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Soil moisture is a crucial variable mediating soil‐vegetation‐atmosphere water exchange. As climate and land use change, the increased frequency and intensity of extreme weather events and disturbances will likely alter feedbacks between ecosystem functions and soil moisture. In this study, we evaluated how extreme drought (2015/2016) and postfire vegetation regrowth affected the seasonality of soil water content (0–8 m depth) in a transitional forest in southeastern Amazonia. The experiment included three treatment plots: an unburned Control, an area burned every three years (B3yr), and an area burned annually (B1yr) between 2004 and 2010. We hypothesized that (a) soil moisture at B1yr and B3yr would be higher than the Control in the first years postfire due to lower transpiration rates, but differences between burned plots would decrease as postfire vegetation regrew; (b) during drought years, the soil water deficit in the dry season would be significantly greater in all plots as plants responded to greater evaporative demand; and (c) postfire recovery in the burned plots would cause an increase in evapotranspiration over time, especially in the topsoil. Contrary to the first expectation, the burned plots had lower volumetric water content than the Control plot. However, we found that droughts significantly reduced soil moisture in all plots compared to non‐drought years (15.6%), and this effect was amplified in the burned plots (19%). Our results indicate that, while compounding disturbances such as wildfires and extreme droughts alter forest dynamics, deep soil moisture is an essential water source for vegetation recovery. Plain Language Summary: As extreme droughts and wildfires have become more common in southeastern Amazonia, they could alter soil moisture availability, but the intensity of these compounding effects still needs to be understood. This study investigates the impact of the extreme drought of 2015/2016, postfire vegetation recovery, the return of water to the atmosphere, and their interacting effects on water distribution across the soil profile in three treatment plots: an unburned Control, an area burned every three years, and an area burned annually from 2004 to 2010. Contrary to expectations, we found that soil moisture in the burned plots decreased in the years following the last experimental fire (2010), even as the vegetation recovered. Drought events significantly reduced soil moisture across all plots, but this effect was amplified in the burned plots. As land use changes increase and climate change intensifies, such drought‐induced soil drying may become more common, exacerbating the impacts of wildfires on ecosystem resilience and forest health across much of the region. Key Points: During the driest months of the year, burned forests showed significant reductions in soil moisture compared with unburned forestsThe drought event of 2015/2016 caused greater reductions in soil moisture in the burned forest than in the unburned forestBoth burned and unburned forests increased water use throughout the 8‐m soil column from 2011 to 2018 [ABSTRACT FROM AUTHOR]

Understanding how savanna soil properties influence vegetation diversity and function is a major challenge in ecological studies. We investigated the effects of soil properties on woody species density, richness, composition, and vegetative phenology (inferred by the Normalized Difference Vegetation Index (NDVI)) in two alluvial and two interfluvial savanna sites (1 block of 10 plots of 20 × 50 m in each site), in the Brazilian Cerrado. We showed that plots in alluvial savannas present less fertile soils and have lower plant densities and species richness and higher seasonality of NDVI than plots in the interfluvial savannas. The species composition of the sites was associated with the P, Fe, K, and Mn content of the soil. Soil K, Fe, and Ca contents were the main variables associated with plant density in a linear mixed model (LMM) that explained 79% of data variability (r2c = 0.79%), and K, Fe, and Al were the main predictors to explain species richness (r2c = 0.81%). Soil K, pH, and Silt were the best predictors of the seasonality in NDVI (r2c = 0.14%). We highlight the all‐encompassing effect of K soil content on species density, richness, composition, and NDVI and argue that this macronutrient and a few other soil properties (e.g., P, Fe, Al, and Silt) are the main factors mediating plant responses to water and nutrient stress in woody savanna communities occurring in the Cerrado–Amazônia transition. [ABSTRACT FROM AUTHOR]

Forest disturbances associated with edge effects, wildfires, and windthrow events have impacted large swaths of the tropics. Defining the levels of forest disturbance that cause ecologically relevant reductions in fruit and seed (FS) production is key to understanding forest resilience to current and future global changes. Here, we tested the hypotheses that: (1) low‐intensity experimental fires alone would cause minor changes in FS production and diversity in a tropical forest, whereas synergistic disturbance effects resulting from edge effects, wildfires, droughts, and blowdowns would drive long‐term reductions in FS diversity and production; and (2) the functional composition of FS in disturbed forests would shift toward tree species with acquisitive strategies. To test these hypotheses, we quantified FS production between 2005 and 2018 in a large‐scale fire experiment in southeast Amazonia. The experimental treatments consisted of three 50‐ha plots: a Control plot, a plot burned annually (B1yr) and a plot burned every three years (B3yr) between 2004 and 2010. These plots were impacted by edge effects, two droughts (2007 and 2010), and a blowdown event in 2012. Our results show that FS production remained relatively high following low‐intensity fires, but declined where fires were most severe (i.e., forest edge of B3yr). The number of species‐producing FS declined sharply when fires co‐occurred with droughts and a windthrow event, and species composition shifted throughout the experiment. Along the edge of both burned plots, the forest community became dominated by species with faster relative growth, thinner leaves, thinner bark, and lower height. We conclude that compounding disturbances changed FS patterns, with a strong effect on species composition and potentially large effects on the next generation of trees. This is largely due to reductions in the diversity of species‐producing FS where fires are severe, causing a shift toward functional traits typically associated with pioneer and generalist species. [ABSTRACT FROM AUTHOR]

