Tropical Dry Forest Region Research Articles

Hysterium madraspatanum (Hysteriaceae), a new species from Tropical Dry Evergreen Forest of Tamil Nadu, India

A new species of Hysterium, is described from tropical dry evergreen forest region of Chennai, Tamil Nadu, India, based on both morphological characteristics and molecular phylogenetic analysis using the Internal Transcribed Spacers (ITS) region of nuclear ribosomal DNA. The key morphological characters of the ascomata include the presence of a longitudinal slit remaining closed even at maturity. The ascospores biseriate having three septa with all the cells evenly pigmented including the terminal cells. The ascus measuring 115–122 × 20–22 μm. Ascospores initially two celled and finally become four celled, hyaline first, later changing to yellow and then dark brown, oblong to ellipsoid, 28–39 × 7–12 μm. The nrITS-based phylogenetic tree inferred from the Bayesian posterior probabilities indicate that H. madraspatanum is closely related to Hysterium pulicare, H. angustatum and H. rhizophorae. However, H. madraspatanum is morphologically distinct from them by having relatively larger spore size, shallow groove in the ascomata, spores with concolorous terminal cells. Therefore, is a novel species under the genus Hysterium. Azadirachta indica is reported in the study as a new host for the genus Hysterium.

Biogeographic analysis of population density of white-tailed deer in Mexico: Importance of the Protected Natural Areas and Wildlife Management Units

The white-tailed deer Odocoileus virginianus is the wildlife species with the greatest geographic distribution and economic importance in Mexico. This article presents a biogeographic analysis of the population density of this deer species by federal states, vegetation types, biogeographic provinces, and field methods, based on 200 selected studies. Estimates are highly variable and potentially biased due to the different field designs and statistical analyses. The national average density was estimated at 6.9 deer/km2 (SD = 5.1); specifically, 75.5 % of the estimates were less than 10 deer/km2, and only 5.5 % were greater than 15 deer/km2. The highest densities were obtained in the northern region by applying the strip transect counts; while estimations using the fecal group count method were more variable and were the most used method in temperate and tropical dry forest regions. The states with the highest densities were Coahuila, Tamaulipas, Jalisco, Morelos, Michoacán, and Durango. The highest densities were estimated in the xerophilous scrublands of the northeast, intermediate for temperate, tropical dry, and sub-deciduous forests; and the lowest in the tropical wet forest. The highest densities were reported for the Tamaulipeca province followed by the Altiplano Chihuahuense, Sierra Madre Occidental, Costa Pacífica, and Depresión del Balsas. The results of this analysis could guide management strategies for the conservation and sustainable use of this species in extensive UMAs and ANPs, and also to test ecological hypotheses. However, applying more rigorous field design and statistical analysis is important to obtain confident estimates of population density and other demographic parameters to monitor population dynamics.

Examining the Potential of Sentinel Imagery and Ensemble Algorithms for Estimating Aboveground Biomass in a Tropical Dry Forest

