Seasonally Dry Tropical Forests Research Articles

Plant dynamics in a tropical dry forest are strongly associated with climate and fire and weakly associated with stabilizing neighborhood effects.

Studies comparing the relative strengths of multiple key drivers of forest dynamics are rare, but can inform both our fundamental understanding of plant communities as well as community-ecology theory. We studied the dynamics of a woody plant community in a southern Indian seasonally-dry tropical forest (SDTF) in relation to environmental factors (precipitation, temperature, fire, soil nutrients, and topography) and conspecific and heterospecific plant neighborhoods to identify which of these best predicted recruitment, survival and growth of dominant species over a 24-year study period. We also assessed the relative prevalence of density-independent and density-dependent responses in the community. Climate and fire were more important than plant neighborhoods and topographic and edaphic variables in explaining variation in plant performance. Recruitment, survival and growth were lower during periods of low precipitation and immediately following fires. Recruitment increased, and growth and survival largely decreased, with increasing temperatures. Smaller-sized individuals were disproportionately strongly affected by the vagaries of climate and fire. Conspecific negative density-dependence, a population-fluctuation stabilizing process, was relatively unimportant. Density-dependent effects decayed rapidly with distance from the focal plant (growth, survival) or quadrat (recruitment); positive density-dependence was frequently found in recruitment, possibly resulting from limited dispersal and/or facilitation. Woody plant dynamics in this SDTF appear to be responding largely to fluctuations in environmental conditions, particularly precipitation, temperature, and fire. In contrast to wetter forests, population-fluctuation stabilizing processes in this ecosystem appear to be relatively weak. Changes in climatic or fire regimes are likely to result in large compositional shifts in this SDTF.

Tracking the xeric biomes of South America: The spatiotemporal diversification of Mandacaru cactus

AbstractAimThe interconnectedness and biotic interchange among Neotropical biomes are thought to play an important role in driving adaptation and diversification. However, how these processes are in synteny to trait evolution in species of open and xeric areas is poorly studied. Here, we investigate the spatial and temporal dimensions of evolution and candidate traits associated with biome shifts in xeric vegetation, focusing on the family Cactaceae.LocationXeric and open areas of South America.TaxonGenus Cereus Mill. (Cactaceae, Cereeae).MethodsWe applied biogeographical reconstructions on a time‐calibrated phylogeny inferred from multilocus data (ddRAD‐Seq) using Bayesian analyses on BEAST2, species distribution modelling in Maxent, the reconstruction of biome affinities and niche shift analyses based on abiotic traits (climate and soil) using Mk‐model in BioGeoBEARS, and phenotypic trait‐based analysis in Mesquite.ResultsThe Cerrado domain is the ancestral area of Cereus, with most diversification events occurring in a time of intense orogenesis, climatic changes, and marine regressions within the last 5 Mya. Events of biome transition from the seasonally dry tropical forest (SDTF) were also associated with trait and niche shifts.Main conclusionsThe diversification of the xerophyte genus Cereus is associated with the climatic and geomorphological instabilities of the Pliocene and Pleistocene epochs. The Cerrado domain states an important region of dispersal for the genus. Some geographical range movements involved biome shifts associated with niche evolution while others were restricted to a simple biogeographical transition without niche change. Particular clades that experienced biome shifts displayed some phenotypic state changes, suggesting a role of biotic traits for environment transition. The results observed in Cereus may be a biogeographical pattern that should be tested with other cactus species, such as Pilosocereus spp., or species of xeric habitats, such as Annonaceae and Vochysiaceae.

