Intraspecific trait variability facilitates tree species persistence along riparian forest edges in Southern Amazonia.

Tropical forest fragmentation from agricultural expansion alters the microclimatic conditions of the remaining forests, with effects on vegetation structure and function. However, little is known about how the functional trait variability within and among tree species in fragmented landscapes influence and facilitate species' persistence in these new environmental conditions. Here, we assessed potential changes in tree species' functional traits in riparian forests within six riparian forests in cropland catchments (Cropland) and four riparian forests in forested catchments (Forest) in southern Amazonia. We sampled 12 common functional traits of 123 species across all sites: 64 common to both croplands and forests, 33 restricted to croplands, and 26 restricted to forests. We found that forest-restricted species had leaves that were thinner, larger, and with higher phosphorus (P) content, compared to cropland-restricted ones. Tree species common to both environments showed higher intraspecific variability in functional traits, with leaf thickness and leaf P concentration varying the most. Species turnover contributed more to differences between forest and cropland environments only for the stem-specific density trait. We conclude that the intraspecific variability of functional traits (leaf thickness, leaf P, and specific leaf area) facilitates species persistence in riparian forests occurring within catchments cleared for agricultural expansion in Amazonia.

Herbaceous vegetation responses to experimental fire in savannas and forests depend on biome and climate.

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.

Cerrado deforestation threatens regional climate and water availability for agriculture and ecosystems.

The Brazilian Cerrado is one of the most biodiverse savannas in the world, yet 46% of its original cover has been cleared to make way for crops and pastures. These extensive land-use transitions (LUTs) are expected to influence regional climate by reducing evapotranspiration (ET), increasing land surface temperature (LST), and ultimately reducing precipitation. Here, we quantify the impacts of LUTs on ET and LST in the Cerrado by combining MODIS satellite data with annual land use and land cover maps from 2006 to 2019. We performed regression analyses to quantify the effects of six common LUTs on ET and LST across the entire gradient of Cerrado landscapes. Results indicate that clearing forests for cropland or pasture increased average LST by ~3.5°C and reduced mean annual ET by 44% and 39%, respectively. Transitions from woody savannas to cropland or pasture increased average LST by 1.9°C and reduced mean annual ET by 27% and 21%, respectively. Converting native grasslands to cropland or pasture increased average LST by 0.9 and 0.6°C, respectively. Conversely, grassland-to-pasture transitions increased mean annual ET by 15%. To date, land changes have caused a 10% reduction in water recycled to the atmosphere annually and a 0.9°C increase in average LST across the biome, compared to the historic baseline under native vegetation. Global climate changes from increased atmospheric greenhouse gas concentrations will only exacerbate these effects. Considering potential future scenarios, we found that abandoning deforestation control policies or allowing legal deforestation to continue (at least 28.4 Mha) would further reduce yearly ET (by -9% and -3%, respectively) and increase average LST (by +0.7 and +0.3°C, respectively) by 2050. In contrast, policies encouraging zero deforestation and restoration of the 5.2 Mha of illegally deforested areas would partially offset the warming and drying impacts of land-use change.

O Cerrado brasileiro é uma das savanas mais biodiversas do mundo. Apesar disso, 46% da sua cobertura original foi desmatada para dar lugar a cultivos agrícolas e pastos. Estas extensas transições de uso do solo (LUT) têm o potencial de influenciar o clima regional, reduzindo a evapotranspiração (ET), aumentando a temperatura da superfície terrestre (LST) e por fim reduzindo a precipitação. O objetivo deste estudo foi quantificar os impactos de LUTs sobre ET e LST no Cerrado, combinando dados do satélite MODIS com mapas anuais de uso e cobertura do solo de 2006-2019. Foram realizadas análises de regressão para quantificar os efeitos de seis LUTs usuais sobre ET e LST, ao longo de todo o gradiente de paisagens do Cerrado. Os resultados indicaram que a retirada de florestas para dar lugar à agricultura ou pastagem aumentou a LST média em ~3.5°C e reduziu a ET média anual em 44% e 39%, respectivamente. Transições de formações savânicas para agricultura ou pastagem aumentaram a LST média em 1.9°C e reduziram a ET média anual em 27% e 21%, respectivamente. A conversão de campos nativos para agricultura ou pastagem aumentou a LST média em 0.9 e 0.6°C, respectivamente. Em contrapartida, transições de formações campestres nativas para pastagens aumentaram a ET média anual em 15%. Até o momento, as mudanças de uso do solo causaram redução de 10% da água reciclada para a atmosfera anualmente e aumento de 0.9°C da LST média ao longo do bioma, em comparação com a linha de base histórica sob vegetação nativa. As mudanças climáticas globais decorrentes do aumento das concentrações atmosféricas de gases do efeito estufa irão exacerbar esses efeitos. Considerando potenciais cenários futuros, observou-se que o abandono das políticas de controle do desmatamento ou o avanço do desmatamento legal (ao menos 28.4 Mha) reduziriam a ET anual (em −9% e −3%, respectivamente) e aumentariam a LST média (em +0.7 e +0.3ºC, respectivamente) até 2050. Por outro lado, políticas que promovam desmatamento zero e restauração dos 5.2 Mha de áreas ilegalmente desmatadas compensariam parte dos impactos de aquecimento e seca causados por alterações de uso do solo.

