The Old-Field Community Climate and Atmospheric Manipulation (OCCAM) experiment at Oak Ridge National Laboratory, Tennessee was established to investigate interactive effects of elevated CO₂, warming, and soil moisture on a multi-species old-field community.  This constructed old-field ecosystem, planted in open-top chambers, consists of C₃ and C₄ grasses, herbaceous dicots, and legumes that have undergone interacting climate change treatments beginning in May 2003.  In the winter of 2007 seeds of three woody seedling species (Pinus taeda, Liquidambar styraciflua, Acer saccharinum) were planted into 10 locations per species within each experimental unit.  Seedling emergence, growth, and survivorship were measured from early spring of 2007, through the 2007 growing season, and into 2008. 

Results/Conclusions

The seeds of A. saccharinum, which germinate in late spring shortly after being disseminated, responded differently from those of the fall-produced seeds of the other two species, which germinate in early spring after overwintering.  Emergence of A. saccharinum was significantly reduced in dry plots, with ~90% of all germination occurring in wet treatments.  L. styraciflua seed emergence was not affected by soil moisture treatments because soil moisture was much higher when they were emerging.  Emergence of L. styraciflua was, however decreased in ambient temperature treatments with elevated CO₂.  Seedling growth throughout the growing season was influenced by the climate change treatments for each species.  For example, the growth of L. styraciflua and P. taeda seedlings was reduced by 29-35% in dry relative to wet treatments.  P. taeda growth was increased 20% in elevated CO₂ plots with elevated temperatures.  In order to determine the success of establishment, seedling survivorship was evaluated both at the end of the growing season and following over wintering in 2008.  Preliminary analysis of survivorship shows increased seedling survival under elevated CO₂ treatments.  Understanding the effects of climatic change factors on tree seedling establishment will be important to make better predictions about how climate change may alter community and ecosystem structure and function.