RNA-Seq reveals different responses to drought in Neotropical trees from savannas and seasonally dry forests

BackgroundWater is one of the main limiting factors for plant growth and crop productivity. Plants constantly monitor water availability and can rapidly adjust their metabolism by altering gene expression. This leads to phenotypic plasticity, which aids rapid adaptation to climate changes. Here, we address phenotypic plasticity under drought stress by analyzing differentially expressed genes (DEG) in four phylogenetically related neotropical Bignoniaceae tree species: two from savanna, Handroanthus ochraceus and Tabebuia aurea, and two from seasonally dry tropical forests (SDTF), Handroanthus impetiginosus and Handroanthus serratifolius. To the best of our knowledge, this is the first report of an RNA-Seq study comparing tree species from seasonally dry tropical forest and savanna ecosystems.ResultsUsing a completely randomized block design with 4 species × 2 treatments (drought and wet) × 3 blocks (24 plants) and an RNA-seq approach, we detected a higher number of DEGs between treatments for the SDTF species H. serratifolius (3153 up-regulated and 2821 down-regulated under drought) and H. impetiginosus (332 and 207), than for the savanna species. H. ochraceus showed the lowest number of DEGs, with only five up and nine down-regulated genes, while T. aurea exhibited 242 up- and 96 down-regulated genes. The number of shared DEGs among species was not related to habitat of origin or phylogenetic relationship, since both T. aurea and H impetiginosus shared a similar number of DEGs with H. serratifolius. All four species shared a low number of enriched gene ontology (GO) terms and, in general, exhibited different mechanisms of response to water deficit. We also found 175 down-regulated and 255 up-regulated transcription factors from several families, indicating the importance of these master regulators in drought response.ConclusionOur findings show that phylogenetically related species may respond differently at gene expression level to drought stress. Savanna species seem to be less responsive to drought at the transcriptional level, likely due to morphological and anatomical adaptations to seasonal drought. The species with the largest geographic range and widest edaphic-climatic niche, H. serratifolius, was the most responsive, exhibiting the highest number of DEG and up- and down-regulated transcription factors (TF).

Chronic Disturbance in a Tropical Dry Forest: Disentangling Direct and Indirect Pathways Behind the Loss of Plant Richness

Chronic disturbance is widely recognized as one of main triggers of diversity loss in seasonally dry tropical forests (SDTFs). However, the pathways through which diffuse disturbance is acting on the forest are little understood. This information is especially demanded in the case of vanishing Neotropical seasonally dry forests such as the Tumbesian ones. We proposed a conceptual model to analyze the factors behind the loss of woody species richness along a forest disturbance gradient, explicitly considering the existence of direct and indirect causal pathways of biodiversity loss. We hypothesized that the chronic disturbance can act on the woody species richness directly, either by selective extraction of resources or by browsing of palatable species for livestock, or indirectly, by modifying characteristics of the forest structure and productivity. To test our model, we sampled forest remnants in a very extensive area submitted to long standing chronic pressure. Our forests cells (200 × 200 m) were characterized both in terms of woody species composition, structure, and human pressure. Our structural equation models (SEMs) showed that chronic disturbance is driving a loss of species richness. This was done mainly by indirect effects through the reduction of large trees density. We assume that changes in tree density modify the environmental conditions, thus increasing the stress and finally filtering some specific species. The analysis of both, direct and indirect, allows us to gain a better understanding of the processes behind plant species loss in this SDTF.

Genetic diversity of Astronium graveolens Jacq. in Colombian seasonally dry tropical forest: support for the dry forest refugia hypothesis?

• The degradation of Colombian dry forest threatens tree species populations • We studied the genetic diversity of Astronium graveolens with nSSRs makers • The populations held healthy levels of genetic diversity • The genetic structure supports the dry forest refugia hypothesis • We identify priority areas for inclusive in situ conservation to support restoration Seasonally Dry Tropical Forest (SDTF) is one of the most threatened ecosystems worldwide and in Colombia it is considered critically endangered according to the national red list of ecosystems. Ongoing processes of fragmentation and degradation of SDTFs are expected to be accompanied by a loss of genetic diversity of the tree populations contained in it. Identifying remaining healthy tree populations is key for the implementation of conservation and restoration programs that embrace genetic diversity to enhance the capacity of populations to adapt to environmental changes. We studied the genetic diversity and structure of Astronium graveolens , one of the most ubiquitous species in Colombian SDTFs, across ten representative populations. We assess the relevance of the dry forest refugia hypothesis (DFRH) for explaining the observed genetic structures. We identified three genetic clusters which may have originated through prolonged isolation of populations. The most diverse cluster ranges from the Caribbean region to the Chicamocha river canyon which may reflect their connectedness during the last glacial period. A second cluster likely originated through isolation in a small area enclosed in the Caribbean region. The third cluster groups populations from the Cauca and Magdalena river valleys, suggesting cross-Andean expansion of populations at one point in time, thus corroborating similar findings for other species of SDTFs. Our results add to a growing number of studies providing support for the DFRH. All the populations sampled showed heterozygosity scores close to the Hardy-Weinberg expectations, suggesting populations might be relatively resistant to habitat fragmentation. However, our suitability modelling results suggest that climate change might imperil numerous areas in SDTFs where the species occurs today, including some that hold unique genetic diversity.

