Tropical Dry Forest Succession Research Articles

Crown cover of a dominant pioneer legume affects tree species regeneration in a secondary tropical dry forest

Background: Individual pioneer tree species often dominate early tropical dry forest succession and thereby affect possible successional pathways. Mimosa acantholoba var. eurycarpa is a highly dominant species in the tropical dry forest in Mexico.
 Hypothesis: Mimosa acantholoba var. eurycarpa exerts an inhibitory effect on the germination, establishment, survival, and early growth of light-demanding pioneers, while facilitating these processes for shade-tolerant old-growth forests species.
 Studied species: Lonchocarpus torresiorum, Lysiloma divaricatum, Mimosa acantholoba var. eurycarpa and Vachellia farnesiana.
 Study site and dates: Nizanda, Oaxaca, Mexico, 2020-2021.
 Methods: In 12 early successional plots, we applied three levels of crown cover removal (100, 50, and 0 %) of established trees of the dominant pioneer legume (M. acantholoba var. eurycarpa). We sowed seeds of the four study species in each experimental plot and recorded their germination, establishment, survival, and early growth over a 2-mo period.
 Results: The removal of crown cover of established M. acantholoba var. eurycarpa trees did not significantly affect germination. Lysiloma divaricatum had the highest germination probability, the fastest germination, and the highest establishment probability regardless of treatment. Lonchocarpus torresiorum had the highest establishment probability in plots where the crown cover of established M. acantholoba var. eurycarpa trees was removed The survival probability of both shade-tolerant species was highest in the 100 % removal treatment.
 Conclusions: Despite successful germination of shade-tolerant species, their survival is inhibited under the dense canopy of the dominant legume. Therefore, interventions to reduce the crown cover area of this dominant legume may stimulate forest recovery.

A flash in the pan? The population dynamics of a dominant pioneer species in tropical dry forest succession

AbstractGlobally, around half of all tropical forests are secondary communities which are recovering from previous disturbances. In these communities, dominant pioneers play a critical role in the successional dynamics due their ability to modify the environment, and thus to facilitate or hinder the performance of other species. In this study, we examined the population dynamics of the dominant pioneer species, Mimosa acantholoba var. eurycarpa, in a tropical dry forest during the process of secondary succession. We collected data from permanent plots over a period of 13 years and used integral projection models to analyze the vital rates and changes in population size. Most vital rates were negatively related to successional age, with resprouting, survival and recruitment of individuals responding more strongly, and individual growth rate more weakly. These vital‐rate trends translated into significant variation of population size over succession, with a maximum size at year four and a rapid decline thereafter. Overall, our findings suggest that this species benefits from its ability to display a large number of resprouts in very early stages of succession, contributing to the rapid increase in population density. However, as succession unfolds, a lack of resprouting and a decline in survival reduce its population size, to the point of local extinction. These results highlight the importance of resprouting in the early dynamics of tropical dry forest communities recovering from disturbance.

Diversity patterns along ecological succession in tropical dry forests: a multi‐taxonomic approach

Evaluating the diversity of multiple taxa is fundamental to understand community assembly and to assess the integrity and functionality of tropical secondary forests. In this study, we analyzed the natural regeneration of tropical dry forests (TDFs) in three regions of Brazil using Hill–Simpson diversity, abundance and β‐diversity of trees and five groups of insects (herbivores, fruit‐feeding butterflies, ants, culicid mosquitoes and dung beetles). Sampling was conducted in 39 0.1 ha plots using a chronosequence approach (13 plots in early, intermediate and old‐growth forests). We evaluated the contribution of three different levels to γ‐diversity: α (within plots), β1 (among plots) and β2 (among successional stages), and further determined the relative importance of turnover (species replacement) and nestedness (differences in species number among sites) to β2. Our results showed that, unexpectedly, the Hill–Simpson diversity was consistently higher in early than old‐growth stages for all regions, but varied more widely in the intermediate stages. For each group separately, the same trend was observed for butterflies, ants, dung beetles and herbivores and did not differ among stages for mosquitoes. Successional differences in abundance were only detected for trees (increasing along the gradient) and for mosquitoes (decreasing). According to our expectations, the additive partitioning analysis showed that β2‐diversity contributed more to γ‐diversity than β1‐diversity, when all taxa were considered together and for most of them separately (except for butterflies and dung beetles). Most of the β2‐diversity was due to species turnover, but this contribution varied among groups and regions, with the highest turnover for herbivores and the lowest for dung beetles. Our results suggest that the Hill–Simpson diversity and changes in species composition (as given by β2‐diversity) are better indicators of forest natural regeneration than raw species richness, corroborating previous studies with plants and animals.

