Tropical Dry Forest Landscape Research Articles

Belowground differentiation among trees in a degraded tropical dry forest landscape: no evidence of a collaboration gradient

Belowground differentiation among trees in a degraded tropical dry forest landscape: no evidence of a collaboration gradient

Land cover and forest health indicator datasets for central India using very-high resolution satellite data

Satellite imagery has been used to provide global and regional estimates of forest cover. Despite increased availability and accessibility of satellite data, approaches for detecting forest degradation have been limited. We produce a very-high resolution 3-meter (m) land cover dataset and develop a normalized index, the Bare Ground Index (BGI), to detect and map exposed bare ground within forests at 90 m resolution in central India. Tree cover and bare ground was identified from Planet Labs Very High-Resolution satellite data using a Random Forest classifier, resulting in a thematic land cover map with 83.00% overall accuracy (95% confidence interval: 61.25%–90.29%). The BGI is a ratio of bare ground to tree cover and was derived by aggregating the land cover. Results from field data indicate that the BGI serves as a proxy for intensity of forest use although open areas occur naturally. The BGI is an indicator of forest health and a baseline to monitor future changes to a tropical dry forest landscape at an unprecedented spatial scale.

Trait-dependent responses of birds and bats to season and dry forest distance in tropical agroforestry

Agricultural expansion and intensification increasingly threaten birds and bats, especially insectivorous species from the tropics. Cacao agroforests in tropical rainforest areas have been shown to support higher bird and bat biodiversity than other land-use systems, but their suitability for tropical dry forest biodiversity remains unclear. We present the first assessment of bird and bat diversity patterns in cacao agroforests inside tropical dry forest landscapes. We investigated the response of bird and bat species richness and abundance to forest distance and season across 12 smallholder, organic cacao agroforests and adjacent tropical dry forests in the Peruvian lowlands of Piura. We found that insectivorous bird abundance and species richness increased with forest distance in the dry but not in the rainy season, indicating the value of cacao agroforests for these birds when resources are scarce in forests. In the case of bats, we observed more species in agroforests with increasing forest distance independent of season, and the abundance of insectivorous species increased along the gradient. Other dietary groups and forest specialists of both taxa did not vary notably across the forest distance gradient. Our findings point to the relevance of cacao agroforests as alternative habitats for insectivorous birds and bats in tropical dry forest landscapes, especially during the dry season. We suggest that the maintenance of wildlife friendly cacao agroforests, parallel to dry forest conservation and restoration, creates win-win situations for both the conservation of tropical dry forest fauna and the maintenance of related ecosystem services from which cacao smallholders may benefit.

Landscape Structure and Seasonality: Effects on Wildlife Species Richness and Occupancy in a Fragmented Dry Forest in Coastal Ecuador

Despite high fragmentation and deforestation, little is known about wildlife species richness and occurrence probabilities in tropical dry forest (TDF) landscapes. To fill this gap in knowledge, we used a Sentinel-2-derived land-cover map, Normalized Difference Vegetation Index (NDVI) data and a multi-species occupancy model to correct for detectability to assess the effect of landscape characteristics on medium and large mammal occurrence and richness in three TDF areas that differ in disturbance and seasonality in Ecuador. We recorded 15 species of medium and large mammals, distributed in 12 families; 1 species is critically Endangered, and 2 are Near-Threatened. The results indicate that species occupancy is related to low forest cover and high vegetation seasonality (i.e., high difference in NDVI between the wet and dry seasons). We believe that the apparent negative effect of forest cover is an indicator of species tolerance for disturbance. The three sampling areas varied from 98% to 40% forest cover, yet species richness and occupancy were not significantly different among them. Vegetation seasonality indicates that more seasonal forests (i.e., those where most tree species lose their leaves during the dry season) tend to have higher mammal species occupancy compared to less seasonal, semi-deciduous forests. Overall, occupancy did not vary between the dry and wet seasons, but species-specific data indicate that some species exhibit higher occupancy during the wet season. This research offers a good understanding of mammal species’ responses to habitat disturbance and fragmentation in TDFs and provides insights to promote their conservation.