Trees balance temporal asynchrony in carbon source and sink activity by accumulating and using non‐structural carbon (NSC). Previous work has demonstrated differences in the amount and distribution of NSC stored in stemwood in tropical tree species and related these patterns in NSC distribution to tree growth and mortality rates. However, we still do not know how changes in the amount and location of starch, a major component of NSC in stemwood, influence the seasonal carbon dynamics of mature trees and how this may reflect storage‐growth trade‐offs.In this work, we hypothesized that combining two life history traits, here leaf habit (evergreen/semi‐deciduous) and the anatomical distribution of starch within the stemwood (parenchyma storage and fibre storage), would allow us to explain differences in the seasonal interplay between carbon sources and sinks and the use and accumulation of starch in the tree stem. We expected semi‐deciduous/fibre‐storing species to have greater seasonal amplitudes of carbon source and sink activity, and therefore greater variation in starch content and stronger storage‐growth trade‐offs than evergreen/parenchyma‐storing species.We measured monthly increments in stem radial growth, soluble sugars and starch every 3 months during 2019 in Dacryodes microcarpa (semi‐deciduous/fibre‐storing species), Ocotea leucoxylon (evergreen/parenchyma‐storing species) and Sacoglottis guianensis (semi‐deciduous/parenchyma‐storing species).We found seasonal changes in starch but not sugars in the semi‐deciduous species, with greater amplitude in the fibre‐storing species that also had greater storage capacity and stem respiration rates. The fibre‐storing species further showed a negative relationship between starch consumption/accumulation and growth during the rainy season, suggesting a trade‐off between growth and storage, with starch accumulating in some cases when growth was low.Synthesis. Our results show the influence of seasonal starch storage on carbon dynamics in three species of tropical trees that differ in leaf phenology and starch storage traits. Semi‐deciduous/fibre‐storing species have greater temporal variation in carbon sink activities and more seasonally dynamic starch content. Since the fibre‐storing species we studied are slower‐growing and longer‐lived trees with lower mortality rates compared to the parenchyma‐storing species, these results may provide clues about how storage traits could influence their survival and life span. [ABSTRACT FROM AUTHOR]

Fire–vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation have yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in herbaceous vegetation abundance for burned versus unburned plots. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C4 grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the vegetation structure of savannas and forests. [ABSTRACT FROM AUTHOR]

Copyright of Global Change Biology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By favouring long-distance dispersal, anemochory is often associated with open and patchy habitats, whereas zoochory enables short-distance dispersal and prevails in closed and extensive habitats. Brazilian savanna (Cerrado) on shallow rocky soils (RS) have open vegetation and are patchily distributed, whereas savanna on deep soils (DS) have dense vegetation and occur in large stands. Thus, we predicted that zoochory would be favoured in DS and anemochory would characterise RS. We tested the hypothesis that vegetation structure and distribution patchiness are related to the characteristic dispersal mechanisms associated with closed and open habitats. We compared the abundance of dispersal mechanisms between DS and RS with generalised linear mixed models and used an indicator species analysis to identify species associated with each vegetation type. There was no difference between DS and RS in the number of species associated with one or the other dispersal mechanism. We found fewer-than-expected zoochorous individuals and more-than-expected anemochorous individuals in RS, and more zoochorous indicator species in DS. Habitat patchiness and openness are related to the composition of dispersal mechanisms. Open vegetation on shallow rocky soils favours long-distance dispersal relative to zoochory. This implies reduced plant establishment and increased leaflessness, being harsher on animal dispersers. Protected areas are often concentrated in RS, whereas DS are rapidly converted into croplands due to their excellent aptitude for mechanised agriculture. Conserving DS and RS requires a balanced complementary approach, that ensures that all landscape elements are adequately represented in protected areas. [ABSTRACT FROM AUTHOR]

Resprouting is an efficient life history strategy by which woody savanna species can recover their aboveground biomass after fire. However, resprouting dynamics after fire and the time it takes to start producing flowers and fruits are still poorly understood, especially for the Brazilian savanna (Cerrado biome), where fire is an important driver of vegetation structure and ecosystem functioning. We investigated the resprouting dynamics and production of flowers and fruits of 26 woody species (20 tree and 6 shrub species for a total of 485 individuals) that were burned and the production of flowers and fruits for a subset of 12 species (139 individuals) in an unburned area in a Brazilian savanna. We classified the species' resprouting strategies as hypogeal (at the soil level, with main stem death), epigeal (on the main stem or crown), and hypogeal + epigeal. We used generalized linear mixed-effect models to identify the post-fire recovery patterns for five years. Individuals with basal resprouts (hypogeal and hypogeal + epigeal resprouting) produced an average of 6 basal resprouts, but only 33% of resprouts survived after five years. Individuals in burned areas produced fewer flowers and fruits than individuals in unburned areas. At least a subset of individuals in all the resprouting strategies started to produce flowers and fruits in the first-year post-fire. About 68% of the species with hypogeal resprouts produced flowers and fruits in the first-year post-fire, but the intensity of flowering and fruiting was lower compared to individuals with other resprouting strategies over time. Although woody species have invested in post-fire growth and sexual reproduction in all resprouting strategies, the long time needed to recover these processes can make these species more vulnerable to frequent fires. [Display omitted] • Top-killed stems produced an average of 6 basal sprouts, but only 33% survived in five years. • Resprout growth was slower after the second burn that occurred eight years later. • Resprouts started producing flowers and fruits in the first year post-fire. • Plants in burned areas produced fewer flowers and fruits than plants in unburned areas. [ABSTRACT FROM AUTHOR]

