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Understanding ecological transitions under recurrent wildfire: A case study in the seasonally dry tropical forests of the Chiquitania, Bolivia
... Wildfires in tropical regions, housing Earth's intricate ecosystems and highest carbon storage [1], have profound destructive consequences. They alter the structure and composition of natural assemblages unadapted to fire effects [2,3]. The extensive scientific literature documents fire's substantial impact on ecological processes and dynamics [4]. ...
... Integrating vulnerability assessments into wildfire management strategies enables targeted interventions to reduce risk and enhance resilience among vulnerable populations. Furthermore, vulnerability mapping facilitates the prioritization of resources and allocation of support to high-risk areas, contributing to more effective wildfire prevention and response efforts [2,6,8]. ...
... It is essential to note that strategies must be tailored to the natural wildfire regime of ecological units, and our study area falls into the category of non-fire-prone. Unlike fire-prone ecological units, which may benefit from managed activities like prescribed burns but suffer from fire suppression [2,91], the ecological units in our study area need to be isolated from fire and focused primarily on wildfire prevention [103]. Therefore, restoring their original resistance by addressing their structure and composition is imperative [104]. ...
Rising wildfire incidents in South America, potentially exacerbated by climate change, require an exploration of sustainable approaches for fire risk reduction. This study investigates wildfire-prone meteorological conditions and assesses the susceptibility in Colombia’s megadiverse northern region. Utilizing this knowledge, we apply a machine learning model and the Monte Carlo approach to evaluate sustainability strategies for mitigating fire risk. The findings indicate that a substantial number of fires occur in the southern region, especially in the first two seasons of the year, and in the northeast in the last two seasons. Both are characterized by high temperatures, minimal precipitation, strong winds, and dry conditions. The developed model demonstrates significant predictive accuracy with the HIT, FAR, and POC of 87.9%, 28.3%, and 95.7%, respectively, providing insights into the probabilistic aspects of fire development. Various scenarios showed that a decrease in soil temperature reduces the risk mostly in lower altitudes and leaf skin reservoir content in the highest altitudes, as well as in the north region. Sustainability strategies, such as tree belts, agroforestry mosaics, and forest corridors emerge as crucial measures. The results underscore the importance of proactive measures in mitigating wildfire impact, offering actionable insights for crafting effective sustainability strategies amid escalating fire risks.
... On the other hand, historical records show that fire has been an integral part of the ecology of the Chiquitanía (Power et al., 2016), and several fire-adapted species with protective traits such as a thick bark are present (Killeen et al., 2006), suggesting that the resilience to fire is higher than generally thought. Much recent work on the effects of fire in the Chiquitanía has been done by Devisscher et al. (2016aDevisscher et al. ( ,b, 2019, who have found shifts in species composition and functional traits with increasing fire frequency that suggest that the Chiquitanía may irreversibly transition into a more fire-adapted state as fires occur more frequently (Devisscher et al., 2016b). However, their field work mainly focused on transition zones within the Chiquitanía, and it remains unknown whether these changes would be similar across the region. ...
... This study is the first to assess the fire resilience of the Chiquitanía at a large regional scale using a remote sensing-derived vegetation index, the normalized burn ratio (NBR). We investigate how results from previous studies at the plot level (e.g., Devisscher et al., 2016b) scale up over the entire Chiquitanía region and identify drivers of spatial variability. ...
... (1) Control areas that didn't burn between 2000 and 2020 (Ctrl). The years 2002, 2007, and 2010 were chosen because these were years which saw significant fire events (Fundación Amigos de la Naturaleza [FAN], 2019) and have been used in a study in the Chiquitanía previously to evaluate the effect of recurrent wildfire on the vegetation (Devisscher et al., 2016b). ...
Wildfires are becoming increasingly frequent and devastating in many tropical forests. Although seasonally dry tropical forests (SDTF) are among the most fire-threatened ecosystems, their long-term response to frequent wildfires remains largely unknown. This study is among the first to investigate the resilience in response to fire of the Chiquitano SDTF in Bolivia, a large ecoregion that has seen an unprecedented increase in fire intensity and frequency in recent years. We used remote sensing data to assess at a large regional and temporal scale (two decades) how fire frequency and environmental factors determine the resilience of the vegetation to fire disturbance. Resilience was measured as the resistance to fire damage and post-fire recovery. Both parameters were monitored for forested areas that burned once (F1), twice (F2), and three times (F3) between 2000 and 2010 and compared to unburned forests. Resistance and recovery were analyzed using time series of the Normalized Burn Ratio (NBR) index derived from Landsat satellite imagery, and climatic, topographic, and a human development-related variable used to evaluate their influence on resilience. The overall resilience was lowest in forests that burned twice and was higher in forests that burned three times, indicating a possible transition state in fire resilience, probably because forests become increasingly adapted during recurrent fires. Climatic variables, particularly rainfall, were most influential in determining resilience. Our results indicate that the Chiquitano dry forest is relatively resilient to recurring fires, has the capacity to recover and adapt, and that climatic differences are the main determinants of the spatial variation observed in resilience. Nevertheless, further research is needed to understand the effect of the higher frequency and intensity of fires expected in the future due to climate change and land use change, which may pose a greater threat to forest resilience.
... Our results showed new evidence that Neotropical, seasonally flooding forests show TH and an increase in floristic similarity as a result of increased fire frequency. The role of fire as a modifying driver of tropical forests has already been recognized, and there is plenty evidence that fire reduces species richness and acts as a local extinction filter of species that are not tolerant to fire Barlow & Peres 2008;Oliveras et al. 2014;Devisscher et al. 2016;Flores et al. 2016), as well as causing long-term shifts in forest structure and species composition of tropical forests (Pinnard et al. 1999;Barlow et al. 2003;Balch et al. 2008;Flores et al. 2014;Oliveras et al. 2014;Devisscher et al. 2016;Durigan & Ratter 2016). Given the short period of time (i.e., 7 years) between censuses and the profound differences that we found in the species composition and forest structure between the two censuses, we highlight the important role of fire as a BH agent in seasonally flooding forests. ...
... Our results showed new evidence that Neotropical, seasonally flooding forests show TH and an increase in floristic similarity as a result of increased fire frequency. The role of fire as a modifying driver of tropical forests has already been recognized, and there is plenty evidence that fire reduces species richness and acts as a local extinction filter of species that are not tolerant to fire Barlow & Peres 2008;Oliveras et al. 2014;Devisscher et al. 2016;Flores et al. 2016), as well as causing long-term shifts in forest structure and species composition of tropical forests (Pinnard et al. 1999;Barlow et al. 2003;Balch et al. 2008;Flores et al. 2014;Oliveras et al. 2014;Devisscher et al. 2016;Durigan & Ratter 2016). Given the short period of time (i.e., 7 years) between censuses and the profound differences that we found in the species composition and forest structure between the two censuses, we highlight the important role of fire as a BH agent in seasonally flooding forests. ...
... (Silveira et al. 2016). Our results showed strong evidence that TH can also be modulated by fire, even in a short period of time, which favours the substitution of fire-sensitive species by fire-tolerant species, similarly to what has already been reported for tropical forests (Pinard et al. 1999;Barlow & Peres 2008;Balch et al. 2011Balch et al. , 2013Oliveras et al. 2014;Devisscher et al. 2016;Silveira et al. 2016). Plant mortality was higher than recruitment in five of the six studied impucas. ...
Recent evidence has shown that most tropical species are declining as a result of global change. Under this scenario, the prevalence of tolerant species to disturbances has driven many biological communities towards biotic homogenization (BH). However, the mechanisms that drive communities towards BH are not yet thoroughly understood. We tested effects of recurring wildfires on woody species richness and composition in six seasonally flooded Amazonian forests and whether these fires reduce species composition (i.e., taxonomic homogenization) over short periods of time. Our results show that these forests are undergoing taxonomic homogenization in response to recurring fire events. Species richness decreased as a result of local extinctions and floristic similarity increased among forest communities. Fire was selecting tolerant (‘winner’) species and eliminating the more sensitive (‘loser’) species. BH leads to biodiversity erosion, which can deeply alter ecosystem processes such as productivity, nutrient cycling and decomposition, resulting in important consequences for conservation.
... Post-fire regeneration in tropical forests depends on the arrival of species tolerant to new environmental conditions, such as the depletion of soil fertility and moisture (Devisscher et al. 2016;Flores et al. 2016). In this case, communities are dominated by invasive species, such as highly inflammable grasses that maintain conditions favorable for fires (Beerling and Osborne 2006;Silvério et al. 2013). ...
... The state of arrested succession and deceleration in regeneration provides strong signals that fire is at the same time a source of disturbance and an environmental filter (Bond and Keeley 2005;Pausas 2015;Berenguer et al. 2018b;He et al. 2019), which can also shape the preservation of stable states, such as those seen in savannas and forests (Cavelier et al. 1998;Hoffmann et al. 2012;Murphy and Bowman 2012;Dantas et al. 2013). In tropical forests, fire can transform areas previously characterized by high canopy cover with a high diversity of shade-tolerant and fire-sensitive species (Cochrane and Schulze 1999;Barlow et al. 2003a, b), into monodominant vegetation composed of early pioneer and secondary species with fire tolerance characteristics (Devisscher et al. 2016;Jakovac et al. 2016;Tepley et al. 2018;Fernandes Neto et al. 2019). ...
The number of papers focusing on ecological interactions in urban environments has increased in recent years. This review aimed to address the panorama of urban ecology and biological surveys in Brazil. A systematic search was carried out using the Web of Science and Scopus platforms for papers on urban ecology to understand which institutions, authors, themes, cities, biomes, states, and regions have addressed the theme in Brazil to date. A total of 932 articles were found, in 196 scientific journals. Most papers were published between 2010 and 2019. This involved 350 municipalities in the five Brazilian regions, with Curitiba, São Paulo, and Rio de Janeiro being the municipalities with the most papers. São Paulo was the state that presented the most papers, with 23.7% of the total, and the Southeast region was the most representative with 36.6%. The biome with the highest concentration of papers (61.2%) was the Atlantic Forest. A total of 2537 authors were registered, affiliated with a total of 413 institutions from 19 countries. The institutions with the most papers were the Federal University of Paraná and University of São Paulo. The most discussed topic was related to botany (69%), and the most used keyword was “urban afforestation”. The number of papers published was greater in municipalities with higher human development index, number of inhabitants and relative urbanized area. This review revealed the scarcity of studies in low-income areas, and the need for greater incorporation of the social aspect, landscape ecology and ecological interactions in urban ecology.
... Post-fire regeneration in tropical forests depends on the arrival of species tolerant to new environmental conditions, such as the depletion of soil fertility and moisture (Devisscher et al. 2016;Flores et al. 2016). In this case, communities are dominated by invasive species, such as highly inflammable grasses that maintain conditions favorable for fires (Beerling and Osborne 2006;Silvério et al. 2013). ...
... The state of arrested succession and deceleration in regeneration provides strong signals that fire is at the same time a source of disturbance and an environmental filter (Bond and Keeley 2005;Pausas 2015;Berenguer et al. 2018b;He et al. 2019), which can also shape the preservation of stable states, such as those seen in savannas and forests (Cavelier et al. 1998;Hoffmann et al. 2012;Murphy and Bowman 2012;Dantas et al. 2013). In tropical forests, fire can transform areas previously characterized by high canopy cover with a high diversity of shade-tolerant and fire-sensitive species (Cochrane and Schulze 1999;Barlow et al. 2003a, b), into monodominant vegetation composed of early pioneer and secondary species with fire tolerance characteristics (Devisscher et al. 2016;Jakovac et al. 2016;Tepley et al. 2018;Fernandes Neto et al. 2019). ...
Fire in tropical forests jeopardizes natural regeneration and can lead to the establishment of an alternative stable state. To address the effects of fire on natural regeneration in a lowland tropical forest, we performed a time series study over 12 years, focusing on the impact of fire frequency and post-fire regeneration time on vegetation structure, diversity, and functional composition in secondary forests. The study was conducted in the Brazilian Atlantic Forest at sites subjected to different fire frequencies (never, once, three, and four times over 44 years) and old-growth forests. During 12 years of monitoring time, no significant difference was observed in community structure and diversity among sites subjected to fire, which suggests an arrested succession pattern and corroborates with the establishment of an alternative stable state. Functional traits associated with fire resistance, including wood density and bark thickness, were higher in areas with fire history compared to old-growth forests. Therefore, our results showed that recurrent fires can lead communities toward an arrested succession pattern with a high divergence in community structure and functional composition compared to old-growth forest. These results have several practical implications for restoration and conservation programs in the Brazilian Atlantic Forest.