Living fences decrease the edge effect on nest predation in a tropical dry forest landscape: evidence from an experiment using artificial nests

Agricultural expansion has contributed to the loss and fragmentation of natural habitats and, as a consequence, the edge effect in these habitats has increased, leading to nest predation rates higher at the edge of fragments than in the interior. Living fences in abandoned croplands, however, add a structural component to the landscape which can help to mitigate the effects of disturbance. We used artificial nests to assess whether a living fence at the edge of a fragment of tropical dry forest, immersed in an agricultural landscape, can assuage the edge effect by decreasing predation rates. We identified the predators that attacked nests at several distances from the living fence and related the frequency of predator attacks with plant height, leaf height diversity, and tree and herb coverage. Vegetation structure of the living fence was vertically more complex than that found inside the fragment. 52% of nests were predated and we did not find a significant relationship between predation rates and the proximity of nests to the living fence, suggesting a null edge effect on predation. Birds were the most frequent predators, followed by rodents and carnivorous mammals, with the composition of predators varying among transects. The composition of predators and vegetation structure of the living fence were the factors that explained the null edge effect on nests predation. Our results indicate that the presence of a living fence at the edge of a fragment in agroforestry systems could mitigate the edge effects on nest predation.

Estructura poblacional de Morpho helenor peleides kollar, 1850 (lepidoptera: nymphalidae) en un paisaje de bosque seco tropical, departamento de Bolivar, Colombia.

Teniendo en cuenta la alta tasa de destrucción de los bosques en la región Caribe colombiana y la escasa información disponible sobre la ecología poblacional de las mariposas del género Morpho, se analizó la variación de estructura poblacional de Morpho helenor peleides Kollar, 1850 en un paisaje de Bosque seco tropical (BST) en los Montes de María, Caribe colombiano. Metodología. Para el estudio de la mariposa, se utilizó el método de captura-marca-recaptura (CMR) en siete estaciones, en las cuales se instalaron trampas Van Someren-Rydon cebadas con una mezcla de frutas fermentadas. Resultados. La abundancia total fue de 287 individuos, con 59 recapturas (20,5%). Se obtuvieron tamaños poblacionales entre 8 y 339 individuos. La proporción sexual macho-hembra fue 3:1. Se capturaron mayores porcentajes de mariposas nuevas (41,8%) e intermedias (38,6%). El tiempo de residencia máximo registrado fue de 38 días. Se calcularon distancias totales de vuelo entre 149 y 1,231m, aunque las hembras presentaron los mayores promedios (303.7±189.4m) de distancia recorrida; pero no se encontraron diferencias significativas entre las distancias recorridas entre sexos (U= 265,5, p>0,05). Conclusiones: La estructura poblacional de M. helenor peleides presentó una variación espacial y temporal en el paisaje de bosque seco estudiado. Adicionalmente, se determinó que la cobertura de dosel natural juega un papel importante en la dinámica temporal y la distribución de la abundancia de este grupo de mariposas en el bosque seco tropical y se resalta la importancia de este ecosistema en la conservación de esta especie.

Extinction–immigration dynamics lag behind environmental filtering in shaping the composition of tropical dry forests within a changing landscape

The impact of rapid habitat loss and fragmentation on biodiversity is a major issue. However, we still lack an integrative understanding of how these changes influence biodiversity dynamics over time. In this study, we investigate the effects of these changes in terms of both niche‐based and neutral dynamics. We hypothesize that habitat loss has delayed effects on neutral immigration–extinction dynamics, while edge effects and environmental heterogeneity in habitat patches have rapid effects on niche‐based dynamics.We analyzed taxonomic and functional composition of 100 tree communities in a tropical dry forest landscape of New‐Caledonia subject to habitat loss and fragmentation. We designed an original, process‐based simulation framework, and performed Approximate Bayesian Computation to infer the influence of niche‐based and neutral processes. Then, we performed partial regressions to evaluate the relationships between inferred parameter values of communities and landscape metrics (distance to edge, patch area, and habitat amount around communities), derived from either recent or past (65 yr ago) aerial photographs, while controlling for the effect of soil and topography.We found that landscape structure influences both environmental filtering and immigration. Immigration rate was positively related to past habitat amount surrounding communities. In contrast, environmental filtering was mostly affected by present landscape structure and mainly influenced by edge vicinity and topography.Our results highlight that landscape changes have contrasting spatio‐temporal influences on niche‐based and neutral assembly dynamics. First, landscape‐level habitat loss and community isolation reduce immigration and increase demographic stochasticity, resulting in slow decline of local species diversity and extinction debt. Second, recent edge creation affects environmental filtering, incurring rapid changes in community composition by favoring species with edge‐adapted strategies. Our study brings new insights about temporal impacts of landscape changes on biodiversity dynamics. We stress that landscape history critically influences these dynamics and should be taken into account in conservation policies.