Understanding the role of environmental conditions and geographic space on species distributions is a major goal of ecological studies. Here, we investigate the effects of soil properties, a native bamboo (Actinocladum verticillatum (Nees) McClure ex Soderstr) ground cover and geographic distance on species richness and turnover in the Brazilian Cerrado. We established three transects along a forest–savanna gradient (14°41′S and 52°20′W), from the lowland next to a stream to the top of a hill, where we sampled the woody plant community (DBH ≥ 3 cm), soil properties and ground cover of A. verticillatum. We evaluated changes in species composition with a principal coordinates analysis, and the effects of the environmental predictors on species richness using generalised linear models and on species turnover using generalised dissimilarity modelling. We found that species richness increases with K concentration in the soil and decreases with Zn concentration in the soil and bamboo cover. The predictors explained 62% of species turnover, with environmental parameters (soil properties, bamboo cover and altitude) having the most significant contribution (80%), followed by the spatially structured environmental variation (20%). The most important environmental predictors of woody species turnover were soil concentration of Zn, P and K, altitude, and bamboo cover. Changes in species richness and composition in the studied gradient were strongly associated with plot height, bamboo cover and soil content of K, Zn and P. Our findings indicate that nutrient availability and competition with bamboo explain vegetation structure and composition in this region. [ABSTRACT FROM AUTHOR]

Summary: Non‐structural carbon (NSC) storage (i.e. starch, soluble sugras and lipids) in tree stems play important roles in metabolism and growth. Their spatial distribution in wood may explain species‐specific differences in carbon storage dynamics, growth and survival. However, quantitative information on the spatial distribution of starch and lipids in wood is sparse due to methodological limitations.Here we assessed differences in wood NSC and lipid storage between tropical tree species with different growth and mortality rates and contrasting functional types. We measured starch and soluble sugars in wood cores up to 4 cm deep into the stem using standard chemical quantification methods and histological slices stained with Lugol's iodine. We also detected neutral lipids using histological slices stained with Oil‐Red‐O.The histological method allowed us to group individuals into two categories according to their starch storage strategy: fiber‐storing trees and parenchyma‐storing trees. The first group had a bigger starch pool, slower growth and lower mortality rates than the second group. Lipid storage was found in wood parenchyma in five species and was related to low mortality rates.The quantification of the spatial distribution of starch and lipids in wood improves our understanding of NSC dynamics in trees and reveals additional dimensions of tree growth and survival strategies. [ABSTRACT FROM AUTHOR]

Aims Different plant functional groups display diverging responses to the same environmental gradients. Here, we assess the effects of environmental and spatial predictors on species turnover of three functional groups of Brazilian savannas (Cerrado) plants—trees, palms and lianas—across the transition zone between the Cerrado and Amazon biomes in central Brazil. Methods We used edaphic, climatic and plant composition data from nine one-hectare plots to assess the effects of the environment and space on species turnover using a Redundancy Analysis and Generalized Dissimilarity Modeling (GDM), associated with variance partitioning. Important Findings We recorded 167 tree species, 5 palms and 4 liana species. Environmental variation was most important in explaining species turnover, relative to geographic distance, but the best predictors differed between functional groups: geographic distance and silt for lianas; silt for palms; geographic distance, temperature and elevation for trees. Geographic distances alone exerted little influence over species turnover for the three functional groups. The pure environmental variation explained most of the liana and palm turnover, while tree turnover was largely explained by the shared spatial and environmental contribution. The effects of geographic distance upon species turnover leveled off at about 300 km for trees, and 200 km for lianas, whereas they were unimportant for palm species turnover. Our results indicate that environmental factors that determine floristic composition and species turnover differ substantially between plant functional groups in savannas. Therefore, we recommend that studies that aim to investigate the role of environmental conditions in determining plant species turnover should examine plant functional groups separately. [ABSTRACT FROM AUTHOR]

Drought, fire, and windstorms can interact to degrade tropical forests and the ecosystem services they provide, but how these forests recover after catastrophic disturbance events remains relatively unknown. Here, we analyze multi‐year measurements of vegetation dynamics and function (fluxes of CO2 and H2O) in forests recovering from 7 years of controlled burns, followed by wind disturbance. Located in southeast Amazonia, the experimental forest consists of three 50‐ha plots burned annually, triennially, or not at all from 2004 to 2010. During the subsequent 6‐year recovery period, postfire tree survivorship and biomass sharply declined, with aboveground C stocks decreasing by 70%–94% along forest edges (0–200 m into the forest) and 36%–40% in the forest interior. Vegetation regrowth in the forest understory triggered partial canopy closure (70%–80%) from 2010 to 2015. The composition and spatial distribution of grasses invading degraded forest evolved rapidly, likely because of the delayed mortality. Four years after the experimental fires ended (2014), the burned plots assimilated 36% less carbon than the Control, but net CO2 exchange and evapotranspiration (ET) had fully recovered 7 years after the experimental fires ended (2017). Carbon uptake recovery occurred largely in response to increased light‐use efficiency and reduced postfire respiration, whereas increased water use associated with postfire growth of new recruits and remaining trees explained the recovery in ET. Although the effects of interacting disturbances (e.g., fires, forest fragmentation, and blowdown events) on mortality and biomass persist over many years, the rapid recovery of carbon and water fluxes can help stabilize local climate. [ABSTRACT FROM AUTHOR]