Accurate estimations of aboveground biomass (AGB) in tropical forests are crucial for maintaining carbon stocks and ensuring effective forest management. By combining remote sensing (RS) data with ensemble algorithms, reliable AGB estimates in forests can be obtained. In this context, the freely available Sentinel-1 (S-1 SAR) and Sentinel 2 multispectral imagery (S-2 MSI) data have a significant role in enhancing accurate AGB estimations at a lower cost, which is relevant for the tropical dry forest (TDF) regions where AGB estimation is uncertain or there is a lack of comprehensive exploration. This study aims to address this gap by presenting a cost-effective and reliable AGB estimation approach in the TDF region of Colombia. For this purpose, we modeled and compared the performance of two ensemble algorithms, random forest (RF) and extreme gradient boosting (XGBoost), to estimate AGB using three predictor categories (polarizations/textures, spectral bands/vegetation indices, and a combination of both). We then examined the modeling potential of S-1 SAR and S-2 MSI imagery in predicting forest AGB and subsequently identified the most suitable variables. To construct AGB models’ field data, we employed a clustered distributed sampling approach involving 100 subsample plots, each with an area of 400 m2. Stepwise multiple linear regression was applied to identify suitable predictors from the original satellite bands, vegetation indices, and texture metrics. To produce a map of AGB, predicted AGB values were calculated for every pixel within a specific satellite subscene using the most effective ensemble algorithm. Our study findings show that the RF model, which employed combined predictor sets, displayed superior performance when evaluated against the independent validation set. The RF model successfully estimated AGB with a high degree of accuracy, achieving an R2 value of 0.78 and an RMSE value of 42.25 Mg/ha−1. In contrast, the XGBoost model performed less accurately, obtaining an R2 value of only 0.60 and an RMSE value of 48.41 Mg/ha−1. The results also indicate that S-2 vegetation indices data were more appropriate for this purpose than S-1 texture data. Despite this, S-1 cross-polarized textures were necessary during the dry season for the combined datasets. The top predictive variables for S-2 images were cab and cw, as well as red-edge bands during the wet season. As for S-1 images, texture D_VH _Hom during the dry season was the most important variable for explaining performance. Overall, the proposed approach of using freely available Sentinel data seems to improve the accuracy of AGB estimation in heterogeneous forest cover and, as such, they should be recommended as a data source for forest AGB assessment.

Disturbance Induced Changes in Diversity of Medicinal Plants in a Dry Tropical Forest of India

Due to overexploitation for forest resources, many important medicinal plants are disappearing from the tropical dry forest (TDF) regions. The present study is aimed to investigate the diversity of medicinal plants exposed to different levels of anthropogenic disturbance in TDFs. For this study, we selected six forest regions, covering a radius of 25 km, and exposed to variable intensity of disturbances, in the form of illegal logging, cattle grazing and fire. Based on the intensity of three disturbances, we categorized the study sites as low (LDS) and high (HDS) disturbed sites, and analyzed differences in soil properties and vegetation parameters in the two disturbance categories. We recorded tree density, tree species richness and herbaceous species richness in 100 m2 quadrats at the selected regions. Results exhibited significantly greater soil organic C (LDS, 4.6%; HDS, 0.9%; P < 0.001), water holding capacity (LDS, 47.4%; HDS, 33.6%; P < 0.001), and sand content (LDS, 53.7%; HDS, 48.3%; P < 0.001) across LDS, whereas significantly higher bulk density (LDS, 1.30 gcm–3; HDS, 1.34 gcm–3; P < 0.05) and gravel content (LDS, 14.6%; HDS, 20.0%; P < 0.001) across HDS. We found considerable shift in relationships between vegetation parameters under the two disturbance regimes. The results indicated that many of the important medicinal plants (e.g., Adina cordifolia, Bauhinia vahlii, Holarrhena antidysenterica, Asparagus racemosus, Curculigo orchioides, Hemidesmus indicus, etc.) which are potential constituents of several ayurvedic preparations as well as of traditional medical systems are lacking from the HDS, either due to direct impact of disturbances or indirectly due to disturbance induced changes in soil properties. For instance, the high grazing pressure increased soil compaction, leading to increase in bulk density and decline in water holding capacity of soil. We suggest that forest managers take into consideration the presence of anthropogenic disturbances in their management and conservation efforts of medicinal plants in TDFs.

Modeling the potential distribution of cacti under climate change scenarios in the largest tropical dry forest region in South America

Climate change projections for the Brazilian semiarid region for the rest of this century include increased temperature, reduced precipitation and aridification. Consequently, alterations in the distribution of species are expected in the largest seasonally dry tropical forest in South America (Caatinga), which covers 75% of Brazil's semiarid region. This study modeled the potential distribution of eight cactus species native (target species) to the Caatinga under future climate scenarios and analyzed the range shifts of these species during the remainder of this century. Two online biodiversity databases, nine environmental variables and the Maxent algorithm were used, considering the time intervals 1961–1990, 2041–2060 and 2061–2080, along with two Representative Concentration Pathway (RCP) scenarios, 4.5 and 8.5. The potential species distribution models predict that: (1) the future climate conditions are likely to cause contraction or expansion of the areas with high habitat suitability (>0.75) of the target species; (2) species with widespread distribution are likely to be vulnerable to climate change; (3) for some cactus species, climate change will provide an opportunity for expansion, but for the majority it will be a threat to survival; and (4) it is premature to claim that the future vegetation of the Caatinga will be dominated by cacti.

