Trees adjust nutrient acquisition strategies across tropical forest secondary succession.

Nutrient limitation may constrain the ability of recovering and mature tropical forests to serve as a carbon sink. However, it is unclear to what extent trees can utilize nutrient acquisition strategies - especially root phosphatase enzymes and mycorrhizal symbioses - to overcome low nutrient availability across secondary succession. Using a large-scale, full factorial nitrogen and phosphorus fertilization experiment of 76 plots along a secondary successional gradient in lowland wet tropical forests of Panama, we tested the extent to which root phosphatase enzyme activity and mycorrhizal colonization are flexible, and if investment shifts over succession, reflective of changing nutrient limitation. We also conducted a meta-analysis to test how tropical trees adjust these strategies in response to nutrient additions and across succession. We find that tropical trees are dynamic, adjusting investment in strategies - particularly root phosphatase - in response to changing nutrient conditions through succession. These changes reflect a shift from strong nitrogen to weak phosphorus limitation over succession. Our meta-analysis findings were consistent with our field study; we found more predictable responses of root phosphatase than mycorrhizal colonization to nutrient availability. Our findings suggest that nutrient acquisition strategies respond to nutrient availability and demand in tropical forests, likely critical for alleviating nutrient limitation.

Changes in floristic and vegetation structure in a chronosequence of abandoned gold-mining lands in a tropical Amazon forest.

This study analyzes floristic and vegetation structure changes during forest succession after disturbances caused by small-scale gold mining in Madre de Dios (Peru). We compared the floristic and vegetation structure of a reference forest against three sites with different periods of abandonment after mining (5, 11 and 23-years). Three 20 × 60 m plots were defined on each site, and all tree species with a DBH >1 cm within the plots were inventoried. To evaluate species diversity and similarity, the Importance Value, effective numbers of species (0D, 1D, and 2D), and Chao-Jaccard similarity index were calculated. We used the Nonmetric multidimensional scaling for similarity ordination and the PERMANOVA test to evaluate differences in floristic composition. We recorded 129 tree species in the study areas and statistically significant differences between initial and intermediate stages were observed regarding floristic composition, basal area, height, and DBH. The transition from the initial successional stage to the reference forest produces an increase in basal area, species diversity, and floristic similarity. The 23-year-old stand had more species in common with the 11-year-old stand than the reference forest. Our results showed a high proportion of pioneer species and anemochory dispersal syndrome in the initial successional stages, but they decreased in later stages of the chronosequence. The floristic and structural attributes of forests throughout the chronosequence showed a fast recovery during secondary succession. After 23 years, the recovery of tree species density was 77 % of reference forest, while the relative recovery of species composition was much slower, on average 23 %. These results provide essential information to guide the selection of suitable species in ecological restoration projects after abandonment. Implementing forest restoration strategies based on reliable information to accelerate the process of vegetation succession is critical for recuperating areas degraded by gold mining at the Peruvian Amazon.

Tree demographic strategies largely overlap across succession in Neotropical wet and dry forest communities.

Secondary tropical forests play an increasingly important role in carbon budgets and biodiversity conservation. Understanding successional trajectories is therefore imperative for guiding forest restoration and climate change mitigation efforts. Forest succession is driven by the demographic strategies-combinations of growth, mortality and recruitment rates-of the tree species in the community. However, our understanding of demographic diversity in tropical tree species stems almost exclusively from old-growth forests. Here, we assembled demographic information from repeated forest inventories along chronosequences in two wet (Costa Rica, Panama) and two dry (Mexico) Neotropical forests to assess whether the ranges of demographic strategies present in a community shift across succession. We calculated demographic rates for >500 tree species while controlling for canopy status to compare demographic diversity (i.e., the ranges of demographic strategies) in early successional (0-30 years), late successional (30-120 years) and old-growth forests using two-dimensional hypervolumes of pairs of demographic rates. Ranges of demographic strategies largely overlapped across successional stages, and early successional stages already covered the full spectrum of demographic strategies found in old-growth forests. An exception was a group of species characterized by exceptionally high mortality rates that was confined to early successional stages in the two wet forests. The range of demographic strategies did not expand with succession. Our results suggest that studies of long-term forest monitoring plots in old-growth forests, from which most of our current understanding of demographic strategies of tropical tree species is derived, are surprisingly representative of demographic diversity in general, but do not replace the need for further studies in secondary forests.

Ecological integrity of tropical secondary forests: concepts and indicators.

Naturally regenerating forests or secondary forests (SFs) are a promising strategy for restoring large expanses of tropical forests at low cost and with high environmental benefits. This expectation is supported by the high resilience of tropical forests after natural disturbances, yet this resilience can be severely reduced by human impacts. Assessing the characteristics of SFs and their ecological integrity (EI) is essential to evaluating their role for conservation, restoration, and provisioning of ecosystem services. In this study, we aim to propose a concept and indicators that allow the assessment and classification of the EI of SFs. To this end, we review the literature to assess how EI has been addressed in different ecosystems and which indicators of EI are most commonly used for tropical forests. Building upon this knowledge we propose a modification of the concept of EI to embrace SFs and suggest indicators of EI that can be applied to different successional stages or stand ages. Additionally, we relate these indicators to ecosystem service provision in order to support the practical application of the theory. EI is generally defined as the ability of ecosystems to support and maintain composition, structure and function similar to the reference conditions of an undisturbed ecosystem. This definition does not consider the temporal dynamics of recovering ecosystems, such as SFs. Therefore, we suggest incorporation of an optimal successional trajectory as a reference in addition to the old-growth forest reference. The optimal successional trajectory represents the maximum EI that can be attained at each successional stage in a given region and enables the evaluation of EI at any given age class. We further suggest a list of indicators, the main ones being: compositional indicators (species diversity/richness and indicator species); structural indicators (basal area, heterogeneity of basal area and canopy cover); function indicators (tree growth and mortality); and landscape proxies (landscape heterogeneity, landscape connectivity). Finally, we discuss how this approach can assist in defining the value of SF patches to provide ecosystem services, restore forests and contribute to ecosystem conservation.