The regulating role of Mimosa acantholoba var. eurycarpa in tropical dry forest succession: stem twisting as a successional accelerating mechanism

Several Fabaceae species dominate tropical dry forest (TDF) early succession thanks to their mechanisms to cope with the harsh environmental conditions prevailing at these successional stages. Mimosa acantholoba var. eurycarpa is one of these dominant species. We studied its dominance effect with special attention to the consequences of a stem deteriorating process here referred to as ‘stem twisting’, which ultimately causes stem breakage and leads to crown de-structuring and possibly premature tree death. Using 16 years of dynamic data gathered in permanent secondary forest plots spanning a broad age range in a Mexican TDF, we evaluated the effect of this species on understorey vegetation attributes. The density of M. acantholoba var. eurycarpa reduced understorey plant density. Almost half (47%) of the trees of this species underwent stem twisting at some point in succession, with the twisting probability being directly related to increments in tree size (crown area and basal area). The death risk of twisted trees (adjusted for crown area, number of stems, and basal area) was three-fold that of non-twisted trees. With age, M. acantholoba var. eurycarpa trees collapse because of their twisted stem condition, altering forest structure and opening the canopy. This phenomenon releases the growth of late-successional species in the understorey, thus accelerating successional development. These results indicate that stem twisting is a key driver of successional speed, given its high occurrence among adult trees of the study species. We conclude that M. acantholoba var. eurycarpa is a keystone taxon capable of controlling the successional pathway in TDF, first through its dominance in early succession and later via its massive death due to stem twisting.

Soil Respiration Is Influenced by Seasonality, Forest Succession and Contrasting Biophysical Controls in a Tropical Dry Forest in Northwestern Mexico

Soil respiration (RS) is an important component of the C cycle because it contributes significant CO2 emissions to the atmosphere that result from metabolism and respiration of its autotrophic and heterotrophic components. However, the relative importance of different biophysical controls that drive the variability of this flux and their influence along forest succession pathways is still unknown. We incorporate multiyear RS, ecosystem flux and meteorological measurements in old-growth (OG), mid-secondary (MS) and early-secondary (ES) tropical dry forests (TDFs) with the goal of assessing the temporal variation of RS and identifying the biophysical controls at each site by applying structural equation models (SEM). Along forest succession, RS followed the pattern of precipitation events; we identified by the end of the wet season that RS was sustained by a longer period at OG, while in MS and ES, RS decreased according to the soil moisture availability. According to SEM, soil moisture and soil temperature exert an effect on the variability of RS in all sites. However, we found that RS was also controlled by the vapor pressure deficit at MS and gross primary production at OG and ES. Our results suggest that seasonality has a different impact on RS along forest succession in TDFs found in northwestern Mexico and highlights the relevance of considering additional biophysical controls of RS for a better understanding this critical process of the C cycle.

Ecosystem services supply and interactions along secondary tropical dry forests succession

Secondary forests will likely dominate future tropical landscapes, and the ecosystem services they provide to humanity will be particularly relevant. However, few empirical studies provide quantitative evidence of how the supply of ecosystem services change along secondary forest succession. The need for such information is particularly pressing for tropical dry forests because of their extensive global coverage and a high degree of disturbance. Here we examine the changes in the potential supply of ecosystem services and the interactions among them along secondary tropical dry forest succession for a site on the Mexican Pacific coast. Using data from a chronosequence of twelve sites followed over ten years, we characterized changes in five ecosystem services along a successional gradient from abandoned farmland to old-growth forests: forage, multiple forest resources, microclimate regulation, carbon storage and carbon sequestration. The long-term recovery trajectory for each service was modelled using linear and non-linear mixed models. Interactions among them were examined over different timeframes using Spearman correlations. The results showed rapid non-linear recovery of multiple forest resources provision, microclimate regulation and carbon storage within the first two decades of succession. Carbon sequestration increased slightly over time, while the supply of forage showed no clear trend. The strength of the interactions among pairs of services changed through successional time, being particularly higher in farmlands and old-growth forests. Our findings suggest that adaptive forest management practices that foster the natural regeneration of tropical dry forests are cost-effective mechanisms to recover the supply of critical ecosystem services for local actors by meeting their livelihood needs as well as those for the global community through climate change mitigation. Maintaining tropical dry forest resilience will highly depend on the maintenance of diversity in terms of species and ecosystem services.

