Spatial patterns of damage and tree mortality in a selectively logged Atlantic Forest

Abstract

Selective logging, a common disturbance in mixed-species and uneven-aged forests, can cause substantial collateral stand damage and tree mortality. Here we explore damage patterns and some mechanisms that increase post-harvest tree mortality in a selectively logged subtropical Atlantic Forest in Argentina. We investigate the spatial relations of felled and damaged trees through spatial point pattern analysis and evaluate the relationships between mortality and different endogenous (size - diameter at breast height: DBH; and wood density: WD) and exogenous (damage and neighboring basal area: NBA) factors. The permanent plots were logged in 1999, and the fates of all pre-logging live trees ≥10 cm DBH were evaluated 20 years later. Of the monitored 3973 trees, 381 with damaged concentrated within 10.5 m of felled tree stumps. Over the next twenty years mean mortality was higher and more variable for damaged than undamaged trees (47 % ± 10 % SE and 39 % ± 2 % SE, respectively), and the presence of damage interacted with the other analyzed factors. For undamaged trees, the probability of mortality declined with DBH and NBA but not with WD. For damaged trees, instead, the probability of mortality was related to an interaction between DBH, WD, and NBA. For damaged trees <30 cm DBH, mortality increased with WD and NBA, whereas for damaged trees ≥30 cm DBH, mortality peaked at both extremes of the WD range. For these large trees with low WD, the probability of mortality decreased with NBA, whereas for trees with high WD, the opposite was observed. Our findings suggest that selective logging affects the dynamics of forests by spatially concentrating damage and may alter subsequent tree deaths. This could have, long-term effects on forest structure. Increases in logging intensity would increase overall damage and spatially isolate trees (i.e., lower NBA), rendering them more vulnerable to wind damage and other external factors. Increased tree mortality will reduce forest carbon stocks and thereby jeopardize global efforts to mitigate climate change.