QUESTION: The encroachment of woody species has been globally reported over much of arid and semiâarid biomes, and has been associated with a decrease in cover and number of herbaceous species. How ...does the encroachment of a woody shrub affect herbaceous community structure and species composition in grasslands of a wetland ecosystem? LOCATION: Seasonally flooded grasslands in a Neotropical Hyperseasonal Savanna, the Pantanal wetland, Brazil. METHODS: We investigated the effect of the encroaching plant Combretum laxum on a herbaceous community from seasonally flooded grasslands in the Pantanal wetland using 29 vegetation samples representing encroachment at different spatioâtemporal stages. The point quadrat method was used to acquire vegetation data, as plant cover, species richness (S) and ShannonâWiener diversity index (Hâ). We evaluated the existence of stages of encroachment related to differences in vegetation structure and species composition using nonâmetric multidimensional scaling ordination and analysis of similarity. The response of the herbaceous community to shrub advance was analysed using linear and quadratic polynomial regression models. Model fitness was tested using the ACI. RESULTS: The advance of the woody encroaching plant C. laxum over the seasonally flooded grassland occurs in three stages: grassland stage, shrub islands stage and shrubland stage. The initial advance of C. laxum over the grassland, represented by the shrub islands stage was correlated to an increase in species richness and a decrease in important native forage grasses. Critical changes in the herbaceous community were observed when the encroaching plant covered >30% of the periodically flooded grassland, when the richness of herbaceous species dropped from 22 to four. CONCLUSIONS: Woody encroachment causes impoverishment and simplification of the herbaceous community. The shift from a grassâ to a shrubâdominated state is related to the reduction in important grasslandâobligate species, forage resources for herbivore livestock and wild animals, affecting the ecological dynamics and the economy of rangelands. Conservation of these grassland ecosystems depends on rangeland management practices guided by scientific knowledge on the causes and consequences of plant community changes.
The possibility that the Amazon forest system could soon reach a tipping point, inducing large-scale collapse, has raised global concern
. For 65 million years, Amazonian forests remained relatively ...resilient to climatic variability. Now, the region is increasingly exposed to unprecedented stress from warming temperatures, extreme droughts, deforestation and fires, even in central and remote parts of the system
. Long existing feedbacks between the forest and environmental conditions are being replaced by novel feedbacks that modify ecosystem resilience, increasing the risk of critical transition. Here we analyse existing evidence for five major drivers of water stress on Amazonian forests, as well as potential critical thresholds of those drivers that, if crossed, could trigger local, regional or even biome-wide forest collapse. By combining spatial information on various disturbances, we estimate that by 2050, 10% to 47% of Amazonian forests will be exposed to compounding disturbances that may trigger unexpected ecosystem transitions and potentially exacerbate regional climate change. Using examples of disturbed forests across the Amazon, we identify the three most plausible ecosystem trajectories, involving different feedbacks and environmental conditions. We discuss how the inherent complexity of the Amazon adds uncertainty about future dynamics, but also reveals opportunities for action. Keeping the Amazon forest resilient in the Anthropocene will depend on a combination of local efforts to end deforestation and degradation and to expand restoration, with global efforts to stop greenhouse gas emissions.
Cambarazais são formações florestais monodominantes de Vochysia divergens Pohl. O rápido espalhamento de cambarazais em campos sazonalmente inundados no Pantanal tem sido considerado um efeito de ...mudanças climáticas ocorridas em ciclos plurianuais. Realizado na RPPN SESC Pantanal, Barão de Melgaço, Mato Grosso (Brasil), o presente estudo, inserido no Programa de Pesquisas Ecológicas de Longa Duração (PELD), teve por objetivo analisar a estrutura do cambarazal presente na Reserva, ao longo de um gradiente hidro-topográfico. Os dados fitossociológicos foram coletados em quatro áreas de 1 ha (100x100 m). Todos os indivíduos com CAP (Circunferência à Altura do Peito) > 5 cm foram identificados, medidos seus perímetros e estimadas suas alturas. Um total de 3.149 indivíduos foi amostrado nos quatro hectares e 83 espécies foram identificadas. A diversidade de espécies ao longo do gradiente mostrou relação inversa com a altura da lâmina de água da inundação. A parcela com menor nível de inundação (P1) obteve o maior índice de diversidade de espécies dentre as parcelas (H' = 2,9) e baixa densidade e dominância de V. divergens. As demais parcelas foram identificadas como formações monodominantes de V. divergens, devido à sua dominância de mais de 50% dentro de cada parcela.