AMAZONIA CAMTRAP: A data set of mammal, bird, and reptile species recorded with camera traps in the Amazon forest.

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.

The Latent Dirichlet Allocation model with covariates (LDAcov): A case study on the effect of fire on species composition in Amazonian forests.

Understanding and predicting the effect of global change phenomena on biodiversity is challenging given that biodiversity data are highly multivariate, containing information from tens to hundreds of species in any given location and time. The Latent Dirichlet Allocation (LDA) model has been recently proposed to decompose biodiversity data into latent communities. While LDA is a very useful exploratory tool and overcomes several limitations of earlier methods, it has limited inferential and predictive skill given that covariates cannot be included in the model. We introduce a modified LDA model (called LDAcov) which allows the incorporation of covariates, enabling inference on the drivers of change of latent communities, spatial interpolation of results, and prediction based on future environmental change scenarios. We show with simulated data that our approach to fitting LDAcov is able to estimate well the number of groups and all model parameters. We illustrate LDAcov using data from two experimental studies on the long-term effects of fire on southeastern Amazonian forests in Brazil. Our results reveal that repeated fires can have a strong impact on plant assemblages, particularly if fuel is allowed to build up between consecutive fires. The effect of fire is exacerbated as distance to the edge of the forest decreases, with small-sized species and species with thin bark being impacted the most. These results highlight the compounding impacts of multiple fire events and fragmentation, a scenario commonly found across the southern edge of Amazon. We believe that LDAcov will be of wide interest to scientists studying the effect of global change phenomena on biodiversity using high-dimensional datasets. Thus, we developed the R package LDAcov to enable the straightforward use of this model.

Starch and lipid storage strategies in tropical trees relate to growth and mortality.

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.

Molybdenum, phosphorus, and pH do not constrain nitrogen fixation in a tropical forest in the southeastern Amazon.

High rates of biological nitrogen fixation (BNF) are commonly reported for tropical forests, but most studies have been conducted in regions that receive substantial inputs of molybdenum (Mo) from atmospheric dust and sea-salt aerosols. Even in these regions, the low availability of Mo can constrain free-living BNF catalyzed by heterotrophic bacteria and archaea. We hypothesized that in regions where atmospheric inputs of Mo are low and soils are highly weathered, such as the southeastern Amazon, Mo would constrain BNF. We also hypothesized that the high soil acidity, characteristic of the Amazon Basin, would further constrain Mo availability and therefore soil BNF. We conducted two field experiments across the wet and dry seasons, adding Mo, phosphorus (P), and lime alone and in combination to the forest floor in the southeastern Amazon. We sampled soils and litter immediately, and then weeks and months after the applications, and measured Mo and P availability through resin extractions and BNF with the acetylene reduction assay. The experimental additions of Mo and P increased their availability and the lime increased soil pH. While the combination of Mo and P increased BNF at some time points, BNF rates did not increase strongly or consistently across the study as a whole, suggesting that Mo, P, and soil pH are not the dominant controls over BNF. In a separate short-term laboratory experiment, BNF did not respond strongly to Mo and P even when labile carbon was added. We postulate that high nitrogen (N) availability in this area of the Amazon, as indicated by the stoichiometry of soils and vegetation and the high nitrate soil stocks, likely suppresses BNF at this site. These patterns may also extend across highly weathered soils with high N availability in other topographically stable regions of the tropics.

