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The Araucaria Mixed Forests (AMF) are subtropical conifer-hardwood mixed forests that are part of the Atlantic forest floristic dominion in Brazil and Argentina. The AMF is dominated by the conifer...

Euterpe precatoria Mart. is the most abundant plant species in the Amazon basin, and one of the main non-timber forest products on the continent. A thorough understanding of the ecology of this species is needed to support sustainable management initiatives. Resource availability, disturbance regime, and human management are some of the main factors influencing population structure. We described the species’ life stages, evaluated its allometric relationships, and assessed the effects of habitat type (floodplain and upland) and proximity to human settlements on population size distribution in the Central Amazon near the Purus River. The height:diameter ratio increased from Seedlings to Juvenile 2, but decreased from Juvenile 2 to Reproductive 2, indicating changing height investment for any given diameter along these life stages. There was a marked habitat dependency in both the density and population size distribution, with populations in upland forests dominated by juveniles, whereas populations in the floodplains were dominated by reproductive palms. Proximity to human settlements was not related to population structure parameters. Our results suggest that the disturbance regime may have opposite meanings in várzea forests, where it limits recruitment under increased light levels, and in terra firme forests, where it may stimulate recruitment under limited light conditions.

Our aims were to quantify and map the plant ecoregions of the Atlantic Forest, a biodiversity hotspot that covers ca 150 million ha in eastern South America. We used a data set on the distribution of 4378 shrub and tree species across 711 localities. Plant ecoregions were identified using analyses of species turnover for both species occurrences and relative abundances. We interpolated NMDS axes of compositional variation over the entire the Atlantic Forest extent, and then classified the compositional dissimilarity according to the number of biogeographical ecoregions previously identified through K‐means analyses. We assessed the ability of environmental, historical vegetation stability and the current human footprint to explain the occurrence of the identified ecoregions through multinomial logistic regression models. We identified 21 spatially cohesive occurrence and 14 abundance ecoregions. Aridity, soil and historical biome stability were retained in the best model explaining both occurrence and abundance ecoregions. Broad compositional zones were identified through UPGMA cluster analysis of ecoregions, and formed north and south compositional blocks. Our work confirms the existence of a broad north–south divide within the Atlantic Forest, previously suggested based on climatic and amphibious data. Differences between the occurrence and abundance maps suggest the location of transition zones to neighbouring domains and endemism centres. Due to the aggregate nature of our analyses, site‐level disturbance degree was not considered, implying that human impacts could be broader then we could detect. There was limited overlap between our results and previous Atlantic Forest regionalization efforts, indicating that multi‐taxa, physiognomic and environmental regionalization schemes based on expert opinion or vegetation maps are poor proxies for compositional ecoregions.

The responses of forest communities to interacting anthropogenic disturbances like climate change and logging are poorly known. Subtropical forests have been heavily modified by humans and their response to climate change is poorly understood. We investigated the 9‐year change observed in a mixed conifer‐hardwood Atlantic forest mosaic that included both mature and selectively logged forest patches in subtropical South America. We used demographic monitoring data within 10 1 ha plots that were subjected to distinct management histories (plots logged until 1955, until 1987, and unlogged) to test the hypothesis that climate change affected forest structure and dynamics differentially depending on past disturbances. We determined the functional group of all species based on life‐history affinities as well as many functional traits like leaf size, specific leaf area, wood density, total height, stem slenderness, and seed size data for the 66 most abundant species. Analysis of climate data revealed that minimum temperatures and rainfall have been increasing in the last few decades of the 20th century. Floristic composition differed mainly with logging history categories, with only minor change over the nine annual census intervals. Aboveground biomass increased in all plots, but increases were higher in mature unlogged forests, which showed signs of forest growth associated with increased CO2, temperature, and rainfall/treefall gap disturbance at the same time. Logged forests showed arrested succession as indicated by reduced abundances of Pioneers and biomass‐accumulators like Large Seeded Pioneers and Araucaria, as well as reduced functional diversity. Management actions aimed at creating regeneration opportunities for long‐lived pioneers are needed to restore community functional diversity, and ecosystem services such as increased aboveground biomass accumulation. We conclude that the effects of climate drivers on the dynamics of Brazilian mixed Atlantic forests vary with land‐use legacies, and can differ importantly from the ones prevalent in better known tropical forests.

