Seasonally Dry Tropical Forests Research Articles

Rainfall and soil properties driver the temporal dynamics of arbuscular mycorrhizal fungal assemblages in a seasonally dry tropical forest

The Seasonally Dry Tropical Forests (SDTF), distributed from Mexico to northern Argentina, are habitat to a unique biodiversity. Among these forests, the Caatinga stands out, occupying a large part of the Brazilian Northeast and is subject to cycles of anthropic disturbance and abandonment of exploited areas. Understanding how microbial communities respond to environmental changes is crucial, especially considering the various ecosystem services provided by microorganisms. Among soil microorganisms, arbuscular mycorrhizal fungi (AMF) play a significant role in the maintenance of terrestrial ecosystems. In this study, we aimed to evaluate the structure, composition, and distribution of AMF assemblages, as well as their main drivers, in regeneration areas of the Caatinga. Soil samples were collected in the Catimbau National Park (Pernambuco State), including an old-growth forest representing undisturbed areas, and in early, intermediate, and late regeneration areas. The composition of AMF assemblages differed among regenerating areas and old-growth forest, but their distribution is not related and conditioned to plant assemblages. Instead, soil properties and rainfall are the main factors structuring these assemblages in SDTF. A total of 83 taxa of AMF were identified. Glomus and Acaulospora, which exhibit respectively ruderal and stress-tolerant life strategies were the most abundant genera. The highest number of unique AMF species was recorded in the old-growth forest, contrasting with the late regeneration areas which had the lowest number. The results showed that deterministic processes (soil and rainfall) are structuring the AMF assemblages in areas under regeneration process in SDTF. Plants and AMF do not recover simultaneously over the evaluated regeneration times.

Unraveling the genetic diversity of Ceiba pubiflora (Malvaceae) in isolated limestone outcrops: Conservation strategies.

Seasonally Dry Tropical Forests (SDTFs) located on limestone outcrops are vulnerable to degradation caused by timber logging and limestone extraction for cement production. Some of these forests represent the last remnants of native vegetation cover, functioning as isolated islands. Ceiba pubiflora (Malvaceae) is a tree frequently found on limestone outcrops in the central region of Brazil. This study aimed to evaluate the genetic diversity and identify suitable populations for the establishment of Management Units (MUs) for conservation. Inter-simple sequence repeat markers were employed to assess the genetic diversity in ten populations sampled from the Caatinga, Cerrado, and Atlantic Forest biomes. The species exhibited substantial genetic diversity (HT = 0.345; PLP = 97.89%). Populations SAH, JAN, and MON demonstrated elevated rates of polymorphic loci (> 84.2%) along with notable genetic diversity (He > 0.325). Additionally, these populations were the primary contributors to gene flow. The analysis of molecular variance (AMOVA) indicated that most genetic variation occurs within populations (91.5%) than between them. In the Bayesian analysis, the ten populations were clustered into five groups, revealing the presence of at least three barriers to gene flow in the landscape: 1) the Central Plateau or Paranã River valley; 2) near the Espinhaço mountains or the São Francisco River valley; and 3) around the Mantiqueira mountain range, Chapada dos Veadeiros plateau, and disturbed areas. A positive and statistically significant correlation was observed between genetic (θB) and geographic distances (r = 0.425, p = 0.008). Based on these findings, we propose the establishment of Management Units in Minas Gerais state, encompassing the (1) southern region (MIN population), (2) central region (SAH population), and (3) north region (MON population), as well as in Goiás state, covering the (4) Central Plateau region. These units can significantly contribute to preserving the genetic diversity of these trees and protecting their habitat against ongoing threats.