Prolonged tropical forest degradation due to compounding disturbances: Implications for CO2 and H2 O fluxes.

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 H2 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 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.

Toward an integrated monitoring framework to assess the effects of tropical forest degradation and recovery on carbon stocks and biodiversity.

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.

Surface fire drives short-term changes in the vegetative phenology of woody species in a Brazilian savanna / A passagem do fogo resulta em mudanças de curto prazo para a fenologia vegetativa de espécies lenhosas em um cerrado stricto sensu

We evaluated the effects of fire on the vegetative phenological behavior (crown foliage cover, sprouting, mature and young leaves) of woody species at two sites in the Brazilian savanna, one of which had been accidentally burned. We used generalized additive mixed models to test the hypothesis that: 1) fire damages total foliage cover, thus leading to changes in vegetative phenological patterns. As this hypothesis was corroborated, we also tested whether 2) the damage caused by fire to the total crown foliage cover and mature leaves is greater in evergreen than in deciduous species, and 3) the negative effects of fire on vegetative phenology persist after the first fire-free year. The first two hypotheses were corroborated, but the third was not. Fire effects on total crown foliage cover and mature leaves were greatest during the first three months following the fire, and were significantly greater in evergreen species. For shoots and young leaves, the greatest differences found between three and seven months post-fire. On the other hand, no differences were observed in phenological events between burned and unburned sites in the second year post-fire, indicating that marked effects of the fire were only observed over a short period. Our results showed immediate negative effects on the vegetative phenophases, but also that these effects are transient, and cannot be discerned after the first fire-free year.

Avaliamos os efeitos do fogo sobre o comportamento fenológico vegetativo (cobertura de copa, brotação, folhas jovens e folhas adultas) de espécies lenhosas em dois sítios de cerrado sensu stricto: um queimado acidentalmente e outro não queimado. Usamos modelos aditivos mistos generalizados para testar a hipótese de que 1) o fogo danifica a cobertura de folhas das copas, o que resulta em alterações nos padrões fenológicos vegetativos das espécies; sendo isso verdadeiro, testamos se 2) os danos causados pelo fogo na cobertura de copa e nas folhas adultas são maiores em espécies sempre verdes do que em espécies decíduas e se 3) os efeitos negativos do fogo sobre a fenologia vegetativa persistem após um ano sem fogo. As duas primeiras hipóteses foram corroboradas, mas a terceira não. Os efeitos do fogo na cobertura de folhagem da copa e nas folhas adultas foram maiores após três meses da ocorrência do fogo e significativamente maiores para espécies sempre verdes. Para brotação e folhas jovens, as maiores diferenças foram entre três e sete meses após a queimada. Por outro lado, não foram percebidas diferenças entre os eventos fenológicos vegetativos dos sítios no segundo ano após a ocorrência do fogo, o que indica que os efeitos do fogo foram expressivos apenas por curto período. Os nossos resultados mostraram que o efeito do fogo sobre os eventos fenológicos vegetativos é negativo e mais intenso logo após a ocorrência da queimada, mas também que estes efeitos são temporários, e não são mais percebidos após o primeiro ano da ocorrência do fogo.

The linkages between photosynthesis, productivity, growth and biomass in lowland Amazonian forests.

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.

Abrupt increases in Amazonian tree mortality due to drought-fire interactions.

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.

Testing the Amazon savannization hypothesis: fire effects on invasion of a neotropical forest by native cerrado and exotic pasture grasses.