Understanding the effects of disturbance on seed rain is critical to predict changes in forest species composition and diversity. Logging effects on seed rain in a mixed conifer-hardwood forest complex in southern Brazil were evaluated. One year of seed rain data were collected from a large-scale observational experiment in logged and protected forests and quantity and average seed size weighted by species abundance (CWM) were compared between old-growth and logged stands 55 years after logging activities. Using these data, variations in frequency of functional groups of species in the seed rain were examined to see if they could be attributed to logging. Results show that the number of seeds per trap was highly right-skewed, ranging from 13 to 12,788 seeds per trap in one year. Seed rain was affected by logging history, with seed traps in old-growth plots receiving significantly less seeds than traps in logged plots. All species included mean seed size weighted by species abundance were significantly smaller in logged than in old-growth forests. This difference persisted after the exclusion of Araucaria angustifolia, a large-seeded pioneer which was intensively logged, although the difference of seed size between the two forest classes was greatly reduced. Species abundance in the seed rain differed significantly from the established tree community, between logged and old-growth stands. The composition of the seed rain was much more variable than the composition of the established tree community and its points more scattered over the ordination space than the points corresponding to the protected forests. The number of collected seeds across different functional groups of species significantly differed between logged and old-growth plots. The seed rain of logged forests reflects their arrested succession as indicated by reduced abundance of functional groups such as pioneers, large seeded pioneers and Araucaria, as well as reduced functional diversity. Seed rain differences between logged and old- growth stands reflect the intensive logging of A. angustifolia.

Significance Identifying and explaining regional differences in tropical forest dynamics, structure, diversity, and composition are critical for anticipating region-specific responses to global environmental change. Floristic classifications are of fundamental importance for these efforts. Here we provide a global tropical forest classification that is explicitly based on community evolutionary similarity, resulting in identification of five major tropical forest regions and their relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. African and American forests are grouped, reflecting their former western Gondwanan connection, while Indo-Pacific forests range from eastern Africa and Madagascar to Australia and the Pacific. The connection between northern-hemisphere Asian and American forests is confirmed, while Dry forests are identified as a single tropical biome., Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.

A core question involving both plant physiology and community ecology is whether traits from different organs are coordinated across species, beyond pairwise trait correlations. The strength of within‐community trait coordination has been hypothesized to increase along gradients of environmental harshness, due to the cost of adopting ecological strategies out of the viable niche space supported by the abiotic conditions. We evaluated the strength of trait relationship and coordination in a stressful environment using 21 leaf and stem traits of 21 deciduous and evergreen woody species from a heath vegetation growing on coastal sandy plain in northeastern South America. The study region faces marked dry season, high soil salinity and acidity, and poor nutritional conditions. Results from multiple factor analyses supported two weak and independent axes of trait coordination, which accounted for 25%–29% of the trait variance using phylogenetically independent contrasts. Trait correlations on the multiple factor analyses main axis fit well with the global plant economic spectrum, with species investing in small leaves and dense stems as opposed to species with softer stems and large leaves. The species’ positions on the main functional axis corresponded to the competitor‐stress‐tolerant side of Grime's CSR triangle of plant strategies. The weak degree of trait coordination displayed by the heath vegetation species contradicted our expectation of high trait coordination in stressful environmental habitats. The distinct biogeographic origins of the species occurring in the study region and the prevalence of a regional environmental filter coupled with local homogeneous conditions could account for prevalence of trait independence we observed.

Our understanding regarding the demography of adult conifers in forest–grassland mosaics is still limited. I studied the landscape-scale demography and spatial distribution of the conifer Araucaria angustifolia (Bertol.) Kuntze in a subtropical forest–grassland mosaic over a 24-year period. Araucaria angustifolia is a long-lived pioneer that is expected to thrive in grasslands and forest edges better than in forest patches. I used the position of trees in aerial photographs taken in 1984 to analyze spatial patterns and a 2008 satellite image to estimate individual survivorship. Spatial distribution of trees in the grassland was aggregated and was not related to the distribution of trees in forest patches. Survivorship was higher in forest patches than in grasslands, where it showed density dependence. In forest patches, survivorship was positively related to both patch area and distance from forest edge. Crown breakage was more common in the grassland than in forest patches. In forest patches, it was positively related to crown size, number of conspecific neighbours, and patch area. Adult Araucaria angustifolia seem to benefit from angiosperm-dominated neighbourhoods relative to isolation in grasslands. Density-dependent effects, known to be widespread among seeds and seedlings, were shown to be important to adult trees as well.

Despite its advantages over other energy sources, hydropower facilities are recognized as causes of terrestrial and freshwater environmental impacts. A deeper understanding of hydropower effects on surrounding riparian forests is thus important to the development hydropower facilities of less impact on the environment as well as to define criteria to manage the vegetation in the vicinity of large hydroelectric dams. We compared tree community structure on forest slopes exposed to a hydropower reservoir created in 2005 with control ones, in the biodiversity-rich subtropical forests of southern Brazil. Field data were collected between 2009 and 2011 on six forest slopes of which three were affected by the rise in water level caused by a hydropower dam, while the other three were in nearby sites unaffected by damming. Ninety 10 × 10 plots were set along six 50 m × 10 m transects. Forest structure was significantly affected by vicinity of reservoir, but this effect differed significantly between different tributaries of the Pelotas River. Rarefaction curves showed homogeneity in species richness among the studied hills. Composition differed significantly between reservoir and control areas. Variance partition results showed that pure reservoir effects explained a fraction of the variance in floristic composition comparable to environmental factors. Vicinity to reservoir was the main factor able to distinguish between communities in the studied system in a multiple regression tree. Our results highlight that hydroelectric facility building produces more extensive damage to remnant native forests than anticipated and that even forests upslope from reservoir border may suffer rapid structural and compositional degradation due to changes in environmental conditions caused by altered hydrology.

