatures. This typically positive temperature growth response is being counterbalanced by soil moisture status which restricts growth during drought. This suggests that forest communities will respond idiosyncratically to climate change. In regions where drought is common, like the piedmont of North Carolina, seedling response may largely be a response to water limitation, while in regions, like western Massachusetts, where water is not as limiting seedling response may be a direct effect of temperature mediated growth. Overall, higher temperatures do not yield higher growth rates. We must understand the interaction of a suite of environmental variables to successfully mitigate the impacts of environmental change on forest communities.