Unraveling centric diatoms from the Caatinga: Coscinodiscophyceae and Mediophyceae in northwestern Ceará, Brazil

Abstract The Caatinga is the largest tropical dry forest region in South America and harbors an impressive biological diversity. However, efforts in the studies of many groups of organisms, especially aquatic ones, are very small compared to other Brazilian regions. The state of Ceará stands out due to the major concentration of surface water in the semi-arid region, and the diatom flora is virtually unknown. We performed a pioneering and extensive taxonomic study on the centric diatoms from the Caatinga, documenting the morphological variation of the species found, expanding their geographic distribution, and reviewing taxonomic and nomenclatural aspects when relevant. The study was based on planktonic and periphytic samples collected in four hydrographic basins located in the northwestern region of Ceará, northeastern Brazil. Fifteen infrageneric diatom taxa were identified, described, and illustrated using light and scanning electron microscopy. Discostella stelligera was first recorded for northeastern Brazil and D. woltereckii is a new record to the country. Diminutive centric diatoms are well represented in the samples and their taxonomy is discussed. Terpsinoë musica occurred in a population with high phenotypic plasticity and we discussed the related taxonomic implications.

Indicators of integrative recovery of vegetation, soil and microclimate in successional fields of a tropical dry forest

Secondary succession involves dynamic feedback among vegetation, environmental conditions and biota. Nevertheless, the recovery of tropical forests after anthropic management is often evaluated based solely on vegetation cover, which is easier to measure and requires less equipment and expertise than the assessment of soil and microclimate, but does not always reflect synchronic and integrative recovery. Given the convenience of measuring vegetation properties, this study aimed to identify the vegetation traits that could best inform on the progress of integrative recovery through the exploration of correlations among changes in soil, vegetation and microclimate over the course of succession and by the selection of the most informative and suitable vegetation indicators. We measured vegetation, soil and microclimate properties along a successional gradient in the tropical dry forest region of the coast of Jalisco, Mexico. Bi- and multi-variate analyses revealed clear correlation between changes in soil and microclimate components. Bivariate and stepwise regressions indicated that basal area, litterfall, plant richness and litter mass were the vegetation properties that were the most related to soil and microclimate recovery. Basal area was the most closely related to soil and microclimate recovery, and it was also related to the recovery of soil P, a key soil property. However, litter mass, which was highly correlated with basal area, is a less time-consuming alternative measurement that may be more manageable for assessing many sites. Litter mass is also a key variable connecting aboveground and belowground recovery processes, making it a particularly useful variable for evaluating integrative recovery. Since all indicators can be affected by natural or human disturbance, the choice of indicators to be used in each evaluation should be cautious and, whenever possible, consider the history of the plot. We discuss and suggest the complementary use of several indicators when disturbance has occurred during secondary succession.

Comparación multitemporal de áreas quemadas en un bosque seco tropical utilizando el índice de área quemada (IAQ)

Los análisis post incendio, como el índice de área quemada (IAQ), permiten discriminar áreas afectadas y severidad de los incendios forestales. En este estudio se comparó según la frecuencia de incendios, el comportamiento anual del IAQ en la región de bosque seco tropical del Área de Conservación Guanacaste, Costa Rica entre los años 1997 al 2019. Los resultados evidencian que las áreas frecuentemente quemadas por incendios forestales muestran un comportamiento diferenciado en el IAQ a lo largo de todos los años. Mostrando una relación directa entre la frecuencia de incendios forestales y los valores de IAQ. Donde a mayor frecuencia de incendios forestales, los valores de IAQ son mayores. Por otro lado, las áreas que han sido poco afectadas o no han sido afectadas del todo mostraron valores bajos de IAQ. Estos resultados podrían validar la hipótesis de que después de dos a tres incendios, el banco de semillas es completamente destruido. Esto debido a que la composición y estructura de los bosques secos tropicales cambia considerablemente después de múltiples incendios.

