The impact of deforestation in Brazilian Amazonia is a global concern, and land occupation in public lands contributes to increased deforestation rates. Little is known about the spread of deforestation in landholdings in undesignated public lands located on cattle-ranching frontiers. We use a case of Matupi District, a hotspot of deforestation along the Transamazon Highway in the southern portion of Brazil’s state of Amazonas, where spontaneous squatters and land grabbers are the main actors occupying landholdings. We assessed the advance of deforestation and the spatial distribution of landholdings in relation to the main road and to land categories (e.g., protected areas and undesignated public land). Landholdings up to 400 ha were the majority in numbers (52%) and larger landholdings (>400 ha) were located farther into the forest, contributing to expanding the deforestation frontier. By 2018, 80% of the remaining forest was in larger landholdings (>400 ha), increasing the susceptibility of this forest to being cleared in the coming years. Thus, greater attention should be given to these larger landholdings to control the spread of deforestation. By analyzing the clearing pattern in the landholdings, deforestation monitoring can focus on specifc sizes of landholdings that contribute most to the advance of the deforestation frontier. Brazil’s current trend to facilitating the legalization of illegal claims in undesignated public lands, such as the large and medium landholdings we studied, implies vast areas of future deforestation and should be reversed.

Invasões de terras públicas criam novo polos de desmatamento na Amazônia

 A atividade madeireira e a pecuária em grandes áreas de terras públicas não destinadas provocam a expansão das fronteiras do desmatamento na Amazônia. Em estudo inédito publicado na revista Regional Environmental Change, pesquisadores de quatro instituições do Brasil e do Exterior alertam para a falta de monitoramento e de ações do poder público para coibir o avanço do desmatamento ilegal.

A pesquisa foi realizada no distrito de Santo Antônio do Matupi, em Manicoré, localizado às margens da BR-230, a Rodovia Transamazônica, que se tornou um dos grandes polos de desmatamento no sul do estado do Amazonas. Para melhor se analisar a área, os pesquisadores dividiram a região de Matupi em diferentes classes de uso, inclusive terras públicas não destinadas, que são áreas federais ou estaduais para as quais o governo não especificou qualquer uso específico, como terra indígena, unidade de conservação ou assentamento.

“O sul do Amazonas é o palco de um rápido avanço do desmatamento que está saindo do tradicional “arco do desmatamento” e migrando para o norte. A geografia dessa atividade deve mudar radicalmente com a planejada ‘reconstrução’ da Rodovia BR-319 (Manaus-Porto Velho) e a construção da AM-366, que sairia da BR-319 para abrir a vasta área de floresta intacta na parte oeste do Amazonas. Isto abrirá uma enorme área de terras públicas sem destinação para a entrada de grileiros, sem-terras, madeireiras, e outros atores. Os processos estudados no atual trabalho seriam repetidos em grande escala”, explica um dos autores do estudo, Philip Fearnside, do Instituto Nacional de Pesquisas da Amazônia (INPA).

Na Amazônia brasileira, o aumento da perda florestal está localizado principalmente em novas fronteiras de desmatamento que estão próximas a áreas de pecuária. Em Matupi, por exemplo, os estudos concluíram que os principais desmatadores são os ocupantes de terras com áreas maiores de 400 hectares.

Outro dado observado é que as terras ocupadas por grileiros, posseiros e grandes fazendeiros refletem o baixo nível de monitoramento e governança nesta área do país. De acordo com Philip Fearnside, o “desmatamento ilegal zero” prometido pelo Brasil na COP26 poderia ser alcançado interrompendo o desmatamento, mas, no atual cenário brasileiro, o caminho sendo tomado para cumprir essa meta é a simples legalização do desmatamento ilegal.

“O entendimento dos processos de ocupação e desmatamento nas terras públicas não destinadas é essencial tanto para desenhar melhores abordagens de controle quanto para subsidiar decisões mais acertadas sobre a construção das estradas que deslancham a ocupação e o desmatamento. Os impactos das estradas que abrem essas áreas são muitíssimo maiores do que os Estudos de Impacto Ambiental/Relatórios de Impacto Ambiental e os discursos políticos levam a crer”, destaca Philip Fearnside.

Contato: Philip Martin Fearnside

Instituto Nacional de Pesquisas da Amazônia (INPA)

philip.fearnside@gmail.com

Highlights

 –  Estudo constatou rápido avanço desmatamento no sul do estado do Amazonas em terras públicas não destinadas (“terras devolutas”).

