Ricardo Flores Haidar

Savanna vegetation-fire-climate relationships differ among continents.

Surveying Savannas Savannas are structurally similar across the three major continents where they occur, leading to the assumption that the factors controlling vegetation structure and function are broadly similar, too. Lehmann et al. (p. 548) report the results of an extensive analysis of ground-based tree abundance in savannas, sampled at more than 2000 sites in Africa, Australia, and South America. All savannas, independent of region, shared a common functional property in the way that moisture and fire regulated tree abundance. However, despite qualitative similarity in the moisture–fire–tree-biomass relationships among continents, key quantitative differences exist among the three regions, presumably as a result of unique evolutionary histories and climatic domains. Evolution cannot be overlooked when aiming to predict the potential global impacts on savanna dynamics in a warming world. Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the magnitude of these effects varied substantially, so that a single model cannot adequately represent savanna woody biomass across these regions. Historical and environmental differences drive the regional variation in the functional relationships between woody vegetation, fire, and climate. These same differences will determine the regional responses of vegetation to future climates, with implications for global carbon stocks.

Deciphering earth mound origins in central Brazil

Mound fields are a common landscape throughout the world and much of the evidence for their origin has been of a circumstantial nature. It has been hypothesized that earth mounds emerge over grasslands by termite activity; alternatively, they might be formed after erosion. We tested whether a mound field in central Brazil was generated by termite activity or erosion. We used soil organic matter isotopic composition, soil chemical, physical and floristic composition to determine the origin of a mound field. If the mounds emerged by termite activity in an established grassland the soil organic matter below the mound should have the isotopic signature of C4 dominated grassland, which contrasts with savanna C3 + C4 signature. Additionally, soil traits should resemble those of the grassland. All markers indicate that the mounds were formed by erosion. The soil isotopic composition, chemical traits and texture below the mound resembled those of the savanna and not those of the grassland. Moreover, most of the species present in the mound were typical of savanna. Concrete evidence is provided that mound fields in the studied area were produced by erosion of a savanna ecosystem and not termite activity. The use of the techniques applied here would improve the assessments of whether analogous landscapes are of a biogenic nature or not.

Florestas estacionais e áreas de ecótono no estado do Tocantins, Brasil: parâmetros estruturais, classificação das fitofisionomias florestais e subsídios para conservação

O objetivo deste estudo foi descrever a riqueza, estrutura e diversidade de especies arboreas em areas de Floresta Estacional e ecotono (Floresta Estacional/Floresta Ombrofila) no estado do Tocantins, buscando subsidios para a conservacao, manejo florestal, compensacao de reserva legal e recuperacao ambiental, alem de discutir as identidades fitogeograficas em comparacao com outras florestas do Brasil. Em 18 bacias hidrograficas, conduziu-se amostragem da vegetacao arborea (DAP > 5 cm) de 22 areas (amostras) por meio do inventario de 477 parcelas de 400 m². Foram elaboradas analises de classificacao pelo metodo TWINSPAN, em duas escalas distintas. A primeira avaliou a diversidade beta entre as parcelas amostradas no estado do Tocantins e a segunda buscou analisar a similaridade das florestas do Tocantins em relacao a outras florestas do bioma Cerrado e suas areas de tensao ecologica. As florestas amostradas apresentaram ampla variacao em termos de riqueza (33 a 243 especies), densidade (486 a 1.179 ind.ha-1), area basal (14,04 e 37,49 m².ha-1), indices de diversidade (H´ = 2,75 a 4,59) e de equabilidade (J´= 0,72 a 0,86). As analises de classificacao convergiram para resultados comuns, identificando quatro ambientes dissimilares em termos floristicos e estruturais no estado do Tocantins: Floresta Estacional Decidual, Floresta Estacional Semidecidual, ecotono Floresta Estacional Semidecidual/Floresta Ombrofila e ecotono Floresta Estacional Decidual/Floresta Ombrofila. A fim de manter a diversidade de plantas e de ambientes na regiao de transicao Floresta Amazonica e Cerrado, sugere-se que o processo de criacao de unidades de conservacao no estado do Tocantins deva ser intensificado e tenha como base para selecao das areas criterios biogeograficos.

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.

The Cerrado Biome: A Forgotten Biodiversity Hotspot

Have you heard of the Cerrado biome? Do you know what a biodiversity hotspot is? In this article, you will learn why we should care about the biodiversity in the Cerrado biome. A biome is a community of plants and animals in a large area that shares the same climate and habitat features. Tropical biomes have the greatest diversity of plants and animals on the planet. However, when it comes to tropical biodiversity, people are quick to think of the Amazon. The Cerrado has a great biodiversity that is just as important to conserve as the Amazon Biome. However, the Cerrado continues to be forgotten and neglected, leading to the devastation of its natural areas. Let us learn more about this fantastic biome and help us spread the word about the urgency of preserving the Cerrado!

Tree diversity and above-ground biomass in the South America Cerrado biome and their conservation implications

Less than half of the original two million square kilometers of the Cerrado vegetation remains standing, and there are still many uncertainties as to how to conserve and prioritize remaining areas effectively. A key limitation is the continuing lack of geographically-extensive evaluation of ecosystem-level properties across the biome. Here we sought to address this gap by comparing the woody vegetation of the typical cerrado of the Cerrado–Amazonia Transition with that of the core area of the Cerrado in terms of both tree diversity and vegetation biomass. We used 21 one-hectare plots in the transition and 18 in the core to compare key structural parameters (tree height, basal area, and above-ground biomass), and diversity metrics between the regions. We also evaluated the effects of temperature and precipitation on biomass, as well as explored the species diversity versus biomass relationship. We found, for the first time, both that the typical cerrado at the transition holds substantially more biomass than at the core, and that higher temperature and greater precipitation can explain this difference. By contrast, plot-level alpha diversity was almost identical in the two regions. Finally, contrary to some theoretical expectations, we found no positive relationship between species diversity and biomass for the Cerrado woody vegetation. This has implications for the development of effective conservation measures, given that areas with high biomass and importance for the compensation of greenhouse gas emissions are often not those with the greatest diversity.