Soil texture and functional traits of trees structure communities of epiphytic mosses in a tropical dry forest

The question which guided our study was: How environmental variables and trees affect the parameters of diversity, composition and abundance of epiphytic moss species at a local scale? Our hypothesis is that these moss communities are shaped by tree functional traits, which in turn are determined according to soil texture. Therefore, we collected moss from 25 permanent plots distributed along six transects (three in each texture of soil) in a Seasonally dry tropical forest (SDTF) in Northeastern Brazil. We assessed the distribution and abundance of epiphytic moss and tree species separately by performing an ordination analysis for each plot and tested if the spatial pattern of mosses was correlated with that of trees by performing a Procrustes analysis. Structural, functional and physico-chemical variables of trees were measured and subjected to uni- and multivariate analyses as potential abiotic filters. We then described the relationship between the response (richness and abundance) and predictor variables (structural, functional and physico-chemical variables) of the trees. As a result, we found that deciduous tree species were more frequent in sandy soils with less water retention. Leaf shedding by deciduous species reduces the total evapotranspiration surface during the dry season compared to evergreens. In contrast, evergreen trees were more frequent in clay soils, which have a higher water retention capacity. These differences in tree functional groups between soil types promoted different moss epiphytic communities in environments with different soil textures. Despite generalist and sun moss species dominating the study area, we found two groups with different environmental requirements based on the abundance of life forms: tuft and weft in drier areas; and mat and dendroid in wetter areas. Epiphytic moss community composition reflects the environmental conditions for each of the formed groups through the pattern of the trees’ functional traits predicted by different soil textures.

The Effect of Forest Management on the Avifauna of a Brazilian Dry Forest

The conversion of tropical habitats has dramatic implications on biodiversity and represents one of the greatest conservation challenges of our time. Seasonally Dry Tropical Forests (SDTF), which are disjointly distributed throughout the Neotropics, are especially susceptible to human activities. The Caatinga Dry Forest, located in the semi-arid interior of northeastern Brazil, represents not only the largest and most biologically diverse nucleus of SDTF, but also the world’s most densely populated semi-arid region, with ever-growing pressure on its natural resources. To prevent illegal logging, conservation agencies looked at forest management, where an area is divided in smaller stands which are gradually logged and allowed to regrow for a period of time, when a new cutting cycle should reinitiate. The impacts of these management schemes on biodiversity, however, remain largely untested. We conducted standardized avian surveys to evaluate the effects of forest management on the avian community at a 1,670 ha privately owned property located on the Chapada do Araripe, northeastern Brazil. This area was divided in 22 forest stands, half of which had already been logged at the time of our sampling, creating a gradient of logged and natural forests and an 11-yr chrono-sequence of forest regeneration. Our results show that logged areas present fewer individuals, fewer species, and different avian assemblages than unlogged forests. Such differences are mostly driven by forest-dependent species, which were overwhelmingly affected by forest management. Our results show that although logged forests tend to recover its height after a decade, they do not recover the originally forest cover, measured by the Normalized Difference Vegetation Index. Likewise, decade-long recovering stands continue to show lower species richness, lower bird abundance, and different avian composition than unlogged forests. We identified a set of bird species that are more affected by forest management (ecological losers) and a group of birds that apparently benefit from the referred changes in land use (ecological winners). We conclude that completely managing an entire area may cause the extirpation of several forest-dependent species. We therefore suggest keeping logged and unlogged plots intermingled, to avoid local extinctions and the complete modification of the original avifauna.