Assessing the accuracy of detected breaks in Landsat time series as predictors of small scale deforestation in tropical dry forests of Mexico and Costa Rica

Tracking the occurrence of deforestation events is an essential task in tropical dry forest (TDF) conservation efforts. Ideally, deforestation monitoring systems would identify a TDF clearing with near real time precision and high spatial detail, and alert park managers and environmental practitioners of illegal forest clearings occurring anywhere in a region of interest. Over the past several years there have been significant advances in the design and application of continuous land cover change mapping algorithms with these capabilities, but no studies have implemented such methods over human dominated TDF environments where small–scale deforestation (<5 ha) is widespread and hard to detect with moderate resolution sensors. The general objective for this research was to evaluate the overall accuracy of the BFASTSpatial R Package for detecting and monitoring small-scale deforestation in four sites located in tropical dry forest landscapes of Mexico and Costa Rica using greenness and moisture spectral indices derived from Landsat time series. Results show a high degree of spatial agreement (90%–94%) between the distribution of TDF clearings occurred during the 2013–2016 period (as indicated by VHR imagery interpretation) and BFASTSpatial outputs. NDMI and NBR2 had the best performance than other indices and this is evidenced by the combined overall, user's and producer's accuracies. In particular, NBR2 were the most accurate predictor of deforestation with an overall accuracy of 94.5%. Our results also imply that monitoring sites at an annual basis is feasible using BFASTSpatial and LTS, but that lower confidence should be given to sub-annual products given significant systematic temporal differences between the BFASTSpatial monthly product and reference data. The possibility of including more clear observations at the spatial resolution of Landsat (30-m) or higher will greatly increase the spatial and temporal accuracies of the method. Given its performance, BFASTSpatial can help monitor hotspots of small-scale TDF loss across Central and North America at little or no cost. Users of the method should have a strong knowledge of the local land use and land cover dynamics and the ecophysiology of vegetation types present in the landscape. This local expertise is necessary for interpreting and validating results as well as communicating its output to decision-makers and stakeholders.

Understanding Land Cover Change in a Fragmented Forest Landscape in a Biodiversity Hotspot of Coastal Ecuador

Understanding forest cover changes is especially important in highly threatened and understudied tropical dry forest landscapes. This research uses Landsat images and a Random Forest classifier (RF) to map old-growth, secondary, and plantation forests and to evaluate changes in their coverage in Ecuador. We used 46 Landsat-derived predictors from the dry and wet seasons to map these forest types and to evaluate the importance of having seasonal variables in classifications. Initial RF models grouped old-growth and secondary forest as a single class because of a lack of secondary forest training data. The model accuracy was improved slightly from 92.8% for the wet season and 94.6% for the dry season to 95% overall by including variables from both seasons. Derived land cover maps indicate that the remaining forest in the landscape occurs mostly along the coastline in a matrix of pastureland, with less than 10% of the landscape covered by plantation forests. To obtain secondary forest training data and evaluate changes in forest cover, we conducted a change analysis between the 1990 and 2015 images. The results indicated that half of the forests present in 1990 were cleared during the 25-year study period and highlighted areas of forest regrowth. We used these areas to extract secondary forest training data and then re-classified the landscape with secondary forest as a class. Classification accuracies decreased with more forest classes, but having data from both seasons resulted in higher accuracy (87.9%) compared to having data from only the wet (85.8%) or dry (82.9%) seasons. The produced cover maps classified the majority of previously identified forest areas as secondary, but these areas likely correspond to forest regrowth and to degraded forests that structurally resemble secondary forests. Among the few areas classified as old-growth forests are known reserves. This research provides evidence of the importance of using bi-seasonal Landsat data to classify forest types and contributes to understanding changes in forest cover of tropical dry forests.