Monodominant forest formations of Vochysia divergens Pohl found in the Pantanal are called "Cambarazais". The climatic changes registered in pluri-annual cycles have been cited as responsible for the sudden spread of these formations into seasonally flooded open areas. This study was carried out at the SESC Pantanal RPPN (Private Natural Heritage Reserve), Barão de Melgaço, Mato Grosso (Brazil), as part of the Long Term Ecological Research Program (PELD). It aims to analyze structural and phytosociological data collected in four areas of one hectare each of "cambarazal" along a hydro-topographical gradient. All individuals with cbh (circumference at breast height) > 5cm were identified, perimeters were measured and heights were estimated. In the entire sample area, 3,149 individuals belonging to 83 species were registered. Species diversity along the gradient showed an inverse relationship with floodwater levels. The plot with the lowest level of flooding (P1) had the highest species diversity index (H' = 2.91) of the sampled plots and the lowest values of V. divergens density and dominance. The other plots were considered to be V. divergens monodominant formations, since relative dominance of this species in these areas was greater than 50%.
Human impacts outpace natural processes in the Amazon Albert, James S; Carnaval, Ana C; Flantua, Suzette G A ...
Science (American Association for the Advancement of Science),
01/2023, Volume:
379, Issue:
6630
Journal Article
Peer reviewed
Amazonian environments are being degraded by modern industrial and agricultural activities at a pace far above anything previously known, imperiling its vast biodiversity reserves and globally ...important ecosystem services. The most substantial threats come from regional deforestation, because of export market demands, and global climate change. The Amazon is currently perched to transition rapidly from a largely forested to a nonforested landscape. These changes are happening much too rapidly for Amazonian species, peoples, and ecosystems to respond adaptively. Policies to prevent the worst outcomes are known and must be enacted immediately. We now need political will and leadership to act on this information. To fail the Amazon is to fail the biosphere, and we fail to act at our peril.
•Expansion of trees over natural pastures is affected by climatic and hydrological conditions.•Bioclimatic models define higher risk of invasion based on abiotic limits to species ...distribution.•Climatic seasonality increases the chances of encroachment by a flood-tolerant tree.•Management of encroaching trees must consider socioeconomic and ecological benefits.
Woody encroachment converts savanna systems to forests, altering the composition and productivity of native forage species and the supply of several ecosystem services. In this study, correlative species distribution models were applied to predict the chances of proliferation of a flood-tolerant encroaching tree (Vochysia divergens, Vochysiaceae) over the large Pantanal savanna floodplain and to provide a management tool with the aim of defining strategies for invasion control and containment over natural pastures. BIOCLIM and DOMAIN, two correlative models based on presence data, were used, accurately defining areas with a higher risk of invasion based on abiotic limits for the species distribution. The results of the models indicate that areas with high precipitation in the warmest period of the year and high annual mean temperature increase the chances of occurrence of this species, thus increasing the risk of invasion. Maintaining the integrity of natural pastures in climatic zones that are favorable to invasion requires management strategies such as low livestock density and maintenance of the hydrological regime, which prevent the degradation of natural pastures. Therefore, the management of encroaching trees must consider the socioeconomic and ecological benefits of removing populations of such trees, while seeking a balance in the conservation of ecosystem services and human livelihoods.
•ES science on South American tropical forests heterogeneously addresses policy domains and ES categories.•Most scientific contributions to ES knowledge on South American tropical forests were ...classified as descriptive.•ES Science on South American tropical forests clusters around central themes of global environmental policy-making.•The research peaks and gaps identified may stimulate research efforts and inform evidence-based policies.