Deforestation and fragmentation trends of seasonal dry tropical forest in Ecuador: impact on conservation

BackgroundFragmentation and deforestation are one of the greatest threats to forests, and these processes are of even more concern in the tropics, where the seasonal dry forest is possibly one of the most threatened ecosystems with the least remaining surface area.MethodsThe deforestation and fragmentation patterns that had occurred in Ecuadorian seasonal dry forests between 1990 and 2018 were verified, while geographic information systems and land cover shapes provided by the Ecuadorian Ministry of the Environment were employed to classify and evaluate three types of seasonal dry forests: deciduous, semi-deciduous, and transition. The study area was tessellated into 10 km2 hexagons, in which six fragmentation parameters were measured: number of patches, mean patch size, median patch size, total edge, edge density and reticular fragmentation index (RFI). The RFI was also measured both outside and inside protected natural areas (unprotected, national protected areas and protected forest). Moreover, the areas with the best and worst conservation status, connectivity and risk of disappearance values were identified by means of a Getis-Ord Gi* statistical analysis.ResultsThe deforestation of seasonal dry forests affected 27.04% of the original surface area still remaining in 1990, with an annual deforestation rate of − 1.12% between 1990 and 2018. The RFI has increased by 11.61% as a result of the fact that small fragments of forest have tended to disappear, while the large fragments have been fragmented into smaller ones. The semi-deciduous forest had the highest levels of fragmentation in 2018. The three categories of protection had significantly different levels of fragmentation, with lower RFI values in national protected areas and greater values in protected forests.ConclusionsThe seasonal dry forest is fragmenting, deforesting and disappearing in some areas. An increased protection and conservation of the Ecuadorian seasonal dry forest is, therefore, necessary owing to the fact that not all protection measures have been effective.

How thinning in a seasonally dry tropical forest contributes towards root biomass, carbon stock and aggregate size in a Vertisol

Forest management activities influence fine root development, total soil carbon (TSC) and size of aggregates. A field experiment was carried out in Vertisols of two adjacent catchments in a seasonally dry tropical forest (SDTF) to investigate the thinning on fine-root biomass, stock of the total soil carbon and aggregate size. The catchments are located in the State of Ceará, Brazil. The control catchment of 2.1 ha has been under regenerating vegetation for 35 years (RC35), while the second catchment (1.1 ha) was subjected to thinning (TC5) in December of 2008. The analysed variables were: fine-root biomass in the 0-10, 10-20 and 20-30 cm soil layers, TSC and mean weight diameter of the soil aggregates in the 0-20, 20-40 e 40-60 cm layers. The data were submitted to Pearson correlation analysis and compared by paired t-test (P < 0.05). The 0-10 cm layer of the TC5 management stored double the average amount of fine-roots found in the RC35. Under the TC5 management, stocks of soil TSC increased by 237 and 151% in the 20-40 and 40-60 cm layers, respectively, when compared with RC35. Aggregates 2.15 times greater than those found under RC35 management were obtained in the topsoil (0-20 cm) under the TC5 management. The implementation of thinning in a Vertisol of a SDTF emerges as an alternative management to be considered in projects for sustainability in the semi-arid region, contributing to an improvement in soil structure as well as an increase in the stocks of total carbon.