Regeneración de un bosque secundario afectado por el Huracán Otto en Costa Rica / Regeneration of a secondary forest affected by Hurricane Otto in Costa Rica

Resumen Introducción: Se han realizado múltiples estudios en bosques afectados por huracanes, pero la información obtenida para Costa Rica es escasa, o nula en el caso de impactos directos como lo fue Otto, por lo que es necesario ampliar el conocimiento que se tiene acerca de los efectos de estos fenómenos en bosques tropicales y los mecanismos de recuperación de estos biomas. Consecuentemente se vuelve necesario identificar la vulnerabilidad de los ecosistemas a largo plazo y cuantificar las pérdidas que se generan a diferentes escalas, producto de los intensos eventos pluviales y los fuertes vientos. Objetivo: Determinar el comportamiento y estado de la recuperación en un bosque secundario afectado directamente por el huracán Otto en Boca Tapada, Pital, San Carlos, Costa Rica. Métodos: Se establecieron 10 unidades de muestreo de 20 x 50 m distribuidas de forma sistemática dentro de un bosque secundario afectado por el huracán Otto en Boca Tapada de San Carlos. Se evaluó la condición actual del bosque, se identificaron las especies que más daño recibieron por consecuencia de los fuertes vientos, así como las que poseen capacidad de recuperarse a través de rebrotes. Se realizó un sobrevuelo con un vehículo no tripulado, y se construyó un ortomosaico que fue posteriormente digitalizado y clasificado de acuerdo con el estado de la cobertura forestal presente en tres tiempos evaluados, condición inicial, después del aprovechamiento forestal y la condición al momento de realizado el muestreo. Se comparó la densidad poblacional, diversidad y área basal con lo presentado para un bosque primario aledaño al sitio de estudio, que también fue afectado por el paso del huracán Otto. Resultados: Se obtuvo que un 69.5 % de los individuos con d ≥ 5 cm se encuentran en buen estado, un 20.3 % fue descopado y un 12.7 % inclinado sin exposición de raíces. La familia que más riqueza de especies aporta es Fabaceae, esta misma es la que más abundancia de individuos dañados posee y la que presentó mayor cantidad de especies con capacidad de rebrotar. La especie que más daños sufrió fue Couma macrocarpa (Euphorbiaceae). El área de cobertura boscosa inicial fue afectada en un 7,63 % por el aprovechamiento forestal, y en un 44.25 % por el paso del huracán Otto. Se determinó que existen diferencias significativas en la diversidad de especies (P = 0.0004; α = 0.05) y en la densidad de individuos (P = 0.0011; α = 0.05), el bosque secundario es quien posee la mayor media. No se presentaron diferencias significativas en los valores de área basal (P = 0.6951; α = 0.05). Conclusiones: Un 30,5 % de la masa forestal fue afectada por el paso del huracán Otto y la familia Fabaceae representa un papel importante en la recuperación del bosque. Además, el aprovechamiento forestal en un bosque puede aumentar el riesgo de afectación por el paso de huracanes y el bosque secundario posee mayor diversidad de especies y mayor densidad de individuos que el bosque primario.

Abstract Introduction: Multiple studies have been carried out in forests affected by hurricanes, but the information obtained for Costa Rica is scarce or null, in the case of direct impacts such as Otto, so it is necessary to expand the existing knowledge about the effects of these phenomena on tropical forests and the recovery mechanisms of these biomes. Consequently, it is necessary to identify the vulnerability of ecosystems in long term and quantify the losses that are generated at different scales, as a result of the intense events of rain and strong winds. Objective: Determining behavior and recovery status in a secondary forest directly affected by Hurricane Otto in Boca Tapada, Pital, San Carlos, Costa Rica. Methods: Ten 20 x 50 m sampling units were systematically distributed within a secondary forest affected by Hurricane Otto in Boca Tapada, San Carlos. The current condition of the forest was evaluated, the species that received the most damage due to high winds were identified, as well as those that have the capacity to recover through regrowths. An overflight was carried out with an unmanned aerial vehicle and an orthomosaic was constructed, subsequently digitized, and classified according to the state of the forest cover presented in three evaluated moments, initial condition, after logging and the condition at the time of sampling. Population density, diversity, and basal area, were compared to data obtained in an adjacent primary forest also affected by the passage of Hurricane Otto. Results: It was obtained that 69.5 % of individuals with d ≥ 5 cm are in good condition, 20.3 % were broken in the tree canopy and 12.7% inclined without exposure of the roots. The family that provided the greatest species richness is Fabaceae, which is the same with the greatest abundance of damaged individuals and the one with the highest number of species with the ability to resprouting. The species that suffered the most damage was Couma macrocarpa (Euphorbiaceae). The initial area of forest cover was reduced by 7.63 % due to logging and 44.25 % due to Hurricane Otto. It was determined that there are significant differences in species diversity (P = 0.0004; α = 0.05) and in the density of individuals (P = 0.0011; α = 0.05). The secondary forest has the highest average in both cases. There are no significant differences in the values of the basal area (P = 0.6951; α = 0.05). Conclusions: 30.5 % of the forest mass was affected by the passage of Hurricane Otto and the Fabaceae family plays an important role in forest recovery. In addition, forest harvesting in a forest can increase the risk of being affected by the passage of hurricanes and the secondary forest has a greater diversity of species and a higher density of individuals than the primary forest.

The role of land-use history in driving successional pathways and its implications for the restoration of tropical forests.

