Shelterwood cut intensity determines recovery pathways of managed Nothofagus pumilio forests

Abstract

Background: Forest harvesting is the main driver of change in forest structure and natural regeneration dynamics during management. Forest recovery after disturbances is important for economic values and ecological processes of natural forests. The aim of the study was to assess recovery paths of Nothofagus pumilio (Poepp. & Endl.) Krasser forests regarding stand structure, environmental characteristics and regeneration values after two harvest intensities of shelterwood regeneration cuts during four different periods after harvesting (YAH). Methods: A total of 59 stands harvested under shelterwood regeneration cuts, including four YAH periods (0-2, 3-10, 11-40, >40 years), and 41 unmanaged stands of N. pumilio forests were sampled in Tierra del Fuego, Argentina. Forest structure, environmental characteristics and regeneration values were measured and compared by analyses of variance, using harvesting intensity, YAH and age structure as main factors. These variables were used to calculate different indices to define recovery pathways for the different treatments. Results: Forest structural variables such as basal area and total volume over bark differed between harvesting intensities, and the differences with unmanaged forests tend to decrease over time. Soil variables did not significantly differ among young and mature unmanaged forests or managed forests under low or high harvesting intensities. In contrast, light availability presented differences in unmanaged forests compared to managed forests among different harvesting intensities and YAH, although the gap decreased with time particularly beyond 40 YAH. Some regeneration variables, such as seedling density, differed among young and mature unmanaged forests, but did not change with harvesting intensity. Other regeneration variables, such as seedling height and sapling density increased with YAH. The forest index (FI), environment index (EI), and regeneration index (RI) showed different pathways for harvested forests over time, where greater changes were observed for high intensity shelterwood cuts. The differences, compared to unmanaged forests, drastically reduced beyond 40 YAH, regardless of harvesting intensity. Conclusions: Forest structural, environmental and regeneration variables followed different pathways over time for the studied harvesting intensities of shelterwood regeneration cuts when compared to unmanaged forests. As expected, greatest differences on all these variables from natural conditions occurred when more intense harvesting was carried out. Our results suggests that N. pumilio forests were resilient to shelterwood regeneration cuts regarding forest structure, regeneration, and environmental conditions (soil properties and light availability), reaching comparable values to unmanaged forests beyond 40 YAH.