Recovery of dung beetle assemblages in regenerating Caatinga dry forests following slash-and-burn agriculture

Understanding patterns of tropical forest resilience is a central challenge in conservation ecology particularly in seasonally-dry tropical forests, where anthropogenic disturbance and climate change are pervasive threats. Here, we investigate the recovery rate and community organization of dung beetles along a Caatinga dry forest regeneration cline in the context of slash-and-burn agriculture in northeast Brazil. Assemblages were described considering a wide set of attributes, including abundance, taxonomic (Hill orders D0, D1 and D2) and functional diversity (functional richness, evenness and redundancy) and taxonomic/functional composition, across a chronosequence consisting of regenerating and old-growth forest stands exposed to different levels of aridity and chronic disturbance. In addition, we use body mass, diet, food relocation behaviour and habitat specificity of dung beetles as ecological attributes. Our results show that Caatinga dry forests supports dense but relatively impoverished dung beetle assemblages at both local and landscape scales, with the same small set of species dominating local assemblages. Dung beetles do not experience successional replacements along the regeneration gradient, with evidence of high resilience. Moreover, disturbance-associated dung beetle species (predominantly small-bodied generalists) resulted in assemblage convergence across the regeneration cline. Finally, chronic anthropogenic disturbance was a decisive driver of changes in abundance and taxonomic diversity, while aridity positively affected species composition and functional richness. These patterns resulted in the occurrence of spatially structured assemblages in response to a combination of both natural and anthropogenic variables, while under little or no influence of forest regeneration status across human-modified Caatinga landscapes. We conclude that the absence of directional changes in dung beetle assemblages through the forest succession pathway of regenerating second-growth forest is associated with the effect of aridity and human disturbances on community organization, including selection for certain species and functional groups, which in turn, can alter important ecological functions and consequently the resilience of dry forests.

Phylogeny and biogeography of Ceiba Mill. (Malvaceae, Bombacoideae)

The Neotropics is the most species-rich area in the world, and the mechanisms that generated and maintain its biodiversity are still debated. This paper contributes to the debate by investigating the evolutionary and biogeographic history of the genus Ceiba Mill. (Malvaceae, Bombacoideae). Ceiba comprises 18 mostly Neotropical species, largely endemic to two major biomes, seasonally dry tropical forests (SDTFs) and rain forests. Its species are among the most characteristic elements of Neotropical SDTF, one of the most threatened biomes in the tropics. Phylogenetic analyses of DNA sequence data (from the nuclear ribosomal internal transcribed spacers [nrITS] for 30 accessions representing 14 species of Ceiba) recovered the genus as monophyletic. The phylogeny showed geographic and ecological structure in three main clades: (i) a rain forest lineage of nine accessions of C. pentandra sister to the remaining species; (ii) a highly supported clade composed of C. schottii and C. aesculifolia from Central American and Mexican SDTF, plus two accessions of C. samauma from semi-humid, inter Andean valleys in Peru; and (iii) a highly supported South American SDTF clade including 10 species showing little sequence variation. Within this South American SDTF clade, no species represented by multiple accessions were resolved as monophyletic. We demonstrate that the patterns of species age, monophyly, and geographic structure previously reported for SDTF species within the Leguminosae family are not shared by Ceiba, suggesting that further phylogenetic studies of unrelated groups are required to understand general patterns.

The Caatinga Orchestra: Acoustic indices track temporal changes in a seasonally dry tropical forest

Advances in technologies for data acquisition, storage and analysis have boosted Acoustic Ecology studies, but protocols are still lacking. There is a need of more research to understand which methodologies can be applied to answer ecological questions in different environments with varying temporal and spatial dynamics. Tropical forests are generally more complex than temperate ones, both in terms of use of acoustic space and species diversity. The seasonally dry tropical forest (SDTF) in Brazil, known as Caatinga, is a threatened biome, with two marked seasons that shape vegetation and animal activity patterns. In this study, we investigate the applicability of passive acoustics in monitoring SDTF, describing the soundscape and tracking diel patterns and seasonal changes. Combining multiple indices, visualization through false colour spectrograms and clustering, we describe the acoustic activity of the main faunal groups that compose the biophonic orchestra in a SDTF area in the Northeast of Brazil. Distinct patterns were found between day – when birds and wind were the main sound sources – and night – with Orthopterans occupying a large frequency band. Other sound sources in the SDTF soundscape included cicada, rain, and anthropogenic influence such as domestic animals, cars and gunshots. Clustering of eleven acoustic indices was useful to distinguish sound patterns from several sources, especially in the dry season. Further investigation within each cluster showed specific relationships among selected indices and different sound sources. Birds were associated with Entropy of the Spectral Peaks (EPS) and Orthopterans also had a relationship with EPS, as well as with Entropy of Average Spectrum (EAS) and High Frequency Cover (HFC). Variation in diel values of these selected indices, as well as the number of samples included in each cluster category, were successfully used to describe the acoustic activity of Birds and Orthopterans and to track changes between rainy and dry seasons. A better understanding of the soundscape dynamics in a highly seasonal tropical environment was achieved by applying cheap and reliable novel methodologies to study biodiversity in geopolitical regions where funding for conservation initiatives is limited.

