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

MARTÍNEZ PASTUR G.; ROSAS Y.M.; LENCINAS M.V.; PERI P.L.

Leipzig

Jornada; International Long Term Ecological Research Network (ILTER); 2019

ILTER

Disturbances have frequently been shown to increase changes in natural communites (e.g. understory plants), and increasing alien plant invasion. Logging was the most common and severe anthropogenic disturbance in Patagonian forests, where regeneraton processes need long periods (e.g. up to 15-20 years). Regeneraton dynamics were closely related to understory development, and can be sensitve to alien plant invasion (e.g. grasses). The objectve was to describe the long-term regeneraton dynamics (15 years-afer-harvestng) in Nothofagus pumilio forests managed through variable retenton (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 compositon under three site conditons created by variable retenton harvestng: 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 regeneraton dynamics presented different paterns according to the remnant tree overstory, closely related to light and soil moisture availability: (i) seed producton was related to canopy closure, but different paterns 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 tme due to alien species introducton and other natve plants that come from other associate environments. DR and DRI supported much higher cover of alien species, which became dominant few years after harvestng, and the startng to decline due to regeneraton growth. Browsing of naturalherbivores over tree regeneraton, such as Lama guanicoe, were related to understory development, which was higher in DR and DRI, and can be variable along the years. Longterm research allowed to understand the regeneraton dynamics, which are the key-factor for the silvicultural management. In consequence, understand the plant dynamics, as well as, browsing patern along the tme was crucial to develop new management strategies to increase the regeneraton performance or to understand the regeneraton failure in harvested areas.