Long-term influence of harvesting over plant understory dynamics and regeneration development in Nothofagus pumilio forests

G MARTÍNEZ PASTUR; YM ROSAS; MV LENCINAS; PL PERI

Leipzig

Congreso; ILTER Open Science Meeting; 2019

ILTER

Disturbances have frequently been shown to increase changes in natural communities (e.g. understory plants), and increasing alien plant invasion. Logging was the most common and severe anthropogenic disturbance in Patagonian forests, where regeneration processes need long periods (e.g. up to 15-20 years). Regeneration dynamics were closely related to understory development, and can be sensitive to alien plant invasion (e.g. grasses). The objective was to describe the long-term regeneration dynamics (15 years-after-harvesting) in Nothofagus pumilio forests managed through variable retention (aggregates and dispersed trees), and correlate it with the understory changes (life-forms, origin, etc). Using annually surveyed permanent plots (n = 72), we analyzed temporal changes of understory structure and composition under three site conditions created by variable retention harvesting: retained forest patches of 30 m radius in a density of 1 patch ha-1 (AR), edges of such retained patches (DRI), retained dispersed single trees (DR); and one old-growth primary forests as a control (PF). Natural regeneration dynamics presented different patterns according to the remnant tree overstory, closely related to light and soil moisture availability: (i) seed production was related to canopy closure, but different patterns were observed in managed than unmanaged forests; (ii) recruitment was related to understory, tree shelter and microenvironments (e.g. debris), as well as survival and growth. In brief, AR supported a high cover of understory species that belongs to primary forests, and declined on time due to alien species introduction and other native plants that come from other associate environments. DR and DRI supported much higher cover of alien species, which became dominant few years after harvesting, and the starting to decline due to regeneration growth. Browsing of natural herbivores over tree regeneration, such as Lama guanicoe, were related to understory development, which was higher in DR and DRI, and can be variable along the years. Long-term research allowed to understand the regeneration dynamics, which are the key-factor for the silvicultural management. In consequence, understand the plant dynamics, as well as, browsing pattern along the time was crucial to develop new management strategies to increase the regeneration performance or to understand the regeneration failure in harvested areas.