Distribuição e geometria de clareiras em floresta da Amazônia central combinando imagens de aeronave remotamente pilotada (ARP) e dados de campo

Abstract

A more refined understanding of the structure and mechanisms of forest gap formation is relevant for robust predictions of carbon stocks in tropical forests and how they are responding to climate change. Considering this, this study aimed to quantify the size distribution, geometry, and seasonality of forest gaps, using combined photogrammetry from Remotely Piloted Aircraft System (RPAS) imagery and field monitoring of a terra firme forest in Central Amazonia. The research was developed on the INVENTA platform, which is located at the Experimental Station of Tropical Forestry (EEST), Manaus, Central Amazon, and covered the period from October 2018 to January 2021. In both methods, their detection generated information from the capture of disturbances formed in the upper canopy and understory. The gaps identified in the period studied ranged from 9.6 m² to 834.7 m². In general, remote sensing metrics did not differ from those obtained in the forest inventory. Gaps smaller than 40 m² contributed with ~ 50% of the total disturbance area. Regarding the modes of death that led to the formation of gaps, in addition to gaps formed by snapping and uprooting, we also detected and quantified the relative importance of those formed by branch fall. Biomass losses were greater in gaps formed by tree snapped and uprooting. Gap formation rate (% of study area per month) correlated directly with the frequency of daily rainfall events above the 99th percentile (i.e., 67 mm day-1). These results show that the combination of detailed forest inventory and remote sensing data at high temporal and spatial resolution allows for a detailed description of the processes regulating canopy dynamics and tree mortality in dense tropical forests. The results also suggest that small-scale disturbances have relatively more importance in the processes regulating canopy dynamics and tree mortality in Central Amazonia.