This data was used to explore how forest biological and physical structure influence productivity.
We collected tree census data (species, diameter at breast height (cm), canopy status, and azimuth & distance from plot center) for each plot, tree cores from approximately 10% of all trees and the measured increment of growth in the most recent 5 years, and rugosity data (a measurement of physical complexity) of each plot.
Each stand contained two or three 0.1 ha plots, with an exception noted below, with plots treated as replicates for calculating stand mean and error. Plots were circular, except for those in the 1998 Cut and Burn stand, which, due to size constraints of the treatment area, contains two rectangular plots of 0.14 and 0.06 ha respectively.
Measures of canopy structure: Canopy structure complexity was quantified as rugosity using a Portable Canopy LiDAR (PCL) system (Hardiman et al., 2013a; Parker et al., 2004). A canopy hit-map was generated along two parallel 40 meter transects running through each plot. Due to size constraints, a modified PCL protocol was used in the 1998 Cut and Burn plots with shortened parallel transects (10m and 20m) running North to South. PCL returns were pooled in 1 m2 bins vertically (with height) and horizontally (along the transect) and canopy rugosity was calculated using published MATLAB code (Hardiman et al., 2013b).
Diversity indices: To determine biological complexity as species diversity, canopy tree stems (DBH > 8cm) were surveyed and used to calculate Simpon’s Index of Diversity (D’). This metric of structural complexity has been shown to correlate with NPP in nearby study sites (Gough et al., 2010).
Wood net primary productivity: Ten trees were randomly selected in each plot and cored with an increment borer. Annual growth increment was calculated for each tree from a 5-year average, and species and site-specific allometric equations and carbon density data were used to calculate carbon mass from DBH. Wood NPP was calculated as the average kg carbon mass increment over five years scaled to a hectare (Gough et al., 2008).