Changes in climate and land use that interact synergistically to increase fire frequencies and intensities in tropical regions are predicted to drive forests to new grass-dominated stable states. To reveal the mechanisms for such a transition, we established 50 ha plots in a transitional forest in the southwestern Brazilian Amazon to different fire treatments (unburned, burned annually (B1yr) or at 3-year intervals (B3yr)). Over an 8-year period since the commencement of these treatments, we documented: (i) the annual rate of pasture and native grass invasion in response to increasing fire frequency; (ii) the establishment of Brachiaria decumbens (an African C4 grass) as a function of decreasing canopy cover and (iii) the effects of grass fine fuel on fire intensity. Grasses invaded approximately 200 m from the edge into the interiors of burned plots (B1yr: 4.31 ha; B3yr: 4.96 ha) but invaded less than 10 m into the unburned plot (0.33 ha). The probability of B. decumbens establishment increased with seed availability and decreased with leaf area index. Fine fuel loads along the forest edge were more than three times higher in grass-dominated areas, which resulted in especially intense fires. Our results indicate that synergies between fires and invasive C4 grasses jeopardize the future of tropical forests.

Fenologia de espécies lenhosas em um cerrado típico no Parque Municipal do Bacaba, Nova Xavantina, Mato Grosso, Brasil / Phenology of woody species in a typical cerrado in the Bacaba Municipal Park, Nova Xavantina, Mato Grosso, Brazil

O objetivo desse estudo foi caracterizar os comportamentos fenológicos de 12 espécies lenhosas, que juntas representam 41 por cento do Valor de Importância (VI) de uma comunidade de cerrado típico no Parque Municipal do Bacaba, Nova Xavantina, MT, e relacioná-los à precipitação, temperaturas mínimas, máximas e Déficit de Pressão de Vapor (DPV). As observações fenológicas foram realizadas em intervalos quinzenais, de setembro 2008 a outubro de 2009. Foram estimadas as intensidades de cobertura total da folhagem na copa, brotamento, proporção relativa de folhas novas, adultas e senescentes, floração e frutificação. Baseado nos eventos fenológicos vegetativos, quatro espécies foram categorizadas como sempre-verde com crescimento contínuo (Myrcia lanuginosa O. Berg., Ouratea hexasperma (A. St.-Hil.) Baill., Ouratea spectabilis (Mart. ex Engl.) Engl. e Roupala montana Aubl.), uma como sempre-verde com crescimento sazonal (Byrsonima pachyphylla Kunth), duas como brevidecíduas (Davilla elliptica A. St.-Hil., Eugenia aurata O. Berg.) e cinco como decíduas (Byrsonima coccolobifolia Kunth, Kielmeyera rubriflora Cambess., Qualea grandiflora Mart., Qualea multiflora Mart. e Qualea parviflora Mart.). A floração de todas as espécies apresentou padrão anual e unimodal, com diferentes espécies florescendo em períodos distintos do ano. A maturação de frutos das espécies com dispersão zoocórica ocorreu principalmente durante o período chuvoso, e das com dispersão anemocórica ocorreu no período seco, ou na transição entre os períodos. A deciduidade foliar, estimada a partir da cobertura de folhagem, foi negativa e significativamente relacionada com temperatura máxima e com déficit de pressão de vapor em 11 das 12 espécies estudadas (exceto R. montana), sugerindo que aumentos na temperatura e na demanda evaporativa do ar induzem a abscisão foliar. O brotamento foi positivo e significativamente relacionado com a temperatura mínima em nove espécies (exceto M. lanuginosa, R.. montana e Q. grandiflora). Os resultados permitem sugerir que há forte relação entre os eventos fenológicos das espécies lenhosas estudadas e as condições climáticas, com associações mais evidentes para os eventos vegetativos como abscisão e brotamento.