To understand changes in land surface energy balance partitioning due to tropical deforestation, we use a physically based analytical formulation of the surface energy balance. Turbulent heat fluxes are constrained by the thermodynamic maximum power limit and a formulation for diurnal heat redistribution within the land‐atmosphere system. The derived turbulent fluxes of sensible and latent heat compare very well to in situ observations for sites with intact rainforest and soybean land cover in southeastern Amazonia. The equilibrium partitioning into sensible and latent heat flux compares well with observations for both sites, except for the soybean site during the dry season where water limitation needs to be explicitly accounted for. Our results show that tropical deforestation primarily affects the absorption of solar radiation and the water limitation of evapotranspiration, but not the overall magnitude of turbulent heat fluxes that is set by the thermodynamic maximum power limit. Plain Language Summary: Tropical deforestation impacts the local energy and water exchange between land surface and atmosphere, typically resulting in regionally warmer and drier climates. General circulation models still disagree in reproducing these changes and little has been done to derive them from first principles. Here, we present an alternative approach to describe the effects of tropical land conversion from forest to soy agriculture, based on a physical theory of land‐atmosphere interactions. We view land‐atmosphere exchange as the result of a heat engine strongly shaped by turbulent heat exchange. This provides a framework to derive analytical expressions of the turbulent fluxes from the limit by how much work this engine can maximally perform. By comparing these with observations from a tropical rainforest and a soybean field in Amazonia, we find that the diurnal variations of turbulent fluxes are very well estimated. This means that turbulent land‐atmosphere exchange is primarily constrained by the thermodynamic limit, irrespective of surface roughness and evapotranspiration, and suggests that one can estimate the primary impacts of tropical land use change from physical principles. Thus, using thermodynamic limits represents an alternative approach to investigate the highly complex nature of land‐atmosphere interactions and global change from first principles. Key Points: Diurnal variations of turbulent heat fluxes are well estimated by the maximum power limit for sites with contrasting land cover in AmazoniaLand cover affected primarily the absorption of solar radiation and the partitioning of turbulent fluxes into sensible and latent heatThermodynamic theory is well suited as a parsimonious approach to describe first‐order controls of land‐atmosphere interactions [ABSTRACT FROM AUTHOR]

Water quality in streams is determined by several factors, including geology, topography, climate, and anthropogenic changes. This study aimed to assess the effects of watershed physical, morphology, and precipitation seasonality on the water quality of two streams that supply drinking water to rural settlements and urban areas in the Cerrado-Amazonia transition region. We monitored 16 physico-chemical attributes of water at six different sample locations over three years (2013–2016). Our results indicate that eight of these physico-chemical attributes did not meet the standards for safe drinking water established by Brazilian legislation. Precipitation seasonality, degradation of riparian zones, stream length, and watershed slope were the most important predictors of impaired water quality. Our results highlight the importance of restoring and conserving riparian forests in order to maintain drinking water quality. [ABSTRACT FROM AUTHOR]

Widespread degradation of tropical forests is caused by a variety of disturbances that interact in ways that are not well understood.To explore potential synergies between edge effects, fire and windstorm damage as causes of Amazonian forest degradation, we quantified vegetation responses to a 30‐min, high‐intensity windstorm that in 2012, swept through a large‐scale fire experiment that borders an agricultural field. Our pre‐ and postwindstorm measurements include tree mortality rates and modes of death, above‐ground biomass, and airborne LiDAR‐based estimates of tree heights and canopy disturbance (i.e., number and size of gaps). The experimental area in the southeastern Amazonia includes three 50‐ha plots established in 2004 that were unburned (Control), burned annually (B1yr), or burned at 3‐year intervals (B3yr).The windstorm caused greater damage to trees (>10 cm DBH) in the burned plots (B1yr: 13 ± 9% of 785 trees; B3yr: 17 ± 13% of 433) than in the Control plot (8 ± 4% of 2,300; ± CI). It substantially reduced vegetation height by 14% in B1yr, 20% in B3yr and 12% in the Control plots, while it reduced above‐ground biomass by 18% of 77.7 Mg/ha (B1yr), 31% of 56.6 (B3yr), and 15% of 120 (Control). Tree damage was greatest near the agricultural field edge in all three plots, especially among large trees and in B3yr. Trunk snapping (70%) and uprooting (20%) were the most common modes of tree damage and mortality, with the height of trunk failure on the burned plots often corresponding with the height of historical fire scars. Of the windstorm‐damaged trees, 80% (B1yr), 90% (B3yr), and 57% (Control) were dead 4 years later. Trees that had crown damage experienced the least mortality (22%–60%), followed by those that were snapped (55%–94%) and uprooted (88%–94%).Synthesis. We demonstrate the synergistic effects of three kinds of disturbances on a tropical forest. Our results show that the effects of windstorms are exacerbated by prior degradation by fire and fragmentation. We highlight that understorey fires can produce long‐lasting effects on tropical forests not only by directly killing trees but also by increasing tree vulnerability to wind damage due to fire scars and a more open canopy. Our study shows that the effects of windstorms are exacerbated by prior degradation by fire and fragmentation. Understorey fires can produce long‐lasting effects on tropical forests not only by directly killing trees but also by increasing tree vulnerability to wind damage due to fire scars and a more open canopy. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Understanding the relationship between photosynthesis, net primary productivity and growth in forest ecosystems is key to understanding how these ecosystems will respond to global anthropogenic change, yet the linkages among these components are rarely explored in detail. We provide the first comprehensive description of the productivity, respiration and carbon allocation of contrasting lowland Amazonian forests spanning gradients in seasonal water deficit and soil fertility. Using the largest data set assembled to date, ten sites in three countries all studied with a standardized methodology, we find that (i) gross primary productivity ( GPP) has a simple relationship with seasonal water deficit, but that (ii) site-to-site variations in GPP have little power in explaining site-to-site spatial variations in net primary productivity ( NPP) or growth because of concomitant changes in carbon use efficiency ( CUE), and conversely, the woody growth rate of a tropical forest is a very poor proxy for its productivity. Moreover, (iii) spatial patterns of biomass are much more driven by patterns of residence times (i.e. tree mortality rates) than by spatial variation in productivity or tree growth. Current theory and models of tropical forest carbon cycling under projected scenarios of global atmospheric change can benefit from advancing beyond a focus on GPP. By improving our understanding of poorly understood processes such as CUE, NPP allocation and biomass turnover times, we can provide more complete and mechanistic approaches to linking climate and tropical forest carbon cycling. [ABSTRACT FROM AUTHOR]

Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes. Based on results of a large-scale, long-term experiment with annual and triennial burn regimes (B1yr and B3yr, respectively) in the Amazon, we found abrupt increases in fire-induced tree mortality (226 and 462%) during a severe drought event, when fuel loads and air temperatures were substantially higher and relative humidity was lower than long-term averages. This threshold mortality response had a cascading effect, causing sharp declines in canopy cover (23 and 31%) and aboveground live biomass (12 and 30%) and favoring widespread invasion by flammable grasses across the forest edge area (80 and 63%), where fires were most intense (e.g., 220 and 820 kW·m-1). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with <1% in nondrought years. These results show that a few extreme drought events, coupled with forest fragmentation and anthropogenic ignition sources, are already causing widespread fire-induced tree mortality and forest degradation across southeastern Amazon forests. Future projections of vegetation responses to climate change across drier portions of the Amazon require more than simulation of global climate forcing alone and must also include interactions of extreme weather events, fire, and land-use change. [ABSTRACT FROM AUTHOR]

Background:The impact of fire on carbon cycling in tropical forests is potentially large, but remains poorly quantified, particularly in the locality of the transition forests that mark the boundaries between humid forests and savannas. Aims:To present the first comprehensive description of the impact of repeated low intensity, understorey fire on carbon cycling in a semi-deciduous, seasonally dry tropical forest on infertile soil in south-eastern Amazonia. Methods:We compared an annually burnt forest plot with a control plot over a three-year period (2009–2011). For each plot we quantified the components of net primary productivity (NPP), autotrophic (Ra) and heterotrophic respiration (Rh), and estimated total plant carbon expenditure (PCE, the sum of NPP andRa) and carbon-use efficiency (CUE, the quotient of NPP/PCE). Results:Total NPP andRawere 15 and 4% lower on the burnt plot than on the control, respectively. Both plots were characterised by a slightly higher CUE of 0.36–0.39, compared to evergreen lowland Amazon forests. Conclusions:These measurements provide the first evidence of a distinctive pattern of carbon cycling within this transitional forest. Overall, regular understorey fire is shown to have little impact on ecosystem-level carbon fluxes. [ABSTRACT FROM PUBLISHER]

éLetter to the Editor [ABSTRACT FROM AUTHOR]

The use of propagules collected in ecotonal regions for restoration purposes is challenging because of the mix of species from different vegetation types and reproductive phenological variability. We used a database of the Xingu Seed Network in Brazil, which contains data on 139 native tree species for 8 years (2011–2018) in the Cerrado–Amazonia transition zone, to answer three questions: (1) What is the spatio‐temporal variability in the seed dispersal of tree species, and how does it relate to the species' preferential habitat? (2) Is there a relationship between the seed dispersal period and climate variables? (3) Is the frequency of tree species with different dispersal syndromes equally distributed among biomes and seed‐size classes? Independent of their preferred ecosystem (Amazonia or Cerrado), some species showed substantial spatio asynchrony in fruit dispersal, extending the dispersal period at a regional scale. The seed dispersal period was strongly correlated (rs > 0.6) with precipitation and minimum or maximum air temperature in 41% (n = 57) of the studied species. We showed that three‐quarters of the species (n = 105) dispersed seeds in the late dry and early rainy periods, with little variation among dispersal syndromes. Our findings will enhance the effectiveness of restoration initiatives by increasing the accuracy of predictions of the location and time for collecting seeds in the extensive Cerrado–Amazonia transition zone. [ABSTRACT FROM AUTHOR]