... Based on previous studies [15,[21][22][23], we first hypothesize that (1) forest biomass and height should be lower in areas affected by fire four to five years prior the measurements (fire occurrence in 2010) in relation to unburned forests and that (2) forest biomass and height should be similar in areas affected by fire eight to ten years prior the measurements (fire occurrence in 2005) than in unburned forests, assuming that these areas already had time to recover their fire-affected forest structure. ...
... Similar to other studies [22,23,75], we showed a significant biomass reduction in forest affected by fire. More interestingly, our LIDAR analysis allowed the detection of subtle changes in the canopy of burned sites in subsequent years after fire. ...
Fire is one of the main factors directly impacting Amazonian forest biomass and dynamics. Because of Amazonia's large geographical extent, remote sensing techniques are required for comprehensively assessing forest fire impacts at the landscape level. In this context, Light Detection and Ranging (LiDAR) stands out as a technology capable of retrieving direct measurements of vegetation vertical arrangement, which can be directly associated with aboveground biomass. This work aims, for the first time, to quantify post-fire changes in forest canopy height and biomass using airborne LiDAR in western Amazonia. For this, the present study evaluated four areas located in the state of Acre, called Rio Branco, Humaitá, Bonal and Talismã. Rio Branco and Humaitá burned in 2005 and Bonal and Talismã burned in 2010. In these areas, we inventoried a total of 25 plots (0.25 ha each) in 2014. Humaitá and Talismã are located in an open forest with bamboo and Bonal and Rio Branco are located in a dense forest. Our results showed that even ten years after the fire event, there was no complete recovery of the height and biomass of the burned areas (p < 0.05). The percentage difference in height between control and burned sites was 2.23% for Rio Branco, 9.26% for Humaitá, 10.03% for Talismã and 20.25% for Bonal. All burned sites had significantly lower biomass values than control sites. In Rio Branco (ten years after fire), Humaitá (nine years after fire), Bonal (four years after fire) and Talismã (five years after fire) biomass was 6.71%, 13.66%, 17.89% and 22.69% lower than control sites, respectively. The total amount of biomass lost for the studied sites was 16,706.3 Mg, with an average loss of 4176.6 Mg for sites burned in 2005 and 2890 Mg for sites burned in 2010, with an average loss of 3615 Mg. Fire impact associated with tree mortality was clearly detected using LiDAR data up to ten years after the fire event. This study indicates that fire disturbance in the Amazon region can cause persistent above-ground biomass loss and subsequent reduction of forest carbon stocks. Continuous monitoring of burned forests is required for depicting the long-term recovery trajectory of fire-affected Amazonian forests.
... Wildfires have been documented to negatively impact tropical forests from population to ecosystem level, including loss of phylogenetic and functional plant diversity (Nobrega et al 2019), and are a major driver of forest degradation in human-modified landscapes (Silverio et al 2013b, Faria et al 2017, Lapola et al 2023. Our findings reinforce the notion that even single forest fires are able to drastically alter forest structure, including stem density and carbon stocks , Barlow and Peres 2008, Devisscher et al 2016, Flores et al 2016. We also show that-four years after the fires-there is a greater difference in canopy stem density than there was for understory forest stems. ...
Wildfires associated with land-use and climate change have considered a key driver to the Amazon forest collapse. However, achieving a detailed understanding of how human-related disturbances impact forest successional trajectories needs comprehensive information spanning forest strata. Here, we investigate the impact of recurrent wildfires on forest structure, species diversity, and composition, making a comprehensive assessment of the regenerating, understory, and canopy tree communities in a sustainable use reserve in the eastern Amazon. Plant communities were described across 16 forest stands (old-growth, burned once and twice) sampling a total of 3620 individuals and 326 tree and palm species. Wildfires affected all attributes of forest structure. Aboveground biomass decreased by 44% in forest burned once, and 71% in twice-burned forest stands. Forest canopy was the most affected strata after the second fire, with a 44%-decrease compared to unburned forest. The same pattern emerged for basal area, which decreased by an average of 27.5% after the first fire and 53.8% following the second fire event. Overall, plant communities experienced a 50%-loss of species richness after two fires, including both dominant and rare species. Plant communities also became more dissimilar as fire events accumulated, with 58%–61% increase in species dissimilarity following two fires events. As wildfires reoccured, the old-growth forests of our focal landscape were converted into a mosaic of regenerating forest stands dominated by local short-lived pioneers (i.e. low-biomass early-regenerating forest stands) and a few tree species less sensitive to fire. Our findings highlight the urgent need to secure a resilient future for Amazonian forests with actions needed to support local livelihoods whilst reducing the prevalence of ignitions sources and allowing forest recovery.
... Extended periods of drought may provide advantages to tree species that can withstand fire, as well as grass invasion in areas where people live. This is because the connection between drought and fires, which are exacerbated by human activities such as logging, may be advantageous (Devisscher et al., 2016). As a result, in regions where the climate is conducive to either, forests may quickly transform into savannahs (Staal et al., 2015). ...
... In this region, the highest deforestation rates from 2011 to 2016 were detected, a total of 76,175 hectares (GeoBolivia, 2019a, b). The area that covers transition zones between the Chaco and Chiquitano Dry Forests deserves attention because of the speed with which changes in vegetation cover have occurred, especially since the year 2000 (Tejada et al., 2016;Devisscher et al., 2016). ...
A região central da América do Sul, onde está localizada a Bacia do Alto Paraguai (UPRB), é considerada um dos maiores reservatórios de carbono acima do solo do planeta. No entanto, a superfície ocupada por essas formações vem diminuindo consideravelmente o que requer ações estratégicas para preservar esses recursos. Nesse contexto, o presente estudo teve como objetivo estimar o estoque de carbono em formações florestais e savânicas da UPRB, analisando as variações ocorridas nos anos de 2013 e 2018, utilizando dados de campo, sensoriamento remoto e geoprocessamento. A abordagem proposta para a área trinacional da bacia é inédita e possibilitou quantificar o carbono na vegetação da UPRB, mostrando uma redução de 3,69% no estoque, o que equivale a aproximadamente 78,5 milhões de MgC emitidos na atmosfera durante o período analisado.6 , -37 x 10 6 e -7,2 x 10 6 MgC, respectivamente, enquanto o Mato Grosso do Sul (Brasil) apresentou um aumento de 8 x 10 6 no estoque de carbono. Dos 108 municípios avaliados, 48 apresentaram variação positiva no estoque de carbono aéreo. O mapeamento das variações de carbono na UPRB permitiu localizar onde devem ser implementadas ou intensificadas atitudes de redução de emissões por desmatamento e mudanças na cobertura da terra. Assim, a aplicação da metodologia proposta pode servir como um dos parâmetros para determinar as variações no estoque de carbono aéreo na região de pesquisa. Changes in vegetation cover and carbon stock in central South America: an analysis using field data and remote sensing Abstract The central region of South America, where the Upper Paraguay River Basin (UPRB) is located, is considered to be one of the largest above ground carbon reservoirs on the planet. However, the surface occupied by these formations has been decreasing considerably which requires strategic actions to preserve these resources. In this context, the present study aimed to estimate the carbon stock in forest and savanna formations of UPRB, analyzing the variations that occurred in the years 2013 and 2018, using field data, remote sensing and geoprocessing. The proposed approach for the tri-national area of the basin is unprecedented and made it possible to quantify carbon in the UPRB vegetation, showing a reduction of 3.69% in the stock, which is equivalent to approximately 78.5 million MgC emitted into the atmosphere during the analyzed period. The portion of the watershed inside Bolivia, Paraguay and Mato Grosso (Brazil) showed negative variations of -42.3x106, -37x106 and -7.2x106 MgC, respectively, while Mato Grosso do Sul (Brazil) showed an increase of 8x106 in the carbon stock. The aboveground carbon stock varied positively in 48 out of the 108 municipalities examined. The mapping of carbon variations in the UPRB allowed us to locate where attitudes towards reducing emissions from deforestation and changes in land cover should be implemented or intensified. Thus, the application of the proposed methodology can serve as one of the parameters for determining the variations in aboveground carbon stock in the research region. Keywords: Cerrado; Chaco; carbon emissions; dry forests; Pantanal; remote sensing.
... The increase in the frequency of forest fires in tropical regions generates changes in forest composition, structure, floristic diversity, and economic value [56,57]. Studies conducted in the Chiquitano Forest found that forest regeneration depends on fire severity levels [10,15] but is also related to fire frequency [58]. For non-forested areas, increasing trends are found mainly in 2-4 times, 5-7 times (23.4%), and once, but of decreasing ones in 2-4 times and only once. ...
In the last 21 years, Bolivia has recorded a series of thousands of wildfires that impacted an area of 24 million hectares, mainly in the departments of Beni and Santa Cruz. In this sense, identifying trends in the increase of natural vegetation after wildfires is a fundamental step in implementing strategies and public policies to ensure ecosystem recovery. The main objective of this study was to evaluate the spatial trends of the increase and decrease in vegetation affected by wild-fires for the whole of Bolivia, for the period 2001-2021, using non-parametric tests, through the analysis of Normalized Difference Vegetation Index (NDVI) remote sensing products. The results indicated that 53.6% of the area showed an increasing trend (p < 0.05) and 15.9% of the area showed a decreasing trend (p < 0.05). In terms of land cover type, forests were proportionally represented by 18.1% of the areas that showed an increasing trend (p < 0.05) and 3.0% of the forests showed a decreasing trend (p < 0.05). In contrast, non-forested areas showed an increasing trend of 35.5% and 12.9% showed a decreasing trend (p < 0.05). It can be concluded that there is a continuous regenera-tion process throughout the country.
... Forest edges are more susceptible to other types of disturbance , especially understory fires (Armenteras, González, et al. 2013;Devisscher et al. 2016;C. H. L. Silva et al. 2018). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Chiquitano forests respond to recurrent fires through a shift in tree species composition with already-present fire-tolerant species becoming more dominant. This transition presented losses in biomass but increases in species richness [135]. Grass-dominated vegetation, not species-diverse natural savanna, replaces degraded tropical forests on the southern edge of the Amazon Basin [136]. ...
This study identifies the spatial and temporal trends, and explores the drivers of fire dynamics in the Bolivian Amazon basin. Bolivia ranks in the top ten countries in terms of total annual burnt, with fires affecting an estimated 2.3 million hectares of forest in 2020. However, in comparison to the Brazilian Amazon, there has been little research into the fire regime in Bolivia. The sparse research and the limited literature on the subject indicate that fire activity is higher in the Bolivian Amazon basin’s dry forests and flooded savanna zones, and that agriculture and drought are the primary causes of fire activity. In this study, trend analysis and emerging hotspot analysis are deployed to identify the spatial and temporal patterns of fire activity and boosted regression tree models to identify the drivers of forest fire within each ecoregion of the Bolivian Amazon basin. Comparable to most of the Brazilian literature, this study finds that fire activity and fire season length is higher in the flooded Beni Savanna, and Chiquitano seasonally dry tropical forests than in the Bolivian Amazon ecoregion. This study also identifies moisture stress and human activity as the main drivers of fire dynamics within the region. It is intended that this research will offer a foundation for future research and conservation activities aimed at better understanding the fire regime of the Bolivian Amazon basin.
... Forest edges are more susceptible to other types of disturbance , especially understory fires (Armenteras, González, et al. 2013;Devisscher et al. 2016;C. H. L. Silva et al. 2018). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Forest edges are more susceptible to other types of disturbance , especially understory fires (Armenteras, González, et al. 2013;Devisscher et al. 2016;C. H. L. Silva et al. 2018). ...
This chapter discusses the main drivers of deforestation and forest degradation in the Amazon, particularly agricultural expansion, road construction, mining, oil and gas development, forest fires, edge effects, logging, and hunting. It also examines these activities’ impacts and synergies between them.
... Forest edges are more susceptible to other types of disturbance , especially understory fires (Armenteras, González, et al. 2013;Devisscher et al. 2016;C. H. L. Silva et al. 2018). ...
