Large Scale (Macrosystem) observations of plant demographics and soil biogeochemical process.

The design of our study includes mapped tree stands where we gather individual level data on maturation status, crown status, diameter growth, survival, and seed rain.  Stands differ in terms of average temperature and elevation, from Piedmont pine-oak to northern hardwoods at Coweeta, and in local moisture status, from bottomland hardwood to xeric ridgelines.  There is variation in climate between sites and over time.  Individual trees vary widely in terms of exposure to sunlight.  Observations include field observations on individual trees and seed traps and increment cores to determine growth rates. 
Climate change is predicted to result in large-scale changes in the relative abundances and distributions of tree populations in eastern North America.  Many species are predicted to migrate north, to higher elevations, or both.  Species now restricted to upper elevations could disappear from the Southeast, possible displaced by immigrants from lower elevations.  The vulnerability is unknown, because it is not clear how climate and competition interact.  Despite the importance of climate, light limitation is the largest risk factor for trees of most species and will mediate effects of climate.  Without estimates of the interactions, we cannot anticipate how climate risk varies across species. 

Design

Mapped stands are the basis for data collection (Fig. 2).  For our analysis in Whitehall Forest we propose to set up approximately four mapped stands 50 m by 50 m supporting 25 seed traps each.  The plots would be located at mixed hardwood stands.   To the extent possible, plots would coincide with ones already in place.  We welcome opportunities for data sharing. 

Plots have a 10 m by 10 m reference grid marked by rebar.  All trees > 2 m in height are tagged (aluminum) at 1.5 m high.  Approximately 20 trees are increment cored in each plot, each year, to begin in year 3.  Seed traps 30 cm by cm will be constructed of treated pine and located in the interior 40 m by 40 m grid corners for a total of 25 traps per plot.  Tree censuses will be conducted at 2 to 4 yr intervals. 
To anticipate responses in settings where individuals of a species do not now occur, it is important to plant seeds in new environments.  Approximately 10 seedling plots 1 m by 2 m will be installed in each of the six plots.  Seeds collected primarily from adjacent forest and will be planted to allow for analysis of climate and competition effects on germination, seedling growth, and survival.  Light estimates come from analysis of canopy photos.