Assessment of habitat connectivity in a highly fragmented ecosystem: The seasonal tropical dry forest in Ecuador

AbstractContextConnectivity is a parameter that plays a fundamental role in highly fragmented ecosystems, such as the seasonal tropical dry forest.ObjectivesThe objective of this research is to calculate the evolution of fragmentation and the functional connectivity of the Ecuadorian seasonal dry forest from 1990 to 2018, and to compare the Ecuadorian state's reforestation plan with our reforestation plan, which is based on maximising connectivity with the smallest possible reforested area.MethodsThe land cover changes, fragmentation and functional connectivity, measured by employing cumulative cost analyses at three different distances (0.5, 5 and 10 km), that occurred in Ecuadorian seasonal dry forests between 1990 and 2018 were verified using GIS environments, vector layers and Graphab software. A reforestation plan was also developed using various connectivity metrics and was then compared with that proposed by the Ecuadorian Ministry of the Environment.ResultsBetween 1990 and 2018, 2647 km2 of dry forest was lost in the study area. Former forest areas were put mainly to agricultural uses, which increased by 12.96%. The total number of patches decreased from 6908 to 5357, signifying a loss of 30% of the forest area and leading to losses of up to 75% of connectivity. Areas with low connectivity and a risk of disappearance were identified, and a new reforestation plan was proposed, which was based on maximising connectivity with small patches.ConclusionsBecause of the fragmentation, the connectivity of the seasonal dry forest in Ecuador is dramatically decreasing in the last decades. Therefore, the reforestation plans should prioritise areas whose reforestation increases habitat functional connectivity, which could provide more benefits than increasing the forest area without considering the global connectivity.

Ecosystem function associated with soil organic carbon declines with tropical dry forest degradation

AbstractForest degradation is increasingly recognized as a major threat to global biodiversity and the multiple ecosystem services forests provide. This study examined the impacts of forest degradation on soil quality and function in a seasonally dry tropical forest (SDTF) of Ecuador. Previous studies of SDTFs have focused on the impacts of land‐use conversion on soils, while this study assessed the less visible but pervasive effects of degradation. We compared soil physical–chemical properties, enzymatic activity, particulate organic carbon (POC) and mineral‐associated organic carbon (MAOC) along a gradient of SDTF degradation in both the dry and rainy season. Our findings showed a consistent and steady reduction in soil quality (total C and N) and function (dehydrogenase and β‐glucosidase activity) that paralleled the loss of vegetative structure and diversity along the degradation gradient. Soil physical–chemical properties were less variable and enzymatic activity was generally higher in the dry season compared to the rainy season. We also showed for the first time a significant and uniform decrease in POC and MAOC with degradation in SDTF. The relative proportion of these two components was constant along the gradient except in the most degraded state (arid land), where POC was higher in proportion to MAOC, suggesting that extreme forest degradation may cause this ecosystem to cross a functional tipping point. These findings address an important knowledge gap for SDTFs by showing a consistent loss of soil quality and functionality with degradation, and suggest that extreme degradation can result in an alternate state with compromised resilience.

Comparative phylogeography shows congruent co‐divergence in Neotropical seasonally dry forest and savanna tree species

AbstractAimThe response of South American seasonally dry tropical forest (SDTF) and savanna species to the Quaternary climate changes is still poorly understood. Here we use multi‐model inference approach to compare the phylogeography and demographic history of five trumpet tree species (also known as pau‐d'arco) and draw general biogeographical patterns: Handroanthus impetiginosus, H. ochraceus, H. serratifolius, Tabebuia aurea and T. roseoalba.LocationAmazonia, Atlantic Forest, Cerrado and Caatinga ecoregions, South America and Brazil.TaxaBignoniaceae, Tabebuia Alliance, trees.MethodsWe compiled genetic data, occurrence records and ecological niche modelling (ENM) from published articles. We used coalescent modelling to test patterns of co‐divergence, and analysed niche breadth and overlap and spatial patterns in genetic diversity using quantile regressions.ResultsSpecies showed concordant lineage divergence times in the Pleistocene. Lineage diversification and phylogeographical patterns are more related to species niche breadth than to biome (savanna or SDTF). Differences in genetic diversity among species matches the expected for the demographic scenarios obtained with coalescent simulations and ENMs: species with wider range expansion during the Last Glacial Maximum had higher diversity than species with range retraction or multiple refugia.Main ConclusionsDiversification burst in the Pliocene, and major diversification of lineages during the Pleistocene seems to be a general pattern in SDTF and savannas in the South America. The high number of haplotypes at the Central Brazil, corresponding to the Cerrado ecoregion, highlights the importance of Protected Areas for SDTFs and savannas, highly threatened biomes in Brazil.