This chapter presents country-specific descriptions of human intervention in the Amazon. In general, a rapid expansion of agricultural and extractive activities, mostly for export but also for domestic markets, and to a lesser degree small scale agriculture, have led to extensive deforestation and environmental degradation without substantially improving the living conditions of the population. Government policies and the extent of State ascendancy in the area also seem to be a powerful determinant of the nature and scale of the process. Despite the common underlying international and domestic economic and political forces in the Amazon, each country has its own particularities. In the case of Colombia, the process was shaped by the guerilla presence and deteriorated after the Peace Treaty, which does not mention “deforestation” and perpetuates Colombia’s extractivist model. Ecuador’s case is representative of the link between fossil fuel extraction, environmental deterioration, and social exclusion. The case of Peru shows an Amazon perceived as a territory awaiting to be “conquered, occupied, and exploited”, subjected to an unwavering extractive and market-orientated drive. In Bolivia, contradictions between conservation and state-led development policies and business activities, which have transformed it into the second deforestation hotspot of Amazonia after Brazil, are presented. The Venezuelan Amazon is subject to rampant violence and illegal activity driven by the political geography of gold in mixed configurations of governance, with blurred boundaries between legality and illegality and prevailing negligence concerning conservation. The Guianas share low deforestation levels and lower environmental pressures, but the recent expansion of gold mining poses a serious threat. The Brazilian case presented in the previous Chapter is referenced here when comparing countries’ experienes. Conservation experiences are also included. In all cases, unsustainable extractivist models have outpaced conservation policies; however, these experiences can prove useful in the design of effective conservation policies, reduction of greenhouse gas emissions, and improvements in living conditions of Indigenous peoples and local communities.
... Forest edges are more susceptible to other types of disturbance , especially understory fires (Armenteras, González, et al. 2013;Devisscher et al. 2016;C. H. L. Silva et al. 2018). ...
The Science Panel for the Amazon (SPA) is an unprecedented initiative convened under the auspices of the United Nations Sustainable Development Solutions Network (SDSN). The SPA is composed of over 200 preeminent scientists and researchers from the eight Amazonian countries, French Guiana, and global partners. These experts came together to debate, analyze, and assemble the accumulated knowledge of the scientific
community, Indigenous peoples, and other stakeholders that live and work in the Amazon.
The Panel is inspired by the Leticia Pact for the Amazon. This is a first-of-its-kind Report which provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy
relevant options for conservation and sustainable development.
The three volumes of the final report can be downloaded from: https://www.theamazonwewant.org/amazon-assessment-report-2021/
... Indeed, they are associated to the three types of forests that proved to be the most affected by fires: Amazon forest, Chiquitano forest and Pantanal forest. For instance, previous studies demonstrated that, during the course of their evolution, the species of trees found in dry forests were exposed to fires of low to moderate severity [65,66]. Therefore, they have a limited capacity to recover naturally following the extensive high-severity fire of the last decades. ...
Wildfires are expected to increase in the near future, mainly because of climate changes and land use management. One of the most vulnerable areas in the world is the forest in central-South America, including Bolivia. Despite that this country is highly prone to wildfires, literature is rather limited here. To fill this gap, we implemented a dataset including the burned area that occurred in the department of Santa Cruz in the period of 2010–2019, and the digital spatial data describing the predisposing factors (i.e., topography, land cover, ecoregions). The main goal was to develop a model, based on Random Forest, in which probabilistic outputs allowed to elaborate wildfires susceptibility maps. The overall accuracy was finally estimated by using 5-fold cross-validation. In addition, the last three years of observations acted as the testing dataset, allowing to evaluate the predictive performance of the model. The quantitative assessment of the variables revealed that “flooded savanna” and “shrub or herbaceous cover, flooded, fresh/saline/brakish water” are respectively the ecoregions and land cover classes with the highest probability of predicting wildfires. This study contributes to the development and validation of an innovative mapping tool for fire risk assessment, implementable at a regional scale in different areas of the globe.
... In tropical forests, fires are likely to become a dominant disturbance due to increasing feedbacks between land cover change and more frequent droughts Devisscher et al. 2016). The long-term consequences of fires on biodiversity and forest carbon stocks depend on fire frequency and intensity (Keeley 2009;Morton et al. 2013). ...
In tropical dry forests, wildfires are likely to become a major disturbance as a result of anthropo-genic pressures and dryer conditions due to climate warming. Based on remote sensing techniques , this paper assesses the probability of fires occurring in the dry region of the Guanacaste Conservation Area (GCA), northwestern Costa Rica, testing the roles as fire determinants of topography, early successional forest stages, between-area susceptibility, and accessibility to human (roads and trails). Probability of fire occurrence and fire danger were determined based on a machine learning algorithm. Fire occurrence model was inferred from burned areas and fire line density; while fire danger was inferred from the probability of fire occurrence, the proportion of burned areas, and the number of fires per area. Results indicate that the presence of early successional vegetation on flat lowlands highly accessible by roads and trails are key components of fire occurrence. Three of the six investigated sectors show high probability of fire occurrence and fire danger, indicating the spatial heterogeneity of fire risk in the landscape. The results could be useful for the management of the conservation area.
... This species is known to grow in Chiquitanía Dry Forest and Cerrado habitats of Bolivia and Brazil (Devisscher et al. 2016). ...
This species is known from the Chiquitania Dry Forest and Cerrado habitats of Bolivia and Brazil. Ateleia guaraya has an area of occupancy of 44 km2 qualifying it for the Endangered category, however this islikely due to under-collection, especially as it has a large extent of occurrence of 53,099 km2 due to its discovery in Brazil. Therefore, this species qualifies as Least Concern. It is strongly recommended that research is undertaken to establish a better understanding of this species' population size, trends and the impact of deforestation. Studies focusing on the life history of A. guaraya would be particularly useful enabling the generation length of this species to be calculated and populations monitored in the
future.
... Fires are frequently used to clear forest areas for agriculture, reducing biomass and preventing recruitment of new trees (Balch et al. 2011;Devisscher et al. 2016). According to Nelson (1994), fire plays an important role in the dominance of lianas in the Brazilian Amazon forest. ...
Key message
A systematic review (1950–2018) summarizes the research on woody lianas and their interaction with trees in the Neotropics. We identify knowledge gaps, propose new directions for future studies and discuss the control, management, and conservation of lianas.
Abstract
Lianas are key components of species composition, structure and dynamics of tropical forests. Current global warming scenario, however, are favoring increases in the abundance and density of lianas in tropical forests, affecting tree growth, fertility, and the number of tree injuries, therefore, increasing tree mortality over time. Here, we present a systematic review of studies on Neotropical lianas and its relation with trees, aiming to (1) establish the current state of ecological research, identifying knowledge gaps and propose new directions and perspectives for future studies; (2) offer baseline knowledge to support the control, management and conservation of lianas. We surveyed the literature on lianas (woody climbers) since 1900 to 2018 retaining 427 papers. We organized the literature by country, vegetation type, topic addressed and whether the study focused exclusively on lianas or lianas and trees. Our review demonstrated the importance of lianas in tropical forests, and the scarcity of studies on woody savannas and especially extremely dry vegetations as the Caatinga seasonally dry forests and xeric shrublands. Regardless of their remarkable importance and their contribution for diversity, biomass and carbon flux, lianas are rarely included in global vegetation models and have been overlooked in restoration, control, and management programs. We must consider the relevance of lianas in maintaining diversity and microclimate, and as resources for native animals, such as pollinators, herbivores, and seed dispersers, as well as for traditional human communities. Research on ecophysiology and functional spectral traits, and management of lianas are among the key areas in the Anthropocene.
... En bosques secos tropicales, hay una alta probabilidad de que los incendios forestales se conviertan en la perturbación más dominante, debido a la rápida expansión de las fronteras agrícolas, los cambios en la cubierta terrestre y las frecuentes sequías resultado del cambio climático [1], [2]. En Centroamérica, la mayoría de los incendios forestales en los bosques secos están relacionados con quemas provocadas para la preparación de campos agrícolas y limpieza de terrenos [3]. ...
Los análisis post incendio, como el índice de área quemada (IAQ), permiten discriminar áreas afectadas y severidad de los incendios forestales. En este estudio se comparó según la frecuencia de incendios, el comportamiento anual del IAQ en la región de bosque seco tropical del Área de Conservación Guanacaste, Costa Rica entre los años 1997 al 2019. Los resultados evidencian que las áreas frecuentemente quemadas por incendios forestales muestran un comportamiento diferenciado en el IAQ a lo largo de todos los años. Mostrando una relación directa entre la frecuencia de incendios forestales y los valores de IAQ. Donde a mayor frecuencia de incendios forestales, los valores de IAQ son mayores. Por otro lado, las áreas que han sido poco afectadas o no han sido afectadas del todo mostraron valores bajos de IAQ. Estos resultados podrían validar la hipótesis de que después de dos a tres incendios, el banco de semillas es completamente destruido. Esto debido a que la composición y estructura de los bosques secos tropicales cambia considerablemente después de múltiples incendios.
... This spatial pattern suggests that shifts between both states might involve changes in soil conditions, and the erosion feedback loop that we describe seems to be a potential underlying mechanism. There is some evidence suggesting that soil erosion can indeed facilitate the expansion of savanna vegetation (Cavelier et al. 1998;Flores et al. 2017), although in most cases, repeatedly disturbed tropical forests tend to persist in a degraded state dominated by forest trees that tolerate fire, low nutrient and water availability, as well as exotic invasive grasses (Barlow and Peres 2008;Berenguer et al. 2018;Devisscher et al. 2016;Jakovac et al. 2016a;Silvério et al. 2013;Veldman and Putz 2011). Considering that tropical forests are increasingly exposed to disturbances, understanding how erosion may act as a resilience drain in these systems may help societies to manage the risk of ecological transitions (Scheffer et al. 2015), for instance by promoting fast recovery and restoration. ...
In the original version of this article, the following text must be added in the acknowledgement. M.H., B.M.F. and R.S.O. acknowledge the project grant from Instituto Serrapilheira/Serra-1709–18983.
... This spatial pattern suggests that shifts between both states might involve changes in soil conditions, and the erosion feedback loop that we describe seems to be a potential underlying mechanism. There is some evidence suggesting that soil erosion can indeed facilitate the expansion of savanna vegetation (Cavelier et al. 1998;Flores et al. 2017), although in most cases, repeatedly disturbed tropical forests tend to persist in a degraded state dominated by forest trees that tolerate fire, low nutrient and water availability, as well as exotic invasive grasses (Barlow and Peres 2008;Berenguer et al. 2018;Devisscher et al. 2016;Jakovac et al. 2016a;Silvério et al. 2013;Veldman and Putz 2011). Considering that tropical forests are increasingly exposed to disturbances, understanding how erosion may act as a resilience drain in these systems may help societies to manage the risk of ecological transitions (Scheffer et al. 2015), for instance by promoting fast recovery and restoration. ...
Background
Tropical forests are threatened by intensifying natural and anthropogenic disturbance regimes. Disturbances reduce tree cover and leave the organic topsoil vulnerable to erosion processes, but when resources are still abundant forests usually recover.
Scope
Across the tropics, variation in rainfall erosivity – a measure of potential soil exposure to water erosion – indicates that soils in the wetter regions would experience high erosion rates if they were not protected by tree cover. However, twenty-first-century global land cover data reveal that in wet South America tropical tree cover is decreasing and bare soil area is increasing. Here we address the role of soil erosion in a positive feedback mechanism that may persistently alter the functioning of disturbed tropical forests.
Conclusions
Based on an extensive literature review, we propose a conceptual model in which soil erosion reinforces disturbance effects on tropical forests, reducing their resilience with time and increasing their likelihood of being trapped in an alternative vegetation state that is persistently vulnerable to erosion. We present supporting field evidence from two distinct forests in central Amazonia that have been repeatedly disturbed. Overall, the strength of the erosion feedback depends on disturbance types and regimes, as well as on local environmental conditions, such as topography, flooding, and soil fertility. As disturbances intensify in tropical landscapes, we argue that the erosion feedback may help to explain why certain forests persist in a degraded state and often undergo critical functional shifts.
... In productive, fire-prone ecosystems such as the conifer forests of the western United States, dry tropical forests of southern Amazonia, and ash eucalypt forests in Australia, warmer temperatures and longer fire seasons are expected to increase the extent and frequency of fire (Abella et al. 2007, Colloff et al. 2016, Devisscher et al. 2016. Management tools to limit potentially transformative crown fires include different types and intensities of fuel treatments (e.g., control burns); allowing naturally ignited fires to burn in mild conditions; rapid fire suppression (Raftoyannis et al. 2013); managing for lower densities or less flammable species mixes (Abella et al. 2007, Cross et al. 2013); or limiting ignitions by restricting visitor access (Baron et al. 2009). ...