Predicting aboveground forest biomass with topographic variables in human‐impacted tropical dry forest landscapes

AbstractTopographic variables such as slope and elevation partially explain spatial variations in aboveground biomass (AGB) within landscapes. Human activities that impact vegetation, such as cattle grazing and shifting cultivation, often follow topographic features and also play a key role in determining AGB patterns, although these effects may be moderated by accessibility. In this study, we evaluated the potential to predict AGB in a rural landscape, using a set of topographical variables in combination with indicators of accessibility. We modeled linear and non‐linear relationships between AGB, topographic variables within the territorial boundaries of six rural communities, and distance to roads. Linear models showed that elevation, slope, topographic wetness index, and tangential curvature could explain up to 21% of AGB. Non‐linear models found threshold values for the relationship between AGB and diffuse insolation, topographic position index at 19 × 19 pixels scale and differentiated between groups of communities, improving AGB predictions to 33%. We also found a continuous and positive effect on AGB with increased distance from roads, but also a piecewise relationship that improves the understanding of intensity of human activities. These findings could enable AGB baselines to be constructed at landscape level using freely available data from topographic maps. Such baselines may be of use in national programs under the international policy Reducing Emissions from Deforestation and Forest Degradation.

Abiotic and biotic changes at the basin scale in a tropical dry forest landscape after Hurricanes Jova and Patricia in Jalisco, Mexico

Given the current evidence of global change, extreme events are projected to be more frequent and intense. At a river basin scale, the immediate effects of hurricanes include changes in soil properties, vegetation structure and composition, and water volume and quality, which lead to changes in species distribution and community structure. The goal of this study was to identify key abiotic and biotic elements for monitoring hurricane events at the river basin scale by linking databases of vegetation cover, small mammal diversity and water quality between 2010 and 2016. Abiotic parameters and biotic communities were monitored in a tropical dry forest (TDF) landscape on the coast of Jalisco, Mexico after two major events: Hurricanes Jova (2011) and Patricia (2015). Three zones (1-upper, 2-middle and 3-lower basin) adjacent to the TDF were analyzed along the Cuitzmala River catchment areas before and after the events. We used the Enhanced Vegetation Index (EVI) as a proxy for vegetation greenness and the diversity index of a small mammal community of rodents and bats as indicators of terrestrial habitat quality, and Fecal Coliform (FC), Fecal Enterococci (FE), and Electrical Conductivity (EC) as indicators of the river-water condition. During the years of hurricanes (2011 and 2015) there was a decrease in the EVI and small mammal diversity, as well as changes in the concentration of FC, FE and EC. The main effects associated with the two hurricanes were observed in the lower basin where hurricanes made landfall and the forest had been converted to other land uses. The EVI, communities of small mammals, and abiotic and biotic water conditions were responsive to the effects of hurricanes and can thus be useful for a long-term ecological monitoring program at the basin scale. This program would allow a faster evaluation and response to future extreme meteorological events. Our results could be implemented through the Urban and Environmental Plans at the state level (Ordenamiento Territorial del Estado de Jalisco), through the regulation of sustainable agricultural and livestock techniques, and by educating local populations of the effects of extreme meteorological events.

Going beyond the green: senesced vegetation material predicts basal area and biomass in remote sensing of tree cover conditions in an African tropical dry forest (miombo woodland) landscape