Secondary forests are increasingly important components of human-modified landscapes in the tropics. Successional pathways, however, can vary enormously across and within landscapes, with divergent regrowth rates, vegetation structure and species composition. While climatic and edaphic conditions drive variations across regions, land-use history plays a central role in driving alternative successional pathways within human-modified landscapes. How land use affects succession depends on its intensity, spatial extent, frequency, duration and management practices, and is mediated by a complex combination of mechanisms acting on different ecosystem components and at different spatial and temporal scales. We review the literature aiming to provide a comprehensive understanding of the mechanisms underlying the long-lasting effects of land use on tropical forest succession and to discuss its implications for forest restoration. We organize it following a framework based on the hierarchical model of succession and ecological filtering theory. This review shows that our knowledge is mostly derived from studies in Neotropical forests regenerating after abandonment of shifting cultivation or pasture systems. Vegetation is the ecological component assessed most often. Little is known regarding how the recovery of belowground processes and microbiota communities is affected by previous land-use history. In published studies, land-use history has been mostly characterized by type, without discrimination of intensity, extent, duration or frequency. We compile and discuss the metrics used to describe land-use history, aiming to facilitate future studies. The literature shows that (i) species availability to succession is affected by transformations in the landscape that affect dispersal, and by management practices and seed predation, which affect the composition and diversity of propagules on site. Once a species successfully reaches an abandoned field, its establishment and performance are dependent on resistance to management practices, tolerance to (modified) soil conditions, herbivory, competition with weeds and invasive species, and facilitation by remnant trees. (ii) Structural and compositional divergences at early stages of succession remain for decades, suggesting that early communities play an important role in governing further ecosystem functioning and processes during succession. Management interventions at early stages could help enhance recovery rates and manipulate successional pathways. (iii) The combination of local and landscape conditions defines the limitations to succession and therefore the potential for natural regeneration to restore ecosystem properties effectively. The knowledge summarized here could enable the identification of conditions in which natural regeneration could efficiently promote forest restoration, and where specific management practices are required to foster succession. Finally, characterization of the landscape context and previous land-use history is essential to understand the limitations to succession and therefore to define cost-effective restoration strategies. Advancing knowledge on these two aspects is key for finding generalizable relations that will increase the predictability of succession and the efficiency of forest restoration under different landscape contexts.

Litter decomposition and nutrient release dynamics of leaves and roots of the babassu palm in eastern Amazonia

The ruderal babassu palm (Attalea speciosa) is expanding on large areas of degraded Amazon landscapes. Decomposition of leaves and roots is in the center of plant:soil interactions. We evaluated decomposition and nutrient concentrations of leaves and fine roots of babassu in comparison with two exotic reference species, Acacia mangium (slow degradability) and Leucaena leucocephala (fast degradability), in a 138-day litterbag assay carried out in secondary forest stands of different age and babassu abundance. We chose 4-mm over 2-mm mesh litterbags based on a pilot study. Babassu leaves degraded slower than leaves of A. mangium and L. leucocephala, and also had lower nitrogen, phosphorus and calcium concentrations in all stages of decomposition. By contrast, potassium concentrations in babassu leaves were higher than in both reference species at 0 and 50 days. Roots of all three species decomposed slower than leaves. Compared to the leaves, both biomass loss and nutrient concentrations differed less between babassu and reference-species roots, except for lower nitrogen concentration in babassu roots. Leaf-litter decomposition of all three species was significantly faster in old than in young secondary forest, suggesting an acceleration of decomposition along succession. Babassu leaves decomposed faster in old babassu-dominated than non-dominated secondary forest, pointing to the existence of specialized decomposer communities in babassu-dominated stands. (AU)

Litter decomposition and nutrient release dynamics of leaves and roots of the babassu palm in eastern Amazonia / Decomposição de serrapilheira e dinâmica de nutrientes de folhas e raízes da palmeira babaçu na periferia leste da Amazônia

The ruderal babassu palm (Attalea speciosa) is expanding on large areas of degraded Amazon landscapes. Decomposition of leaves and roots is in the center of plant:soil interactions. We evaluated decomposition and nutrient concentrations of leaves and fine roots of babassu in comparison with two exotic reference species, Acacia mangium (slow degradability) and Leucaena leucocephala (fast degradability), in a 138-day litterbag assay carried out in secondary forest stands of different age and babassu abundance. We chose 4-mm over 2-mm mesh litterbags based on a pilot study. Babassu leaves degraded slower than leaves of A. mangium and L. leucocephala, and also had lower nitrogen, phosphorus and calcium concentrations in all stages of decomposition. By contrast, potassium concentrations in babassu leaves were higher than in both reference species at 0 and 50 days. Roots of all three species decomposed slower than leaves. Compared to the leaves, both biomass loss and nutrient concentrations differed less between babassu and reference-species roots, except for lower nitrogen concentration in babassu roots. Leaf-litter decomposition of all three species was significantly faster in old than in young secondary forest, suggesting an acceleration of decomposition along succession. Babassu leaves decomposed faster in old babassu-dominated than non-dominated secondary forest, pointing to the existence of specialized decomposer communities in babassu-dominated stands.(AU)

A palmeira ruderal babaçu (Attalea speciosa) se expande em grandes áreas da Amazônia já desmatada e degradada. A decomposição é chave na dinâmica sucessional e nas interações planta:solo. Avaliamos decomposição e concentração de nutrientes de folhas e raízes finas de babaçu e de duas espécies exóticas de referência, Acacia mangium (decomposição lenta) e Leucaena leucocephala (decomposição rápida), em capoeiras de diferente idade e grau de dominância de babaçu usando litterbags durante 138 dias. Usamos litterbags com malha de 4 mm em vez de 2 mm, com base em um estudo-piloto. As folhas de babaçu se decompuseram mais lentamente que as de A. mangium e L. leucocephala, e apresentaram concentrações mais baixas de nitrogênio, fósforo e cálcio em todos os estágios de decomposição. Em contraste, a concentração de potássio em folhas de babaçu foi mais alta que nas espécies de referência aos 0 e 50 dias. Raízes se decompuseram mais lentamente que folhas nas três espécies. Tanto a perda de massa, como a concentração de nutrientes diferiram menos entre as raízes que entre as folhas de babaçu e as espécies de referência, exceto a concentração de nitrogênio nas raízes de babaçu. A decomposição foliar das três espécies foi significantemente mais rápida em capoeira velha que em capoeira jovem, sugerindo uma aceleração da decomposição ao longo dos estágios sucessionais. A decomposição foliar do babaçu foi mais rápida em capoeira velha com alta dominância de babaçu que em capoeira velha com baixa dominância, apontando para a existência de comunidades especializadas de decompositores em áreas dominadas por babaçu.(AU)

Secondary Succession under invasive species (Pteridium aquilinum) conditions in a seasonal dry tropical forest in southeastern Mexico.

