PARENT SESSION
Oral Session # 79: Forest Ecology V: Structure; Dispersal; Competition.
Presiding: J Schnurr
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 104.
A multivariate analysis of structural development in Tulip Poplar Association forests.
Berger, Michelle*,1, Parker, Geoffrey1, 1 Smithsonian Environmental Research Center, Edgewater, MD
ABSTRACT- We combined measurements of the vertical distribution of leaves in the canopy with more common stem measurements in a multivariate analysis of structural development in Tulip Poplar association forests. Eighteen variables were measured or derived for a 240 year chronosequence of 46 forest plots in the vicinity of the Smithsonian Environmental Research Center in Edgewater, MD. With a factor analysis, the original variables were reduced to three independent factors that together accounted for >82% of the variability in the dataset. Variables that change early in development, when height growth is greatest and before crowns begin to differentiate, loaded strongly onto the first factor. This factor was positively correlated (r2 = 0.68, p<0.0001) with age, particularly for forests younger than 70 years. Variables that change as the canopy differentiates and the understory begins to grow loaded onto the second factor. This factor was negatively correlated (r2 = -0.36, p=0.014) with age. Only Leaf Area Index and total leaf biomass loaded strongly onto the third factor, which was not significantly correlated with stand age. We conclude that: 1. Common measurements of stem height and diameter used in many studies of forest development do not capture all of the structural changes that occur, particularly in older forests. 2. The only leaf variables usually measured, LAI and leaf biomass, do not change much during development in this forest type. Additionally, the changes in the vertical distribution of leaves within the canopy can have clear implications for how a forest functions as it ages.
Key words: development, multivariate statistics, forest structure, canopy