Carbon Dynamics in a Human-Modified Tropical Forest: A Case Study Using Multi-Temporal LiDAR Data

Yhasmin Mendes De Moura,Erone G Santos,Heiko Balzter,Mariano Garcia,Lênio S Galvão,Ricardo Dalagnol,Raimundo C Oliveira,Fernando Espírito-Santo,Yosio E Shimabukuro,Polyanna Da Conceição Bispo

doi:10.3390/rs12030430

Abstract

Tropical forests hold significant amounts of carbon and play a critical role on Earth´s climate system. To date, carbon dynamics over tropical forests have been poorly assessed, especially over vast areas of the tropics that have been affected by some type of disturbance (e.g., selective logging, understory fires, and fragmentation). Understanding the multi-temporal dynamics of carbon stocks over human-modified tropical forests (HMTF) is crucial to close the carbon cycle balance in the tropics. Here, we used multi-temporal and high-spatial resolution airborne LiDAR data to quantify rates of carbon dynamics over a large patch of HMTF in eastern Amazon, Brazil. We described a robust approach to monitor changes in aboveground forest carbon stocks between 2012 and 2018. Our results showed that this particular HMTF lost 0.57 m·yr−1 in mean forest canopy height and 1.38 Mg·C·ha−1·yr−1 of forest carbon between 2012 and 2018. LiDAR-based estimates of Aboveground Carbon Density (ACD) showed progressive loss through the years, from 77.9 Mg·C·ha−1 in 2012 to 53.1 Mg·C·ha−1 in 2018, thus a decrease of 31.8%. Rates of carbon stock changes were negative for all time intervals analyzed, yielding average annual carbon loss rates of −1.34 Mg·C·ha−1·yr−1. This suggests that this HMTF is acting more as a source of carbon than a sink, having great negative implications for carbon emission scenarios in tropical forests. Although more studies of forest dynamics in HMTFs are necessary to reduce the current remaining uncertainties in the carbon cycle, our results highlight the persistent effects of carbon losses for the study area. HMTFs are likely to expand across the Amazon in the near future. The resultant carbon source conditions, directly associated with disturbances, may be essential when considering climate projections and carbon accounting methods.

Highlights

Tropical forests play a significant role in the global carbon cycle [1] and biodiversity functioning of our planet [2]
As tree growth and tree mortality are related to the increase and decrease of forest canopy height (CHM), we investigated the relationship between changes in forest canopy heights (∆Canopy Height Model (CHM)) that likely lead to changes in aboveground carbon stocks (∆Aboveground Carbon Density (ACD))
Several studies of forest succession based on chronosequence statistics of forest carbon-age allometry [25,27] suggested that undisturbed and secondary forests have been accumulating carbon, we found that the reduction of pristine tropical forests and the increase of human-modified tropical forests (HMTF) could have a great influence on the carbon cycle in the tropical environment

Summary

Introduction

Tropical forests play a significant role in the global carbon cycle [1] and biodiversity functioning of our planet [2]. In the Brazilian Amazon, high levels of anthropogenic disturbances, such as deforestation, fragmentation, logging, and fires, are changing the terrestrial carbon cycle of these forests from sink to sources of carbon [3]. Forest degradation has been reported in the literature as a significant contributor to carbon emissions [4,7,8,9] It is rarely accounted for in national and international emissions inventories. This is especially due to the challenges associated with the monitoring of forest degradation and to the lack of an internationally accepted definition that could build on a framework for an operational approach [10]

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