Changes in Earth's climate are accelerating, prompting increasing calls to ensure that investments in ecological restoration and nature conservation accommodate such changes. To acknowledge this need, we propose the term “ecological renovation” to describe ecological management and nature conservation actions that actively allow for environmental change. To evaluate and progress the development of ecological renovation and related intervention options in a climate change context, we reviewed the literature and established a typology of options that have been proposed. We explored how these options address emerging principles underpinning climate‐adapted conservation goals and whether the balance of approaches reflected in our typology is likely to be sufficient given expected rapid rates of climate change. Our typology recognizes a matrix of 23 intervention option types arranged on the basis of underpinning ecological mechanisms (“ameliorate changing conditions” or “build adaptive capacity”) on one axis, and the nature of the tools used to manipulate them (“low regrets” or “climate targeted”) on the other. Despite a burgeoning literature since 2008, we found that the majority of effort has consistently focused on low‐regrets adaptation approaches that aim to build adaptive capacity. This is in many ways desirable, but a paradigm shift enabling greater attention to climate‐targeted approaches is likely to be needed as climate change accelerates. When assessed against five emerging principles for setting nature conservation goals in a changing climate, only one option type could deliver to all five, and we identified a conflict between climate‐targeted options and “wildness” values that calls for deeper evaluation. Importantly, much of the inference in the 473 reviewed studies was drawn from ecological reasoning and modeling, with only 16% offering new empirical evidence. We also noted significant biases toward North America and Europe, forest ecosystems, trees, and vertebrates. To address these limitations and help shift the paradigm toward humans as “renovators” rather than “restorers” of a prior world, we propose that ecological researchers contribute by (1) informing societal discourse toward adapting nature conservation goals to climate change, (2) adjusting and upscaling conservation planning to accommodate this suite of climate‐adapted goals, and (3) reconceptualizing experimental approaches to increase empirical evidence and expedite innovation of tools to address change.
... Research activities regarding forest fires in general, and WUI fires in particular have been carried out for decades in South American countries although they appear to be decoupled from either national or regional strategies to address the problem. The highest activity is concentrated in Argentina, Brazil, and Chile, but other countries like Colombia [42], and Bolivia [43] have produced scientific output on the topic. Research related to fire science, however, is more limited, and only recently the WUI fire problem has received attention. ...
... Se seleccionaron tres zonas con alta ocurrencia del fuego (Figura 1): Bosques Amazónicos de Colombia en proceso de fragmentación y cambio en el uso del suelo con alta ocurrencia del fuego (Armenteras et al., 2017); Bosque Amazónico en transición a Bosque Chiquitano de Bolivia, notablemente afectado por el fuego (Rodríguez-Montellano et al., 2015) y sometido a procesos de fragmentación por el cambio en el uso del suelo (Devisscher et al., 2015); y un área de El Chaco seco de Argentina, región que está entre las más afectadas por el avance de la frontera agrícola a escala global (Sofía et al., 2017). En general el aumento de la demanda global de productos agrícolas implica también un avance en el proceso de intensificación y expansión de las fronteras agrícolas. ...
p>There are large omission errors in the estimation of burned area in map products that are generated at a global scale. This error is then inherited by other models, for instance, those used to report Greenhouse Gas Emissions using a “bottom up” approach. This study evaluates temporal methods to improve burned area detection using Landsat 5-TM and 8-OLI. In this process, the normalized burn ratio (NBR) was used to highlight burned areas and thresholds to classify burned and non-burned areas. In order to maximize the burned area detection two alternatives to the temporal dNBR method were evaluated: the relative form of the temporal difference RdNBR and the use of time series metrics. The processing, algorithm development and access to Landsat data was made on the Google Earth Engine GEE platform. Three regions of Latin America with large fire occurrence were selected: The Amazon Forest in Colombia, the transition from Chiquitano to Amazon Forest in Bolivia, and El Chaco Region in Argentina. The accuracy assessment of these new products was based on burned area protocols. The best model classified 85% of burned areas in the Chiquitano Forests of Bolivia, 63% of the burned areas of the Amazon Forests of Colombia and 69% of burned areas in El Chaco of Argentina.</p
... (Navarro 2001 (Navarro 2001). During the dry season, the deciduous and semi-deciduous vegetation loses most of its foliage and there is even a reduction in the flowering and growth of herbaceous plants (Navarro 2011, Devisscher et al 2016, in contrast to the wet season where the constant rains allow the flowering of the different strata that make up the forest including lianas and different epiphytes (Navarro 2001, Ibich & Merida 2003. ...
Samples of corbicular and stored pollen gathered by Tetragonisca angustula (Latreille, 1811) in an Amazon-Chiquitano transitional forest during the dry season were analyzed. The pollen spectrum was established as well as the dynamics of the relationship between the stingless bee and the surrounding flora. Pollen samples obtained from three rational hives were subjected to acetolysis and 55 pollen types were identified, the most frequent being from Anadenanthera (Fabaceae), Chenopodiaceae, and Dydimopanax (Araliaceae). Significant differences in pollen families used between hives along the months of collection were found in stored pollen and non-significant differences in corbicular pollen. Mean values of alpha diversity (H′) showed T. angustula as a generalist while beta diversity qualitatively showed that pollen composition was similar between two hives both of which differed from the third hive. Pollen types in corbicular and stored pollen were in general related with richness of flowering plants in the foraging area; the pollen offer was less diverse than the pollen collected, and a trend to prefer the collection of pollen from the most abundant flowering species could be discerned. T. angustula showed polylectic feeding habits and a capacity to adapt to food availability.
... Se seleccionaron tres zonas con alta ocurrencia del fuego (Figura 1): Bosques Amazónicos de Colombia en proceso de fragmentación y cambio en el uso del suelo con alta ocurrencia del fuego (Armenteras et al., 2017); Bosque Amazónico en transición a Bosque Chiquitano de Bolivia, notablemente afectado por el fuego (Rodríguez-Montellano et al., 2015) y sometido a procesos de fragmentación por el cambio en el uso del suelo (Devisscher et al., 2015); y un área de El Chaco seco de Argentina, región que está entre las más afectadas por el avance de la frontera agrícola a escala global (Sofía et al., 2017). En general el aumento de la demanda global de productos agrícolas implica también un avance en el proceso de intensificación y expansión de las fronteras agrícolas. ...
... Neotropical lowland forests (Balch et al., 2011;Devisscher, Malhi, Rojas Landiar, & Oliveras, 2016). Palaeoecological studies provide evidence that fire has been present in TMCFs since the beginning of the Holocene (e.g. ...
Tropical montane cloud forests (TMCFs) harbour high levels of biodiversity and large carbon stocks. Their location at high elevations make them especially sensitive to climate change, because a warming climate is enhancing upslope species migration, but human disturbance (especially fire) may in many cases be pushing the treeline downslope. TMCFs are increasingly being affected by fire, and the long-term effects of fire are still unknown. Here we present a 28-years chronosequence to assess the effects of fire and recovery pathways of burned TMCFs, with a detailed analysis of carbon stocks, forest structure and diversity. We assessed rates of change of carbon
... Frequent, severe, or combined fires limit the establishment of fire-sensitive forest tree species and favor pyrophilic grass and shrub establishment by increasing mortality of seed trees, reducing density and diversity of seedlings, and inhibiting tree seed germination (Silvério et al. 2013;Paritsis et al. 2015). As a result of these positive feedbacks, forest disturbance can lead to rapid overstory canopy loss, resulting in a switch from a fire-resistant forest to fire-dependent vegetation maintained by a self-reinforcing negative fire feedback (Devisscher et al. 2016). ...
Context: Terrestrial ecosystems, including tropical forests, are hypothesized to have tipping points beyond which environmental change triggers rapid and radical shifts to novel alternative states.
Objective: We explored the overarching hypothesis that fire-mediated alternative stable states exist in the semi-deciduous tropical forest zone of Ghana, and that increased fire activity has pushed some forests to a new state in which a novel ecosystem with low tree density is maintained by fire.
Methods: We combined a 30-year time series of remotely-sensed data with field measurements to assess land cover trends, the effects of fire on forest vegetation, and the reciprocal effects of vegetation change on fire regimes, in four forest reserves. We analyzed precipitation trends to determine if shifts in vegetation and fire regime reflected a shift to a drier climate.
Results: Two of the reserves experienced forest loss, were impacted by frequent fires, and transitioned to a vegetation community dominated by shrubs and grasses, which was maintained by fire–vegetation feedbacks. The other two reserves experienced less fire, retained higher levels of forest cover, and resisted fire encroachment from surrounding agricultural areas. Precipitation remained relatively stable, suggesting a hysteresis effect in which different vegetation states and fire regimes coexist within a similar climate.
Conclusion: There is potential for human land use and fire to create novel and persistent non-forest vegetation communities in areas that are climatically suitable for tropical forests. These disturbance-mediated regime shifts should be taken into account when assessing future trajectories of forest landscape change in West Africa.
... Due to the insulating capacity of thick bark, adult trees become insensitive to fire, however at the sapling stage they require protection from fire (Backéus et al., 1994;Eriksson et al., 2003). It has been anticipated that the disturbance associated with frequent wildfires may lead to long-term change in vegetation composition (Griscom and Ashton, 2011;Devisscher et al., 2016). ...
... where B l is the potential aboveground biomass loss (Mg ha -1 ) after fire, B i is the initial aboveground biomass (Mg ha -1 ), and α is the proportion of AGB remaining post-fire ranging from 0.7084 [21] to 0.90 [95]. The range of potential AGB loss estimated with Eq (1) accounts for biomass loss between 1 and 5 years after fire occurrence, without accounting for fire recurrence. ...
Wildfires are becoming increasingly dominant in tropical landscapes due to reinforcing feedbacks between land cover change and more severe dry conditions. This study focused on the Bolivian Chiquitania, a region located at the southern edge of Amazonia. The extensive, unique and well-conserved tropical dry forest in this region is susceptible to wildfires due to a marked seasonality. We used a novel approach to assess fire risk at the regional level driven by different development trajectories interacting with changing climatic conditions. Possible future risk scenarios were simulated using maximum entropy modelling with presence-only data, combining land cover, anthropogenic and climatic variables. We found that important determinants of fire risk in the region are distance to roads, recent deforestation and density of human settlements. Severely dry conditions alone increased the area of high fire risk by 69%, affecting all categories of land use and land cover. Interactions between extreme dry conditions and rapid frontier expansion further increased fire risk, resulting in potential biomass loss of 2.44±0.8 Tg in high risk area, about 1.8 times higher than the estimates for the 2010 drought. These interactions showed particularly high fire risk in land used for 'extensive cattle ranching', 'agro-silvopastoral use' and 'intensive cattle ranching and agriculture'. These findings have serious implications for subsistence activities and the economy in the Chiquitania, which greatly depend on the forestry, agriculture and livestock sectors. Results are particularly concerning if considering the current development policies promoting frontier expansion. Departmental protected areas inhibited wildfires when strategically established in areas of high risk, even under drought conditions. However, further research is needed to assess their effectiveness accounting for more specific contextual factors. This novel and simple modelling approach can inform fire and land management decisions in the Chiquitania and other tropical forest landscapes to better anticipate and manage large wildfires in the future.
... Long-term changes in the species and functional composition of the forest could either mitigate or exacerbate impacts on the carbon cycle, depending on the effect on carbon sequestration [33]. In landscapes with humans, interactions between drought and fires, exacerbated by logging and other disturbances, will also lead to changes in species composition, favoring fire-tolerant tree species and/or grass invasion in areas with a long dry season [36,76]. This could lead to the rapid conversion of forest to savanna in areas where the climate is suitable for either [77]. ...
Tropical forests exchange more carbon dioxide with the atmosphere than any other vegetation type and thus form a crucial component of the global carbon cycle. However, the impacts of anthropogenic climate change on drought occurrence and intensity could weaken the tropical forest carbon sink, with resulting feedback to future climates. We urgently need a better understanding of the mechanisms and processes involved in order to predict future responses of tropical forest carbon sequestration to climate change. Recent progress has been made in the study of drought responses at the molecular, cellular, organ, individual, species, community and landscape levels. Although understanding of the mechanisms is incomplete, the models used to predict drought impacts could be significantly improved by incorporating existing knowledge.