In sub-Saharan Africa (SSA), tropical dry forests and savannas cover over 2.5 million km2 and support livelihoods for millions in fast-growing nations. Intensifying land use pressures have driven rapid changes in tree cover structure (basal area, biomass) that remain poorly characterized at regional scales. Here, we posed the hypothesis that tree cover structure related strongly to senesced and non-photosynthetic (NPV) vegetation features in a SSA tropical dry forest landscape, offering improved means for satellite remote sensing of tree cover structure compared to vegetation greenness-based methods. Across regrowth miombo woodland sites in Tanzania, we analyzed relationships among field data on tree structure, land cover, and satellite indices of green and NPV features based on spectral mixture analyses and normalized difference vegetation index calculated from Landsat 8 data. From satellite-field data relationships, we mapped regional basal area and biomass using NPV and greenness-based metrics, and compared map performances at landscape scales. Total canopy cover related significantly to stem basal area (r2 = 0.815, p < 0.01) and biomass (r2 = 0.635, p < 0.01), and NPV dominated ground cover (> 60%) at all sites. From these two conditions emerged a key inverse relationship: skyward exposure of NPV ground cover was high at sites with low tree basal area and biomass, and decreased with increasing stem basal area and biomass. This pattern scaled to Landsat NPV metrics, which showed strong inverse correlations to basal area (Pearson r = −0.85, p < 0.01) and biomass (r = −0.86, p < 0.01). Biomass estimates from Landsat NPV-based maps matched field data, and significantly differentiated landscape gradients in woody biomass that greenness metrics failed to track. The results suggest senesced vegetation metrics at Landsat scales are a promising means for improved monitoring of tree structure across disturbance and ecological gradients in African and other tropical dry forests.

Topographic position, but not slope aspect, drives the dominance of functional strategies of tropical dry forest trees

In seasonal plant communities, it is recognized that topography-related variation in water availability and solar radiation determine vegetation structure and community composition; however, the effects on functional structure, particularly through changes in resource use strategies of plants are still poorly understood. This study examines the effects of slope aspect and topographic position on functional trait dominance in a tropical dry forest landscape and explores whether strategies for coping with drought (avoidance vs. tolerance) segregate spatially along the water stress gradient created by the interaction of these two topographic factors. The study was conducted in the Balsas river basin in south-central Mexico. Functional traits were evaluated in 63 species of trees (≥ 2.5 cm diameter at breast height) dominant in plots located at three topographic positions (low, medium and high) and on two slope aspects (north and south). Eight leaf and four stem functional traits, relating to the plants’ ability to avoid or tolerate water and temperature stress, were measured. Community-level functional traits were strongly affected by topographic position while only a weak signal was detected by the slope aspect. Contrary to our expectations, attributes associated with drought tolerance predominated on the lower topographic positions of the slopes, (moister and warmer sites), while on the upper parts with drier soil, but cooler air, attributes associated with water stress avoidance dominated. In addition, variation in the dominance of leaf pulvini and trichomes along the topographic gradient suggests environmental filtering by elevated air temperatures and water stress, respectively. Overall, our results suggest that the upper topographic positions that generate a shorter and more fluctuating water-availability window, favor readily-deciduous plants with high levels of water storage in their tissues, traits allowing for a rapid avoid of water stress, whereas on the lower topographic positions, where the soil remains moist for longer periods of time, tardily-deciduous species thrive with dense, low-water content tissues, attributes that are associated with physiological tolerance to drought.

Patterns and correlates of plant diversity differ between common and rare species in a neotropical dry forest

Determining which factors affect species richness is important for conservation theory and practice. However, richness of common and rare species may be affected by different factors. We use an extensive inventory of woody plants from a tropical dry forest landscape in Yucatan, Mexico to assess the unique effects of environmental variables, spatial dependence of sampling sites, forest stand age and the combined effect of all groups of variables on species richness of woody plants with different levels of rarity (common, intermediate, rare, very rare)—according to their abundance, habitat specificity and spatial distribution range in the landscape. Analyzing separately common species and those with different levels of rarity uncovered contrasting patterns and correlates of species richness that were not apparent when focusing on all woody plants. In particular, richness of common and intermediate species was influenced mainly by environmental factors, whereas richness of very rare species was affected mostly by the unique effect of spatial dependence of sampling sites, suggesting a main role of environmental filtering and dispersal limitation, respectively. However, common and very rare species also responded inversely to some landscape metrics, revealing contrasting environmental preferences of these groups of species. These contrasting results suggest different underlying mechanisms and the need for very different conservation strategies. Therefore, basic and applied research on tropical forest biodiversity should consider separately species with different levels of rarity, focusing on which factors control variation in each level, and paying special attention to very rare species, generally the most specious and vulnerable to local extinction.

