Canadian Forest Service Publications
Uncovering spatial and ecological variability in gap size frequency distributions in the Canadian boreal forest. 2020. Goodbody, T.R.H., Tompalski, P., Coops, N.C., White, J.C., Wulder, M.A., Sanelli, M. Sci Rep 10, 6069.
Issued by: Pacific Forestry Centre
Catalog ID: 40127
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Analyses characterizing canopy gaps are required to improve our understanding of spatial and structural variations in forest canopies and provide insight into ecosystem-level successional processes. Gap size frequency distributions (GSFD) are indicative of ecological processes and disturbance patterns. To date, GSFD in boreal forest ecosystems have not been systematically quantified over large areas using a single consistent data source. Herein we characterized GSFDs across the entirety of the Canadian boreal forest using transects of airborne laser scanning (ALS) data. ALS transects were representatively sampled within eight distinct Canadian boreal ecozones. Gaps were detected and delineated from the ALS-derived canopy height model as contiguous canopy openings ≥8 m2 with canopy heights ≤3 m. Gaps were then stratified by ecozone and forest type (i.e. coniferous, broadleaf, mixedwood, wetland-treed), and combinations thereof, and GSFDs were calculated for each stratum. GSFDs were characterized by the scaling parameter of the power-law probability distribution, lambda (λ) and Kolmogorov-Smirnov tests confirmed that GSFDs for each stratum followed a power-law distribution. Pairwise comparisons between ecozones, forest types, and combinations thereof indicated significant differences between estimates of λ. Scaling parameters were found to be more variable by ecozone (1.96–2.31) than by forest type (2.15–2.21). These results contrast those of similar studies done in tropical forest environments, whereby λ was found to be relatively consistent across a range of site types, geological substrates, and forest types. The geographic range considered herein is much larger than that of previous studies, and broad-scale patterns in climate, landforms, and soils that are reflected in the definition of unique ecozones, likely also influence gap characteristics.
Plain Language Summary
In the paper we introduce canopy gaps and how they influence forest processes, structure, and species composition. From a unique, representative, airborne laser scanning dataset spanning 25,000 km across the Canadian boreal forest, we delineate and characterize canopy gap-size frequency distributions (GSFD) across eight distinct ecological units (ecozones) and four forest types (coniferous, deciduous, mixed, wetland treed). Our results suggest that forest type explained more variation in GSFD than ecozones confirming that tree morphology, crown shape and size, and growth characteristics dominate gaps dynamics than geographical region, topography or climate. In accordance with previous findings in tropical and temperate forests, we find consistency in GSFD across the Canadian boreal forest and in these other biomes, indicating that we are closer to a global GSFD which is uniform regardless of biome and forest type.