Brazilian tropical dry forest (Caatinga) in the spotlight: an overview of species of Aspergillus, Penicillium and Talaromyces (Eurotiales) and the description of P. vascosobrinhous sp. nov.

ABSTRACT A literature-based checklist of species of Aspergillus, Penicillium, and Talaromyces recorded in the Brazilian tropical dry forest (Caatinga), the largest tropical dry forest region in South America, is provided. A total of 130 species (60 Aspergillus, 57 Penicillium, and 13 Talaromyces) are reported. Soil was the most common substrate, with 122 species records. Various reported species are well known in biotechnological processes. This checklist reflects the limited knowledge of fungal species in tropical dry environments. These data provide a good starting point for biogeographical studies on species of Aspergillus, Penicillium, and Talaromyces in dry environments worldwide. In addition, the new species Penicillium vascosobrinhous is introduced, an endophytic fungus isolated from cactus of the Caatinga forest in Brazil.

Monitoring Woody Cover Dynamics in Tropical Dry Forest Ecosystems Using Sentinel-2 Satellite Imagery

Dry forests in Sub-Saharan Africa are of critical importance for the livelihood of the local population given their strong dependence on forest products. Yet these forests are threatened due to rapid population growth and predicted changes in rainfall patterns. As such, large-scale woody cover monitoring of tropical dry forests is urgently required. Although promising, remote sensing-based estimation of woody cover in tropical dry forest ecosystems is challenging due to the heterogeneous woody and herbaceous vegetation structure and the large intra-annual variability in the vegetation due to the seasonal rainfall. To test the capability of Sentinel-2 satellite imagery for producing accurate woody cover estimations, two contrasting study sites in Ethiopia and Tanzania were used. The estimation accuracy of a linear regression model using the Normalised Difference Vegetation Index (NDVI), a Partial Least Squares Regression (PLSR), and a Random Forest regression model using both single-date and multi-temporal Sentinel-2 images were compared. Additionally, the robustness and site transferability of these methods were tested. Overall, the multi-temporal PLSR model achieved the most accurate and transferable estimations (R2 = 0.70, RMSE = 4.12%). This model was then used to monitor the potential increase in woody coverage within several reforestation projects in the Degua Tembien district. In six of these projects, a significant increase in woody cover could be measured since the start of the project, which could be linked to their initial vegetation, location and shape. It can be concluded that a PLSR model combined with Sentinel-2 satellite imagery is capable of monitoring woody cover in these tropical dry forest regions, which can be used in support of reforestation efforts.

Resilience of soil aggregation and exocellular enzymatic functions associated with arbuscular mycorrhizal fungal communities along a successional gradient in a tropical dry forest

Arbuscular mycorrhizal (AM) fungi are well-known contributors to soil aggregation and nutrient cycling functions, but we still know little about their capacity to resist or recover from persistent disturbance. Rangeland management may deteriorate these functions by affecting the activity of soil biota, including AM fungi, among other consequences. If affected, some soil properties show recovery when management stops and natural regeneration is allowed. We conducted an experiment to evaluate if the functions related to soil aggregation and promotion of exocellular enzymatic activities associated with AM fungal communities had been affected by rangeland management and, if they had, whether they recovered with successional time when management stopped. AM fungal communities from ten sites with different successional ages in a tropical dry forest region were inoculated to the same host growing in pots divided by mesh into a plant compartment and an AM mycelium compartment. We examined soil stable aggregates fractions and enzymatic activities produced or promoted by AM fungi. Soil aggregation changed significantly only after the study had run for 3years, was higher in the hyphosphere than in the root compartment, and showed a low but positive relation with the successional age of the communities. The activity of phosphatase, but not casein-protease and beta-glucosidase, increased with successional age. Therefore, soil aggregation and enzyme activities associated with AM fungal communities seemed resilient because casein-protease and beta-glucosidase were unchanged, and aggregation and phosphatase were reduced by rangeland management but recovered with successional time.