– As áreas mais desmatadas são ocupadas por grileiros, posseiros e fazendeiros em ramais partindo da Rodovia Transamazônica.

– Terras públicas correm alto risco de desmatamento devido à especulação fundiária na região e a ausência de políticas públicas que coíbem a grilagem de terras.

By 2014 approximately 2.2 million km2 (~43%) ofBrazil’s Legal Amazonia region had been incorporated into anextensive network of 718 protected areas, which are com-prised by 372 indigenous lands, 313 federal, state and munic-ipal (county) conservation units, and 33 Maroon territories(Quilombos). Although protected areas occupy vast expansesin Amazonia, their importance as carbon reserves needs to bebetter understood. In this study, we estimate the total carbon in2014 held in protected areas in Brazil’s BLegal Amazonia^and BAmazonia biome^ regions, and the carbon loss in theportions of these protected areas that were cleared by 2014. In 2014, a total of 33.4 Pg C or 57.0% of all carbon stored inLegal Amazonia was held in protected areas and 32.7 Pg C or58.5% of all the carbon stored in the Amazonia biome washeld in protected areas. By 2014, carbon lost due to clearing inprotected areas in Legal Amazonia and the Amazonia biometotaled, respectively, 0.787 (or 2.3%) and 0.702 (or 2.1%)Pg C if one assumes that previously each protected area wasentirely covered by native vegetation. If the protection of theseareas is effective, about half of the carbon in BrazilianAmazonia will be maintained. Carbon in protected areas hasstrategic value for environmental conservation and for mitiga-tion of climate change because these areas are under lower riskof being emitted to the atmosphere than carbon stored in veg-etation located outside of protected areas, although the effec-tiveness of protected areas varies.

Estimates of carbon-stock changes in forest ecosystems require information on dead wood decomposition rates. In the Amazon, the lack of data is dramatic due to the small number of studies and the large range of forest types. The aim of this study was to estimate the decomposition rate of coarse woody debris (CWD) in two oligotrophic undisturbed forest formations of the northern Brazilian Amazon: seasonally flooded and unflooded. We analyzed 20 arboreal individuals (11 tree species and 3 palm species) with distinct wood-density categories. The mean annual decomposition rate of all samples independent of forest formation ranged from 0.044 to 0.963 yr⁻¹, considering two observation periods (12 and 24 months). The highest rate (0.732 ± 0.206 [SD] yr⁻¹) was observed for the lowest wood-density class of palms, whereas the lowest rate (0.119 ± 0.101 yr⁻¹) was determined for trees with high wood density. In terms of forest formation, the rates values differ when weighted by the wood-density classes, indicating that unflooded forest (0.181 ± 0.083 [SE] yr⁻¹; mean decay time 11–30 years) has a decomposition rate ∼19% higher than the seasonally flooded formations (0.152 ± 0.072 yr⁻¹; 13–37 years). This result reflects the dominance of species with high wood density in seasonally flooded formations. In both formations 95% of the dead wood is expected to disappear within 30–40 years. Based on our results, we conclude that the CWD decomposition in the studied area is slower in forests on nutrient-poor seasonally flooded soils, where structure and species composition result in ∼40% of the aboveground biomass being in tree species with high wood density. Thus, it is estimated that CWD in seasonally flooded forest formations has longer residence time and slower carbon release by decomposition (respiration) than in unflooded forests. These results improve our ability to model stocks and fluxes of carbon derived from decomposition of dead wood in undisturbed oligotrophic forests in the Rio Negro-Rio Branco Basin, northern Brazilian Amazon.

Amazon forest stocks large quantities of carbon both in plant biomass and in soil. Deforestation has accelerated the process of forest fragmentation in the Brazilian Amazon, resulting in changes in carbon stocks in both biomass and soil. Logging, including that under legal forest management, can create edge-like conditions inside the forest. We investigated the relationship between changes in carbon stocks in the soil and the distance to the nearest edge in forest remnants after about 30 years of isolation. We assessed the effect of edges using geographically weighted regression (GWR), which considers the non-stationary character of soil carbon stocks and assigns relative weights to the observations according to the distance between them. Data from 265 georeferenced plots distributed over 28 ha of forest fragments in the Manaus region were included in these analyses. Soil-carbon stocks were estimated for areas before (1984–1986) and after (2012–2013) isolation of the fragments. The GWR model indicated an apparent relationship between change in carbon stocks and distance from the edge (R2 = 0.79). The largest changes occurred in plots located closest to the edges. In 202 plots ⩽100 m from an edge, soil-carbon stock increased significantly (p = 0.01) by a mean of 1.34 Mg ha−1 over the ∼30-year period. Such changes in soil carbon stocks appear to be associated with higher rates of tree mortality caused by microclimatic changes in these areas. Increased necromass inputs combined with changes in composition and structure of vegetation may result in increased rates of decomposition of organic matter, transferring carbon to the soil compartment and increasing soil carbon stocks. Considering both “hard” edges adjacent to deforestation and “soft” edges in logging areas, the soil-carbon increase we measured implies an absorption of 6 × 106 MgC in Brazilian Amazonia. In hard edges maintained for ∼30 years, the soil-carbon increase offsets 8.3% of the carbon losses from “biomass collapse” in the first 100 m from a clearing. Soil carbon did not change significantly in 63 forest-interior plots, suggesting that global climate change has not yet had a detectible effect on this forest carbon compartment.