Spectral asynchrony as a measure of ecosystem response diversity

AbstractSpecies diversity is crucial for promoting ecosystem resilience and stability. Species diversity promotes complementarity in resource use, resulting in a wider range of responses to adverse conditions. This enables populations of different species to fluctuate asynchronously, maintaining ecosystem functioning during extreme climatic events. However, incorporating such mechanisms into conservation decisions and ecosystem modelling requires scalable metrics that represent species diversity, which is currently lacking. To address this, we introduce spectral asynchrony, a metric that captures the spatial heterogeneity of species’ functional responses occurring in distinct pixels. Here, we use remote sensing datasets to investigate the relationship between spectral asynchrony and productivity responses of seasonally dry tropical forests (SDTF) to climatic fluctuations. Our findings reveal that spectral asynchrony is associated with increased resistance and recovery of SDTF productivity in following extreme drought years, as well as greater productivity stability over two decades. Furthermore, higher spectral asynchrony was associated with relatively wetter regions, suggesting that increasing aridity across SDTF could potentially reduce landscape heterogeneity and limit ecosystem resilience to increasing droughts in the future. Spectral asynchrony provides an easily measurable and monitorable metric for assessing ecosystem responses to global changes, reflecting and scaling‐up the effects of species diversity at the local level.

Molecular Discrimination for Two Anadenanthera Species of Seasonally Dry Tropical Forest Remnants in Brazil

Anadenanthera colubrina (Acol) and Anadenanthera peregrina (Aper) (Fabaceae) are two species popularly known as “angicos” that occur in seasonally dry tropical forest (SDTR) remnants in Brazil. Since many of the morphological characteristics of Anadenanthera species are superimposed and species-specific characteristics are difficult to observe, their identification is complex. Therefore, in this research, a set of ISSR (Inter-Simple Sequence Repeat Polymorphic DNA) molecular markers was standardized, aiming to characterize A. colubrina and A. peregrina species and study the genetic diversity of three populations of each species located within a fragmented landscape in São Paulo State, southeastern Brazil. Seven ISSR markers (UBC 2, 820, 851, 858, 864, 866, and 886) that show polymorphism for both species were used. The Bayesian cluster, PCoA and dendrogram analysis show that the total sample divides into two groups corresponding to each species. Also, a genetic divergence (Gst = 0.143) and a high number of migrants per generation (Nm = 3.0) were detected between them. The Acol populations showed significantly higher values for mean genetic diversity (h = 0.30) than Aper (h = 0.25) (p < 0.05). The ISSR marker UBC2250bp showed species-specific electrophoretic fingerprints for both species. The molecular tools generated herein support the conservation of Anadenanthera sp. and the restoration of vegetation where the species naturally occurs.

The desert wolf-spider genus Xenoctenus: two endemic species from the Brazilian Caatinga, and a redescription of the type-species, X. unguiculatus (Araneae: Xenoctenidae).

The Caatinga is a nucleus of seasonally dry tropical forest (SDTF) known as a hotspot of diversification and endemism. Despite its importance, this biome is still insufficiently sampled, resulting in extensive knowledge gaps regarding its species richness and composition. In this study we report two species of Xenoctenidae that are endemic to, and widely distributed in the Caatinga. We redescribe and illustrate Odo vittatus (Mello-Leito, 1936), the only xenoctenid species previously known from the Caatinga. We transfer this species to Xenoctenus Mello-Leito,1938, a genus currently known from six species restricted to Argentina, Bolivia, and Colombia. We also newly describe the male of Xenoctenus vittatus comb. nov. and provide new records of this species, which was hitherto known only from the type-locality, throughout the Caatinga and nearby semiarid vegetation formations. We also describe and illustrate a new species, Xenoctenus kaatinga sp. nov., based on males and female specimens collected throughout the Caatinga. Additionally, we propose diagnostic characters for Xenoctenus and redescribe the type-species, X. unguiculatus.