The role of invasive species in ecosystem functioning represents one of the main challenges in ecology. Pteridium aquilinum is a successful cosmopolitan invasive species with negative effects on the ecological mechanisms that allow secondary succession. In this study, we evaluated the influence of P. aquilinumon secondary succession under different disturbances in a seasonal dry forest of the Yucatán Peninsula. We determined species richness, composition and the relative importance value in four sampling units. Fabaceae followed by Asteraceae, Meliaceae, Rubiaceae, Sapindaceae and Verbenaceae were the most species rich families. A dissimilarity analysis determined significant differences in beta diversity between sampling units. With a generalized linear model we found that species richness was best explained by site conditions, followed by calcium and soil organic matter. Also, the generalized linear model showed that abundance resulted in a strong correlation with site conditions and soil characteristics. Specific soil conditions related to phosphoro and calcium were also detected as beneficiary to the successional processes. Our results suggest that applying fire restriction and periodic cutting of the bracken fern, this can increase a higher diversity of species.

Shade tolerance within the context of the successional process in tropical rain forests

Shade tolerance (the capacity to survive and grow over long periods under shade) is a key component of plant fitness and the foundation of current theories of forest succession in tropical rain forests. It serves as a paradigm to understand the optimal allocation of limited resources under dynamic light regimes. I analyze how tropical rain forest succession influences the expression of ecophysiological mechanisms leading to shade tolerance, and identify future areas that will increase our understanding of the ecological and evolutionary consequences of this phenomenon. Shade tolerance is a multivariate, continuous functional trait reflecting the growth-mortality trade-off of investing resources under limited light vs. exploiting high light conditions. I propose the life cycle successional trajectory model of Gómez-Pompa & Vázquez-Yanes as an integrative tool to understand tropical rain forest succession. This model shows how species distribute along the successional environmental gradient based on their degree of shade tolerance and represents a more integrative paradigm to understand the interface between different aspects of species diversity (ontogenetic variation and functional diversity) throughout succession. It proposes that different trait combinations determining shade tolerance are expressed at different stages of the life cycle, which affects how and when plants enter the successional trajectory. Models explaining the expression of shade tolerance (resource availability, carbon gain, CSR, resource competition) are based on whole-plant economics and are not mutually exclusive. The analysis of shade tolerance is biased towards tree seedlings in the understory of mature forests. Other life stages (juvenile and adult trees), life forms, and microhabitats throughout the forest profile are almost always excluded from these analyses. More integrative explanations based on the distribution of functional traits among species, ontogenetic stages, and the nature of the environmental gradient are being developed based on long-term data and chronosequence comparisons. In summary, shade-tolerance is a complex phenomenon, is determined by multiple characters that change ontogenetically over space and time and entails considerable plasticity. Current methods do not account for this plasticity. Understanding the nature of shade tolerance and its functional basis is critical to comprehending plant performance and improving the management, restoration and conservation of tropical rain forests given the combined threats of global warming and habitat loss.

La tolerancia a la sombra (la capacidad de sobrevivir y crecer durante largos períodos bajo sombra profunda) es un componente clave del valor adaptativo de la planta y la base de las teorías actuales de la sucesión forestal de la selva tropical. Sirve como un paradigma para entender la asignación óptima de recursos limitados bajo regímenes dinámicos de luz. En esta revisión analizo cómo la sucesión de los bosques tropicales lluviosos influye en la expresión de los mecanismos ecofisiológicos que conducen a la tolerancia a la sombra, e identifico áreas futuras que pueden aumentar nuestra comprensión de las consecuencias ecológicas y evolutivas de este fenómeno. La tolerancia a la sombra es un rasgo funcional continuo y multivariable que refleja el balance de invertir recursos bajo condiciones de luz limitada versus crecer más rápidamente en condiciones de luz intensa. Propongo el modelo de ciclo de vida a lo largo de la trayectoria de sucesión de Gómez-Pompa y Vázquez-Yanes como una herramienta integradora para entender la sucesión de la selva tropical. Este modelo muestra cómo las especies se distribuyen a lo largo del gradiente ambiental en función de su grado de tolerancia a la sombra, y representa un paradigma más integrador para comprender la interacción entre los diferentes componentes de la diversidad de especies (diversidad taxonómica y funcional y variación ontogenética) a lo largo de la sucesión. El modelo propone que las diferentes combinaciones de caracteres funcionales que determinan la tolerancia a la sombra se expresan en diferentes etapas del ciclo de vida, y afectan cómo y cuándo las plantas ingresan en el proceso de sucesión. Los modelos que explican la expresión de tolerancia a la sombra (disponibilidad de recursos, ganancia de carbono, CSR, competencia de recursos) se basan en la economía de toda la planta y no son mutuamente excluyentes. Se están desarrollando explicaciones más integradoras basadas en la distribución de caracteres funcionales entre especies, etapas ontogenéticas, y micrositios, mediante el uso de estudios de cronosecuencia y metadatos colectados a largo plazo. El análisis de la tolerancia a la sombra está sesgado hacia las plántulas de árboles y el sotobosque. Otras formas de vida y microhábitats dentro del perfil del bosque están casi excluidas de estos análisis. En resumen, la tolerancia a la sombra es un fenómeno complejo, está determinada por múltiples caracteres funcionales que cambian ontogenéticamente en el espacio y el tiempo, e implica una considerable plasticidad. Los métodos actuales no toman en cuenta esta plasticidad. Comprender la naturaleza de la tolerancia a la sombra y su base funcional es fundamental para entender el crecimiento de la planta y mejorar la gestión, restauración, y conservación de los bosques tropicales, los cuales enfrentan las amenazas combinadas del calentamiento global y la pérdida de hábitat.

Successional and seasonal changes of leaf beetles and their indicator value in a fragmented low thorn forest of northeastern Mexico (Coleoptera, Chrysomelidae).