Deforestation (the complete removal of an area’s forest cover) and forest degradation (the significant loss of forest structure, functions, and processes) are the result of the interaction between various direct drivers, often operating together. By 2018, the Amazon forest had lost approximately 870,000 km² of its original cover, mainly due to expansion of agriculture and ranching. Other direct drivers of forest loss include the opening of new roads, construction of hydroelectric dams, exploitation of minerals and oil, and urbanization. Impacts of deforestation range from local to global, including local changes in landscape configuration, climate, and biodiversity, regional impacts on hydrological cycles, and global increase of greenhouse gas emissions. Of the remaining Amazonian forests, 17% are degraded, corresponding to 1,036,080 km². Forest degradation has various anthropogenic drivers, including understory fires, edge effects, selective logging, hunting, and climate change. Degraded forests have significantly different structure, microclimate, and biodiversity as compared to undisturbed ones. These forests tend to have higher tree mortality, lower carbon stocks, more canopy gaps, higher temperatures, lower humidity, higher wind exposure, and exhibit compositional and functional shifts in both fauna and flora. Degraded forests can come to resemble their undisturbed counterparts, but this depends on the type, duration, intensity, and frequency of the disturbance event. In some cases this may impede the return to a historic baseline. Avoiding further loss and degradation of Amazonian forests is crucial to ensuring that they continue to provide valuable and life-supporting ecosystem services.
KEYWORDS: deforestation; forest degradation; wildfires; edge effects; logging
Wildfires have increased in protected areas (PAs) of the Colombian Amazon following the 2016 peace agreement between the Government and the Revolutionary Armed Forced of Colombia (FARC—Spanish acronym). Recent study efforts to understand this issue suffer from data scarcity and limited consultation of local stakeholder perspectives on factors affecting wildfires.
This study uses a social–ecological systems framework to investigate local perceptions of factors driving and/or preventing wildfires in the Los Picachos, La Macarena and Tinigua PAs, which are shared by two Amazonian departments experiencing wildfire increase. Four stakeholder categories were selected to represent varied and possibly conflicting interests: cattle ranchers, the national park service, local authorities and cross‐sectional stakeholders. We combined a participative mapping approach with interviews to illustrate stakeholder perceptions of interactions between key variables in graphical causal models. Network analyses were used to determine areas of agreement on key variables, and to compare local priorities with those of key informants at the national level.
Local stakeholders and key informants widely agreed on the roles of extensive cattle ranching and land grabbing as key drivers of wildfires. The analysis identified areas for further research into wildfire occurrence within PAs. These include lack of governance and untitled land, as well as the effects of poor access to basic public services on unsustainable ranching methods.
This study revealed contested opinions between ranchers and other stakeholders over interactions between ranching, roads and illicit crops, and consequently their effects on wildfire occurrence. This indicates the need for cautious implementation of the National Development Plan, prioritising road maintenance over expansion, integrating arable alternatives to cattle ranching and considering multiple stakeholders in regional decision‐making around wildfire reduction. The strengths and limitations of the participative mapping approach employed here are discussed with a view to aiding decision‐making in post‐conflict regions of the Global South.
This study reports the extraction of oil from baru (Dipteryx alata vogel) seeds using compressed propane, supercritical CO2 (scCO2) with ethanol as solvents and the conventional (Soxhlet) extraction using ethanol and hexane. Results indicated that the compressed propane presented the highest extraction yield (36.87%) at 10 MPa, 60 °C, with 10 min of confinement time and using an average particle size of 0.5 mm. Higher extraction yields were also reached using scCO2 but the addition of ethanol as cosolvent was needed. Tocopherols and antioxidant activity in all samples presented better results in contrast with the literature. The fatty acid profile was similar for all samples, where oleic (within 50–54%), linoleic (23–25%), palmitic (around 5%), stearic (around 5%) and arachidonic acid (around 4%) are the major fatty acids found. Finally, residues of the extraction presented high content of proteins (32%). The oil obtained is very promising for food and pharmaceuticals applications.
Carbon inventory was done on two savannah ecosystems (sites I & II) of Kanyakumari Wildlife Sanctuary, Western
Ghats, India. Ten plots of 20 m × 20 m each were laid in each site to study woody vegetation and a total of forty quadrats (4 in each
plot) of 1 m × 1 m were laid in each site for the understorey. Both sites showed remarkable variations in biomass and carbon
accumulation patterns. Site I (213 Mg C/ha) had higher woody biomass carbon than site II (185.9 Mg C/ha). However, the latter had
greater understorey biomass carbon (site I – 3.2 Mg C/ha; site II –20.7 Mg C/ha). Overall, the total vegetation carbon accounted to
216.2 Mg C/ha in site I and 206.6 Mg C/ha in site II. On the other hand, soil carbon was higher in site II (183.5 Mg C/ha) than site I
(172.3 Mg C/ha). Soil bulk density increased with increase in soil depth in both sites. Cumulatively, even though both sites had
almost equal carbon stocks, they show considerable variation in the amount of carbon stocked in their carbon pools. Woody biomass
was the largest carbon pool, followed by soil and understorey biomass. The observed variations could be due to differences in terrain
characteristics, edaphic factors, incidence of fires, etc. The study emphasizes the important role of savannahs in stocking
considerable amounts of carbon in their different carbon pools.
Wildfires are becoming increasingly dominant in tropical landscapes due to reinforcing feedbacks between land cover change and more severe dry conditions. This study focused on the Bolivian Chiquitania, a region located at the southern edge of Amazonia. The extensive, unique and well-conserved tropical dry forest in this region is susceptible to wildfires due to a marked seasonality. We used a novel approach to assess fire risk at the regional level driven by different development trajectories interacting with changing climatic conditions. Possible future risk scenarios were simulated using maximum entropy modelling with presence-only data, combining land cover, anthropogenic and climatic variables. We found that important determinants of fire risk in the region are distance to roads, recent deforestation and density of human settlements. Severely dry conditions alone increased the area of high fire risk by 69%, affecting all categories of land use and land cover. Interactions between extreme dry conditions and rapid frontier expansion further increased fire risk, resulting in potential biomass loss of 2.44±0.8 Tg in high risk area, about 1.8 times higher than the estimates for the 2010 drought. These interactions showed particularly high fire risk in land used for 'extensive cattle ranching', 'agro-silvopastoral use' and 'intensive cattle ranching and agriculture'. These findings have serious implications for subsistence activities and the economy in the Chiquitania, which greatly depend on the forestry, agriculture and livestock sectors. Results are particularly concerning if considering the current development policies promoting frontier expansion. Departmental protected areas inhibited wildfires when strategically established in areas of high risk, even under drought conditions. However, further research is needed to assess their effectiveness accounting for more specific contextual factors. This novel and simple modelling approach can inform fire and land management decisions in the Chiquitania and other tropical forest landscapes to better anticipate and manage large wildfires in the future.
RESUMEN Guadua paniculata Munro es un bambú adaptado al fuego que predomina en grandes regiones del bosque seco Chiquitano en el oriente de Bolivia. En este artículo presento datos de ocho sitios (" guapasales " con 35 a 100 % cobertura de Guadua) ubicados en distintas regiones de la Chiquitania con los siguientes objetivos: 1) investigar la interacción entre la presencia de Guadua, los incendios forestales y los árboles, y proveer una descripción de la vegetación asociada a Guadua; y 2) estimar la producción de forraje de Guadua y analizar su contenido nutritivo para el ganado. Los guapasales tuvieron baja densidad y área basal de árboles (240 árboles/ha, ≥5cm DAP; 5,8 m 2 /ha) debido a la combinación de frecuentes incendios y la elevada cantidad de combustible fino producido por el bambú mismo. Guadua puede producir hasta 16 Mg/ha de biomasa fina (<25 mm grosor; 8±4 Mg/ha, promedio ± 1DES) que aumenta la intensidad de incendios y la inflamabilidad del bosque. Guadua parece capaz de convertir bosques a guapasales por medio de la inducción del fuego que produce una alta mortalidad de árboles de bosque. Por lo tanto, es importante incluir Guadua en más estudios de conservación y manejo en esta región propensa a los incendios. Las hojas de Guadua sirven para la ganadería pero falta estudiar cómo manejar el forraje producido por esta gramínea para que sea más accesible para el ganado. No obstante, en este estudio demuestro que Guadua produce hasta 4,7 Mg/ha de forraje de buena calidad (10,5% contenido de proteína) y sugiero que Guadua puede ser utilizada como un forraje nativo en una región que está experimentando altas tasas de deforestación por el establecimiento de extensos pastizales de especies exóticas de pastos.
ABSTRACT Guadua paniculata Munro is a fire adapted bamboo that dominates large regions of the Chiquitano dry forest in eastern Bolivia. In this study I present data from eight sites (bamboo stands with 35-100 % Guadua cover) located across the Chiquitania region in order: 1) to investigate the interaction between Guadua, fire, and trees, and to provide a description of the vegetation associated with these bamboo stands; and 2) to estimate Guadua forage production and analyze its nutrient content. Guadua stands had both low densities of trees and low tree basal area (240 trees/ha, ≥5cm DBH; 5.8 m 2 /ha) due to a combination of frequent fires and fine fuel loads created by the bamboo itself. Guadua is able to produce up to 16 Mg/ha of fine and small biomass (<25mm; 8 ±4 Mg/ha, mean±1SD) that increases flammability and fire intensity. Guadua appears able to convert tree dominated forests to bamboo stands by contributing to fire-induced tree mortality. As such, it will be important to include Guadua in more studies of the conservation and management in this fire susceptible region. The leaves of Guadua serve as cattle forage but more research is needed to determine how to make the forage produced by this grass available for animal production. Nonetheless, I demonstrate that Guadua produces up to 4.7 Mg/ha of high quality forage (10.5% protein content) and suggest that Guadua could be utilized as a native forage species in a region that is experiencing high deforestation rates due to the cultivation of exotic pasture grasses.
Background: The dry transitional forests of the southern Amazonia have received little attention from a carbon cycling and ecosystem function perspective, yet they represent ecosystems that may be impacted by global climate change in the future. Aims: To compare the full carbon cycle for two 1-ha forest plots that straddle the ecotone between humid forest and dry forest in Amazonia, ca. 100 km from Santa Cruz, Bolivia. Methods: 2.5 years of measurements of the components of net primary production (NPP) and autotrophic respiration were collected. Results: Total NPP was 15.5 ± 0.89 Mg C ha−1 year−1 at the humid site and 11.27 ± 0.68 Mg C ha−1 year−1 at the dry site; a total Gross Primary Production (GPP) of 34.14 ± 2.92 Mg C ha−1 year−1 and 26.88 ± 2.70 Mg C ha−1 year−1 at the two sites. Carbon use efficiency for both sites was higher than reported for other Amazonian forests (0.45 ± 0.05 and 0.42 ± 0.05). Conclusions: Drier soil conditions selected for the dry deciduous tree species which had higher leaf photosynthesis and total GPP. NPP allocation patterns were similar at the two sites, suggesting that in terms of carbon allocation, the dry forests of the southern Amazonia behave as a scaled-down version of wetter humid forests.
Forest structure and dynamics vary across the Amazon Basin in an east-west gradient coincident with variations in soil fertility and geology. This has resulted in the hypothesis that soil fertility may play an important role in explaining Basin-wide variations in forest biomass, growth and stem turnover rates. Soil samples were collected in a total of 59 different forest plots across the Amazon Basin and analysed for exchangeable cations, carbon, nitrogen and pH, with several phosphorus fractions of likely different plant availability also quantified. Physical properties were additionally examined and an index of soil physical quality developed. Bivariate relationships of soil and climatic properties with above-ground wood productivity, stand-level tree turnover rates, above-ground wood biomass and wood density were first examined with multivariate regression models then applied. Both forms of analysis were undertaken with and without considerations regarding the underlying spatial structure of the dataset. Despite the presence of autocorrelated spatial structures complicating many analyses, forest structure and dynamics were found to be strongly and quantitatively related to edaphic as well as climatic conditions. Basin-wide differences in stand-level turnover rates are mostly influenced by soil physical properties with variations in rates of coarse
wood production mostly related to soil phosphorus status. Total soil P was a better predictor of wood production rates than any of the fractionated organic- or inorganic-P pools. This suggests that it is not only the immediately available P forms, but probably the entire soil phosphorus pool that is interacting with forest growth on longer timescales. A role for soil potassium in modulating Amazon forest dynamics through its effects on stand-level wood density was also detected. Taking this into account, otherwise enigmatic variations in stand-level biomass across the Basin were then accounted for through the interacting effects of soil physical and chemical properties with climate. A hypothesis of selfmaintaining forest dynamic feedback mechanisms initiated by edaphic conditions is proposed. It is further suggested that this is a major factor determining endogenous disturbance levels, species composition, and forest productivity across the Amazon Basin.
