Optimizing biomass estimates of savanna woodland at different spatial scales in the Brazilian Cerrado: Re-evaluating allometric equations and environmental influences

Abstract

Cerrado is the second largest biome in South America and accounted for the second largest contribution to carbon emissions in Brazil for the last 10 years, mainly due to land-use changes. It comprises approximately 2 million km2 and is divided into 22 ecoregions, based on environmental conditions and vegetation. The most dominant vegetation type is cerrado sensu stricto (cerrado ss), a savanna woodland. Quantifying variation of biomass density of this vegetation is crucial for climate change mitigation policies. Integrating remote sensing data with adequate allometric equations and field-based data sets can provide large-scale estimates of biomass. We developed individual-tree aboveground biomass (AGB) allometric models to compare different regression techniques and explanatory variables. We applied the model with the strongest fit to a comprehensive ground-based data set (77 sites, 893 plots, and 95,484 trees) to describe AGB density variation of cerrado ss. We also investigated the influence of physiographic and climatological variables on AGB density; this analysis was restricted to 68 sites because eight sites could not be classified into a specific ecoregion, and one site had no soil texture data. In addition, we developed two models to estimate plot AGB density based on plot basal area. Our data show that for individual-tree AGB models a) log-log linear models provided better estimates than nonlinear power models; b) including species as a random effect improved model fit; c) diameter at 30 cm above ground was a reliable predictor for individual-tree AGB, and although height significantly improved model fit, species wood density did not. Mean tree AGB density in cerrado ss was 22.9 tons ha-1 (95% confidence interval = ± 2.2) and varied widely between ecoregions (8.8 to 42.2 tons ha-1), within ecoregions (e.g. 4.8 to 39.5 tons ha-1), and even within sites (24.3 to 69.9 tons ha-1). Biomass density tended to be higher in sites close to the Amazon. Ecoregion explained 42% of biomass variation between the 68 sites (P < 0.01) and shows strong potential as a parameter for classifying regional biomass variation in the Cerrado.

Spatial and Temporal Variations in Aboveground Woody Carbon Storage for Cerrado Forests and Woodlands of Mato Grosso, Brazil

“…Mean estimates of aboveground woody C pool size ( C w ) were lower for grass‐dominated cerrado (mixed‐grassland and woodland) and higher for cerrado forests, which is consistent with previous studies (Grace et al, ; Miranda et al, ; Ribeiro et al, ; Roitman et al, ; Schöngart et al, ). Estimates of C w for riparian forests ranged from 8 Mg/ha for young (64 years old) stands to 97 Mg/ha for older (124 years old) stands (Schöngart et al, ), which is similar to that reported here (Figure a).…”

“…Mean estimates of aboveground woody C pool size (C w ) were lower for grass-dominated cerrado (mixedgrassland and woodland) and higher for cerrado forests, which is consistent with previous studies (Grace et al, 2006;Miranda et al, 2014;Ribeiro et al, 2011;Roitman et al, 2018;Schöngart et al, 2011).…”

“…Estimates of C w for riparian forests ranged from 8 Mg/ha for young (64 years old) stands to 97 Mg/ha for older (124 years old) stands (Schöngart et al, 2011), which is similar to that reported here (Figure 1a). Cerrado woodlands (sensu stricto) reportedly store between 9 and 68 Mg/ha of biomass in wood (Miranda et al, 2014;Ribeiro et al, 2011;Roitman et al, 2018) or 4.5-34 MgC/ha assuming a C concentration of 50%, which is lower than the 30-83 MgC/ha reported for the upland and hyperseasonal woodlands studied here (Figure 1a). Woody C storage for mixed-grasslands (campo sujo) is reportedly about 3.5 MgC/ha (Grace et al, 2006;Miranda et al, 2014), which is approximately 50% of what was observed for the CB in this study.…”

Mapping Three Decades of Changes in the Brazilian Savanna Native Vegetation Using Landsat Data Processed in the Google Earth Engine Platform

“…Total plant biomass and carbon stocks in the Cerrado vary according to the type of vegetation, with an average of 18.5 t C ha −1 in grasslands, 39.9 t C ha −1 in savannas, and 68.6 t C ha −1 in forests [29]. Data on biomass and vegetation structure from 262 field inventory plots in the Cerrado compiled by Roitman et al [38] were used to assess the spectral metrics that defined the different NV types, as detailed in the next session. The biome was partitioned in a regular grid of tiles compatible with the 1:250,000 international cartographic charts, where individual classifications were run for each tile.…”

Biomassa Aérea E Fatores De Expansão De Uma Floresta Estacional Decidual Em Niquelândia, Goiás

“…Existem alguns vários estudos voltados para estimativa biomassa e/ou carbono do componente arbóreo acima do solo no Cerrado para diferentes fitofisionomias. cerrado sentido restrito (ABDALA et al, 1998;CASTRO ;KAUFFMAN, 1998;LILIENFEIN et al, 2001;OTTMAR et al, 2001;REZENDE et al, 2006;MIRANDA, 2012;MIRANDA et al, 2014;ROITMAN et al, 2018); cerradão (MORAIS et al, 2012;MIGUEL et al, 2017); mata ciliar: MOREIRA-BURGER ; DELITTI, 1999); floresta estacional (VITAL et al, (2004;VOGEL et al, 2006;CERRUTO et al, 2009;GODINHO et al, 2014;BACCARIN et al, 2016). Trabalhos relacionados com a quantificação de biomassa de outros compartimentos do subbosque de florestas no Cerrado são mais escassos (CASTRO ; KAUFFMAN, 1998;MOREIRA-BURGER ;DELITTI, 1999;VITAL et al, 2004;MORAIS et al, 2012;GODINHO et al, 2014;MIGUEL et al, 2017).…”