Encounters Between Experiences and Measurements: The Role of Local Knowledge in Climate Change Research

Innovative approaches could enhance scientific insights into how climate change affects mountain ecosystems and livelihoods and enrich climate action. Using an inter- and transdisciplinary approach in a remote tropical dry forest region of the Andes in southern Ecuador, this article combines local knowledge about climate change and adaptation, based on perceptions and experiences, with quantitative climate measurements. Our theoretical framework is based on the concept of vulnerability and sustainable livelihoods perspectives. Methodologically, we draw on the Participatory Rural Appraisal approach. Participatory workshops and qualitative interviews were carried out in the canton of Macara between 2015 and 2017. Local and regional climate data series were analyzed for climate trends and extreme events. Our study improves understanding of the social and physical dimension of climate change. Especially in mountain areas, differing scales of climate data must be considered to capture local climate conditions and changes. Thus, local knowledge could make a major contribution to selecting representative climate datasets, estimating local impacts of climate change, and developing adaptation policies.

Wood density, deposits and mineral inclusions of successional tropical dry forest species

Wood water content, wood dry mass fraction, wood deposits and mineral inclusions separately affect wood mechanical properties, as well as plant survival and growth rates. Tree species occurring in recovering vegetation from deforestation face water stress, which is a particularly strong environmental filter in tropical dry forest regions. In this study, we analyze wood density and its associated variables of tree species present in early and late successional communities. We assessed and compared their wood density, wood water content, wood dry mass fraction, as well as wood cellular deposits, secretory elements and mineral inclusions which were described through anatomical sections. Wood density ranged from 0.10 g/cm3 (Jacaratia mexicana in late successional community) to 0.92 g/cm3 (Lysiloma divaricatum in early successional community). Successional species showed low intraspecific variability, despite large differences in the environmental conditions in the communities where they grow. Species with high wood water content were restricted to late successional communities, and pioneers showed higher wood density than non-pioneer species, which supports the linkage between high wood density and harsh environmental filtering through hydraulic safety. Wood density did not differ between columnar cacti (Pachycereus pecten-aboriginum and Pilosocereus collinsii) and tree species such as Bursera simaruba. Starch, tannins and crystals were abundant in most successional species and some species had gums; these deposits could potentially influence wood density and hydraulic, defense and storage plant functions. Our results suggest that modifications in the life cycle of successional tropical dry forest tree species due to anthropogenic activities may not be an important source of wood density variation.

Hummingbird-plant visitation networks in agricultural and forested areas in a tropical dry forest region of Guatemala

Tropical dry forest, especially in Central America, has experienced high rates of deforestation primarily due to conversion to agricultural fields and pastures. Yet little is known about the effects of the conversion of Central American tropical dry forest on the pollination interactions between hummingbirds and native plants. A better understanding of hummingbird-plant communities in transformed tropical dry forest ecosystems can be useful for the development of conservation strategies to maintain hummingbird diversity and plant-pollinator interactions. As a consequence, in this study, we evaluated how habitat conversion and seasonality affect the total number of recorded hummingbird-plant interactions in a tropical dry forest of Central America. We used network analysis to assess the effects of habitat conversion on the structure and dynamics of the plant-hummingbird assemblages at our study sites. Data on hummingbird visitation to native flowering plants were collected along four transects located in patches of tropical dry forest and four transects in agricultural areas. Each transect was visited twice during the dry season and twice during the rainy season. Our data suggest that, at a local scale, seasonality is a stronger predictor than habitat type of the recorded number of hummingbird-plant interactions at our study sites. The lack of differences in the number of interactions with respect to habitat type is probably related to the generalist nature of our studied hummingbird-plant assemblages, allowing plants and hummingbirds to persist and form new interactions in the transformed environment. Our data also suggest that, although hummingbird-plant assemblages can persist in agricultural environments, habitat conversion to agriculture can cause changes in network patterns such as lower interaction diversity, lower partner diversity, and a higher level of generalization, which have negative implications for the conservation of mutualist pollination interactions. Therefore, our data highlight the importance of natural and semi-natural tropical dry forest remnants within agricultural landscapes for the conservation of pollinators and pollination services necessary for the reproduction of native plants.