Using large-scale tropical dry forest restoration to test successional theory.

Microclimatic conditions change dramatically as forests age and impose strong filters on community assembly during succession. Light availability is the most limiting environmental factor in tropical wet forest succession; by contrast, water availability is predicted to strongly influence tropical dry forest (TDF) successional dynamics. While mechanisms underlying TDF successional trajectories are not well understood, observational studies have demonstrated that TDF communities transition from being dominated by species with conservative traits to species with acquisitive traits, the opposite of tropical wet forest. Determining how functional traits predict TDF tree species' responses to changing environmental conditions could elucidate mechanisms underlying tree performance during TDF succession. We implemented a 6-ha restoration experiment on a degraded Vertisol in Costa Rica to determine (1) how TDF tree species with different resource-use strategies performed along a successional gradient and (2) how ecophysiological functional traits correlated with tree performance in simulated successional stages. We used two management treatments to simulate distinct successional stages including: clearing all remnant vegetation (early-succession), or interplanting seedlings with no clearing (mid-succession). We crossed these two management treatments (cleared/interplanted) with two species mixes with different resource-use strategies (acquisitive/conservative) to examine their interaction. Overall seedling survival after 2 yr was low, 15.1-26.4% in the four resource-use-strategy×management-treatment combinations, and did not differ between the management treatments or resource-use-strategy groups. However, seedling growth rates were dramatically higher for all species in the cleared treatment (year 1, 69.1% higher; year 2, 143.3% higher) and defined resource-use strategies had some capacity to explain seedling performance. Overall, ecophysiological traits were better predictors of species' growth and survival than resource-use strategies defined by leaf and stem traits such as specific leaf area. Moreover, ecophysiological traits related to water use had a stronger influence on seedling performance in the cleared, early-successional treatment, indicating that the influence of microclimatic conditions on tree survival and growth shifts predictably during TDF succession. Our findings suggest that ecophysiological traits should be explicitly considered to understand shifts in TDF functional composition during succession and that using these traits to design species mixes could greatly improve TDF restoration outcomes.

Removal of cattle accelerates tropical dry forest succession in Northwestern Mexico

AbstractDomestic livestock influence patterns of secondary succession across forest ecosystems. However, the effects of cattle on the regeneration of tropical dry forests (TDF) in Mexico are poorly understood, largely because it is difficult to locate forests that are not grazed by cattle or other livestock. We describe changes in forest composition and structure along a successional chronosequence of TDF stands with and without cattle (chronic grazing or exclusion from grazing for ~ 8 year). Forest stands were grouped into five successional stages, ranging from recently abandoned to mature forest, for a total of 2.7 ha of the sampled area. The absence of cattle increased woody plant (tree and shrub) density and species richness, particularly in mid‐successional and mature forest stands. Species diversity and evenness were generally greater in sites where cattle were removed and cattle grazing in early successional stands reduced establishment and/or recruitment of new individuals and species. Removal of cattle from forest stands undergoing succession appears to facilitate a progressive and non‐linear change of forest structure and compositional attributes associated with rapid recovery, while cattle browsing acts as a chronic disturbance factor that compromises the resilience and structural and functional integrity of the TDF in northwestern Mexico. These results are important for the conservation, management, and restoration of Neotropical dry forests.

Bioacoustic analyses reveal that bird communities recover with forest succession in tropical dry forests

Owen, K. C., A. D. Melin, F. A. Campos, L. M. Fedigan, T. W. Gillespie, and D. J. Mennill. 2020. Bioacoustic analyses reveal that bird communities recover with forest succession in tropical dry forests. Avian Conservation and Ecology 15(1):25. https://doi.org/10.5751/ACE-01615-150125

Wood anatomy of dominant species with contrasting ecological performance in tropical dry forest succession

