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

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.

Vegetation near Santa Teresinha, NE Mato Grosso

The Santa Tenesinha region in northeaster Mato Grosso has a varied vegetation which is principally hammock pantanal. The flat clayey alluvial ground between the hummocks is coveted with a continuous non-cerrado ground cover dominated by grasses but which harbors sedges and a lange herb flora. No woody plants grow in it. The tops of the 10-20m wide, slightly elliptical hummocks, 1.5-2 m high, 10-40 per hectare, are covered with cerrado plants: herbs, semlshrubs, thin- and thick-stemmed shrubs and low trees. For 4-5 months during the latter part of the rainy season, the regional water table rises to the surface and the ground between the hummocks becomes saturated or floods up to 1.5-2 m deep. The tops of the hummocks almost always remain above high water level. In the dry season the surface soil dries out completely. This alternation of saturation or shallow flooding and dryness, prevents woody plant, growth between the hummocks, and except for a few tolerant species, also prevents woody plant. growth on the lower part of the hummochs. The gallery forests in the pantanal are seasonally flooded more deeply but their soil does not dry out so thonoughly in the dry season so woody plant growth is not prevented.

Os arredores da cidade de Santa Teresinha, no Nordeste do mato Grosso, têm uma variada vegetação, de floresta terra firme, floresta ribeirinha, estacionalmente inundada, cerrado sobre terreno plano com solo profundo e sobre topos de espigões com solo arenoso raso e rochoso, bem como algumas veredas estreitas e áreas mais extensas de buritizais. Entretanto, a maior parte dos arredores da cidade, como é também o caso na Ilha do Bananal, no outro lado do Rio Araguaia, é coberta com um tipo de pantanal chamado "varjão", terreno não florestado, anualmente encharcado ou rasamente inundado por 4 - 5 meses de dezembro a março ou abril e fortemente ressecado durante a estação seca de junho a setembro. O varjão é salpicado com "monchões", montículas de terra de 10-20 m de diâmetro e 1,5-2 m de altura, 10-40 por hectare, originados provavelmente pela erosão diferencial da água que estacionalmente cobre o varjão. Os topos dos monchões que quase nunca estão cobertos pela água, sustentam uma flora de cerrado, com ervas, semi-arbustos, arbustos e árvores baixas. O solo argiloso, plano, aluvial, entre os monchões traz uma flora não de cerrado, de somente uma camada rasteira dominada por gramíneas de até 0.5 m de altura mas com muitas espécies de ervas e sem plantas lenhosas.