Direct and indirect estimations of aerial forage net primary productivity in Nothofagus antarctica forests under silvopastoral systems in northwest of Chubut, Argentina

Abstract

We evaluated the annual net primary productivity (ANPP) on understory in secondary Nothofagus antarctica forests under silvopastoral systems in Patagonia. We assessed the effect of thinning and estimated understory ANPP using biomass cropping and remote sensing. Thinning was conducted with a remaining tree cover of 50–60% in high and intermediate forest condition. Exclusion fencing was implemented in grazing areas to establish 44 paired plots and 9 open surrounding areas. Two annual harvests were conducted over three growing seasons. Remote sensing was employed to indirectly estimate forest-covered area ANPP, using linear regressions adjusted to normalized difference vegetation index, active photosynthetically absorbed radiation, fraction of PAR absorbed by photosynthetic tissue in a vegetation canopy, canopy cover density, and ANPP. Understory ANPP found in thinned plots versus control plots were 788 versus 234 kg DM ha−1 year−1, respectively, with higher understory ANPP observed in intermediate compared to high forest condition. Adjusted models for estimating understory ANPP under ñire forest canopy showed 80% precision. It was possible to indirectly estimate understory ANPP under thinned ñire forest using optical remote sensing. The results of this study offer a valuable remote sensing decision making tool for stakeholders, enabling insights to be scaled up to broader territory and aiding in adjusting agroforestry systems’ livestock carrying capacity. Silvopastoral systems of N. antarctica subjected to moderate thinning experience increased forage production under remaining canopy, more than doubling production compared to control forests with full density, although it remains approximately half of production observed in open areas.