Long-term Trend of Leaf Area, Greenness and Solar-Induced Chlorophyll Fluorescence in Amazon Forest from 2000 to 2019

Abstract:

Amazon forests contain nearly 50% of the tropical forest carbon stocks and play a major but still uncertain role in the global carbon budget. Due to the frequent human activity, the area of rainforest decreased from 5.9 million km² (2001) to 5.66 million km² (2018) according to MODerate-resolution Imaging Spectroradiometer (MODIS) land cover product (MCD12C1.006). Aside from deforestation, Amazon forest endures 3 severe droughts (2005, 2010, 2015/2016) in the past two decades. However, the long-term trend of Amazon rainforest since 2000 is controversial and the possible reasons may include the different satellite observations and the parameters selected. Here we select the MODIS C6 Leaf Area Index (LAI) and Vegetation Indices (NDVI/EVI) datasets from 2000 to 2019 and Solar-Induced Chlorophyll Fluorescence (SIF) dataset (2001-2016) to evaluate the aggradation/degradation of Amazon basin. The intact Evergreen Broadleaf Forest (EBF) showed weak greening trends (p-value < 0.1) of LAI (+0.0037 LAI unit per year), VIs (+0.0005 NDVI unit per year and +0.004 EVI unit per year) and SIF (+0.0007 SIF unit per year), while the Savannas and Grassland showed no trend. The study indicated that there was 3.62% deforestation in the Amazon basin but no evidence supporting degradation of forests.