Importance of riparian habitat for frugivorous bats in a tropical dry forest in western Mexico

Abstract:Riparian forests (RF) provide shelter, feeding resources and commuting areas and are fundamental for local fauna during long drought periods in tropical dry forests. Nevertheless, information regarding vertebrate ecology in tropical RF is scarce. The studies of bats in riparian habitats have been mostly focused on insectivorous assemblages in non-tropical regions. We contrasted the occurrence of frugivorous bats between RF and upland dry forest (UDF) in a Neotropical dry forest region and evaluated how vegetation structure modulates frugivorous bat presence and abundance. We sampled bat ensembles and vegetation structure in three UDF and three RF sites in Jalisco, Mexico. Bat ensembles and populations were analysed with generalized linear models, including as independent factors: (1) habitat and (2) vegetation attributes. In 72 nights we captured 840 bats belonging to seven species. No effect of habitat type or vegetation structure on species richness was found, but habitat type did affect bat species composition and abundance. Moreover, vegetation structural traits affected frugivorous bat abundance. Frugivore abundance was higher in RF than in UDF probably because RF provides greater resources and more roosting sites. Riparian forests also present more canopy cover and accessible flight spaces. Our results support the importance of RF for frugivorous bats in terms of abundance and composition. Additionally, the lack of differences in species richness between UDF and RF highlights the importance of both habitats for maintaining frugivorous bats, as well as the related ecosystem processes and services in tropical dry forest landscapes.

Response of the copro-necrophagous beetle (Coleoptera: Scarabaeinae) assemblage to a range of soil characteristics and livestock management in a tropical landscape

Understanding changes in copro-necrophagous beetle diversity related to characteristics of habitat and soil associated with livestock management systems can provide a tool for the conservation of edaphic fauna and improved use of natural resources. We evaluated changes in species diversity and assemblage structure in copro-necrophagous beetles under different livestock management systems in an anthropized tropical dry forest landscape in Mexico. We used a standard sampling protocol to capture copro-necrophagous beetles in three livestock management systems: silvopastoral systems with Guazuma ulmifolia Lam. (SPS) associated with grasses, treeless pastures (monocultures) and managed tree fallows of tropical dry forest with livestock. We characterized the habitat structure, management practices and physico-chemical parameters of the soil in each system. We recorded a total of 1423 specimens belonging to 15 species. The results show a greater beetle species richness in the SPS with G. ulmifolia, which declines with reduced site complexity and soil quality and increased management practice intensity. There was a positive relationship between beetle species abundance and the soil physico-chemical characteristics such as moisture and nutrient content, as well as with the density of plants. A negative effect of management practices (use of insecticides, anti-parasite treatments and burning) was observed on beetle abundance; when the analyzed variables were related to each individual species, only four species responded to differences in levels of nitrogen and magnesium, as well as to the management practice and density of plants. Systems where perennial woody plants (trees and/or shrubs) interact with traditional components (animals and herbaceous forage plants) under integrated management can provide favorable conditions for the maintenance of a relatively high diversity of beetle species as well as a refuge for species with different habitat requirements.

Identification and quantification of drivers of forest degradation in tropical dry forests: A case study in Western Mexico

The intensity of forest degradation is linked to landowners’ decisions on management of their shifting cultivation systems. Understanding the processes involved in this land use type is therefore essential for the design of sustainable forest management practices. However, knowledge of the processes and patterns of forest transition that result from this practice is extremely limited. In this study, we used spatially-explicit binary logistic regression to study the proximate factors that relate to forest degradation by combining biophysical and socio-economic variables. Our study region is within the Ayuquila Basin, in Western Mexico, a typical fragmented tropical dry forest landscape dominated by shifting cultivation. Through a survey and semi-structured interviews with community leaders, we obtained data on the forest resources and on the uses that people make of them. Detailed forest cover maps for 2004 and 2010 were produced from high-resolution SPOT 5 data, and ancillary geographical data were used to extract spatial variables. The degree of social marginalization of each community and the ratio of forest area to population size were the main factors positively correlated with the probability of the occurrence of forest degradation. Livestock management and use of fence posts by the communities were also positively associated with forest degradation. Among biophysical factors, forest degradation is more likely to occur in flatter areas. We conclude that local drivers of forest degradation include both socioeconomic and physical variables and that both of these factors need to be addressed at the landscape level while developing measures for activities related to REDD+.