Environmental restrictions faced by successional species (those occurring in recovering vegetation) change gradually between early and late succession. In tropical dry forest (TDF), legume species dominate early succession, that is, accumulate more biomass than coexisting species, but later are gradually replaced by late successional species. Stem anatomical traits are involved in water conduction efficiency and safety, and thus biomass accumulation. We hypothesized that anatomical characteristics of dominant species may explain their status in their respective successional community. We analyzed the wood anatomy of TDF dominant successional species: Mimosa eurycarpa and M. tenuiflora (early successional), Lysiloma divaricatum (late successional), and Euphorbia schlechtendalii (successionally ambiguous). Anatomical variables and indices were estimated and compared between species through linear modeling. Unexpectedly, Mimosa species differed in porosity type, which is one characteristic linked to water stress tolerance. M. eurycarpa and L. divaricatum are ring-porous (an uncommon feature in tropical species), whereas M. tenuiflora and E. schlechtendalii displayed diffuse porosity. M. eurycarpa had the lowest vulnerability index (VI) and the highest relative hydraulic conductivity. Within-individual differences in relative water conduction in ring-porous species, driven by high vessel density in earlywood and low VI in latewood, likely represent a highly advantageous strategy in water-stressed successional environments.

Rodent community responses to vegetation and landscape changes in early successional stages of tropical dry forest

The extent to which the array of land covers dominating anthropogenic landscapes impacts on biodiversity remains today an open question of great relevance. The characteristics of the animal communities inhabiting tropical forest early successional stages can determine, to a large extent, the course of secondary succession and natural regeneration. In this study, we evaluated the response of terrestrial rodents to variations in vegetation and landscape attributes, in early stages of tropical dry forest succession, at three integration levels: (1) communities, (2) populations, and (3) individuals. Our results reveal a rodent response to the variation in vegetation and landscape attributes, which indeed was largely modulated by seasonality, and determined by the focal spatial scale considered. In general, most of the species were favored by vegetation structure simplification and increase in understory density, probably due to the increase in refuge and trophic resources. Nevertheless, one species, Lyomis pictus, was sensitive to variation in vegetation composition and negatively affected by a reduction in vegetation structural complexity, which could be explained by the high number of tree seeds included in their diet. We found a higher diversity of rodents in sites surrounded by a high coverage and connectivity of dry and riparian forest, probably because large forest patches act as sources of species and the forest connectivity favors the colonization process toward sites under regeneration. Our results showed that preserving remnants of the original vegetation and implementing management actions at different spatial scales in anthropogenic landscapes is critical for preventing: (1) an increase in generalist populations, (2) rapid faunal homogenization, (3) defaunation, and (4) the loss of specialist species; with profound implications for the ecology of forest, ecosystem services and human health.

Contrasting patterns of leaf trait variation among and within species during tropical dry forest succession in Costa Rica

A coordinated response to environmental drivers amongst individual functional traits is central to the plant strategy concept. However, whether the trait co-ordination observed at the global scale occurs at other ecological scales (especially within species) remains an open question. Here, for sapling communities of two tropical dry forest types in Costa Rica, we show large differences amongst traits in the relative contribution of species turnover and intraspecific variation to their directional changes in response to environmental changes along a successional gradient. We studied the response of functional traits associated with the leaf economics spectrum and drought tolerance using intensive sampling to analyse inter- and intra-specific responses to environmental changes and ontogeny. Although the overall functional composition of the sapling communities changed during succession more through species turnover than through intraspecific trait variation, their relative contributions differed greatly amongst traits. For instance, community mean specific leaf area changed mostly due to intraspecific variation. Traits of the leaf economics spectrum showed decoupled responses to environmental drivers and ontogeny. These findings emphasise how divergent ecological mechanisms combine to cause great differences in changes of individual functional traits over environmental gradients and ecological scales.

Can terrestrial laser scanners (TLSs) and hemispherical photographs predict tropical dry forest succession with liana abundance?

Abstract. Tropical dry forests (TDFs) are ecosystems with long drought periods, a mean temperature of 25 °C, a mean annual precipitation that ranges from 900 to 2000 mm, and that possess a high abundance of deciduous species (trees and lianas). What remains of the original extent of TDFs in the Americas remains highly fragmented and at different levels of ecological succession. It is estimated that one of the main fingerprints left by global environmental and climate change in tropical environments is an increase in liana coverage. Lianas are non-structural elements of the forest canopy that eventually kill their host trees. In this paper we evaluate the use of a terrestrial laser scanner (TLS) in combination with hemispherical photographs (HPs) to characterize changes in forest structure as a function of ecological succession and liana abundance. We deployed a TLS and HP system in 28 plots throughout secondary forests of different ages and with different levels of liana abundance. Using a canonical correlation analysis (CCA), we addressed how the VEGNET, a terrestrial laser scanner, and HPs could predict TDF structure. Likewise, using univariate analyses of correlations, we show how the liana abundance could affect the prediction of the forest structure. Our results suggest that TLSs and HPs can predict the differences in the forest structure at different successional stages but that these differences disappear as liana abundance increases. Therefore, in well known ecosystems such as the tropical dry forest of Costa Rica, these biases of prediction could be considered as structural effects of liana presence. This research contributes to the understanding of the potential effects of lianas in secondary dry forests and highlights the role of TLSs combined with HPs in monitoring structural changes in secondary TDFs.