Significance
Climate change alone is unlikely to drive severe tropical forest degradation in the next few decades, but an alternative process associated with severe weather and forest fires is already operating in southeastern Amazonia. Recent droughts caused greatly elevated fire-induced tree mortality in a fire experiment and widespread regional forest fires that burned 5–12% of southeastern Amazon forests. These results suggest that feedbacks between fires and extreme climatic conditions could increase the likelihood of an Amazon forest “dieback” in the near-term. To secure the integrity of seasonally dry Amazon forests, efforts to end deforestation must be accompanied by initiatives that reduce the accidental spread of land management fires into neighboring forest reserves and effectively suppress forest fires when they start.
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Observations of tropical South American precipitation over the last three decades indicate an increasing rainfall trend to the north and a decreasing trend to the south. Given that tropical South America has experienced significant land use change over the same period, it is of interest to assess the extent to which changing land use may have contributed to the precipitation trends. Simulations of the National Center for Atmospheric Research Community Atmosphere Model (NCAR CAM3) analyzed here suggest a non-negligible impact of land use on this precipitation behavior. While forcing the model by imposed historical sea surface temperatures (SSTs) alone produces a plausible north-south precipitation dipole over South America, NCAR CAM substantially underestimates the magnitude of the observed southern decrease in rainfall unless forcing associated with human-induced land use change is included. The impact of land use change on simulated precipitation occurs primarily during the local dry season and in regions of relatively low annual-mean rainfall, as the incidence of very low monthly-mean accumulations (
Short-term responses to stem wounding were measured over a 60-day period on six tree species found in seasonally dry tropical forest in Bolivia. Three types of wounds were inflicted to simulate mechanical bark damage and bark damage caused by low- and high-intensity fires. Extent of wood discoloration associated with wounding varied with wound type and severity, with high-intensity burns associated with the greatest amount of discoloration, low-intensity burns the least, and mechanical wounds intermediate. Two thin-barked species produced a distinct ligno suberised boundary zone in the bark earlier than thicker barked species; however, all species produced a distinct wound periderm by 60 days postwounding. The amount of wood discoloration associated with wounding appeared to be independent of the thickness of the lignosuberized boundary zone. Bark thickness provided a useful measure of species' resistance to wood discoloration with low-intensity burns but not with high-intensity burns where bark occasionally separated from the cambium or developed cracks and fissures. Variability in short-term responses to wounding and other factors may result in differences in the composition and abundance of microorganisms that colonize the wounds, with implications for reductions in wood quality and decay development.
Severe wildfires devastated the southeastern Bolivian lowlands during 1999–2001. In response, the Bolivian government instituted an education campaign to reduce rural burning. Working with Chiquitano Indians in the southeastern lowlands, we were interested in finding out (1) the level of knowledge of fire behavior and the ecological role of fire in shaping forest and savannah ecosystems, and (2) current attitudes in Lomerio toward fire as a land management tool. We conducted key informant interviews in the Chiquitano territory of Lomerio to document Chiquitano knowledge of and attitudes toward fire practices. Informants expressed knowledge of fire behavior and effects, recognizing the effects of wind, relative humidity, and fuel moisture on fire intensity, and the effects of fire intensity on soil fertility. Informants revealed a complex understanding of the role of fire in maintaining the structure and composition of savannahs and how fire interacts with changing cattle production, climatic, and demographic conditions.
Background: There is no generally agreed classification scheme for the many different vegetation formation types occurring in the tropics. This hinders cross-continental comparisons and causes confusion as words such as ‘forest’ and ‘savanna’ have different meanings to different people. Tropical vegetation formations are therefore usually imprecisely and/or ambiguously defined in modelling, remote sensing and ecological studies.
Aims: To integrate observed variations in tropical vegetation structure and floristic composition into a single classification scheme.
Methods: Using structural and floristic measurements made on three continents, discrete tropical vegetation groupings were defined on the basis of overstorey and understorey structure and species compositions by using clustering techniques.
Results: Twelve structural groupings were identified based on height and canopy cover of the dominant upper stratum and the extent of lower-strata woody shrub cover and grass cover. Structural classifications did not, however, always agree with those based on floristic composition, especially for plots located in the forest–savanna transition zone. This duality is incorporated into a new tropical vegetation classification scheme.
Conclusions: Both floristics and stand structure are important criteria for the meaningful delineation of tropical vegetation formations, especially in the forest/savanna transition zone. A new tropical vegetation classification scheme incorporating this information has been developed.
Keywords: canopy cover, cluster analysis forest, savanna, tropics, vegetation categorisation
This review suggests that the ecology and patchy global distribution of seasonally dry tropical forest (SDTF) has distinctively structured the evolutionary history and biogeography of woody plant groups that are confined to it. SDTFs have few widespread woody plant species causing high β-diversity between separate areas of forests. These separate areas contain geologically old, monophyletic clades of endemic plant species that often have geographically structured intraspecific genetic variation. These patterns of diversity, endemism, and phylogeny indicate a stable, dispersal-limited SDTF system. SDTF species tend to belong to larger clades confined to this vegetation, exemplifying phylogenetic niche conservatism, and we argue that this is evidence that the SDTF is a metacommunity (biome) for woody plant clades. That phylogenetic, population genetic, biogeographic, and community ecological patterns differ in woody plants from tropical rain forests and savannas suggests a hypothesis that broad ecological s...
Recent Amazonian droughts have drawn attention to the vulnerability of tropical forests to climate perturbations. Satellite and in situ observations have shown an increase in fire occurrence during drought years and tree mortality following severe droughts, but to date there has been no assessment of long-term impacts of these droughts across landscapes in Amazonia. Here, we use satellite microwave observations of rainfall and canopy backscatter to show that more than 70 million hectares of forest in western Amazonia experienced a strong water deficit during the dry season of 2005 and a closely corresponding decline in canopy structure and moisture. Remarkably, and despite the gradual recovery in total rainfall in subsequent years, the decrease in canopy backscatter persisted until the next major drought, in 2010. The decline in backscatter is attributed to changes in structure and water content associated with the forest upper canopy. The persistence of low backscatter supports the slow recovery (>4 y) of forest canopy structure after the severe drought in 2005. The result suggests that the occurrence of droughts in Amazonia at 5-10 y frequency may lead to persistent alteration of the forest canopy.
Tree characteristics were recorded from 2829 standing trees in 24 0.25-ha terra
firme forest plots in central Amazonia, 3 y after a surface fire had swept through the study area. Sixteen of the plots were within forest that burnt for the first time at the end of the 1997-98 El Niño (ENSO) event, and the remaining eight plots were within unburnt primary forest. In order to investigate the morphological correlates of tree mortality, we measured tree diameter at breast height (dbh) and bark thickness, and recorded burn height, bark roughness and the presence of latex, resin and buttress roots. Leaf litter depth was also recorded at the base of all trees in the unburnt forest. Using logistic regression models, tree mortality was best explained by the burn height, although dbh and the presence of buttresses were also important. Buttressed trees were associated with deeper leaf litter accumulation at their bases and higher char heights than trees without buttresses. Moreover, trees surviving the fire had significantly thicker bark than living trees in unburnt forest plots, indicating that thin-barked trees are more prone to selective mortality induced by heat stress. Latex did not appear to have had any significant effects on mortality, though resins were less abundant amongst the live trees in the burnt forest than in the unburnt controls. Levels of fire-mediated tree mortality in this study are compared with those in other Amazonian forest regions in light of historical factors affecting tree resistance to fires.
En este estudio se presentan la cuantificación de superficies afectadas por incendios y quemas que permitan evaluar daños, la localización de sitios de mayor presión e identificar patrones de conversión del bosque a través de teledetección. Para construir las trayectorias de quemas históricas en Bolivia se utilizó el producto de áreas quemadas MCD45A1 del sensor MODIS (Moderate Resolution Imaging Spectroradiometer) con una resolución de 500 m para una serie de once años (2000-2010). La validación de este análisis se realizó aplicando el cociente normalizado de quemas (NBR) a imágenes Landsat TM con una resolución de 30 m, permitiendo clasificar las cicatrices de quema. Se seleccionaron las regiones de la Amazonía y la Chiquitanía para estimar la exactitud en la detección. El monitoreo de áreas quemadas en Bolivia para la serie de once años mostró que se quemaron 22.012.910 hectáreas en total, de las cuales el 20% (4.287.512 ha) corresponden a incendios forestales y la mayor parte de las superficies de quemas en pastos y sabanas, superando enormemente las estimaciones realizadas antes de este estudio. Históricamente los mayores incendios forestales sucedieron en 2007 y 2010, abarcando superficies de 3.691.815 ha y 4.343.156 ha, respectivamente. La exactitud global en la detección fue del 81%, y en cuanto a la exactitud de la magnitud de las áreas quemadas está entre 63% para la Chiquitanía y 57% para la Amazonía.
Surface fires in Amazonian forests could contribute as much as 5% of annual carbon emissions from all anthropogenic sources during severe El Niño years. However, these estimates are based on short-term figures of post-burn tree mortality, when large thicker barked trees (representing a disproportionate amount of the forest biomass) appear to resist the fires. On the basis of a longer term study, we report that the mortality of large trees increased markedly between 1 and 3 years, more than doubling current estimates of biomass loss and committed carbon emissions from low-intensity fires in tropical forests.
Water availability is the main determinant of species’ distribution in lowland tropical forests. Species’ occurrence along water availability gradients depends on their ability to tolerate drought.
To identify species’ traits underlying drought‐tolerance we excavated first year seedlings of 62 dry and moist forest tree species at the onset of the dry season. We evaluate how morphological seedling traits differ between forests, and whether functional groups of species can be identified based on trait relations. We also compare seedling traits along independent axes of drought and shade‐tolerance to assess a hypothesized trade‐off.
Seedlings of dry forest species improve water foraging capacity in deep soil layers by an increased below‐ground biomass allocation and by having deep roots. They minimize the risk of cavitation by making dense stems, and reduce transpiration by producing less leaf tissue. Moist forest seedlings have large leaf areas and a greater above‐ground biomass, to maximize light interception, and long, cheap, branched root systems, to increase water and nutrient capture.
Associations among seedling traits reveal three major drought strategies: (i) evergreen drought‐tolerant species have high biomass investment in enduring organs, minimize cavitation and minimize transpiration to persist under dry conditions; (ii) drought‐avoiding species maximize resource capture during a limited growing season and then avoid stress with a deciduous leaf habit in the dry season; (iii) drought‐intolerant species maximize both below‐ and above‐ground resource capture to increase competitiveness for light, but are consequently precluded from dry habitats.
We found no direct trade‐off between drought‐ and shade‐tolerance, because they depend largely on different morphological adaptations. Drought‐tolerance is supported by a high biomass investment to the root system, whereas shade‐tolerance is mainly promoted by a low growth rate and low SLA.
Synthesis . We conclude that there are three general adaptation strategies of drought‐tolerance, which seemingly hold true across biomes and for different life forms. Drought‐ and shade‐tolerance are largely independent from one another, suggesting a high potential for niche differentiation, as species’ specialization can occur at different combinations of water and light availability.
Detrended correspondence analysis (DCA) is an improvement upon the reciprocal averaging (RA) ordination technique. RA has two main faults: the second axis is often an arch or horseshoe distortion of the first axis, and distances in the ordination space do not have a consistent meaning in terms of compositional change (in particular, distances at the ends of the first RA axis are compressed relative to the middle). DCA corrects these two faults. Tests with simulated and field data show DCA superior to RA and to nonmetric multidimensional sealing in giving clear, interpretable results. DCA has several advantages. (a) Its performance is the best of the ordination techniques tested, and both species and sample ordinations are produced simultaneously. (b) The axes are scaled in standard deviation units with a definite meaning, (c) As implemented in a FORTRAN program called DECORANA, computing time rises only linearly with the amount of data analyzed, and only positive entries in the data matrix are stored in memory, so very large data sets present no difficulty. However, DCA has limitations, making it best to remove extreme outliers and discontinuities prior to analysis. DCA consistently gives the most interpretable ordination results, but as always the interpretation of results remains a matter of ecological insight and is improved by field experience and by integration of supplementary environmental data for the vegetation sample sites.