Riparian forests play key roles in protecting biodiversity and water resources, making them priorities for conservation in human-dominated landscapes, but fragmentation associated with expanding tropical croplands threatens their ecological integrity. We compared the structure of tropical riparian forests within intact and cropland catchments in a region of intensive soybean production in the southeastern Brazilian Amazon. We studied forest plots (varying from 120 to 210 m long) that bisected riparian zone forests and headwater streams in ten catchments. Four plots were within large areas of intact primary forest and six were in bands of protected riparian forest along streams within croplands as required by the Brazilian Forest Code. We found that riparian forests in croplands harbored fewer species of trees and seedlings/saplings, and had higher proportions of opportunistic, pioneer tree species. We also found greater variation in tree species composition, and higher internal dissimilarity in croplands compared with forests. The observed patterns in tree species composition were driven mainly by differences between riparian forest-cropland edges and those bordering intact upland forests. Forests nearest to streams in cropland and forested catchments were more similar to one another. Results suggest that wider buffers are needed at the edges of croplands to maintain riparian forest structure. The minimum 30-m riparian buffers now required by the Brazilian Forest Code may thus be insufficient to prevent long-term shifts in riparian forest species composition and structure. Unlabelled Image • Riparian forests are fundamental for the maintenance of biodiversity and water resources in agricultural landscapes. • Forest loss and degradation in southern Amazonian exposes riparian forests to edge effects. • Riparian forest tree species diversity vulnerable to edge effects in cropland catchments • Riparian forests surrounded by agricultural cultivation areas undergo changes in the composition of tree species. • The preservation and conservation of riparian forests is fundamental for future generations. [ABSTRACT FROM AUTHOR]

• Fire behaviour and carbon emissions differ between Cerrado vegetation types. • The importance of fire behaviour drivers does not vary between vegetation types. • The VPD is the main driver of fire behaviour in all vegetation types. • Carbon emissions increase with the amount of fine fuel load. An understanding of fire behaviour and its impacts on natural ecosystems is essential for developing management strategies, specifically for planning prescribed fires. It is well known that vegetation and microclimate factors are important predictors of fire behaviour. However, the relative importance of these factors and how fire behaviour responds to changes in these factors are still understood, especially in the Brazilian Cerrado, which has strong seasonality and high vegetation heterogeneity. Here, we compiled literature data from 65 experimental fire plots in three vegetation types in the Cerrado biome—grasslands, savannas, and forests—corresponding to a gradient of increasing of woody cover. First, we evaluated how aspects of fire behaviour (fire spread rate, fire intensity, and heat released) and of fire-associated emissions (fine fuel consumption, combustion factor, and carbon emissions associated with fine fuel consumption) vary according to vegetation type. Subsequently, we evaluated the relative importance of vegetation (represented by woody cover and fine fuel load) and microclimatic factors (represented by vapour pressure deficit [VPD] and wind speed) in determining the fire behaviour and fire-associated emissions. Using generalised linear models, we evaluated the simultaneous influences of vegetation and microclimate variables (only for independent and non-collinear variables) on fire behaviour and fire-associated emissions. We found that aspects of fire behaviour and fire-associated emissions differed among the vegetation types: compared to forests, grasslands and savannas showed higher fire spread rates and fire intensities, consumed more fine fuel biomass, had larger combustion factors, released more heat, and emitted more carbon. The results show that the vegetation type, VPD and fine fuel load are key metrics for explain fire behaviour and fire-associated emissions in the Cerrado. The VPD was found to be the primary driver of the fire spread rate and fire intensity for all vegetation types and fine fuel load was the primary driver of heat released, fine fuel consumption, combustion factor, and carbon emissions in all vegetation types. [ABSTRACT FROM AUTHOR]

• First study applying terrestrial laser scanning in the Brazilian savanna. • TLS effectively estimated aboveground biomass at plot-scales in sparser savannas. • In dense and tall forests, vegetation structure was less adequately characterized. • TLS accurately captured the structural differences between vegetation formations. • Results present a step forward in applying TLS for biomass estimation in savannas. Understanding structural variations in natural systems can help us understand their responses to disturbance and environmental changes and plan for the mitigation of human-induced impacts. Terrestrial laser scanning (TLS) is a technological solution to quickly and accurately capture and model vegetation structure. In the Brazilian Cerrado biome, characterized by highly heterogeneous plant formations and marked seasonality, TLS may help improve aboveground biomass (AGB) estimates. This study aimed to use single-scan TLS-derived metrics to predict plot-scale aboveground biomass for three vegetation types with high structural diversity and biomass content (woodland savanna, forested savanna, and gallery forest). Ten plots were scanned in each vegetation type, and variables related to point density at different strata and height distribution were extracted from the point cloud to predict AGB measured in local field inventories. The woodland savanna provided good fit models with only two metrics (rainy season: proportion of points below 1.37 m and height of the 99th percentile; adj-R2 = 0.92, RMSE (root mean square error) = 2.67 Mg/ha or 12%; and dry season: height of the 20th and the 99th percentiles; adj-R2 = 0.88, RMSE = 3.32 Mg/ha or 15%). The model for the forested savanna had relatively less explanatory power with one influential predictor (forested savanna: height of the 20th percentile; adj-R2 = 0.58, RMSE = 6.85 Mg/ha or 21%). For the gallery forest, however, the canopy structure could not be adequately characterized due to occlusion of laser returns by dense sub-canopy strata. Our study shows the strong potential of the terrestrial LiDAR technology for estimation of plot-based biomass across diverse savanna vegetation types, where the sparse tree structure allows for better laser penetration the accurate generation of height profiles. [ABSTRACT FROM AUTHOR]

