Shifts in structural diversity of Amazonian forest edges detected using terrestrial laser scanning

Eduardo Eiji Maeda,Matheus Henrique Nunes,Kim Calders,Yhasmin Mendes De Moura,Pasi Raumonen,Hanna Tuomisto,Philippe Verley,Gregoire Vincent,Gabriela Zuquim,José Luís Camargo

doi:10.1016/j.rse.2022.112895

Abstract

Forest edges are an increasingly common feature of Amazonian landscapes due to human-induced forest fragmentation. Substantial evidence shows that edge effects cause profound changes in forest biodiversity and productivity. However, the broader impacts of edge effects on ecosystem functioning remain unclear. Assessing the three-dimensional arrangement of forest elements has the potential to unveil structural traits that are scalable and closely linked to important functional characteristics of the forest. Using over 600 high-resolution terrestrial laser scanning measurements, we present a detailed assessment of forest structural metrics linked to ecosystem processes such as energy harvesting and light use efficiency. Our results show a persistent change in forest structural characteristics along the edges of forest fragments, which resulted in a significantly lower structural diversity, in comparison with the interior of the forest fragments. These structural changes could be observed up to 35 m from the forest edges and are likely to reflect even deeper impacts on other ecosystem variables such as microclimate and biodiversity. Traits related to vertical plant material allocation were more affected than traits related to canopy height. We demonstrate a divergent response from the forest understory (higher vegetation density close to the edge) and the upper canopy (lower vegetation density close to the edge), indicating that assessing forest disturbances using vertically integrated metrics, such as total plant area index, can lead to an erroneous interpretation of no change. Our results demonstrate the strong potential of terrestrial laser scanning for benchmarking broader-scale (e.g. airborne and space-borne) remote sensing assessments of forest disturbances, as well as to provide a more robust interpretation of biophysical changes detected at coarser resolutions.

Highlights

Forest fragmentation has a pervasive influence on the composition of tropical ecosystems
We evaluated structural traits of fragmented Amazo nian forests based on 624 terrestrial laser scanning measurements, providing a detailed overview on the impacts of fragmentation on the three-dimensional distribution of forest plant material
We report changes in the structural diversity of forest edges formed 40 years ago, demonstrating persistent impacts of edge effects on metrics closely linked to energy harvesting and light use efficiency

Summary

Introduction

Forest fragmentation has a pervasive influence on the composition of tropical ecosystems. Fragmented forests have more abiotically dispersed plant species and fewer animal-dispersed species than continuous forests, and altered tree size distribution (Laurance et al, 2018, 2006). These changes have substantial impacts on the carbon cycle, leading to an additional emission of 0.34Gt of carbon per year, which represents almost one third of the currently estimated annual carbon releases due to deforestation in the tropics (Brinck et al, 2017; Silva Junior et al, 2020). The integrity of an ecosystem can be generally defined as a measure of how much a system is free from human induced changes of its structure, composition, and function (Parrish et al, 2003)

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