Leaf beetles (Chrysomelidae: Coleoptera) constitute a highly diverse family of phytophagous insects with high ecological relevance, due to their host plant specificity and their close association to vegetation variables. Therefore, secondary succession and seasonal changes after loss of vegetal cover will have a significant influence on their community patterns. Accordingly, responses of leaf beetles to such environmental heterogeneity make them a suitable taxon for monitoring disturbance, which is more important for endangered habitats such as the low thorn forests (LTF) in northeastern Mexico. We conducted a study in a LTF fragment in order to assess the effects of secondary succession and seasonality on leaf beetle communities, as well as to quantify the importance of Chrysomelidae as an indicator taxon. Landsat scenes were used for delimiting a successional gradient, in which four succession categories were selected: four years, 17 years, and 31 years since loss of vegetal cover, and conserved areas. Eight plots of 100 m2 were randomly delimited in each category; plots were sampled monthly, using an entomological sweep net, from May 2016 to April 2017. In total, 384 samples were collected by the end of study, from which 6978 specimens, six subfamilies, 57 genera, and 85 species were obtained. Species richness was higher in early succession areas. Abundance declined significantly from early successional to conserved areas, but the conserved areas had the higher diversity. Furthermore, differences in abundance were significant between rainy and dry seasons in areas of four, 17, and 31 years of succession, but not in conserved areas; also, all categories had a similar abundance during the dry season. Intermediate (17 and 31 years) and conserved areas differed in the season of higher diversity. Regarding inventory completeness, it was close to or above 70 % for all comparisons, although it was very low for the 17-year category during the rainy season. Faunistic similarity was higher between intermediate categories. A total of 24 species had a significant indicator value. Effects of succession time and seasonality on leaf beetle communities are here quantified for first time in LTF forests. Influences of environmental heterogeneity and intermediate disturbance are discussed as main drivers of the results obtained. Several leaf beetle species are proposed that could be useful for monitoring succession time and secondary LTF vegetation in northeastern Mexico. However, studies must be replicated at other regions, in order to obtain a better characterization of disturbance influence on leaf beetles.

Seasonal microclimatic variation in a succession gradient of low thorn forest in Northeastern Mexico / Variación microclimática estacional en un gradiente sucesional de selva baja espinosa en el Noreste de México

Abstract Global increase in land cover change and deforestation bring about fragmentation of a high proportion of native vegetation areas. Microclimate is among the first modified factors after vegetation loss, effects of such disturbances are critical for species performance. However, both secondary succession and seasonality provoke further modifications in abiotic environment after disturbances. Although microclimate patterns during succession are well studied for several ecosystems, they are practically unknown for low thorn forests. In Northern Mexico, this is an endangered ecosystem characterized by harboring a high percentage of endemics. Measurement of microclimatic factors is crucial for understanding possible consequences of post-disturbance time on species inhabiting this ecosystem. This work aimed to assess seasonal variation of microclimatic patterns in a succession gradient of four categories (conserved areas, 31, 17 and four years of succession). The study area was delimited using Landsat satellite images (1973, 1986, 2000, 2005, and 2013) in a fragment of low thorn forest in Northeastern Mexico. For microclimate characterization we studied wind speed, temperature, relative humidity, heat index, dew point, and evapotranspiration. Variables were measured monthly on eight plots, in each of the four successional categories, during two different seasons: wet (May through October 2016) and dry season (November 2016 through April 2017). A multivariate discriminant function analysis showed that microclimate differs among successional stages. In the wet season, early succession areas were characterized by higher values of heat index and wind speed, contrary to conserved areas. In the dry season, successional differences were attributed to wind speed and relative humidity. Moreover, microclimate differences between categories and importance of variables measured were both higher only during the dry season. Our results show that seasonality influences greatly microclimatic patterns during secondary succession. In addition, each one of the successional categories exhibited unique microclimatic conditions. Remarkably, four, 17, and even 31 years succession categories differed from conserved areas. This work provides evidence on the great relevance of seasonality and microclimate for studying secondary succession. It is suggested to take both factors into consideration when implementing conservation programs concerning endangered habitats such as low thorn forests. As an ecosystem poorly studied, microclimate characterization provided herein, shall help to a better understanding and management of these areas.(AU)

Resumen El aumento global en el cambio de cobertura vegetal y la deforestación han fragmentado una elevada proporción de áreas de vegetación nativa. El microclima es un factor que se modifica después de la pérdida de vegetación, y los efectos de tales perturbaciones son trascendentales para las especies. Sin embargo, tanto la sucesión secundaria como la estacionalidad implican modificaciones adicionales en el medio abiótico después del disturbio. Aunque los patrones microclimáticos durante la sucesión son conocidos en varios ecosistemas, no se han evaluado en áreas de selva baja espinosa, que constituye un ecosistema amenazado en el norte de México. La medición de tales factores microclimáticos es crucial para comprender las consecuencias de la recuperación post-disturbio en las especies. Por lo tanto, el objetivo del estudio fue evaluar la variación estacional del microclima en un gradiente de sucesión de cuatro categorías (áreas conservadas, 31, 17 y cuatro años de sucesión), delimitadas mediante imágenes de satélite LANDSAT (1973, 1986, 2000, 2005 y 2013) en un fragmento de selva baja espinosa en el noreste de México. Para caracterizar el microclima se consideraron la velocidad del viento, temperatura, humedad relativa, índice de calor, punto de rocío y evapotranspiración. Las variables se midieron de forma mensual, durante un año, en ocho sitios de muestreo en cada una de las cuatro categorías sucesionales, durante dos estaciones diferentes: húmeda (mayo a octubre 2016) y seca (noviembre 2016 hasta abril 2017). A través de un análisis multivariado de funciones discriminantes, se determinó que las categorías sucesionales en la selva baja espinosa son diferentes dependiendo del microclima. En la estación húmeda, las áreas con poco tiempo de sucesión se caracterizaron por valores más altos de índice de calor y velocidad del viento, al contrario de las áreas conservadas. En la estación seca, las diferencias sucesionales se atribuyeron a la velocidad del viento y la humedad relativa. Además, tanto la discriminación entre categorías como la importancia de las variables fueron mayores solo durante la estación seca. Por lo tanto, la estacionalidad determina los patrones microclimáticos durante la sucesión secundaria. Además, cada categoría sucesional representa condiciones microclimáticas únicas, pero difieren de las áreas conservadas incluso después de 31 años de sucesión. De acuerdo con nuestros resultados, la estacionalidad y el microclima son de gran relevancia para el estudio de la sucesión secundaria. Se sugiere considerar ambos factores cuando se implementan programas de conservación de ecosistemas en riesgo, como la selva baja espinosa en el noreste de México. Al ser este un ecosistema poco estudiado, la caracterización microclimática que aquí se proporciona, ayudará a un mejor entendimiento y manejo forestal de dichas áreas.(AU)

