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We analyze here how much carbon is being accumulated annually by secondary tropical dry forests (TDFs) and how structure, composition, time since abandonment, and climate can influence the dynamics of forest carbon accumulation. The study was carried out in Santa Rosa National Park in Guanacaste province, Costa Rica and Mata Seca State Park in Minas Gerais, Brazil. Total carbon storage and carbon accumulation were obtained for both sites from the sum of the aboveground carbon and belowground carbon gain plus the annual litterfall. Carbon accumulation of these TDFs varied from 2.6 Mg C ha−1 y−1 to 6.3 Mg C ha−1 y−1, depending on the age of the forest stands. Time since abandonment and number of stems per plot were the best predictors for carbon storage, annual carbon gains, and losses. Mortality rates and carbon losses were also associated with seasonal climate variability. We found significant correlations between tree mortality, carbon losses and mean seasonal temperature, mean seasonal precipitation, potential evapotranspiration, and the Oceanic Niño Index. Carbon dynamics in tropical dry forests are driven by time since abandonment and forest structure; however, rising temperature and El Niño Southern Oscillation (ENSO) events can have a significant impact on tree mortality and carbon losses. Depending on their location and land-use history, some dry forests are more impacted by climatic extremes than others, and differences between secondary stages are expected.

The Guanacaste Province of Costa Rica is home to highly diverse forests which are under threat of degradation due to ongoing climatic changes. There is concern that increasing temperatures and changes in precipitation will force these forests outside of their optimal growth ranges leading to widespread degradation of forest productivity. The objectives of this study are, therefore, to project and assess climatic changes in Guanacaste and to build a relationship between these climatic changes and forest productivity with the goal of projecting productivity trends into the future. The ClimateSA model was used to project RCP4.5 and 8.5 scenarios from 2018 to 2080 and then assess these projections for the mean and extreme future conditions. Furthermore, the MODIS gross primary productivity (GPP) algorithm was used to build a relationship between forest productivity and the vapour pressure deficit scalar (VPD scalar) and project GPP alteration under future climatic scenarios both seasonally and annually. Results indicate that Guanacaste’s mean annual precipitation will stay within the historic levels for both the RCP4.5 and 8.5 scenarios. The monthly and annual temperatures increase in all projections. Results also indicate that the productivity-climate relationship follows a quadratic relationship between GPP and the VPD scalar. This quadratic relationship leads to areas with higher precipitation (high VPD scalar) experiencing an increase in GPP as they dry in the future. In drier areas (low VPD scalar), reduced precipitation will stabilize or decrease GPP.

Tropical secondary forests recover quickly (decades) in tree species richness but slowly (centuries) in species composition., Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of five decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both old-growth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modified tropical landscapes.

SUMMARYThere is an increasing consensus on the importance of understanding ecosystem service (ES) provision in order to facilitate decision making and the sustainable management of Neotropical dry forests (NTDFs), yet research on the ESs provided by NTDFs is limited. We identified the main existing gaps and trends in the quantification of provisioning, regulating and supporting ESs in NTDFs. Systematic web-based searches showed that research has been increasing in recent decades in NTDFs, supporting greater ES knowledge and assessment. Carbon storage and biodiversity are the main subjects under study, while ESs relating to water and soil lack investigation. The most common approaches for assessing ES were fauna and plant inventories, carbon dynamics and ecological processes.

Leaf Area Index (LAI) has been defined as the total leaf area (one-sided) in relation to the ground. LAI has an impact on tree growth and recruitment through the interception of light, which in turn affects primary productivity. Even though many instruments exist for estimating LAI from ground, they are often laborious and costly to run continuously. Measurements of LAI from the field using traditional sensors (e.g., LAI-2000) require multiple visits to the field under very specific sky conditions, making them unsuitable to operate in inaccessible areas and forests with dense vegetation, as well as areas where persistent sunny conditions are the norm like tropical dry forests. With this context, we proposed a methodology to characterize light diffusion based on NDVI and LAI measurements taken from the field in two successional stages in the tropical dry forest of Santa Rosa National Park in Costa Rica. We estimate a "K" coefficient to characterize light diffusion by the canopy, based on field NDVI measurements derived from optical phenology instruments and MODIS NDVI. From the coefficients determined, we estimated LAI values and compared them with ground measurements of LAI. In both successional stages ground measurements of LAI had no significant difference to the tower-derived LAI and the estimated LAI from MODIS NDVI.