Temporal variation in pollination services to Cucurbita moschata is determined by bee gender and diversity

AbstractIt has been proposed that species‐rich insect communities and species turnover across landscapes enhance the pollination efficiency of crops through complementarity, where both the dominant and less abundant species contribute to reaching a yield threshold from pollination. Alternatively, fluctuations in the most abundant pollinator species, rather than changes in species richness, may drive temporal variation in pollination services. In this study, we used Cucurbita moschata as a model to investigate temporal variation in pollinator communities in a Mexican tropical dry forest region. We sampled floral visitors in the coastal region of Jalisco during the wet and dry seasons and determined the pollination efficiency of all floral visitors. Our results showed that there was temporal variation in the pollinator community and in the pollination efficiency of the main pollinators of Cucurbita moschata crops. In the wet season, native bees of the genus Peponapis were the most frequent and effective pollinators of C. moschata, whereas in the dry season, Peponapis bees were scarce and Apis mellifera became the most frequent floral visitor. Apis mellifera transfers smaller pollen loads than Peponapis, but it provides an effective pollination service in conjunction with other native bees during the dry season. There was also an interaction between flower gender and pollinator species, where A. mellifera had higher visitation rate to female C. moschata flowers, and Peponapis bees to staminate flowers. Mean visitation rate by Peponapis female bees was 17 times higher than visitation rate by male bees. This is the first report of a vis‐à‐vis relationship of pollinator gender with respect to plant gender in which plants of the genus Cucurbita that produce unisexual staminate and pistillate flowers are differentially visited by Peponapis male and female bees, where females are the main pollinators. Understanding the temporal variation in pollinator communities and the contribution of the different species of pollinators to the reproductive success of different crop species and varieties can be crucial to maintaining pollination services under the current global pollination crisis.

Good ant, bad ant? Soil engineering by ants in the Brazilian Caatinga differs by species

It is commonly acknowledged that ants improve the hydraulic properties of soils in which they build their nests. To date, however, most studies of such soil modifications have focused on one ant species and one type of ecosystem, rather than investigating how different ant species affect different types of land cover within the same landscape. Our study focused on modifications to water infiltration and surface texture of Haplic Luvisols by two ant species—one of them present only in a forest and the other present only in a pasture. These two sites are located near each other in the Caatinga, a tropical dry forest region of Brazil, and have similar climatic conditions and soil type. We found that in the forest site, soils undisturbed by ant activity already showed water infiltration 13 times higher than the similarly undisturbed soils of the pasture site; and that the ant Dinoponera quadriceps more than doubled water infiltration in their nest annular zones compared with the surrounding forest areas. In addition, D. quadriceps increased clay content in their mound soils by 50% compared with the soils of the surrounding forest. In contrast, at the pasture site, the leaf-cutter ant Atta laevigata had a mixed effect on water infiltration: compared with pasture matrix soils, their nest-building activities led to a threefold increase in infiltration of the mound soils, but a threefold decrease in the nest annular zones. In addition, compared with the pasture matrix, A. laevigata almost doubled sand content in their mounds—which explains the comparatively high infiltration rates. These results suggest that the contrasting soil modifications by the two species could lead to amplifying feedbacks in opposite directions: an ant species that depends on healthy forests is improving water infiltration and soil texture (and thus increasing water available to plants) in its environment, while another ant species that is known to profit from disturbances is having the opposite effect.

Idiosyncratic responses of aquatic and terrestrial insects to different levels of environmental integrity in riparian zones in a karst tropical dry forest region

Decisions about biodiversity conservation depend on how different taxonomic groups respond to human influenced environmental change. Here, we ask whether richness and composition of terrestrial (frugivorous butterflies and dung beetles) and aquatic insects (Plecoptera, Trichoptera, Ephemeroptera, Odonata and Coleoptera) change in a congruent manner across a gradient of riparian habitat degradation in a karst tropical dry forest region of Brazil, the Bodoquena Plateau. Our results showed incongruent ordination patterns based taxonomic groups can be masked by the predominant presence of generalist species in tropical dry forests and by historical factors related to the adaptability of several species to changing ecosystems.