Rebrote arbóreo en la regeneración del bosque tropical de Calakmul, Campeche, México / Arboreal resprouting in the Calakmul, Campeche, Mexico tropical forest regeneration

Resumen Los estudios detallados para comprender como los bosques neotropicales se reestablecen en el tiempo, a través de la sucesión secundaria aún resultan necesarios. Entre los mecanismos de regeneración que actúan en los bosques tropicales, el rebrote de árboles predomina en especies leñosas, con la ventaja de reiniciar el crecimiento de raíces establecidas, que permiten restituir el dosel forestal. El objetivo de este estudio fue identificar y cuantificar las especies arbóreas con capacidad de rebrote en distintas etapas de la sucesión secundaria (barbecho) después del sistema agrícola tradicional de milpa, comparadas con las comunidades del bosque tropical predominante en la Reserva de la Biósfera de Calakmul, y cómo influyen estas especies en la recuperación de la composición de este ecosistema. Se calculó el porcentaje de especies con y sin rebrote para cada etapa sucesional. Se registraron 13 972 individuos (32 % con rebrote y 68 % sin rebrote) y 168 especies (79 % con rebrote y 21 % sin rebrote), el porcentaje de individuos con rebrote va disminuyendo conforme avanza la edad de la sucesión. El número de individuos con rebrote y la composición de especies fueron significativamente diferentes entre etapas. Se puede concluir que la mayoría de especies arbóreas del bosque en Calakmul, presentan la capacidad de rebrotar, lo cual tiene influencia en el rápido proceso sucesional del bosque después de la roza-tumba y quema, restituyendo la cobertura y estructura forestal, así como la composición de las especies originales.(AU)

Abstract Detailed studies to understand recovering of Neotropical forests over time, through secondary succession, are still necessaries. Between acting mechanisms of regeneration in the tropical forests, the arboreal resprout predominates in woody species, with the advantage of restart the growth from still rooting plants, allowing the restoring of forest canopy. The study aim was to identify and quantify the tree species with resprouting capacity in different stages of secondary succession (tree-fallow) after the traditional milpa agricultural system, compared with tropical forest communities in the Calakmul Biosphere Reserve and, enlightening how these species influences the recovery of the composition of this ecosystem. Was calculated the proportions of species with or without resprouting by successional stage. There were 13 972 individuals (32 % resprouting and 68 % not resprouting) and 168 species (79 % resprouting and 21 % not resprouting), the percentage of individuals regrowing decreases as the successional stage progresses. The number of individuals resprouting and species composition were significantly different between successional stages. In conclusion, mostly arboreal species in the region of Calakmul, can regrow, which influences the successional development of the forest after slash-and-burn, helping to restore the coverage, structure, as well as species composition original.(AU)

Determining the K coefficient to leaf area index estimations in a tropical dry forest.

Vegetation indices are useful tools to remotely estimate several important parameters related to ecosystem functioning. However, improving and validating estimations for a wide range of vegetation types are necessary. In this study, we provide a methodology for the estimation of the leaf area index (LAI) in a tropical dry forest (TDF) using the light diffusion through the canopy as a function of the successional stage. For this purpose, we estimated the K coefficient, a parameter that relates the normalized difference vegetation index (NDVI) to LAI, based on photosynthetically active radiation (PAR) and solar radiation. The study was conducted in the Mata Seca State Park, in southeastern Brazil, from 2012 to 2013. We defined four successional stages (very early, early, intermediate, and late) and established one optical phenology tower at one plot of 20 × 20 m per stage. Towers measured the incoming and reflected solar radiation and PAR for NDVI calculation. For each plot, we established 24 points for LAI sampling through hemispherical photographs. Because leaf cover is highly seasonal in TDFs, we determined ΔK (leaf growth phase) and Kmax (leaf maturity phase). We detected a strong correlation between NDVI and LAI, which is necessary for a reliable determination of the K coefficient. Both NDVI and LAI varied significantly between successional stages, indicating sensitivity to structural changes in forest regeneration. Furthermore, the K values differed between successional stages and correlated significantly with other environmental variables such as air temperature and humidity, fraction of absorbed PAR, and soil moisture. Thus, we established a model based on spectral properties of the vegetation coupled with biophysical characteristics in a TDF that makes possible to estimate LAI from NDVI values. The application of the K coefficient can improve remote estimations of forest primary productivity and gases and energy exchanges between vegetation and atmosphere. This model can be applied to distinguish different successional stages of TDFs, supporting environmental monitoring and conservation policies towards this biome.

Generalist birds promote tropical forest regeneration and increase plant diversity via rare-biased seed dispersal.

Regenerated forests now compose over half of the world's tropical forest cover and are increasingly important as providers of ecosystem services, freshwater, and biodiversity conservation. Much of the value and functionality of regenerating forests depends on the plant diversity they contain. Tropical forest diversity is strongly shaped by mutualistic interactions between plants and fruit-eating animals (frugivores) that disperse seeds. Here we show how seed dispersal by birds can influence the speed and diversity of early successional forests in Puerto Rico. For two years, we monitored the monthly fruit production of bird-dispersed plants on a fragmented landscape, and measured seed dispersal activity of birds and plant establishment in experimental plots located in deforested areas. Two predominantly omnivorous bird species, the Northern Mockingbird (Mimus polyglottos) and the Gray Kingbird (Tyrannus dominicensis), proved critical for speeding up the establishment of woody plants and increasing the species richness and diversity of the seed rain in deforested areas. Seed dispersal by these generalists increased the odds for rare plant species to disperse and establish in experimental forest-regeneration plots. Results indicate that birds that mix fruit and insects in their diets and actively forage across open and forested habitats can play keystone roles in the regeneration of mutualistic plant-animal communities. Furthermore, our analyses reveal that rare-biased (antiapostatic) frugivory and seed dispersal is the mechanism responsible for increasing plant diversity in the early-regenerating community.