Droughts can exert a strong influence on the regional energy balance of the Amazon and Cerrado, as can the replacement of native vegetation by croplands. What remains unclear is how these two forcing factors interact and whether land cover changes fundamentally alter the sensitivity of the energy balance components to drought events. To fill this gap, we used remote sensing data to evaluate the impacts of drought on evapotranspiration (ET), land surface temperature (LST), and albedo on cultivated areas, savannas, and forests. Our results (for seasonal drought) indicate that increases in monthly dryness across Mato Grosso state (southern Amazonia and northern Cerrado) drive greater increases in LST and albedo in croplands than in forests. Furthermore, during the 2007 and 2010 droughts, croplands became hotter (0.1–0.8 °C) than savannas (0.3–0.6 °C) and forests (0.2–0.3 °C). However, forest ET was consistently higher than ET in all other land uses. This finding likely indicates that forests can access deeper soil water during droughts. Overall, our findings suggest that forest remnants can play a fundamental role in the mitigation of the negative impacts of extreme drought events, contributing to a higher ET and lower LST. [ABSTRACT FROM AUTHOR]

• Fire-induced mortality is more random for small compared to large trees. • High phylogenetic and functional diversity losses related to fire. • Fire-related declines in tree diversity occurred mostly after high-intensity fires. Although tropical forest fires are naturally rare, they have become more frequent and intense in response to recent changes in land use and climate. This shift in fire regime may drive widespread forest degradation in Amazonia, with important consequences not only for species richness but also for functional and phylogenetic diversity. Here, we test the overall hypothesis that fire-induced tree mortality causes more losses in phylogenetic and functional diversity than in taxonomic diversity, because fire kills trees non-randomly. To test this hypothesis, we established a large-scale, long-term (nine-year) fire experiment in southeast Amazonia in three 50-ha plots, with unburned Control and two different fire regimes (burned annually and burned every three years), between 2004 and 2010. Overall, tree assemblages exposed to experimental fires lost more phylogenetic and functional diversity compared to unburned areas, especially where the experimental fires were more intense (in areas burned every three years). The rate of loss of phylogenetic and functional diversity per species-unit was higher for larger trees than for small ones, which indicates that fire-induced mortality is more random for small trees. Our results indicate that fire acts as a selective pressure, filtering species with similar phylogenetic and functional traits. Given that forest fires are likely to become more common and frequent in the region, it is essential to understand their impact above and beyond taxonomic diversity. [ABSTRACT FROM AUTHOR]

The role of tropical forests in climate is most often expressed in terms of the carbon they keep out of the atmosphere if deforestation is avoided or the carbon they remove from the atmosphere as they grow. The direct role of forests, particularly in the tropics, in maintaining low surface temperatures and relatively high precipitation has been underappreciated. Recent studies in the Brazilian agricultural frontier indicate that tropical deforestation, for pasture and crop production, has led to significant regional climate change in the last 40 years of a scale much larger than that attributed to the carbon released from deforestation. Deforestation reduces net surface radiation and evapotranspiration, thus increasing sensible heat flux and land surface temperature. In Mato Grosso state, the temperature of the forested Xingu Indigenous Park is 3℃ cooler than the surrounding mosaic of pasturelands, croplands, and remaining forest fragments. In the neighboring state of Rondônia, rainfall has significantly decreased and the dry season lengthened as deforestation occurred. Numerical model studies strongly suggest that Brazil’s agricultural frontier will be much warmer and dryer in coming decades as greenhouse gas concentrations increase. Thus, in Brazil, it is becoming clear that, because of their capacity to moderate regional climate, preserving tropical forests will be a key component of mitigating exogenously driven future climate change. [ABSTRACT FROM AUTHOR]

• The Amazon forest is becoming more flammable over time. • Reducing deforestation is key to avoid more common and intense wildfires. • Current increases in deforestation could force Brazil to adopt more extreme measures. The Amazon forest's main protection against fire is its capacity to create a moist understory microclimate. Roads, deforestation, droughts, and climate change have made this natural firebreak less effective. The southern Amazon, in particular, has become more flammable and vulnerable to wildfires during recent droughts. The drought of 1997/98 first showed that fires could escape from agricultural fields and burn standing primary forests that were once considered impenetrable to fire. The spread of forest fires during other 21st-century droughts suggests that this pattern may well be the new normal. With the landscape becoming more flammable, reducing sources of ignition and the negative effects of deforestation is crucial for avoiding severe degradation of Amazon forests. Unfortunately, recent increases in deforestation suggest that Brazil is moving in the opposite direction. Keeping pace with the rapid changes in the region's fire regimes would require innovation; cooperation across political boundaries; and interagency communication on a scale never seen before. While Brazil's past success in reducing deforestation suggests that it could be an effective leader in this regard, its sluggish response to the 2019 fires tells quite a different story. But the fact remains that the future of the Amazon depends on decisive action now. [ABSTRACT FROM AUTHOR]