The goal of this study was to characterize the phenological behavior of 12 woody species, which together represent 41 percent of the Importance Value Index (IVI) of a typical cerrado (Brazilian savanna) in the Bacaba Municipal Park (Nova Xavantina, Mato Grosso), and to relate it to climatic variables, including precipitation, minimum temperatures, maximum temperatures and Vapor Pressure Deficit (VPD). Phenological observations were made every 15 days, from September 2008 to October 2009. Estimates were made of total leaf cover in the canopy, leaf flushing, relative proportion of young, adult, and senescent leaves and flowering and fruiting. Based on phenological vegetative events, four species were classified as evergreen with continuous growth (Myrcia lanuginosa O. Berg., Ouratea hexasperma (A. St.-Hil.) Baill., Ouratea spectabilis (Mart. ex Engl.) Engl. e Roupala montana Aubl.), one as evergreen with seasonal growth (Byrsonima pachyphylla Kunth), two as brevideciduous (Davilla elliptica A. St.-Hil., Eugenia aurata O. Berg.), and five as deciduous (Byrsonima coccolobifolia Kunth, Kielmeyera rubriflora Cambess., Qualea grandiflora Mart., Qualea multiflora Mart. and Qualea parviflora Mart.). All species showed an annual, unimodal flowering pattern, with different species flowering during distinct periods of the year. The fruit maturation of autochoric and anemochoric species occurred within the dry season mostly; zoochoric species dispersed seeds mainly during the wet season or during the transition between dry and rainy seasons. Leaf fall, estimated from leaf canopy cover, was negatively and significantly correlated to maximum temperature and vapor pressure deficit in 11 out of 12 species studied (except R. montana), suggesting that increasing temperature and evaporative demand induce foliar abscission. Leaf flushing was positively and significantly correlated to minimum temperature in nine species (except M. lanuginosa, R. montana and Q. grandiflora). Our results suggest that there is a strong relationship between the phenological events of the studied woody species and climatic conditions, with vegetative events like abscission and flushing showing the strongest associations.

Impactos do agrupamento do bambu Actinocladum verticillatum (Nees) McClure ex Soderstr. (POACEAE) sobre a vegetação lenhosa de duas fitofisionomias de Cerrado na transição Cerrado-Floresta Amazônica / Impact of Actinocladum verticillatum (Nees) McClure ex Soderstr. (POACEAE) clumps on the woody vegetation in two Cerrado physiognomies in transition Cerrado & Floresta Amazônica, east of Mato Grosso, Brazil

Este estudo analisou os efeitos do agrupamento de uma espécie de bambu nativa do Cerrado (Actinocladum verticillatum) sobre a composição florística, diversidade e estrutura da vegetação lenhosa de um cerradão e de um cerrado típico adjacentes no Parque Municipal do Bacaba, Nova Xavantina-MT. Foram instaladas 60 parcelas de 10x10 m, sendo 30 no cerradão e 30 no cerrado típico. Em cada fitofisionomia, foram instaladas 15 parcelas em um sítio sem bambu (SB) e 15 em um sítio com cobertura estimada de folhagem de bambu superior a 90% (CB). Foram amostrados todos os indivíduos arbustivo-arbóreos com diâmetro a 30 centímetros do solo (DAS) ≥ 3 cm. Foi avaliada a riqueza, a diversidade de espécies, a similaridade florística, a distribuição de diâmetros e alturas e o índice de valor de importância das espécies (VI). De forma geral, os sítios CB das duas fitofisionomias apresentaram menores valores quanto ao número de indivíduos, espécies, gêneros, famílias, densidades e áreas basais em relação aos sítios SB, com redução mais acentuada nestes parâmetros no cerrado típico em relação ao cerradão. Os resultados sugerem que a ocupação do espaço e a redução da incidência luminosa causada pelas touceiras do bambu dificultam a germinação das sementes e o estabelecimento das plântulas de espécies arbustivo-arbóreas, selecionando as espécies mais tolerantes ao sombreamento modificando a composição florística e a estrutura da vegetação.

This study evaluated the effects of a Cerrado native bamboo species (Actinocladum verticillatum) clumps on the floristic composition, diversity and structure of the woody vegetation in two adjacent areas of "cerradão" and typical "cerrado" in the Bacaba Municipal Park, Nova Xavantina, state of Mato Grosso, Brazil. Sixty plots of 10 x 10 m were established, 30 in each forest physiognomy. In each physiognomy, 15 plots were placed in a bamboo-free site (SB) and 15 in a site with an estimated bamboo leaf cover of over 90% (CB). All individuals (shrubs and trees) with a diameter at soil height (DSH = 30 cm aboveground) ≥ 3 cm were sampled. Species richness and diversity, floristic similarity, diameter and height distribution, and the species importance value index (IVI) were evaluated. In general, CB sites of both physiognomies had lower values of number of individuals, species, genera, families, density and basal area compared to SB sites, with marked decrease in these parameters in the cerrado in relation to cerradão. Results suggest that the space occupation and reduction of light incidence caused by bamboo clumping affect seed germination and seedling establishment of Cerrado shrubs and trees, selecting more shade-tolerant species and changing the floristic composition and vegetation structure.