Soil changes in a subtropical seasonal forest chronosequences in the south of Brazil / Mudanças no solo em cronossequências da floresta estacional subtropical no sul do Brasil

ABSTRACT:The abandonment of field crops and the vegetation recovery in exhausted soils have been a recently studied subject as a way to assess the forest role on the soil recovering. The aim of this study was assess changes in the chemical(14 variables) and grain size (sand, silt, and clay) soil features in four forests chronosequences grew over abandoned field crops in the edge of the Brazilian Southern plateau, Rio Grande do Sul State. There were selected 25 forests aging from 5 to >100 years old in areas of slopes and highlands where samples of Leptosols and Regosols were collected at 15cm in depth. The Fisher's Discriminant Analysis showed that some variable groups of soils can distinguish significantly the soils under different forest ages. Six chemical features of soil fertility were the best monitoring indicators of areas impacted by agriculture. Changes in soil did not occur in a linear way towards time.

RESUMO:O abandono de terras agrícolas e a recuperação da vegetação e dos solos exauridos têm sido um tema recentemente investigado como forma de avaliar o papel da floresta na recuperação do solo. O objetivo deste estudo foi verificar as mudanças nas propriedades químicas (14 variáveis) e granulométricos (areia, silte e argila) em quatro cronossequências florestais originadas após o cultivo agrícola no rebordo do Planalto Meridional, sul do Brasil. Foram selecionadas 25 florestas com idades variando de 5 a >100 anos, localizadas em áreas de encostas e patamares onde amostras de Neossolos Litólicos e Regolíticos Eutróficos foram coletados a 15cm de profundidade. A análise discriminante de Fisher demonstrou que alguns grupos de variáveis dos solos podem distinguir significativamente os solos sob as diferentes idades florestais. Seis atributos químicos relacionados com a fertilidade do solo poderiam ser considerados os melhores indicadores de monitoramento das áreas impactadas pela agricultura. As mudanças no solo não ocorreram de forma linear ao longo do tempo.

Soil changes in a subtropical seasonal forest chronosequences in the south of Brazil / Mudanças no solo em cronossequências da floresta estacional subtropical no sul do Brasil

The abandonment of field crops and the vegetation recovery in exhausted soils have been a recently studied subject as a way to assess the forest role on the soil recovering. The aim of this study was assess changes in the chemical(14 variables) and grain size (sand, silt, and clay) soil features in four forests chronosequences grew over abandoned field crops in the edge of the Brazilian Southern plateau, Rio Grande do Sul State. There were selected 25 forests aging from 5 to >100 years old in areas of slopes and highlands where samples of Leptosols and Regosols were collected at 15cm in depth. The Fisher's Discriminant Analysis showed that some variable groups of soils can distinguish significantly the soils under different forest ages. Six chemical features of soil fertility were the best monitoring indicators of areas impacted by agriculture. Changes in soil did not occur in a linear way towards time.(AU)

O abandono de terras agrícolas e a recuperação da vegetação e dos solos exauridos têm sido um tema recentemente investigado como forma de avaliar o papel da floresta na recuperação do solo. O objetivo deste estudo foi verificar as mudanças nas propriedades químicas (14 variáveis) e granulométricos (areia, silte e argila) em quatro cronossequências florestais originadas após o cultivo agrícola no rebordo do Planalto Meridional, sul do Brasil. Foram selecionadas 25 florestas com idades variando de 5 a >100 anos, localizadas em áreas de encostas e patamares onde amostras de Neossolos Litólicos e Regolíticos Eutróficos foram coletados a 15cm de profundidade. A análise discriminante de Fisher demonstrou que alguns grupos de variáveis dos solos podem distinguir significativamente os solos sob as diferentes idades florestais. Seis atributos químicos relacionados com a fertilidade do solo poderiam ser considerados os melhores indicadores de monitoramento das áreas impactadas pela agricultura. As mudanças no solo não ocorreram de forma linear ao longo do tempo.(AU)

Estructura, divrrsidad y dinámica de la vegetacón en el ecotono bosque-páramo:: revisión de la evidencia en la cordillera de mérida / Vegetation Structure, Diversity and Dynamics in the Forest-Paramo Ecotone: A Review of the Evidence in the Cordillera de Mérida

En los Andes tropicales, el límite altitudinal de los bosques corresponde a una compleja zona de transición entre el bosque paramero y el páramo andino. En el límite inferior de esta zona ocurre a su vez una transición gradual entre el bosque y las selvas nubladas. La ordenación del territorio en estos ecosistemas se ha convertido en un tema prioritario en virtud de la creciente amenaza que representan para su conservación las actividades agropecuarias y la minería. En este trabajo se revisaron las investigaciones realizadas en la Cordillera de Mérida (Venezuela) sobre los cambios en la estructura, diversidad y respuesta a disturbios de la vegetación a lo largo del ecotono bosque-páramo. Los resultados de estas investigaciones documentan la alta riqueza de especies y formas de vida que caracterizan la vegetación del ecotono, así como una alta tasa de recambio de especies a lo largo del gradiente de elevación. Así mismo, estudios sobre la dinámica sucesional de la vegetación en áreas intervenidas por la agricultura en diferentes posiciones a lo largo de la transición, indican que las leñosas del bosque muestran una capacidad mucho menor de colonización de las áreas perturbadas que las especies dominantes del páramo. Con base en la evidencia disponible, se discuten elementos estructurales que pueden servir de base para la delimitación de los ecosistemas presentes en la zona de transición y se enfatiza la necesidad de diseñar estrategias de conservación y restauración asistida que partan de interpretar el ecotono bosque-páramo como una unidad dinámica integrada.