Effects of human-induced land degradation on water and carbon fluxes in two different Brazilian dryland soil covers

The Brazilian semiarid region presents a physical water scarcity and high seasonal and interannual irregularities of precipitation, known as a region with periodic droughts. This region is mainly covered by the Caatinga biome, recognized as a Seasonally Dry Tropical Forest (SDTF). Soil water availability directly impacts the ecosystem's functioning, characterized by low fertility and sparse vegetation cover during the dry season, making it a fragile ecosystem vulnerable to climatic variations. Additionally, this region has been suffering from several issues due to human activities over the centuries, which has resulted in extensive areas being severely degraded, which aggravates the impacts from climatic variations and the susceptibility to desertification. Thus, studying the soil-plant-atmosphere continuum in this region can help better understand the seasonal and annual behavior of the water and carbon fluxes. This study investigated the dynamics of water and carbon fluxes during four years (2013–2016) by using eddy covariance (EC) measurements within two areas of Caatinga (dense Caatinga (DC) and sparse Caatinga (SC)) that suffered anthropic pressures. The two study areas showed similar behavior in relation to physical parameters (air temperature, incoming radiation, vapor pressure deficit, and relative humidity), except for soil temperature. The SC area presented a surface temperature of 3 °C higher than the DC, related to their vegetation cover differences. The SC area had higher annual evapotranspiration, representing 74% of the precipitation for the DC area and 90% for the SC area. The two areas acted as a carbon sink during the study period, with the SC area showing a lower CO2 absorption capacity. On average, the DC area absorbs 2.5 times more carbon than the SC area, indicating that Caatinga deforestation affects evaporative fluxes, reducing atmospheric carbon fixation and influencing the ability to mitigate the effects of increased greenhouse gas concentrations in the atmosphere.

Biogeographic regionalization by spatial and environmental components: Numerical proposal.

Regionalization through the analysis of species groups offers important advantages in conservation biology, compared to the single taxon approach in areas of high species richness. We use a systematic framework for biogeographic regionalization at a regional scale based on species turnover and environmental drivers (climate variables and soil properties) mainly of herbaceous plant species richness. To identify phytogeographic regions in the Balsas Depression (BD), we use Asteraceae species, a family widely distributed in Seasonally Dry Tropical Forest (SDTF) and the most diverse of the vascular plants in Mexico. Occurrence records of 571 species were used to apply a quantitative analysis based on the species turnover, the rate of changes in their composition between sites (β-Simpson index) and the analysis of the identified environmental drivers. Also, the environmental predictors that influence species richness in the SDTF were determined with a redundancy analysis. We identified and named two phytogeographic districts within the SDTF of the BD (Upper Balsas and Lower Balsas). According to the multi-response permutation procedure, floristic composition of the two districts differs significantly, and the richness of exclusive species in Upper Balsas was higher (292 species) than in the Lower Balsas (32 species). The proportion of Mg and Ca in the soil and the precipitation of the driest three-month period were the environmental factors with greatest positive influence on species richness. The division of geographic districts subordinated to the province level, based on diverse families such as Asteraceae, proved to be appropriate to set up strategies for the conservation of the regional flora, since at this scale, variation in species richness is more evident. Our findings are consistent with a growing body of biogeographic literature that indicates that the identification of smaller biotic districts is more efficient for the conservation of biodiversity, particularly of endemic or rare plants, whose distribution responds more to microhabitats variation.