High Resilience of Herpetofaunal Communities in a Human-Modified Tropical Dry Forest Landscape in Western Mexico

Secondary forests are replacing mature primary forests in the tropics because of increasing demand for agricultural land to support the growing human population. It is important to determine the potential of these secondary forests to support old-growth forest species, particularly threatened animal groups such as reptiles and amphibians. Moreover, existing studies are biased towards tropical rain forests, even though tropical dry forests (TDF) are comparatively more threatened. Here we examine how different TDF successional stages support old-growth forest species of amphibians and reptiles in the Chamela region, western Mexico. Over the course of two years we conducted seven surveys for amphibians and reptiles in 15 one-ha plots representing four different stages of the succession chronosequence of the TDF, ranging from pasture to old-growth forest. We found that anurans, lizards and snakes did not differ greatly in abundance and species richness among vegetation successional stages. Moreover, dominant species were shared among most of the vegetation stages, indicating low habitat specialization. Herpetofauna species composition did not differ among vegetation stages, and species turnover among stages was relatively low. These results differ greatly from those found in some tropical rainforest sites, where characteristics of herpetofauna communities differ markedly among vegetation successional stages. Our results suggest that secondary TDF in human-dominated landscapes might support substantial reptile and amphibian diversity.

Beetle succession and diversity between clothed sun-exposed and shaded pig carrion in a tropical dry forest landscape in Southern Mexico

Over a 31-day period, the decomposition process, beetle diversity and succession on clothed pig (Sus scrofa L.) carcasses were studied in open (agricultural land) and shaded habitat (secondary forest) in Southern Mexico. The decomposition process was categorised into five stages: fresh, bloated, active decay, advanced decay and remains. Except for the bloated stage, the elapsed time for each decomposition stage was similar between open and shaded habitats, all carcasses reached an advanced decay stage in seven days, and the fifth stage (remains) was not recorded in any carcass during the time of this study. A total of 6344 beetles, belonging to 130 species and 21 families, were collected during the entire decomposition process, and abundances increased from fresh to advanced decay stages. Staphylinidae, Scarabaeidae and Histeridae were taxonomically and numerically dominant, accounting for 61% of the species richness and 87% of the total abundance. Similar numbers of species (87 and 88 species for open and shaded habitats, respectively), levels of diversity and proportions (open 49%; shaded 48%) of exclusive species were recorded at each habitat. There were significantly distinct beetle communities between habitats and for each stage of decomposition. An indicator species analysis (“IndVal”) identified six species associated to open habitats, 10 species to shaded habitats and eight species to advanced decay stages. In addition, 23 beetle species are cited for the first time in the forensic literature. These results showed that open and shaded habitats both provide suitable habitat conditions for the carrion beetle diversity with significant differences in community structure and identity of the species associated to each habitat. This research provides the first empirical evidence of beetle ecological succession and diversity on carrion in Mexican agro-pastoral landscapes.

Monitoring deforestation with MODIS Active Fires in Neotropical dry forests: An analysis of local-scale assessments in Mexico, Brazil and Bolivia

The detection of vegetation fires using remote sensing has proven useful for highlighting areas undergoing rapid conversion in humid forests, but not in tropical dry forest (TDF). To further understand this relationship, we explored the correlation between MODIS Active Fires and forest cover change at local scales using 3 × 3 km sampling grids in three TDF landscapes in Bolivia; Mexico, and Brazil. Our analysis showed no single overall correlation among sites between the frequency of fires reported by the MODIS Active Fire Mapping product and forest cover change. Also, aggregated patterns of fire occurrence in Brazil and Bolivia did not correspond to areas with high percentage of forest loss, which indicates that the fire/deforestation relationship in TDF is not apparent in a simple fire frequency map. However, statistically significant correlations were found in sampling boxes with 50–60%, 50–70%, 50–95% forest cover at “initial state” of the time series in the Mexican site, Bolivian site and Brazilian site, respectively. Our findings suggest that complex interactions between anthropogenic fire-use, satellite-detected fires, and deforestation in highly fragmented TDF landscapes are difficult to describe at regional scales and might only be possible to analyze using finer resolution sampling grids.