When the goal of natural forest management is to maintain the biodiversity and ecological integrity of the forest while harvesting timber, the silvicultural systems employed must promote timber production and reduce negative impacts on non-timber resources. To foster development of such a system in a seasonally dry tropical forest in Lomerı́o, Bolivia, we classified tree species according to their relative timber value, importance as food for vertebrate frugivores, and vulnerability to population declines when subjected to logging. We used this classification to identify a management system appropriate for the commercial species and to evaluate the compatibility of the system with the regeneration requirements of tree species that produce important food for mammalian wildlife. About half of the tree species in the site are commercially valuable for their timber and a similar proportion are considered of value as food for wildlife. A tree species rating for vulnerability to disturbance appeared to be independent of both timber and wildlife values. A silvicultural system that includes even-aged groups of trees within an uneven-aged matrix appears more suitable to the multiple goals of management in this forest than either an even-aged or uneven-aged (single tree selection) management system.
Logging is an integral component of most conceptual models that relate human land-use and climate change to tropical deforestation via positive-feedbacks involving fire. Given that grass invasions can substantially alter fire regimes, we studied grass distributions in a tropical dry forest 1–5 yr after selective logging, and experimentally tested the effect of forest fire on populations of invasive grasses. In unlogged forests and in microhabitats created by selective logging we found a total of four alien and 16 native grass species. Grasses covered 2% of unlogged and 4% of logged forest, with grass cover in logged forest concentrated in areas directly disturbed by logging; log landings and roads had relatively greater grass cover (37% and 17%, respectively) than did skid trails (10%) and felling gaps (8%). Total grass cover and grass species richness increased with canopy openness and were greatest in sites most severely disturbed by logging. The grass flora of these disturbed areas was composed mostly of native ruderal species (e.g., Digitaria insularis, Leptochloa virgata), a native bamboo (Guadua paniculata), and Urochloa (Panicum) maxima, a caespitose C4 pasture grass introduced from Africa. Urochloa maxima formed monodominant stands (up to 91% cover and 2–3 m tall) and grew on 69% of log landings and 38% of roads. To better understand the potentially synergistic effects of logging and fire on the early stages of grass invasion, we tested the effect of a 12-ha experimental fire on U. maxima populations in a selectively logged forest. Three years after the fire, the area covered by alien grass in burned forest increased fourfold from 400 m2 (pre-fire) to 1660 m2; over the same period in a logged but unburned (control) area, U. maxima cover decreased from 398 m2 to 276 m2. Increased canopy openness due to fire-induced tree mortality corresponded with the greater magnitude of grass invasion following fire. Selective logging of this dry forest on the southern edge of the Amazon Basin promotes alien grass invasion; when coupled with fire, the rate of invasion substantially increased. Recognition of the grass-promoting potential of selective logging is important for understanding the possible fates of tropical forests in fire-prone regions.
We examined the effect of disturbances of varying intensity on the dominant modes of regeneration among woody plants in tropical dry forest in lowland Bolivia. Seed survival and density, mortality, height, crown area, and basal diameters of seedlings and sprouts were compared among four treatments of varying disturbance intensity (high-intensity burn, low-intensity burn, plant removal, and harvesting gap) over a period of 18 months following treatments. High- and low-intensity burns reduced densities of viable seed by an average of 94 and 50%, respectively. Tree seedlings were more abundant than tree sprouts in all treatments. There were few differences in seedling density among treatments. Sprouts were most common in the plant removal and low-intensity burn treatments than in harvesting gap and high-intensity burn treatments. Seedling mortality was higher than sprout mortality during the first year following treatments. Sprouts were taller, had more stems per individual, larger crown areas, and larger basal diameters than seedlings. Origin of sprout differed among treatments. Eighteen months following treatments, 85% of individuals >2.5 m tall were sprouts. Most seedlings >2.5 m tall after 18 months had established in high-intensity burn treatments. Sprouting individuals dominated regeneration after all treatments, however, in high-intensity burn treatments, sprouts were relatively less dominant due to smaller sprouts and larger seedlings after high-intensity burns.
Agricultural expansion and climate variability have become important agents of disturbance in the Amazon basin. Recent studies have demonstrated considerable resilience of Amazonian forests to moderate annual drought, but they also show that interactions between deforestation, fire and drought potentially lead to losses of carbon storage and changes in regional precipitation patterns and river discharge. Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles, there are some signs of a transition to a disturbance-dominated regime. These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin.
The incidence and importance of fire in the Amazon have increased substantially during the past decade, but the effects of
this disturbance force are still poorly understood. The forest fire dynamics in two regions of the eastern Amazon were studied.
Accidental fires have affected nearly 50 percent of the remaining forests and have caused more deforestation than has intentional
clearing in recent years. Forest fires create positive feedbacks in future fire susceptibility, fuel loading, and fire intensity.
Unless current land use and fire use practices are changed, fire has the potential to transform large areas of tropical forest
into scrub or savanna.
"Measuring Biological Diversity assumes no specialist mathematical knowledge and includes worked examples and links to web-based software. It will be essential reading for all students, researchers, and managers who need to measure biological diversity."--BOOK JACKET.
An exhaustive floristic inventory was conducted in a 400-ha block of tropical semideciduous forest in the Chiquitanía region of Santa Cruz, Bolivia. A total of 501 species were collected using both quantitative and traditional plant collecting methods. Trees represented the most diverse life form (124 spp), followed by herbs (101 spp), lianas (85), shrubs (66), herbaceous climbers epiphytes (15) and parasites (two). Floristic diversity was greatest for the forest floor community, when compared to either the understorey or canopy tree communities. Quantitative data were obtained for 336 species in 100 plots which contained a series of nested subplots to sample smaller-stature plants. Stem density for trees (dbh[greater-than-or-equal]5 cm) was 914 trees ha[minus sign]1, with a total density for all life forms estimated to be 135,000 plants ha[minus sign]1; the total basal area for the forest was estimated to be 27.6 m2 ha[minus sign]1. Species richness when measured by standard methods was found to be one of the highest for a dry forest region reported for the Neotropics with a mean of 70.8 spp 0.1 ha[minus sign]1 (dbh [greater-than-or-equal] 2.5 cm) and 50 spp ha[minus sign]1 (dbh [greater-than-or-equal] 10 cm). Comparison of life forms and vertical strata showed that the flora on the forest floor was more diverse than all other vertical strata combined. Habitat heterogeneity was studied using ordination procedures based on floristic data and to identify the characteristic species of three plant communities: granite outcrops, valley forest and upland forest. The most abundant tree species in the study area were Acosmium cardenasii, Neea hermaphrodita, Aspidosperma tomentosa and Galipea trifoliata, while the species with the greatest basal area were Anadenanthera colubrina, Acosmium cardenasii, Caesalpinia floribunda, Aspidosperma tomentosa, Piptadenia viridiflora, Chorisia speciosa, Tabebuia impetiginosa, Centrolobium microchaete, and Machaerium scleroxylon. Most canopy and understorey tree species had a population structure characterized by numerous juveniles and relatively few large trees, while emergent species tended to have a size-class distribution with relatively few juvenile individuals. Lianas and canopy trees were predominantly anemochorous, while understorey trees and shrubs were predominantly zoochorous; herbaceous species were largely autochorous, with only fern species relying on wind dispersal (sporochory). A comparison of structural attributes with other dry forest areas in the Neotropics, demonstrates the heterogeneous nature of vegetation types that are commonly assigned to this ecosystem. The Chiquitano dry forest shares many floristic elements with the semideciduous forests of the Andean piedmont of northwestern Argentina, the Misiones region of eastern Paraguay and northeastern Argentina, as well as the Caatinga region of northeastern Brazil.
The growing prevalence of fragmentation and fire in tropical forests makes it imperative to quant fy changes in these disturbances and to understand the ways in which they interact across the landscape. I used a multitemporal series of Landsat images to study the incidence and coincidence of fire and fragmentation in two areas of Para state in the eastern Brazilian Amazon,, Tailandia and Paragominase. In both areas, deforestation and forest fires were quantified for time series of 6-10years. The Tailandia study area typifies a landscape with The herringbone pattern of government-settled colonists, and the Paragominas area is dominated by large cattle ranches. In both areas, over 90% of the forests affected by fire were associated with form est edges. Although most burned forest occurred within 500 m of forest edges, some fires occurred in deep forest, several kilometers from any edge. The obvious synergism between forest fragmentation and fire poses serious risks to tropical ecosystems and has important implications for land management.
The effects of fire on forest structure and composition were studied in a severely fire-impacted landscape in the eastern Amazon. Extensive sampling of area forests was used to compare structure and compositional differences between burned and unburned forest stands. Burned forests were extremely heterogeneous, with substantial variation in forest structure and fire damage recorded over distances of <50 m. Unburned forest patches occurred within burned areas, but accounted for only six percent of the sample area. Canopy cover, living biomass, and living adult stem densities decreased with increasing fire intensity/frequency, and were as low as 10-30 percent of unburned forest values. Even light burns removed >70 percent of the sapling and vine populations. Pioneer abundance increased dramatically with burn intensity, with pioneers dominating the understory in severely damaged areas. Species richness was inversely related to burn severity, but no clear pattern of species selection was observed. Fire appears to be a cyclical event in the study region: <30 percent of the burned forest sample had been subjected to only one burn. Based on estimated solar radiation intensities, burning substantially increases fire susceptibility of forests. At least 50 percent of the total area of all burned forests is predicted to become flammable within 16 rainless days, as opposed to only 4 percent of the unburned forest. In heavily burned forest subjected to recurrent fires, 95 percent of the area is predicted to become flammable in <9 rain-free days. As a recurrent disturbance phenomenon, fire shows unparalleled potential to impoverish and alter the forests of the eastern Amazon.
This work compares the effects of neoliberal and post-neoliberal land-use policies on forest cover along the Corredor Bioceánico of southeastern Bolivia to determine if rates of agriculturally driven forest clearance have changed since the Morales’ administration came to office in 2005. Satellite image analysis, supported by semi-structured interviews with farmers and representatives of key institutions, shows that deforestation for commercial agriculture in Santa Cruz continues and has increased in certain “hotspots”. Previous research has shown that the environmental effects of neoliberalism on forest cover are varied, but more broadly, reduced state intervention has meant less environmental regulation and greater deforestation, while strong government is better able to curtail deforestation. Although neoliberal policies triggered an unprecedented level of forest clearing in Bolivia, rates have generally continued to increase and can be indirectly linked to the administration's new agrarian reform and pro-environmental regulations. This trend is counterintuitive and stems from unanticipated responses such as deforestation through fire to prove productive use under the reform's socio-economic function requirements. Given increased regulation and enforcement of forest clearing and burning under Morales, in contrast to the neoliberal era, our analyses suggest that rates will continue to increase under the current political climate, which has further polarized the opposition in Santa Cruz.