The vegetal stratum defined the forage bromatology more than the season in seasonal dry tropical forest rangelands

The vegetal stratum defined the forage bromatology more than the season in seasonal dry tropical forest rangelands

Biogeography of different life forms of the southernmost neotropical tank bromeliad

AbstractAimFactors affecting bromeliad distribution depend on the life forms of the studied species; some could grow as terrestrial, saxicolous, or epiphytic depending on the type of habitat. We analysed the distribution patterns of the life forms of a bromeliad species in different biogeographic domains and associated them with environmental variables and vegetation types.LocationChaquenian, Amazonian, and Seasonally Dry Tropical Forest domains; South America.TaxonThe tank bromeliad Aechmea distichantha (Bromeliaceae: Bromelioideae).MethodsWe compiled records of the biogeographic distribution and the vegetation types where A. distichantha occurs based on bibliographic data, digital datasets, herbaria, and personal observations. We associated the distributional records of this species with altitude, five selected bioclimatic variables, four soil variables, and with the vegetation types where it occurs.ResultsA. distichantha has been recorded as epiphytic, terrestrial and saxicolous in all biogeographic domains but showed contrasting patterns in life form proportions among them. In the Amazonian domain, characterized by evergreen tropical and subtropical forests with high precipitation, it mainly grows as epiphytic. In the Chaquenian domain, dominated by xerophytic forests with low rainfall, high soil pH and base saturation, it mainly grows as terrestrial, whereas in the Seasonally Dry Tropical Forest domain, the three life forms were recorded in similar proportions. In azonal plant communities of all domains, it mainly grows as saxicolous.Main ConclusionsThis tank bromeliad species can thrive in sites with contrasting habitat and environmental conditions. Its ability to survive in different environments could be associated with its high frost tolerance, the presence of the CAM photosynthetic pathway, a well‐developed phytotelma, and high phenotypic plasticity. The life form prevailing in each domain is influenced by water availability (i.e., the quantity of water available during each year, the precipitation in the driest month, and the plant water supply relative to demand).

Effects of chronic anthropogenic disturbances on flesh fly (Diptera, Sarcophagidae) assemblages in areas of seasonally dry tropical forest

Seasonally dry tropical forests (SDTF) are among the most vulnerable ecosystems to chronic anthropogenic disturbances (CAD) such as agriculture, livestock and exploitation of wood and non-timber forest products which can negatively affect the local biota. We evaluated the influence of CAD and rainfall on the diversity of flesh flies (Diptera, Sarcophagidae) in the Brazilian Caatinga. We expected that the increase in CAD would negatively affect the specialist Sarcophagidae species and promote homogenisation of the assemblage. Specimens were collected using traps baited with fish, bovine spleen or human feces in six environments with different intensities of CAD—low, intermediate and high, based on land use and conservation status. We collected 29,810 specimens (3760 males, identified to 14 genera, 32 species). We observed a positive relationship between disturbance intensity and the abundance of synanthropic flies, mainly Tricharaea occidua. The diversity of common species and dominant species were affected only by CAD. There was also a marked substitution of species throughout the Caatinga environments (βSIM = 0.91), with few taxa (less than 50%) occurring indiscriminately in the areas under the three levels of impact. Chronic disturbances pose a constant threat to the conservation of flesh fly species. CAD act as a trigger for the homogenisation of Sarcophagidae assemblages, and magnify the dominance of synanthropic and generalist species. Empirical data on the effect of chronic disturbances can subsidize quantitative studies addressing local extinction. Our data strengthen the use of Sarcophagidae as biological indicators of anthropogenic action and can subsidize protocols for monitoring anthropogenic impacts in dry forests.