Tropical forests are widely recognized for providing valuable ecosystem services (ES), but their existence is increasingly under pressure. The production of policy-relevant ES science is important to effectively convey their value. The main objective of this review is to insight into the associations between scientific knowledge, policy domains and ES categories to identify gaps for advancing further research and improve ES policy-making. For this purpose, we developed a classification system and conducted a systematic review of publications between 2000 and 2020 that focus on the Amazon, Cerrado and Atlantic Forest, the main tropical forest and tropical savannah biomes of South America. The review results indicated high heterogeneity across the biomes. Valuation studies were least prominent in comparison with other categories, whereas descriptive studies dominated ES science in South America. Scientific contributions tended to cluster around central themes of global environmental governance, including GHG emissions. The research peaks and gaps identified for the three biomes can stimulate new knowledge production efforts and inform regionally specific evidence-based policies for enhancing ES programs and policies in South America.
AIMS: We evaluated whether habitat association is consistent between two tree life history stages, young and adult, and whether spatial gradients explain species composition variation. METHODS: We ...investigated habitat association of tree assemblages using multivariate regression tree analysis (MRT). Habitat preference was assayed using indicator species analysis. We addressed the contribution of pure environment (i.e. habitat), spatially structured environment and pure space on species composition variation using variation partitioning by partial redundancy analysis (pRDA). Principal coordinates of neighbor matrices (PCNM) were used to produce spatial regressors. RESULTS: Habitat association changed during plant ontogeny. Flooding depth explained differences in species composition at young tree stages. Distribution pattern of adult trees was explained by spatial variation in soil fertility. Pure space explained a higher fraction of community variability of young trees (16Â %) than habitat (5Â %). In contrast, adult trees were structured mostly by habitat (10Â %). CONCLUSIONS: Niche expansion was observed along tree ontogeny, with adult trees occupying a wider range of flooding conditions. The higher effect of pure space on young tree distribution highlights the importance of distance-dependent processes (e.g. dispersal) on the variation in community composition. The large unexplained component resulted from variation partitioning indicates that stochastic environmental events (e.g. climate histories) might contribute to explaining tree assemblage dynamics in the Pantanal system.
Cambarazais são formações florestais monodominantes de Vochysia divergens Pohl. O rápido espalhamento de cambarazais em campos sazonalmente inundados no Pantanal tem sido considerado um efeito de ...mudanças climáticas ocorridas em ciclos plurianuais. Realizado na RPPN SESC Pantanal, Barão de Melgaço, Mato Grosso (Brasil), o presente estudo, inserido no Programa de Pesquisas Ecológicas de Longa Duração (PELD), teve por objetivo analisar a estrutura do cambarazal presente na Reserva, ao longo de um gradiente hidro-topográfico. Os dados fitossociológicos foram coletados em quatro áreas de 1 ha (100×100 m). Todos os indivíduos com CAP (Circunferência à Altura do Peito) > 5 cm foram identificados, medidos seus perímetros e estimadas suas alturas. Um total de 3.149 indivíduos foi amostrado nos quatro hectares e 83 espécies foram identificadas. A diversidade de espécies ao longo do gradiente mostrou relação inversa com a altura da lâmina de água da inundação. A parcela com menor nível de inundação (P1) obteve o maior índice de diversidade de espécies dentre as parcelas (H' = 2,9) e baixa densidade e dominância de V. divergens. As demais parcelas foram identificadas como formações monodominantes de V. divergens, devido à sua dominância de mais de 50% dentro de cada parcela.Monodominant forest formations of Vochysia divergens Pohl found in the Pantanal are called "Cambarazais". The climatic changes registered in pluri-annual cycles have been cited as responsible for the sudden spread of these formations into seasonally flooded open areas. This study was carried out at the SESC Pantanal RPPN (Private Natural Heritage Reserve), Barão de Melgaço, Mato Grosso (Brazil), as part of the Long Term Ecological Research Program (PELD). It aims to analyze structural and phytosociological data collected in four areas of one hectare each of "cambarazal" along a hydro-topographical gradient. All individuals with cbh (circumference at breast height) > 5cm were identified, perimeters were measured and heights were estimated. In the entire sample area, 3,149 individuals belonging to 83 species were registered. Species diversity along the gradient showed an inverse relationship with floodwater levels. The plot with the lowest level of flooding (P1) had the highest species diversity index (H' = 2.91) of the sampled plots and the lowest values of V. divergens density and dominance. The other plots were considered to be V. divergens monodominant formations, since relative dominance of this species in these areas was greater than 50%.
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