Disturbances alter stand structure and composition, which may lead to changes in forest function. Canopy structural complexity (CSC) is an important functional characteristic of forests that describes variability in physical locations of canopy structural elements. CSC influences numerous physical processes within the canopy, including radiation transfer, wind penetration, and gas diffusion rates, which may affect Net Primary Productivity (NPP) and its response to disturbance. Observational studies have suggested that NPP response to disturbance is mediated by CSC, but further research is needed to separate the specific effects of pre-disturbance conditions, disturbance severity, and disturbance induced changes in CSC as drivers of NPP response. We addressed this need by designing and implementing a replicated field experiment in which stands similar in initial composition and structure were explicitly manipulated to different levels of CSC. Treatments targeting 20% basal area removal and increased (≥ 40%), decreased (≥ 40%) or maintained (+- 20%) CSC were devised by manipulating Terrestrial Laser Scanner (TLS) point clouds generated from scans of twelve 0.5ha plots arrayed across four temperate forest sites.
Results/Conclusions
TLS scans of each plot were aligned and registered to generate a digital point cloud of the forest, which was then segmented into individual trees using a nearest-neighbor-based algorithm. Retained trees were selected based on crown width and class, and their representative point clouds merged to create a digital model of the desired post-treatment stand. Plot-level CSC was calculated from pre- and post-manipulation point clouds using the forestr package in R, and the differences were used to verify treatment criteria were met. Plots are being scanned periodically following treatment to validate treatment targets for CSC and assess temporal changes in canopy structure following disturbance. Measurements of bole diameter are collected on an annual basis to determine wood increment, and results will be combined with region- and species-specific allometric equations to evaluate the role of CSC in determining NPP response to forest disturbance. A random subset of trees in each plot will be increment cored 5-years post treatment and analyzed to verify annual diameter-tape measurements. The TLS processing methodology developed through this work serves as a baseline for future studies evaluating forest structure-function relationships. Ongoing monitoring will provide insights into CSC-disturbance-productivity relationships useful in silviculture and forest ecosystem model parameterization.