Habitat use and feeding behavior of domestic free-ranging goats in a seasonal tropical dry forest

Traditional pastoralism based on free-ranging goats is indispensable for the rural economy of millions of people in the Brazilian Caatinga drylands. The use of landscape as rangelands for domestic herbivores benefits humans, but understanding its impacts on vegetation is crucial to sustainable strategies. Here we assessed how free-ranging domestic goats use mixed working landscapes in the largest dry forest of the Americas. We evaluated habitat use via GPS tracking and analysis of feeding preferences. Goats preferentially used open areas near human settlements and their impact on plant community may be negligible because they feed mostly on plants widely available in modified environments. Although free-ranging, the area of use was nearly constant (95.44 ha), but the size of herds varied (2–100 animals). Our study suggests that domestic goats can be considered dwellers of human-modified landscapes, foraging close to villages, on open (i.e., degraded) areas where abundant plant species thrive. Therefore, the extensive goat pastoralism in the Caatinga may have little impact on natural vegetation and could be sustainably managed under traditional management practices.

Ecological aspects of mosquitoes (Diptera: Culicidae) in a fragment of seasonal dry tropical forest (Caatinga) in Brazil

Seasonally dry tropical forests are among the most vulnerable ecosystems to the effects of anthropogenic disturbances, and yet their biodiversity is still poorly known. In this study we investigated the composition, activity, structure, and effect of seasonality in mosquitoes’ assemblages of a conservation Caatinga domain unit. The collections consisted of the monthly installation of two Shannon traps, set at a distance of 8 km between them, and operated by two captors, who collected simultaneously for 3 h (17:00h to 20:00h), totaling 288 h of sampling over two years. In total, 1261 specimens belonging to at least 20 sp. of the subfamilies Anophelinae and Culicinae were captured. Culicinae was the most representative subfamily, with 99.3% of all collected specimens, while for Anophelinae only nine specimens of the species Anopheles albitarsis Lynch Arribálzaga, 1878 s.l. were registered. Among the species of Culicinae, Aedes scapularis was the most abundant (39.9%), followed by Mansonia wilsoni (21.6%), Culex spp. (12.8%) and Aedes taeniorhynchus (12.4%). The Culicidae assemblage was more abundant and diverse in the wettest months and the twilight hours (17:00h to 18:00h). Our data indicate that Anopheles species are sensitive to Caatinga arid conditions and that mosquito populations are controlled by rainfall.

Adjusting xylem anatomy and growth to inter-annual climate variability in two Fabaceae species (Centrolobium microchaete, Cenostigma pluviosum) from Bolivian dry tropical forests

Climate-growth relationships are strong in seasonally dry tropical forests (SDTFs). To better understand the ecological processes controlling these relationships we need to assess the long-term responses of wood anatomy and radial growth to year-to-year climate variability. We assessed how wood-anatomical traits (mean vessel area –MVA– and vessel density –VD–, percentage of conductive area –CA–, xylem-specific estimated hydraulic conductivity –Ks–) and growth responded to local climate (mean temperature, total precipitation, estimated moisture) variability and teleconnections (Pacific Decadal Oscillation) between 1970 and 2011 in two Fabaceae tree species (Centrolobium microchaete and Cenostigma pluviosum) coexisting in a Bolivian SDTF. We found that C. microchaete produced wider vessels and was more responsive to both local climate conditions and teleconnections than C. pluviosum. In C. microchaete VD positively responded to average temperature in the late-wet season and in the previous dry season, and CA and Ks were higher in years with warmer wet and previous early-dry seasons, as well as in years with higher PDO values. These responses were independent from ring-width variability only for C. microchaete. For C. pluviosum, vessel chronologies were more responsive to local temperature variability, and only MVA and CA positively and negatively responded to moisture in the early-dry and the previous dry seasons, respectively. Our results show that wood hydraulic structure in SDTFs is responsive to climate fluctuations. The combined study of ring width and wood anatomy allows having a more complete picture of the influence of climate on growth, particularly in species as C. microchaete which show low collinearity of tree-ring width and wood plasticity in response to climate variability.