In the tropical Andes, the mountain treeline corresponds to a complex transition zone between páramo forests and páramos. In the lower limit of this ecotone there is a more or less gradual transition between mountain cloud forests and páramo forests. Land planning in these ecosystems has become a highly topical subject given the growing threat for conservation generated by agricultural and mining activities. In this paper we review the research carried out in the Cordillera de Mérida (Venezuela) on the changes in vegetation structure, diversity and response to disturbance along the forest-páramo transition zone. The results of these studies document the high species and life form richness which characterize the ecotone vegetation, as well as a high rate of species turnover (beta diversity) along the elevation gradient. Studies on elevation changes in vegetation successional dynamics in plots disturbed by agriculture at different altitudes along the transition zone indicate that forest woody species have a lower capacity to colonize disturbed areas than dominant páramo species, a process that results in forests patches with a paramo physiognomy. On the basis of the available evidence, the structural elements that could be used for delimiting the different ecosystems present along transition zone are discussed, emphasizing the need to design conservation and restoration strategies which interpret the forest-páramo ecotone as a dynamic and integrated system.

Regeneración natural de la vegetación como base para el desarrollo de estrategias de restauración ecológica en tres biotopos protegidos en la reserva de biosfera maya, Guatemala / Natural vegetal regeneration as a basis for the development of strategies for ecological restoration in three protected biotopes in the maya biosphere reserve, Guatemala

Los ecosistemas naturales de la Reserva de Biosfera Maya contienen una alta diversidad biológica que brinda bienes y servicios ambientales a la sociedad, por lo que su conservación es estratégica para el desarrollo local y regional. Sin embargo, se presenta la tendencia a la perturbación de estos ecosistemas como consecuencia de las actividades humanas, siendo necesario el desarrollo de estrategias que minimicen los impactos negativos y permitan la recuperación de ecosistemas naturales degradados. La información existente sobre el funcionamiento de procesos ecológicos esenciales de los ecosistemas locales es escasa y se halla dispersa, limitando el desarrollo de estrategias. Se planteó estudiar la dinámica de la regeneración natural de la vegetación como fundamento para la definición de estrategias de restauración ecológica en tres biotopos protegidos de Petén y zonas adyacentes, mediante la caracterización de la estructura y composición de la vegetación en seis categorías de regeneración natural y bosque sin perturbación reciente. Se trazaron dos parcelas modificadas de Whitaker de 0.1 ha por categoría y se colectaron muestras del banco de semillas. Con esta información se desarrolló un marco conceptual de la regeneración natural para ser aplicado en estrategias de restauración a escalas local y de paisaje.

The natural ecosystems of the Maya Biosphere Reserve contain high levels of biodiversity providing environmental goods and services to society, so their conservation is strategic for local and regional development. However, there is a increasing tendency to disturb these ecosystems as a result of human activities, so is necessary to develop strategies that minimize the negative impacts and allow the recovery of degraded natural ecosystems. Existing information on the functioning of essential ecological processes of local ecosystems is sparse and is scattered, limiting the development of strategies. It was proposed to study the dynamics of natural regeneration of vegetation as a basis for defining strategies of ecological restoration in three protected biotopes in Peten and adjacent areas, by characterizing the structure and composition of vegetation in six categories of natural regeneration and forest without recent disturbance. Two modified Whitaker 0.1 ha plots were plotted by category and seed bank samples were collected. With this information a conceptual framework of natural regeneration was developed for application in restoration strategies at local and landscape scales.

Natural forest regeneration in abandoned sugarcane fields in northeastern Brazil: floristic changes / Regeneração natural de mata em áreas de cana abandonadas no nordeste do Brasil: mudanças florísticas

Surveys were undertaken to examine the floristic changes during secondary succession in three areas of 12 and three of 20-year-old secondary forests in Pernambuco State, Brazil. Two hundred and six species were identified, with 136 being found in the 12-year-old secondary forest and 161 species in the 20-year-old forest. Fabaceae and Myrtaceae were the most important families, increasing in species numbers with regeneration age. Of the 216 species, 115 were trees, 48 shrubs, 16 herbaceous plants, and 24 woody lianas, without significant differences between the two regeneration site ages. NMDS analysis revealed a formation of two floristic groups, distinguishing secondary and mature forests, with a further division within secondary forests in accordance with the time since abandonment. Similarity analysis ANOSIM confirmed the significance of the groups, which had floristic composition significant distinct (R=0.96) and 63% of dissimilarity (SIMPER). However, the sharing of 68 arboreal species between the secondary and mature forests suggests a floristic convergence. DCA analysis of the arboreal component as well as the other plant habits suggested that the separation of the subgroups is correlated with physical and chemical variables of the soils. All of these results indicate that, within the chronosequence analyzed, the velocity and direction of the floristic composition during secondary succession was influenced not only by the time of their abandonment, but also by a wide range of environmental variables.

Com objetivo de detectar mudanças florísticas ao longo da sucessão secundária e subsidiar futuros projetos de recuperação florestal foi realizado levantamento florístico de seis áreas de floresta secundária (capoeira) de 12 e 20 anos em Pernambuco. Foram registradas 206 espécies, sendo 136 nas capoeiras de 12 anos e 161 nas de 20 anos. Fabaceae e Myrtaceae foram as famílias mais importantes, aumentando no número de espécies com a idade de regeneração. Do total de espécies, 115 foram árvores, 48 arbustos, 16 herbáceas e 24 trepadeiras, sem diferença significativa por idade de regeneração. Análise de NMDS indicou a separação dos grupos florísticos das florestas maduras e das capoeiras, assim como a formação de subgrupos de capoeiras (SF1-2-3 e SF4-5-6) com idade de regeneração distinta. A análise de similaridade ANOSIM mostrou que os grupos formados apresentaram composição florística significativamente distintas (R = 0.96) e 63% de dissimilaridade (SIMPER). Entretanto, a presença nas capoeiras de 67 espécies em comum com as florestas maduras indicam uma tendência de convergência florística. A análise de DCA do componente arbóreo e dos outros hábitos sugere que a separação dos subgrupos por idade estaria correlacionada com variáveis edáficas físicas e químicas. Todos esses resultados indicam que, numa análise de cronossequência, não apenas o tempo de abandono, mas todas as variáveis ambientais influenciam a velocidade e direção de formação da composição florística durante a sucessão secundária.