• We evaluated how tree functional traits vary across two contrasting savannas. • In typical savanna – prevail fertile soils with good water-holding capacity. • In alluvial savanna – sandy soils with a low water-holding capacity are prevalent. • Tree species on alluvial savannas tend to adopt acquisitive strategies while on typical savannas invest in water conservation and fire tolerance. Environmental filters and functional adjustments of species to local conditions are major determinants of plant communities in stressing habitats. We set out to understand the role of different substrates in functional trait variation in wood plants by investigating key functional traits at the community and intraspecific levels in different types of Brazilian savanna: two sites of alluvial savannas (lowland savannas that occur in old alluvial deposits in riverbeds with sandy soils and low water-holding capacity), and two sites of typical savannas (upland savannas that occur in interfluvial zones, far from the influence of rivers, in which clay soils with higher fertility and water-holding capacity predominate). We conducted this study in four sites with savanna vegetation in the northeast region of the Cerrado Biome, nearby the transition with the Amazon. In each site we sampled six functional traits for each tree species: leaf area, leaf thickness, specific leaf area (SLA), stem-specific density, relative bark thickness and maximum plant height. We sampled 101 wood species, ranging from 26 to 62 species within each site. In both community and intraspecific levels, alluvial savanna plants showed higher SLA and specific-stem density, and lower leaf area, leaf thickness, bark thickness, and plant height compared with the typical savanna. We also found that, at a given leaf thickness, species from typical savanna exhibited ∼20% higher SLA. In addition, at a given plant height, typical species showed ∼56% higher bark thickness and ∼20% lower specific-stem density. Our findings suggest that savanna tree species growing on alluvial savannas tend to adopt strategies related to water acquisition while species growing on typical savannas invest in both water conservation strategies and protection against high-intensity fires. We conclude that water deficit and fire, both related to substrate properties, play a key role in determining the woody plant communities functioning in savannas. [ABSTRACT FROM AUTHOR]

The Amazon forest has the highest biodiversity on Earth. However, information on Amazonian vertebrate diversity is still deficient and scattered across the published, peer-reviewed, and gray literature and in unpublished raw data. Camera traps are an effective non-invasive method of surveying vertebrates, applicable to different scales of time and space. In this study, we organized and standardized camera trap records from different Amazon regions to compile the most extensive data set of inventories of mammal, bird, and reptile species ever assembled for the area. The complete data set comprises 154,123 records of 317 species (185 birds, 119 mammals, and 13 reptiles) gathered from surveys from the Amazonian portion of eight countries (Brazil, Bolivia, Colombia, Ecuador, French Guiana, Peru, Suriname, and Venezuela). The most frequently recorded species per taxa were: mammals: Cuniculus paca (11,907 records); birds: Pauxi tuberosa (3713 records); and reptiles: Tupinambis teguixin (716 records). The information detailed in this data paper opens up opportunities for new ecological studies at different spatial and temporal scales, allowing for a more accurate evaluation of the effects of habitat loss, fragmentation, climate change, and other human-mediated defaunation processes in one of the most important and threatened tropical environments in the world. The data set is not copyright restricted; please cite this data paper when using its data in publications and we also request that researchers and educators inform us of how they are using these data., (© 2022 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Drought, fire, and windstorms can interact to degrade tropical forests and the ecosystem services they provide, but how these forests recover after catastrophic disturbance events remains relatively unknown. Here, we analyze multi-year measurements of vegetation dynamics and function (fluxes of CO 2 and H 2 O) in forests recovering from 7 years of controlled burns, followed by wind disturbance. Located in southeast Amazonia, the experimental forest consists of three 50-ha plots burned annually, triennially, or not at all from 2004 to 2010. During the subsequent 6-year recovery period, postfire tree survivorship and biomass sharply declined, with aboveground C stocks decreasing by 70%-94% along forest edges (0-200 m into the forest) and 36%-40% in the forest interior. Vegetation regrowth in the forest understory triggered partial canopy closure (70%-80%) from 2010 to 2015. The composition and spatial distribution of grasses invading degraded forest evolved rapidly, likely because of the delayed mortality. Four years after the experimental fires ended (2014), the burned plots assimilated 36% less carbon than the Control, but net CO 2 exchange and evapotranspiration (ET) had fully recovered 7 years after the experimental fires ended (2017). Carbon uptake recovery occurred largely in response to increased light-use efficiency and reduced postfire respiration, whereas increased water use associated with postfire growth of new recruits and remaining trees explained the recovery in ET. Although the effects of interacting disturbances (e.g., fires, forest fragmentation, and blowdown events) on mortality and biomass persist over many years, the rapid recovery of carbon and water fluxes can help stabilize local climate., (© 2019 John Wiley & Sons Ltd.)

Tropical forests harbor a significant portion of global biodiversity and are a critical component of the climate system. Reducing deforestation and forest degradation contributes to global climate-change mitigation efforts, yet emissions and removals from forest dynamics are still poorly quantified. We reviewed the main challenges to estimate changes in carbon stocks and biodiversity due to degradation and recovery of tropical forests, focusing on three main areas: (1) the combination of field surveys and remote sensing; (2) evaluation of biodiversity and carbon values under a unified strategy; and (3) research efforts needed to understand and quantify forest degradation and recovery. The improvement of models and estimates of changes of forest carbon can foster process-oriented monitoring of forest dynamics, including different variables and using spatially explicit algorithms that account for regional and local differences, such as variation in climate, soil, nutrient content, topography, biodiversity, disturbance history, recovery pathways, and socioeconomic factors. Generating the data for these models requires affordable large-scale remote-sensing tools associated with a robust network of field plots that can generate spatially explicit information on a range of variables through time. By combining ecosystem models, multiscale remote sensing, and networks of field plots, we will be able to evaluate forest degradation and recovery and their interactions with biodiversity and carbon cycling. Improving monitoring strategies will allow a better understanding of the role of forest dynamics in climate-change mitigation, adaptation, and carbon cycle feedbacks, thereby reducing uncertainties in models of the key processes in the carbon cycle, including their impacts on biodiversity, which are fundamental to support forest governance policies, such as Reducing Emissions from Deforestation and Forest Degradation., (© 2015 John Wiley & Sons Ltd.)