In spite of recent advances, the relative roles of deterministic and stochastic processes in community assembly remains disputed. We tested community assembly hypotheses in a disturbance gradient in a logged mixed conifer-hardwood forest complex in southern Brazil. If abiotic heterogeneity was strong enough (Selection hypothesis), we expected niche clustering and reduced niche overlap between species and between ecological groups, phylogenetic clustering, significant β-diversity departure from a random expectation after controlling for α-diversity variation, and non-random trait distribution due to abiotic filtering and limiting similarity. Null expectations were predicted under the Neutral hypothesis. Under the Quasi-Neutral hypothesis, we expected niche clustering and reduced niche overlap as in the Selection hypothesis, but random phylogenetic distribution, random β-diversity variation, and random trait distribution due to niche-based specialization but weak habitat matching resulting from dispersal limitation and drift. We used a series of null models to provide an integrative evaluation of community assembly including species abundances, environmental preferences, phylogenetic relatedness, and trait distribution. Results supported the Quasi-Neutral hypothesis due to a combination of reduced niche overlap, niche clustering along soil and disturbance gradients, evidence for abiotic filtering of functional traits but absent phylogenetic structure and random β-diversity variation. Support to the Quasi-Neutral hypothesis provides evidence for niche-based species selection along environmental gradients, coupled with poor matches between species distributions and environmental factors due to stochastic processes. It also highlights the importance of an integrative approach to the evaluation of community patterns indicative of assembly processes. Had only a subset of the approaches used been employed and different conclusions would have been reached: niche overlap and trait distribution analyses would have indicated a stronger role for selection, while phylogenetic and abundance analyses would have indicated stochastic community assembly. Future research should include different disturbance regimes along with environmental variation in order to assess the interplay of the different drivers that shape the community assembly process, as well as the potential of the Quasi-Neutral hypothesis as an explanation for the assembly process of complex and species-rich subtropical forests.

Despite its implications for carbon storage, animal conservation, and plant regeneration, the variation in the structure of heath vegetation in South America is still poorly studied. In this study, we aimed at examining the edaphic and topographic determinants of this variation along 85 plots (5 × 5 m) randomly distributed in a restinga heath vegetation occurring on coastal dune fields in northeastern Brazil. We carried out a PCA analysis to reduce eleven vegetation descriptors into a small number of structural gradients, which were then assessed by a stepwise standard least-squares multiple regression to reveal the effects of the abiotic environment on structure. The three following hypotheses were tested: (1) both soils and topography are important to explain variation in vegetation structure at local scale; (2) herbaceous plants, cactus, and woody plants show differential responses to soil and topographic variations; and (3) soil acidity and salinity are more important determinants of herbaceous cover than woody plant variation. PCA analysis revealed three major structural gradients related to biomass, herbaceous cover, and leaning plants, respectively. These gradients were only related to calcium and nitrogen contents, which partially supports our first hypothesis. Our results also suggest that different groups of plants have different responses to abiotic gradients that are exposed. The effect of the soil acidity and salinity did not appear to present an immediate strong influence on the herbaceous community. It seems that a reduced number of edaphic factors promote the variation in vegetation structure in the restinga heath vegetation.

Our aims were to quantify and map the plant sub regions of the the Caatinga, that covers 844,453 km2 and is the largest block of seasonally dry forest in South America. We performed spatial analyses of the largest dataset of woody plant distributions in this region assembled to date (of 2,666 shrub and tree species; 260 localities), compared these distributions with the current phytogeographic regionalizations, and investigated the potential environmental drivers of the floristic patterns in these sub regions. Phytogeographical regions were identified using quantitative analyses of species turnover calculated as Simpson dissimilarity index. We applied an interpolation method to map NMDS axes of compositional variation over the entire extent of the Caatinga, and then classified the compositional dissimilarity according to the number of biogeographical sub regions identified a priori using k-means analysis. We used multinomial logistic regression models to investigate the influence of contemporary climatic productivity, topographic complexity, soil characteristics, climate stability since the last glacial maximum, and the human footprint in explaining the identified sub regions. We identified nine spatially cohesive biogeographical sub regions. Current productivity, as indicated by an aridity index, was the only explanatory variable retained in the best model, explaining nearly half of the floristic variability between sub regions. The highest rates of endemism within the Caatinga were in the Core and Periphery Chapada Diamantina sub regions. Our findings suggest that the topographic complexity, soil variation, and human footprint in the Caatinga act on woody plant distributions at local scales and not as determinants of broad floristic patterns. The lack of effect of climatic stability since the last glacial maximum probably results from the fact that a single measure of climatic stability does not adequately capture the highly dynamic climatic shifts the region suffered during the Pleistocene. There was limited overlap between our results and previous Caatinga classifications.