Multiscale analysis of factors influencing herpetofaunal assemblages in early successional stages of a tropical dry forest in western Mexico

The Tropical Dry Forest (TDF) is one of the most highly transformed and threatened neotropical systems in the world and much of its original area has been replaced by secondary forests. Therefore, it is important to understand the process of ecological succession underlying the natural regeneration of TDF, especially the role of early successional stages as drivers of the course of secondary succession. In this study, we investigated the response of herpetofaunal assemblages to vegetation and landscape attributes in areas dominated by early successional stages of TDF. Such response was evaluated in terms of assemblage's composition, richness, taxonomic diversity and functional diversity. We found a high variation in composition, richness and diversity of herpetofaunal assemblages at the initial stages of TDF succession. According to our hypothesis, in general we found the richest herpetofaunal assemblages in sites embedded in the most conserved matrix with higher levels of vegetation cover. Additionally, patch density of forest was also associated to the variation in assemblages' richness. We found high specificity on the response of frogs, lizards and snakes to the surveyed local and landscape attributes. This response involved both taxonomic and functional diversity. This study shows that composition and quality of the surrounding matrix can actually drive the maintenance of herpetofauna species in early successional stages. Considering that these stages greatly influence the course of secondary succession, the natural regeneration of the herpetofauna communities of TDF will depend not only on the local vegetation attributes but also on the initial status of the surrounding matrix. Thus, in order to preserve the resilience of the herpetofaunal assemblages it is important an adequate management of the system, maintaining high levels of the original vegetation in anthropogenic landscapes.

The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests

AbstractUnderstanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy‐forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the ‘stress gradient hypothesis’ in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination—either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators—are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long‐term studies evaluating how these effects change with ontogeny, and studies focusing on the species‐specificity of interactions.

Mapping tropical dry forest succession using multiple criteria spectral mixture analysis

Tropical dry forests (TDFs) in the Americas are considered the first frontier of economic development with less than 1% of their total original coverage under protection. Accordingly, accurate estimates of their spatial extent, fragmentation, and degree of regeneration are critical in evaluating the success of current conservation policies. This study focused on a well-protected secondary TDF in Santa Rosa National Park (SRNP) Environmental Monitoring Super Site, Guanacaste, Costa Rica. We used spectral signature analysis of TDF ecosystem succession (early, intermediate, and late successional stages), and its intrinsic variability, to propose a new multiple criteria spectral mixture analysis (MCSMA) method on the shortwave infrared (SWIR) of HyMap image. Unlike most existing iterative mixture analysis (IMA) techniques, MCSMA tries to extract and make use of representative endmembers with spectral and spatial information. MCSMA then considers three criteria that influence the comparative importance of different endmember combinations (endmember models): root mean square error (RMSE); spatial distance (SD); and fraction consistency (FC), to create an evaluation framework to select a best-fit model. The spectral analysis demonstrated that TDFs have a high spectral variability as a result of biomass variability. By adopting two search strategies, the unmixing results showed that our new MCSMA approach had a better performance in root mean square error (early: 0.160/0.159; intermediate: 0.322/0.321; and late: 0.239/0.235); mean absolute error (early: 0.132/0.128; intermediate: 0.254/0.251; and late: 0.191/0.188); and systematic error (early: 0.045/0.055; intermediate: −0.211/−0.214; and late: 0.161/0.160), compared to the multiple endmember spectral mixture analysis (MESMA). This study highlights the importance of SWIR in differentiating successional stages in TDFs. The proposed MCSMA provides a more flexible and generalized means for the best-fit model determination than common IMA methods.

