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Release episodes at the periphery of gaps: a modeling assessment of gap impact extent

2002; NRC Research Press; Volume: 32; Issue: 9 Linguagem: Inglês

10.1139/x02-090

1208-6037

André Ménard, P. Dubé, André Bouchard, Danielle J. Marceau,

Plant Water Relations and Carbon Dynamics

Gaps are recognized as important features of temperate forest dynamics and have been extensively studied in the last decades. Their definition has progressively evolved from the simplistic physical projection of the canopy opening to a more resource-based and functional approach (extended and species extended gaps). However, to truly define gap extent, the peripheral impact of gaps on the trees has to be considered. This study was undertaken to characterize the impact extent of gaps on their periphery using the SORTIE forest succession model. The sapling growth responses to gaps of different sizes (500–2000 m 2 ) was used as an indicator of the impact extent. Ten replicates of a simulation (for each gap size) were performed (305 years, 25-ha lattice). Gaps were introduced after 300 years. Growth ratios (pregap/postgap growth) for each sapling were computed and compared with a release threshold to determine sapling release episodes. These release episodes were analyzed to assess the extent of gap impact. Results indicate that gap effect extends significantly into the adjacent forest. Release episode orientations are concentrated in the northern hemisphere of gaps, and release episodes mostly appear in the first 20 m from gaps. Based on different degrees of release occurrence, new gap areas were defined and compared with areas from existing gap definitions. The differences are substantial and reveal that gap spatial extent observed through release patterns surpasses gap areas defined by traditional definitions.