Anthropogenic understory fires have affected large areas of tropical forest in recent decades, particularly during severe droughts. Yet, the mechanisms that control fire-induced mortality of tropical trees and lianas remain ambiguous due to the challenges associated with documenting mortality given variation in fire behavior and forest heterogeneity. In a seasonally dry Amazon forest, we conducted a burn experiment to quantify how increasing understory fires alter patterns of stem mortality. From 2004 to 2007, tree and liana mortality was measured in adjacent 50-ha plots that were intact (B0 – control), burned once (B1), and burned annually for 3 years (B3). After 3 years, cumulative tree and liana mortality (≥1 cm dbh) in the B1 (5.8% yr−1) and B3 (7.0% yr−1) plots significantly exceeded mortality in the control (3.2% yr−1). However, these fire-induced mortality rates are substantially lower than those reported from more humid Amazonian forests. Small stems were highly vulnerable to fire-induced death, contrasting with drought-induced mortality (measured in other studies) that increases with tree size. For example, one low-intensity burn killed >50% of stems <10 cm within a year. Independent of stem size, species-specific mortality rates varied substantially from 0% to 17% yr−1 in the control, 0% to 26% yr−1 in B1, and 1% to 23% yr−1 in B3, with several species displaying high variation in their vulnerability to fire-induced mortality. Protium guianense (Burseraceae) exhibited the highest fire-induced mortality rates in B1 and B3, which were 10- and 9-fold greater than the baseline rate. In contrast, Aspidosperma excelsum (Apocynaceae), appeared relatively unaffected by fire (0.3% to 1.0% mortality yr−1 across plots), which may be explained by fenestration that protects the inner concave trunk portions from fire. For stems ≥10 cm, both char height (approximating fire intensity) and number of successive burns were significant predictors of fire-induced mortality, whereas only the number of consecutive annual burns was a strong predictor for stems <10 cm. Three years after the initial burn, 62 ± 26 Mg ha−1 (s.e.) of live biomass, predominantly stems <30 cm, was transferred to the dead biomass pool, compared with 8 ± 3 Mg ha−1 in the control. This biomass loss from fire represents ∼30% of this forest's aboveground live biomass (192 (±3) Mg ha−1; >1 cm DBH). Although forest transition to savanna has been predicted based on future climate scenarios, our results indicate that wildfires from agricultural expansion pose a more immediate threat to the current carbon stocks in Amazonian forests.Research highlights▶ After single and repeat burns, tree and liana mortality was double baseline rates. ▶ Small stems were highly vulnerable to fire-induced death. ▶ Four common species had fire-induced mortality rates quadruple the control. ▶ A third of the aboveground biomass was killed by a single fire. ▶ Wildfires pose an immediate threat to carbon stocks of Amazonian forests.
As forest fragmentation and intentional burning of grasslands increase, the frequency of fires penetrating the dry and subhumid tropical forests of Bolivia is also likely to increase. To expand our understanding of the role of fire in tropical dry forest, the physical and thermal properties of barks of tree species were studied to determine their relative resistances to cambial damage by fire. For 16 tree species found in the dry forest of the Lomerío region of eastern Bolivia, bark thickness, moisture content, and specific gravity were measured. Insulating capabilities of bark were measured by obtaining cambial and surface temperatures during experimental wick fires. Bark thickness on trees 5-100 cm dbh (diameter at 1.4 m) ranged from 2–51 mm and both thick- and thin-barked species were represented. For all species, bark thickness increased as stem diameter increased. Bark thickness explained more (63%) of the variation in peak cambial temperatures during fires than did bark moisture content (4%) or specific gravity (1%). A threshold bark thickness of 18 mm was associated with the ability to withstand lethal cambial temperatures during the experimental, low intensity fires. For 13 of the 16 species included in this study, trees ≤20 cm dbh have bark thickness below the threshold 18 mm and, therefore, are likely to experience cambial injury from low intensity fires. Our results suggest that the forest presently characteristic of the Lomerío region did not develop with frequent fires and that species composition is likely to be substantially affected by an increase in fire frequency.
There is increasing consensus that the global climate will continue to warm over the next century. The biodiversity-rich Amazon forest is a region of growing concern because many global climate model (GCM) scenarios of climate change forecast reduced precipitation and, in some cases, coupled vegetation models predict dieback of the forest. To date, fires have generally been spatially co-located with road networks and associated human land use because almost all fires in this region are anthropogenic in origin. Climate change, if severe enough, could alter this situation, potentially changing the fire regime to one of increased fire frequency and severity for vast portions of the Amazon forest. High moisture contents and dense canopies have historically made Amazonian forests extremely resistant to fire spread. Climate will affect the fire situation in the Amazon directly, through changes in temperature and precipitation, and indirectly, through climate-forced changes in vegetation composition and structure. The frequency of drought will be a prime determinant of both how often forest fires occur and how extensive they become. Fire risk management needs to take into account landscape configuration, land cover types and forest disturbance history as well as climate and weather. Maintaining large blocks of unsettled forest is critical for managing landscape level fire in the Amazon. The Amazon has resisted previous climate changes and should adapt to future climates as well if landscapes can be managed to maintain natural fire regimes in the majority of forest remnants.
The effects of fire on forest structure and composition were studied in a severely fire‐impacted landscape in the eastern Amazon. Extensive sampling of area forests was used to compare structure and compositional differences between burned and unburned forest stands.
Burned forests were extremely heterogeneous, with substantial variation in forest structure and fire damage recorded over distances of <50 m. Unburned forest patches occurred within burned areas, but accounted for only six percent of the sample area. Canopy cover, living biomass, and living adult stem densities decreased with increasing fire inrensiry / frequency, and were as low as 10–30 percent of unburned forest values. Even light burns removed >70 percent of the sapling and vine populations. Pioneer abundance increased dramatically with burn intensity, with pioneers dominating the understory in severely damaged areas. Species richness was inversely related to burn severity, but no clear pattern of species selection was observed.
Fire appears to be a cyclical event in the study region: <30 percent of the burned forest sample had been subjected to only one burn. Based on estimated solar radiation intensities, burning substantially increases fire susceptibility of forests. At least 50 percent of the total area of all burned forests is predicted to become flammable within 16 rainless days, as opposed to only 4 percent of the unburned forest. In heavily burned forest subjected to recurrent fires, 95 percent of the area is predicted to become flammable in <9 rain‐free days. As a recurrent disturbance phenomenon, fire shows unparalleled potential to impoverish and alter the forests of the eastern Amazon.
Anthropogenic understory fires affect large areas of tropical forest, particularly during severe droughts. Yet, the mechanisms that control tropical forests' susceptibility to fire remain ambiguous. We tested the widely accepted hypothesis that Amazon forest fires increase susceptibility to further burning by conducting a 150 ha fire experiment in a closed-canopy forest near the southeastern Amazon forest–savanna boundary. Forest flammability and its possible determinants were measured in adjacent 50 ha forest plots that were burned annually for 3 consecutive years (B3), once (B1), and not at all (B0). Contrary to expectation, an annual burning regime led to a decline in forest flammability during the third burn. Microclimate conditions were more favorable compared with the first burn (i.e. vapor pressure deficit increased and litter moisture decreased), yet flame heights declined and burned area halved. A slight decline in fine fuels after the second burn appears to have limited fire spread and intensity. Supporting this conclusion, fire spread rates doubled and burned area increased fivefold in B3 subplots that received fine fuel additions. Slow replacement of surface fine fuels in this forest may be explained by (i) low leaf litter production (4.3 Mg ha−1 yr−1), half that of other Amazon forests; and (ii) low fire-induced tree and liana mortality (5.5±0.5% yr−1, SE, in B3), the lowest measured in closed-canopy Amazonian forests. In this transitional forest, where severe seasonal drought removed moisture constraints on fire propagation, a lack of fine fuels inhibited the intensity and spread of recurrent fire in a negative feedback. This reduction in flammability, however, may be short-lived if delayed tree mortality or treefall increases surface fuels in future years. This study highlights that understanding fuel input rate and timing relative to fire frequency is fundamental to predicting transitional forest flammability – which has important implications for carbon emissions and potential replacement by scrub vegetation.
Lianas contribute to many aspects of tropical forest diversity and dynamics, and interest in liana ecology has grown substantially in recent years. Methods to census lianas and estimate biomass, however, differ among studies, possibly hindering attempts to compare liana communities. At Nouragues Research Station (French Guiana), we tested the extent to which liana abundance, basal area, and estimated biomass differed depending on stem diameter measurement location, inclusion of ramets, inclusion of lianas rooted within versus passing through the plot, and plot shape. We found that the mean per plot abundance and basal area of lianas were significantly greater when lianas were measured low on the stem, when ramets were included, and when lianas were sampled in transects (2 × 50 m) than in square plots (10 × 10 m). Mean per plot liana abundance and basal area were 21 percent and 58 percent greater, when stems were measured at the largest spot on the stem compared to 130 cm from the ground, respectively. Including liana ramets increased average per plot liana abundance, basal area, and estimated biomass by 19, 17, and 16 percent, respectively. To facilitate cross-study comparisons, we developed conversion equations that equate liana abundance, diameter, and basal area based on the measurements taken at four different stem locations. We tested these equations at Lambir Hills National Park, Malaysia and found that they did not differ significantly between the two sites, suggesting that the equations may be broadly applicable. Finally, we present a new allometric equation relating diameter and biomass developed from 424 lianas from five independent data sets collected in four countries.
In 1994, 1×106 ha of subhumid forest in eastern Bolivia burned in an uncontrolled wildfire; the objective of this study was to measure tree and liana mortality a year after this fire. About 60% of 500 trees sampled were either killed or damaged by the fire. Proportionally more small trees (74% of trees >2 m tall but <5 cm dbh) were killed than large trees (27% of 10–40 cm, 16% of trees ≥40 cm dbh), and mortality varied with species. Basal cambial damage was found on 30–40% of living trees ≥10 cm dbh. About 75% of liana stems (1–8 cm dbh) were killed; 15% of the dead liana stems resprouted from the base. In lianas, basal resprouting of killed stems was independent of diameter class, whereas in trees smaller stems were more likely to resprout than larger stems. The proliferation of herbaceous vines plus lianas <1 cm dbh (mean density 21 000 ha-1) in the burned forest may impede tree regeneration and supply fine fuels capable of supporting frequent fires. Although anthropogenic and natural fires have probably played important roles in the development of tropical subhumid forests, the amount of damage and mortality observed in this study suggest that, in forests managed for timber production, fire-protection practices are warranted to reduce forest susceptibility to wildfire.
Amazonian forests play a key role in the global carbon cycle, but there is much uncertainty about the quantity and distribution of carbon stored in these forests. We quantified total aboveground dry biomass (TAGB) in undisturbed central Amazonian rainforests, based on detailed estimates of all live and dead plant material within 20 1 ha plots spanning an extensive (ca. 1000 km2) study area. TAGB values in our study area were very high, averaging . The most important component of aboveground biomass was large (≥10 cm diameter-at-breast-height (DBH)) trees, which comprised 81.9% of TAGB, followed by downed wood debris (7.0%), small trees, saplings, and seedlings (<10 cm DBH; 5.3%), lianas (2.1%), litter (1.9%), snags (1.5%), and stemless palms (0.3%). Among large trees, aboveground biomass was greatest in intermediate-sized (20–50 cm DBH) stems (46.7% of TAGB), with very large (≥60 cm DBH) trees also containing substantial biomass (13.4% of TAGB). There were no significant correlations between large tree biomass and that of any other live or dead biomass component. An analysis based on the variability of our samples suggested that just 3–4 randomly positioned 1 ha plots would be sufficient to provide a reasonable estimate of mean TAGB in a landscape such as ours (with 95% confidence intervals being <10% of the mean). This suggests that efforts to quantify Amazon forest biomass should be extensive rather than intensive; researchers should sample many geographically separate areas with a few plots each, rather than sampling a small number of areas more intensively.
Fire poses the greatest threat to the forests of Amazônia. The magnitude of this threat is amplified by three positive feedback loops that drive the expansion of forest fire in the region: (1) Fire promotes drought, and therefore more fire, by releasing smoke into the atmosphere, thus reducing rainfall. Fire-assisted conversion of forests to pastures may also promote drought by increasing albedo and decreasing water vapor flux to the atmosphere, further inhibiting rainfall. (2) Fire increases the susceptibility of forests to recurrent burning by killing trees, thereby allowing sunlight to penetrate the forest interior, and increasing the fuel load on the forest floor. (3) Finally, fires also self-perpetuate by burning agricultural and forestry systems, discouraging landholders from making those fire-sensitive investments in their land that would allow them to move beyond their dependence upon fire as a management tool.
Several characteristics of successional species and communities typical of the lowland, humid tropics are compared with those of drier and colder tropical environments. Suggested trends of successional species characteristics along a gradient from benevolent to harsh tropical environments include: fewer but more specialized taxa; more striking ecological equivalence between biogeographic regions; increased vegetative reproduction; less palatable leaves; denser wood; and decreased importance of chlorophyllous stems. Hypothesized trends of the communities along this same gradient include: slower regrowth; increased resilience (drier sites only); fewer seral stages; and patchier distribution of leaf area. As tropical soils are degraded through misuse, there is a tendency for ruderal vegetation from drier (or colder) environments to invade degraded landscapes in wetter (or warmer) areas. Regrowth and resilience of high-elevation tropical forests are so slow that these communities may never reestablish after clearing.