Multiscale phenology of seasonally dry tropical forests in an aridity gradient

The leaf phenology of seasonally dry tropical forests (SDTFs) is highly seasonal, marked by synchronized flushing of new leaves triggered by the first rains of the wet season. Such phenological transitions may not be accurately detected by remote sensing vegetation indices and derived transition dates (TDs) due to the coarse spatial and temporal resolutions of satellite data. The aim of this study was to compared TDs from PhenoCams and satellite remote sensing (RS) and used the TDs calculated from PhenoCams to select the best thresholds for RS time series and calculate TDs. For this purpose, we assembled cameras in seven sites along an aridity gradient in the Brazilian Caatinga, a region dominated by SDTFs. The leafing patterns were registered during one to three growing seasons from 2017 to 2020. We drew a region of interest (ROI) in the images to calculate the normalized green chromatic coordinate index. We compared the camera data with the NDVI time series (2000–2019) derived from near-infrared (NIR) and red bands from MODIS product data. Using calibrated PhenoCam thresholds reduced the mean absolute error by 5 days for SOS and 34 days for EOS, compared to common thresholds in land surface phenology studies. On average, growing season length (LOS) did not differ significantly among vegetation types, but the driest sites showed the highest interannual variation. This pattern was applied to leaf flushing (SOS) and leaf fall (EOS) as well. We found a positive relationship between the accumulated precipitation and the LOS and between the accumulated precipitation and maximum and minimum temperatures and the vegetation productivity (peak and accumulated NDVI). Our results demonstrated that (A) the fine temporal resolution of phenocamera phenology time series improved the definitions of TDs and thresholds for RS landscape phenology; (b) long-term RS greening responded to the variability in rainfall, adjusting their timing of green-up and green-down, and (C) the amount of rainfall, although not determinant for the length of the growing season, is related to the estimates of vegetation productivity.

Activity budget and gut microbiota stability and flexibility across reproductive states in wild capuchin monkeys in a seasonal tropical dry forest

BackgroundEnergy demands associated with pregnancy and lactation are significant forces in mammalian evolution. To mitigate increased energy costs associated with reproduction, female mammals have evolved behavioural and physiological responses. Some species alter activity to conserve energy during pregnancy and lactation, while others experience changes in metabolism and fat deposition. Restructuring of gut microbiota with shifting reproductive states may also help females increase the energy gained from foods, especially during pregnancy. The goal of this study was to examine the relationships among behaviour, gut microbiota composition, and reproductive state in a wild, non-human primate to better understand reproductive ecology. We combined life history data with > 13,000 behavioural scans and 298 fecal samples collected longitudinally across multiple years from 33 white-faced capuchin monkey (Cebus imitator) females. We sequenced the V4 region of the 16S rRNA gene and used the DADA2 pipeline to analyze microbial diversity. We used PICRUSt2 to assess putative functions.ResultsReproductive state explained some variation in activity, but overall resting behaviours were relatively stable across pregnancy and lactation. Foraging was less frequent among females in the early stage of nursing compared to the cycling stage, though otherwise remained at comparable levels. Maximum temperature was a strong, significantly positive predictor of resting, while social dominance had a small but significantly negative effect on resting. Ecological variables such as available fruit biomass and rainfall had a small but significantly positive effects on measures of foraging time. Gut microbial community structure, including richness, alpha diversity, and beta diversity remained stable across the reproductive cycle. In pairwise comparisons, pregnant females exhibited increased relative abundances of multiple microbial ASVs, suggesting small changes in relation to reproductive state. Reproductive state was not linked to differential abundance of putative metabolic pathways.ConclusionsPrevious data suggest that activity budget and the gut microbiome shifts considerably during reproduction. The present study finds that both activity and gut microbial communities are less associated with reproduction compared to other predictors, including ecological contexts. This suggests that behavioural flexibility and gut microbial community plasticity is contrained by ecological factors in this population. These data contribute to a broader understanding of plasticity and stability in response to physiological shifts associated with mammalian reproduction.