Myracrodruon urundeuva, better known in Brazil as “Aroeira”, is an arboreal species highly used for its commercial and pharmacological value. Despite the high commercial value in the timber market, this species lacks studies analyzing the recovery time and growth in different stages of succession in the Brazilian tropical dry forests. The main objective of this study was to determine growth rates of this species in three successional stages of a tropical dry forest in Mata Seca State Park, in Minas Gerais, Brazil. We measured all individuals (≥5cm of DBH) annually in 18 permanent plots in early, intermediate, and late successional stages over a period of 8 years (2006-2014). We calculated the annual diameter increments for each individual of this species, for each successional stage and by diameter class. We obtained the following mean annual increments by successional stage: early (10.53 mm/yr), intermediate (2.09 mm/yr), and late (2.90 mm/yr). Increment growth rates were similar between the intermediate and late successional stages. The highest incremental increase in diameter was obtained in the diameter classes 5-15 cm and 15-25 cm in the early stage, and for the intermediate stage, maximum increments were found in the 5-15 cm diameter class and 35-45 cm class for the late stage. Results from this study support the conclusion that this tree is not only a pioneering species but that it also tolerates the conditions of advanced successional stages. Given the fast and high diametric increments observed in the early stage of succession and the smaller diametric classes, this species demonstrates great potential for silvicultural management. RESUMO Myracrodruon urundeuva, mais conhecida no Brasil como “Aroeira”, é uma espécie arbórea altamente utilizada por seu valor comercial e farmacológico. Apesar do alto valor comercial no mercado, esta espécie carece de estudos sobre o tempo de recuperação e crescimento em diferentes estágios de sucessão nas florestas secas tropicais brasileiras. O principal objetivo deste estudo foi determinar as taxas de crescimento diamétrico das árvores em três estágios sucessionais da floresta tropical seca no Parque Estadual Mata Seca, em Minas Gerais, Brasil. Nós medimos todos os indivíduos (≥5cm de DAP) anualmente em 18 parcelas permanentes em estágios sucessionais inicial, intermediário e tardio durante um período de 8 anos (2006-2014). Calculamos os incrementos anuais de diâmetro para cada indivíduo desta espécie, para cada estágio sucessional e por classe diamétrica. Foram obtidos os seguintes incrementos médios anuais por estágio sucessional: inicial (10,53 mm/ano), intermediário (2,09 mm/ano) e tardio (2,90 mm/ano). As taxas de incremento foram semelhantes entre os estágios sucessionais intermediário e tardio. O maior aumento incremental de diâmetro foi obtido nas classes de diâmetro 5-15 cm e 15-25 cm no estágio inicial, e para o estágio intermediário, incrementos máximos foram encontrados na classe de 5-15 cm de diâmetro e na classe de 35-45 cm no estágio tardio. Os resultados deste estudo permitem concluir que esta árvore não é apenas uma espécie pioneira, mas que também tolera as condições de estágios sucessionais avançados. Tendo em conta os incrementos diametrais rápidos e elevados observados no estágio inicial de sucessão e nas classes de diâmetro menores, esta espécie demonstra grande potencial para o manejo silvicultural.

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.

We describe changes in forest structure and floristic composition of three successional stages for Mata Seca State Park, in Minas Gerais, Brazil, through the measurement of all trees greater than 5 cm of diameter at breast height (DBH) of 18 permanent plots (6 per stage) for early, intermediate, and late successional stages of a tropical dry forest during a 5-year period. Using this information, we calculated the Importance Value Index (IVI), Holdridge Complexity Index, Jaccard Similarity Coefficient, and Shannon Diversity Index for each stage of succession. The floristic composition and structure of the successional stages expressed by the Holdridge Complexity Index, showed that complexity increases gradually as we advance through the successional stages, while the Shannon Diversity Index indicated that species diversity was higher in the intermediate stage of succession. The Jaccard Similarity Coefficients showed that the intermediate and late successional stages had high similarity, whereas the early successional stage had low similarity with these two successional stages. Mortality rates were higher in the early stage, especially in stems with smaller diameters (5-10cm). This information contributes to the dissemination of important knowledge for the conservation of the tropical dry forests of Brazil, which are the most threatened ecosystems in this country and, at the same time, the least studied.

he tropical dry forests of Brazil are classified as the most threatened and disturbed ecosystems in the country. We estimate the diameter growth in three successional stages in the Mata Seca State Park, in Minas Gerais, Brazil, through annual measurement of all individuals with more than 5 cm of diameter at breast height in 18 permanent plots (6 plots for each succession stage) in the early, intermediate, and late successional stages, over a period of 5 years (2006-2011). With this information the annual diameter increments for each individual were calculated to determine the diameter increments per stage, plot, and diameter class. The results show the following annual increments for each stage of succession: early (5.02 mm/year), intermediate (2.55 mm/year), and late (1.91 mm/year). We found high similarity in incremental growth between the plots in the intermediate and late stages. The greatest increments in the early stage was in the 15-20 cm diameter class, in the intermediate stage in the 30-35 cm class, and in the late stage in the 45-50 cm class. The dominant species with the highest increments were Myracrodruon urundeuva (9.33 mm/year) and Mimosa hostilis (10.35 mm/year). Species with lower increments were mostly those of the late stage. The high diameter increment in the early stage and the differences we observed between stages were associated with species composition and biophysical factors that regulate the growth and structure of each forest.