Mapping Tropical Dry Forest Succession With CHRIS/PROBA Hyperspectral Images Using Nonparametric Decision Trees

Most satellites for environmental monitoring point ground targets from a perpendicular position to the terrain, also known as nadir. The CHRIS/PROBA platform provides four extra angles of observation, plus nadir pointing: -55°, -36°, 0°, +36°, and +55°. The purpose of this study is to investigate the best season (wet or dry season) and angle of observation to map tropical dry forest succession in Brazil. Nonparametric decision trees were used to build up classification maps based on principal component analysis (PCA) inputs. Our results indicate that the use of off-nadir data improves the map accuracy of successional stages of tropical dry forests and riparian forests. Particularly, extreme and negative angles of observation generate higher map accuracies, suggesting that tree shadows are enhancing spectral differences between the studied vegetation classes. Images from the dry season provide better total and classes' map accuracies for late and intermediate stages of tropical dry forests. On the other hand, some classes, such as riparian forests and early stage of tropical forests need the use of off-nadir angles of observation to reach a minimum accuracy and best scores are reached using wet season's images.

Testing Chronosequences through Dynamic Approaches: Time and Site Effects on Tropical Dry Forest Succession

AbstractChronosequences, commonly used to assess succession, have been questioned because of their failure to project successional trajectories. Here, we develop a simple analytical approach combining both chronosequence and dynamic data to test the power of age of abandonment and site factors to explain and predict succession. The approach proceeds by first fitting statistical models relating age to attribute values (the chronosequence model) and their observed changes (the dynamic model) to test explanatory power. Predictive power is then tested by bootstrapping the chronosequence model to derive confidence intervals for expected changes and comparing them with the dynamic model. Finally, residuals from both models are tested against site factors. The procedure was applied to six attributes (basal area, plant density, mean plant height, species richness, evenness, and composition) of the woody community (plants >1 cm dbh within 0.1‐ha plots) in nine abandoned cattle pastures (0–12 yr) and three old growth tropical dry forests monitored over 6 yr. Age explained 60–97 percent of the variance in community attributes and only 32–57 percent in observed changes. It significantly overestimated basal area and mean height, while species richness and composition were highly predicted. Besides age, management history also explained successional dynamics. Our results suggest age is not necessarily a reliable predictor of short‐term successional dynamics, and explanatory power is not indicative of predictive power. Because of this low reliability, caution is needed when applying chronosequences to evaluate ecosystem services' recovery. The analytical approach developed here contributes to a better exploration of those possible limitations.

Quantifying tropical dry forest succession in the Americas using CHRIS/PROBA

This study explores the possibility of estimating different stages of ecological succession in tropical dry forests using CHRIS/PROBA hyperspectral and multi-angular satellite images. Tropical dry forests (TDFs) in the Americas are considered one of the most threatened ecosystems in region, experiencing also high rates of secondary growth. In this study, TDFs are studied along three successional stages (early, intermediate and late) in sites across a latitudinal gradient in the Americas. Sites are located in Mexico, Nicaragua and Brazil. Due to their strong annual phenological signal, reflectance values of CHRIS/PROBA Mode-4 were extracted for the dry and wet season, and afterwards analyzed using scatterplots, n-D visualization tools, and Transformed Divergence separability tests. Spectral separation of three successional stages within TDFs was observed in images corresponding to the dry season, at all study sites. In this season, it is possible to discriminate the different successional stages in all viewing angles. For the spectral separation of the three successional stages in images of the wet season, it is required the use of the 18 bands of the sensor. Our analysis also indicates that better spectral separation is achieved at ±55°, in both seasons. Our results confirm the utility of multi-angular and hyperspectral sensors as a critical tool for environmental planning in TDFs environments.

Drought resistance in early and late secondary successional species from a tropical dry forest: the interplay between xylem resistance to embolism, sapwood water storage and leaf shedding

The mechanisms of drought resistance that allow plants to successfully establish at different stages of secondary succession in tropical dry forests are not well understood. We characterized mechanisms of drought resistance in early and late-successional species and tested whether risk of drought differs across sites at different successional stages, and whether early and late-successional species differ in resistance to experimentally imposed soil drought. The microenvironment in early successional sites was warmer and drier than in mature forest. Nevertheless, successional groups did not differ in resistance to soil drought. Late-successional species resisted drought through two independent mechanisms: high resistance of xylem to embolism, or reliance on high stem water storage capacity. High sapwood water reserves delayed the effects of soil drying by transiently decoupling plant and soil water status. Resistance to soil drought resulted from the interplay between variations in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction, leading to a tradeoff of avoidance against tolerance of soil drought, along which successional groups were not differentiated. Overall, our data suggest that ranking species' performance under soil drought based solely on xylem resistance to embolism may be misleading, especially for species with high sapwood water storage capacity.