Phylogeographic analysis reveals early Pleistocene divergence and strong genetic structure in Euphorbia phosphorea (Euphorbiaceae), an endemic species to the semi-arid Caatinga Biome

Abstract The largest continuous patch of Seasonally Dry Tropical Forests (SDTF) is the Caatinga Biome in north-eastern Brazil, which has the greatest biodiversity and highest degree of endemism compared to any other SDTF patch of South America. Our aim was to conduct a phylogeographic study with Euphorbia phosphorea to understand the evolutionary history of this species endemic to the Caatinga Biome. We studied genetic diversity and structure, demographic dynamics, as well as intraspecific phylogenetic relationships, based on plastidial and nuclear DNA. In addition, we conducted species distribution modelling (SDM) to infer connectivity since the Last Interglacial. Our results recovered a stronger genetic structure for plastidial than for nuclear genome, which probably result from distinct species capability to seed and pollen dispersal, and low levels of genetic diversity within populations. Although SDM results suggest higher connectivity during Last Maximum Glacial, demographic analyses detected no signs of demographic expansion in this period. In agreement with previous studies with rock specialists, our data reveal remarkable among-population differentiation and low within-population genetic diversity, which make populations more prone to drift effects. Furthermore, our results shed light on the importance of early Pleistocene events in the diversification of lineages within the Caatinga Biome, although further comparative work is required.

Factors shaping a lizard community structure in a semiarid region of north-eastern Brazil

We assessed the roles of historical and recent factors on the structure of a Neotropical lizard community from Serra da Capivara, in the semiarid Caatinga of north-eastern Brazil. We found no phylogenetic structure in community composition. Spatial niche overlap was high for most species pairwise comparisons. Null model analyses indicated that mean spatial and trophic niche overlaps did not differ, while mean morphological niche overlap was significantly lower than expected by chance, indicating a community structured along the morphological niche axis but not along the trophic nor spatial niche axes. We suggest that the lack of spatial niche segregation and species association may be related to current environmental conditions, such as habitat homogeneity and climatic variables. Morphological and dietary niches were influenced by historical factors, with phylogeny accounting for most of the variation in our data. Most of the variation is accounted for by the divergence of basal lineages (Gekkota/Scincomorpha/Iguania). These segregations influence behaviour and foraging modes of the given clades. Finally, these results are quite like those found for lizard communities in Seasonal Tropical Dry Forests (STDFs) and Cerrado savannahs, which can be a starting point to discuss the relationship between these formations to Caatinga domain.

How Forest Management with Clear-Cutting Affects the Regeneration, Diversity and Structure of a Seasonally Dry Tropical Forest in Brazil

In Brazil, logging in the Seasonally Dry Tropical Forest (SDTF) under management plans that include clear-cutting has increased in recent decades, and the structure, composition, diversity and functioning of the forest likely must have been affected. The aim of this study was to understand the growth dynamics of shrub–tree biomass (STB), species richness and vegetation structure as a function of regeneration time after clear-cutting (treatments), taking the Legal Reserve (40 years of regeneration) as reference. The study was carried out in 2018 at the Ramalhete Settlement, General Sampaio, in the state of Ceará. All plants with a circumference at breast height (CBH) ≥ 6 cm were identified and the CBH was measured across 42 sample plots (20.0 m × 20.0 m), using seven plots per treatment (3, 5, 8, 11 and 15 years after clear-cutting, and the Legal Reserve, 40 years of regeneration). The following were determined: STB (total and by species), density and basal area (by ecological group and diameter class), basal area (species of higher added value), diversity (Hill numbers), and the importance value index (IVI). It was found that during the early years (up to at least 11 years), many important forest characteristics related to the composition of the ecological groups and vegetation structure were strongly affected, and major impacts can be seen, the effects of which, however, decreased over time of regeneration, having almost no effect after 15 years. After 15 years following clear-cutting, the SDTF presented accumulated STB, species richness and structure similar to the area undergoing regeneration for 40 years. However, the small number of indicator species of more-preserved areas (even at T15 and T40) points out that management needs to be improved. However, promoting species of greater added value and determining whether the forest recovers its structure and diversity after successive cutting cycles also still need to be addressed.

