Impacts of Fire on Forest Biomass Dynamics at the Southern Amazon Edge

Abstract

SummaryOver recent decades, biomass gains in remaining old-growth Amazonia forests have declined due to environmental change. Amazonia’s huge size and complexity makes understanding these changes, drivers, and consequences very challenging. Here, using a network of permanent monitoring plots at the Amazon–Cerrado transition, we quantify recent biomass carbon changes and explore their environmental drivers. Our study area covers 30 plots of upland and riparian forests sampled at least twice between 1996 and 2016 and subject to various levels of fire and drought. Using these plots, we aimed to: (1) estimate the long-term biomass change rate; (2) determine the extent to which forest changes are influenced by forest type; and (3) assess the threat to forests from ongoing environmental change. Overall, there was no net change in biomass, but there was clear variation among different forest types. Burning occurred at least once in 8 of the 12 riparian forests, while only 1 of the 18 upland forests burned, resulting in losses of carbon in burned riparian forests. Net biomass gains prevailed among other riparian and upland forests throughout Amazonia. Our results reveal an unanticipated vulnerability of riparian forests to fire, likely aggravated by drought, and threatening ecosystem conservation at the Amazon southern margins.

Fire Affects Asymbiotic Nitrogen Fixation in Southern Amazon Forests

“…Between 2007 and 2016 (the most recent survey), aboveground biomass loss (Nogueira et al, 2019), increased floristic similarity, and higher plant mortality than recruitment (da Silva et al, 2018;Maracahipes et al, 2014) were reported for the same stands included in this study ( Table 1). The most recent survey data (2014 and 2016), including trees with a diameter at breast height-DBH ≥ 10 cm in each stand, are presented in supporting information Tables S1 (species abundance), S2 (beta diversity matrix), and S3 (density, basal area, and relative basal area of trees belonging to Fabaceae).…”

“…Stand basal area range from 15.3 m 2 per hectare in F5 to 33.5 m 2 per hectare in F1. All these changes in the vegetation have been attributed to longer dry seasons and higher frequency of fire events by da Silva et al (), Maracahipes et al (), and Nogueira et al () but not to a particular fire event detected between 2007 (first survey year) and 2013 (last year of the fire frequency record).…”

“…The frequent fires in southern Amazonia have led to aboveground biomass loss in the studied forests (da Silva et al, ; Maracahipes et al, ; Nogueira et al, ) with, as of yet, unquantified consequences for microbially mediated soil processes. Fire‐induced aboveground biomass loss may influence ANF through, among other factors, reduced C inputs from photosynthesis into the soil (Perakis et al, ) and changes in litterfall mass, decomposition, and resulting shifts in forest N and P cycling (Butler et al, ; Mataix‐Solera et al, ; Nardoto et al, ; Reed et al, ; Sayer & Tanner, ).…”

The impact of long dry periods on the aboveground biomass in tropical forests: 20 years of monitoring

“…A particular gap is the huge area of endangered forests at the transition between the Amazon and adjacent Cerrado in central Brazil. In spite of a few recent studies in eastern end of these systems [37,38] we know little about how such transition zones -potentially already on the edge climatically due to their marginal status -are faring in the changing climates of the early twenty-rst century. In the Amazon-Cerrado transition, several types of forest formations occur [37,38].…”

“…In spite of a few recent studies in eastern end of these systems [37,38] we know little about how such transition zones -potentially already on the edge climatically due to their marginal status -are faring in the changing climates of the early twenty-rst century. In the Amazon-Cerrado transition, several types of forest formations occur [37,38]. We have been monitoring a moist tropical forest outlier in southern Mato Grosso, central Brazil, for 20 years (1996-2016) using a careful permanent plot methodology with regular reinventories of woody vegetation in a valley forest.…”