Forest biomass is an important variable for calculating carbon stocks and greenhouse gas emissions from deforestation and forest fires in Brazilian Amazonia. Its spatial distribution has caused controversy due to disagreements over the application of different calculation methodologies. Standardized networks of forest surveys provide an alternative to solve this problem. This study models the spatial distribution and original total stock of forest biomass (Aboveground + Belowground + Fine and coarse litter) in Brazil’s state of Roraima, taking advantage of data from georeferenced forest surveys in the region. Commercial volume (bole volume) from surveys was expanded to total biomass. Kriging techniques were used to model the spatial distribution of biomass stocks and generate a benchmark map. All results were associated with phytophysiognomic groups, climatic regions and land uses (protected areas; agricultural use). We estimate forest in the state of Roraima to have an original biomass stock of 6.32 × 109 Mg. Forest biomasses in areas with shorter dry seasons were higher as compared to forests in regions with longer dry seasons. The original vegetation in protected areas, independent of phytophysiognomic group, has higher biomass compared to areas currently under agricultural use. Protected areas support 65.8% of Roraima’s stock of forest biomass, indicating an important potential role in REDD projects for conservation of forest carbon. Information on spatial distribution of biomass stocks at a more refined scale is needed to reduce uncertainties about the regional character of carbon pools in Amazonia.

The Amazon Basin is a special contributor to global biogeochemistry, particularly from the white water region related to the Andes mountains, a source of major Amazon river tributaries. White water composition and properties are rarely determined. Therefore, it is essential to know the spatial distribution and temporal variability of these waters to assess possible human influences on their chemical characterization. In this paper, a study performed in the Southwestern Amazon region, examining the chemical composition of the Acre River water is presented. This part of the Amazon Basin has not been studied sufficiently to determine the geochemistry of its white waters. pH, electric conductivity (EC), turbidity, and concentration of metals, anions and dissolved organic carbon (DOC) were measured from 2008 to 2014. Approximately 60% of the pH measurements had values between 6.5 and 7.3; 55% of the conductivity measurements had values between 30 and 60 -S cm-1; and 50 % of the turbidity measurements had values less than 100 NTU. The major soluble elements were Ca, Si and K. These species have a natural origin (clay minerals and quartz). Toxic elements (e.g., V, Ni, Cr and Pb) and the anions NO3- and SO42- were present at concentrations below the Brazilian Standards. The Na+, SO42- and Al concentrations are seasonally variable depending on water discharge. Major ions such as Mg and Ca showed a positive linear correlation with DOC.

The purpose of this study was to determine the chemical and mineralogical composition of suspended sediments from the Acre River, located in the Purus Basin, upper Amazon basin, a region associated with the Fitzcarrald Arch. The elemental and mineralogical compositions of the sediments were assessed by using mass and atomic spectroscopy, and X-ray diffraction. A total of 46 samples were collected between 2008 and 2011 from four sites in the study area during wet and dry seasons. The suspended sediments contained feldspar, kaolinite, illite and quartz as well as the elements Hg, Zn, V, Ti, Si, Pb, Ni, Na, Mn, Mg, K, Fe, Cu, Cr, Cd, Ca, Al, S, and P in different proportions that were associated with the various weathering reactions linked to physical, chemical and biological processes in the region. The obtained results represent the first set of values and relationships regarding the mineralogy and chemical identification of the suspended sediments in the Acre River and can be used as a reference for the geochemical characteristics of the Purus Basin. Such regional studies will become increasingly necessary to observe the impacts of climate change and human activities on the suspended sediment load and composition of the Amazon River.