Can size make a difference? Cross-predation occurrences between lizards and scorpions in the Brazilian seasonal dry tropical forest

Can size make a difference? Cross-predation occurrences between lizards and scorpions in the Brazilian seasonal dry tropical forest

Wind farm noise and anuran diversity patterns: a case study in Brazilian seasonal dry tropical forest

ABSTRACT Noise pollution contributes to the global biodiversity crisis, however the consequences of this pollution on anuran diversity patterns are poorly understood. This is especially true of less evident sources of noise like wind farms and highly exploited areas, as in the Brazilian semi-arid region. Here, we evaluated the influence of wind farm noise on anuran assemblages’ diversity at the Caatinga, a seasonal dry tropical forest in Brazil. We tested the hypothesis that wind farm noise negatively affects the diversity of anuran assemblages in terms of abundance, species richness and composition. Anurans were sampled in 19 temporary ponds along a noise gradient in two wind farms over a rainy season (March to August). A total of 2,047 individuals belonging to 20 species were recorded. Our results suggest that wind farm noise has a non-significant relationship with anuran diversity patterns (species richness, composition and abundance). To our knowledge, this is the first investigation into the effects of wind farm noise on anuran assemblages in the Caatinga dry forest. Despite our results suggesting that anuran diversity is insensitive to noise pollution caused by wind farms, identification of emerging threats is essential to mitigate impacts on anuran populations which are declining globally.

Registro de depredación intragremial del escorpión Physoctonus debilis (C. L. Koch, 1840) (Scorpiones: Buthidae) por la chinche Microtomus tibialis Stichel, 1926 (Hemiptera: Reduviidae)

Scorpions and assassin bugs are arthropod predators that may impact in trophic chain, coexisting in similar microhabitats and exhibiting antagonistic interactions. This study reports the first case of predation of the scorpion Physoctonus debilis by the assassin bug Microtomus tibialis in a Brazilian Seasonal Dry Tropical Forest biome. During a nocturnal collection, an adult individual of M. tibialis was observed, with the head and body facing downwards, while holding a female of P. debilis, with the aid of the mouthparts under the vegetation. Reports like these are important to understand the evolutionary dynamics and natural history of predators that cohabit in the same microhabitat.

Phylogenomics of One of the World’s Most Intriguing Groups of CAM Plants, the Opuntioids (Opuntioideae: Cactaceae): Adaptation to Tropical Dry Forests Helped Drive Prominent Morphological Features in the Clade

Opuntioideae, composed of roughly 370 species, occur in almost every biome in the Americas, from seasonally dry tropical forests (SDTF) to high-elevation Andean grasslands, American deserts and temperate zones. The interrelationships among the three major clades of Opuntioideae (Cylindropuntieae, Opuntieae and Tephrocacteae) are not well resolved, and thus, the ancestral habitat, biogeographic history and evolution of morphological characters, such as large photosynthetic leaves and flattened stems, are poorly understood. To test their geographic origin and evolution of key morphological characters, we built the largest phylogenomic dataset for Cactaceae to date using 103 plastid genes of 107 taxa of Opuntioideae. The subfamily Opuntioideae likely evolved in South America in a combination of seasonally dry tropical forest (SDTF)/desert habitats. Opuntieae most likely evolved in South America in SDTF and, from there, moved into desert regions, Chaco and temperate/subtropical zones, while Tephrocacteae and Cylindropuntieae evolved in South America in desert regions and moved into SDTF, Chaco and temperate/subtropical zones. Analyses of morphological evolution suggest that, although large leaves are plesiomorphic in Opuntioideae, long-lived, photosynthetically active leaves in Cylindropuntieae and Tephrocacteae are homoplasious and do not represent retained plesiomorphy, as is often assumed. Flattened stems are synapomorphic for Opuntieae, possibly representing adaptation to competition for light resources in SDTF, their most likely ancestral area.