EFFECTIVE PRECIPTATION, SOIL LOSS AND PLANT COVER SYSTEMS IN THE CAATINGA BIOME, BRAZIL

ABSTRACT The objective of this work was to evaluate the influence of anthropic activities on the effective precipitation (eP) and soil loss in watersheds under different land uses in a tropical dry forest region. The experimental area was located in the central part of the State of Ceará, Brazil. The land uses evaluated were: fallow Caatinga (FC), thinned Caatinga (TC) and deforested Caatinga followed by a burning procedure and pasture cultivation (DBP). The areas were monitored in the rainy season (January to May, 2010), when 57 natural rainfalls occurred, totaling 941 mm of precipitation. The eP and sediment productions were quantified by the sum of all occurrences during the study period, and the soil loss was represented by suspended and dragged sediments. The eP was 15.13 mm and sediment produced was 167.81 kg ha-1 in FC conditions. The eP values was smaller (11.28 mm) in the watershed with TC, which had soil loss sum of 42.04 kg ha-1. The largest annual eP was found in the DBP area, with 112.88 mm yr-1 of accumulated water depth, which also showed the greater annual soil loss (3114.97 kg ha-1). The greatest interference of plant cover in the two variables evaluated occurred in the first precipitation events, when the plants were not yet fully developed.

Hydrology Affects Environmental and Spatial Structuring of Microalgal Metacommunities in Tropical Pacific Coast Wetlands.

The alternating climate between wet and dry periods has important effects on the hydrology and therefore on niche-based processes of water bodies in tropical areas. Additionally, assemblages of microorganism can show spatial patterns, in the form of a distance decay relationship due to their size or life form. We aimed to test spatial and environmental effects, modulated by a seasonal flooding climatic pattern, on the distribution of microalgae in 30 wetlands of a tropical dry forest region: the Pacific coast of Costa Rica and Nicaragua. Three surveys were conducted corresponding to the beginning, the highest peak, and the end of the hydrological year during the wet season, and species abundance and composition of planktonic and benthic microalgae was determined. Variation partitioning analysis (as explained by spatial distance or environmental factors) was applied to each seasonal dataset by means of partial redundancy analysis. Our results show that microalgal assemblages were structured by spatial and environmental factors depending on the hydrological period of the year. At the onset of hydroperiod and during flooding, neutral effects dominated community dynamics, but niche-based local effects resulted in more structured algal communities at the final periods of desiccating water bodies. Results suggest that climate-mediated effects on hydrology can influence the relative role of spatial and environmental factors on metacommunities of microalgae. Such variability needs to be accounted in order to describe accurately community dynamics in tropical coastal wetlands.

Trade-offs between ecosystem services and alternative pathways toward sustainability in a tropical dry forest region

The design of strategies aimed at sustainable resource management requires an understanding of the trade-offs between the ecosystem services at stake, to determine appropriate ways in which to navigate them. We assess trade-offs between forage production for cattle ranching and the maintenance of carbon stocks or tree diversity in a Mexican tropical dry forest. Trade-offs between pairs of services were assessed by identifying their efficiency frontiers at both site and landscape scales. We also estimated service outcomes under current and hypothetical land-management conditions. We found stark trade-offs between fodder and carbon stocks and between fodder and tree species richness at the site scale. At the landscape scale, the efficiency frontier was concave, with a much less pronounced trade-off in the fodder-species richness case. Our estimates of current service supply levels showed a reduction of 18-21% for C stock and 41-43% for fodder biomass, relative to the maximum feasible values along the efficiency frontier. Choice of the optimum management strategy to reduce such inefficiency depended on deforestation level: secondary forest regeneration was most suitable when deforestation is low, whereas increased fodder productivity in the pastures is best when deforestation is high. Pasture enrichment with forage trees and secondary forest growth are potential management alternatives for achieving sustainability given the range of enabling ecological factors and to balance ecological and social sustainability given the requirements and preferences of local stakeholders. Given that analogous trade-offs are found across the tropics, this work contributes to reconciling tropical forest maintenance and its use for sustainable rural livelihoods.