The role of chronic anthropogenic disturbances in plant community assembly along a water availability gradient in Brazil’s semiarid Caatinga region

The effects of anthropogenic disturbances on the structure and function of seasonally dry tropical forests (SDTFs) are mediated both by disturbance type and intensity, and the environmental conditions, including climate. In a climate change scenario, the interaction between low water availability and chronic anthropogenic disturbances may potentially have drastic consequences on SDTF dynamics and the ecosystem services it provides. We hypothesized that in these naturally stressed systems, the effects of human disturbance are strongest in the most water-stressed sites, implying a worrisome synergism between harsh abiotic conditions (lower precipitation, higher temperature) and human effects, ultimately resulting in a less developed community structure and reduced diversity. By integrating information for the adult and regenerating vegetation strata in 21 sites distributed across climatic, plant cover and disturbance gradients in the Caatinga (seasonally dry tropical) forest of Brazil, we analyzed the individual and combined effects of chronic anthropogenic disturbances, as measured through the Cattle Pressure Index and the Human Activity Index, along climate gradients, on community structure, diversity, and composition. As expected, the Cattle Pressure Index was negatively related to diameter at ground level, basal area, and diversity in the adult stratum, whereas for the regenerating stratum, litter stock had the strongest effect on vegetation structure. Climatic factors were poor predictors of the variation in the three true diversity measures (0D, 1D, and 2D) of the regenerating community. Our results revealed important cross-site differences in both vegetation strata over a small range of climatic variation. We conclude that the most stressful conditions associated with a very low precipitation regime enhance the effects on chronic disturbances, gradually driving SDTF communities into new alternative states and rendering these environments more prone to desertification.

A new, disjunct species of Bahiana (Euphorbiaceae, Acalyphoideae): Phytogeographic connections between the seasonally dry tropical forests of Peru and Brazil, and a review of spinescence in the family.

Bahiana is expanded from 1 to 2 species with the description of B.occidentalis K. Wurdack, sp. nov. as a new endemic of the seasonally dry tropical forests (SDTFs) of Peru. The disjunct distribution of Bahiana with populations of B.occidentalis on opposite sides of the Andes in northwestern Peru (Tumbes, San Martín) and B.pyriformis in eastern Brazil (Bahia) adds to the phytogeographic links among the widely scattered New World SDTFs. Although B.occidentalis remains imperfectly known due to the lack of flowering collections, molecular phylogenetic results from four loci (plastid matK, rbcL, and trnL-F; and nuclear ITS) unite the two species as does gross vegetative morphology, notably their spinose stipules, and androecial structure. Spinescence in Euphorbiaceae was surveyed and found on vegetative organs in 25 genera, which mostly have modified sharp branch tips. Among New World taxa, spines that originate from stipule modifications only occur in Bahiana and Acidocroton, while the intrastipular spines of Philyra are of uncertain homologies.

Ensemble Machine Learning for Mapping Tree Species Alpha-Diversity Using Multi-Source Satellite Data in an Ecuadorian Seasonally Dry Forest

The increased variety of satellite remote sensing platforms creates opportunities for estimating tropical forest diversity needed for environmental decision-making. As little as 10% of the original seasonally dry tropical forest (SDTF) remains for Ecuador, Peru, and Colombia. Remnant forests show high rates of species endemism, but experience degradation from climate change, wood-cutting, and livestock-grazing. Forest census data provide a vital resource for examining remote sensing methods to estimate diversity levels. We used spatially referenced trees ≥5 cm in diameter and simulated 0.10 ha plots measured from a 9 ha SDTF in southwestern Ecuador to compare machine learning (ML) models for six α-diversity indices. We developed 1 m tree canopy height and elevation models from stem mapped trees, at a scale conventionally derived from light detection and ranging (LiDAR). We then used an ensemble ML approach comparing single- and combined-sensor models from RapidEye, Sentinel-2 and interpolated canopy height and topography surfaces. Validation data showed that combined models often outperformed single-sensor approaches. Combined sensor and model ensembles for tree species richness, Shannon’s H, inverse Simpson’s, unbiased Simpson’s, and Fisher’s alpha indices typically showed lower root mean squared error (RMSE) and increased goodness of fit (R2). Piélou’s J, a measure of evenness, was poorly predicted. Mapped tree species richness (R2 = 0.54, F = 27.3, p = <0.001) and Shannon’s H′ (R2 = 0.54, F = 26.9, p = <0.001) showed the most favorable agreement with field validation observations (n = 25). Small-scale model experiments revealed essential relationships between dry forest tree diversity and data from multiple satellite sensors with repeated global coverage that can help guide larger-scale biodiversity mapping efforts.