Forest biomass density across large climate gradients in northern South America is related to water availability but not with temperature.

Understanding and predicting the likely response of ecosystems to climate change are crucial challenges for ecology and for conservation biology. Nowhere is this challenge greater than in the tropics as these forests store more than half the total atmospheric carbon stock in their biomass. Biomass is determined by the balance between biomass inputs (i.e., growth) and outputs (mortality). We can expect therefore that conditions that favor high growth rates, such as abundant water supply, warmth, and nutrient-rich soils will tend to correlate with high biomass stocks. Our main objective is to describe the patterns of above ground biomass (AGB) stocks across major tropical forests across climatic gradients in Northwestern South America. We gathered data from 200 plots across the region, at elevations ranging between 0 to 3400 m. We estimated AGB based on allometric equations and values for stem density, basal area, and wood density weighted by basal area at the plot-level. We used two groups of climatic variables, namely mean annual temperature and actual evapotranspiration as surrogates of environmental energy, and annual precipitation, precipitation seasonality, and water availability as surrogates of water availability. We found that AGB is more closely related to water availability variables than to energy variables. In northwest South America, water availability influences carbon stocks principally by determining stand structure, i.e. basal area. When water deficits increase in tropical forests we can expect negative impact on biomass and hence carbon storage.

Pod production, and dasometric variables, of the tree Senna spectabilis (Fabaceae) in a tropical dry forest / Producción de vainas, y variables dasométricas, del árbol Senna spectabilis (Fabaceae) en un bosque seco tropical

Introduction: Senna spectabilis is a multipurpose pantropical tree, used in agroforestry systems. Objective: To determine pod production (Pp) and their relationship with dasometric variables in S. spectabilis in the tropical dry forest. Methods: From August 2016 to February 2017, thirty trees in production stage were randomly selected. The random selection was formed of the more isolated trees from the total dispersion. The trees were monitored at the beginning and end of the study period, to determine dasometric measurements such as total height (Th), height to the first branch (Hb), crown height (Ch), Stem diameter (at 0.2 m height from the ground) (Db), crown diameter (Cd), and crown volume (Cv) measured. Pods were harvested by the researcher with cutting and height cutting tongs when their color began to change. Pearson correlations and univariate and multivariate regression analyses were performed between the dasometric variables and pod production. The potential number of trees/ha (NPa) was calculated by determining the occlusion percentage (Op) and the shadow area/tree (Ca); to estimate the production potential of fruits/ha, the production of fruits/tree was multiplied by (NPa). Results: Th was 6.16 ± 1.23 m, Hb 2.75 ± 0.52 m, Ch 3.41 ± 0.98 m, Db 20.43 ± 4.80 cm, Cd 7.46 ± 1.20 m and Cv 108.43 ± 61.38 m3/tree. There was a significant positive correlation between Hb, Cd, Db, with Pp of 0.592**, 0.592**, and 0.446* respectively. Pp was 32.73 ± 16.13 kg/tree and the dry matter production (MSP) was 17.84 ± 8.80 kg/tree. The result of the multivariate regression indicated that the second-order polynomial model presented best goodness of fit. Op was 73.4 7.92 %, the cup area was 49.3 m2/tree, Ca was 36.2 m2/tree, and NPa was 83 trees. Conclusions: The production of fresh pods/ tree in the S. spectabilis presents a potential in its availability as feed for ruminant or seed production. The potential production of pods in silvopastoral with S. spectabilis could be 2.72 t/ ha, and 1.64 t/ ha of dry pods, this shows the importance of trees and of pods production and nutritional contribution obtained for dry ecosystems.

Introducción: Senna spectabilis es un árbol pantropical multipropósito, utilizado en sistemas agroforestales. Objetivo: Determinar la producción de vainas (Pv) y la relación con las variables dasométricas en S. spectabilis en el bosque seco tropical. El número potencial de árboles/ha (NPa) fue calculado determinando el porcentaje de oclusión (Po) y el área de sombra/árbol (As); para calcular la producción potencial de frutos/ha, la producción de frutos/árbol fue multiplicada por (NPa). Métodos: Desde agosto del 2016 hasta febrero de 2017, treinta árboles en etapa de producción fueron seleccionados al azar, los más aislados del total de árboles dispersos fueron seleccionados, y fueron monitoreados al inicio y al final del período de estudio, para determinar las mediciones dasométricas como la altura total (At), altura a la primera rama (Apr), altura de la copa (Ac), diámetro del tallo (a 0.2 m altura desde el suelo) (Dt), diámetro de la copa (Dc) y volumen de copa (Vc). Las vainas se cosecharon cuando su color comenzó a cambiar. Se realizaron correlaciones de Pearson y análisis de regresión univariada y multivariada entre las variables dasométricas y la producción de vainas. El número potencial de árboles/ha (NPa) se calculó determinando el porcentaje de oclusión (Po) y el área de sombra/árbol (Asa); para estimar el potencial de producción de las vainas/ha, la producción de vainas/árbol se multiplicó por NPa. Resultados: La At fue de 6.16 ± 1.23 m, Apr 2.75 ± 0.52 m, Ac 3.41 ± 0.98 m, Db 20.43 ± 4.80 cm, Dc 7.46 ± 1.20 m y Vc 108.43 ± 61.38 m3/árbol. Existió una correlación positiva significativa entre Apr, Dc, Db, Pv de 0.592**, 0.592 ** y 0.446 * respectivamente. La Pv fue de 32.73 ± 16.13 kg y la producción de materia seca (PMS) fue de 17.84 ± 8.80 kg/árbol. El resultado de la regresión multivariada indicó que el modelo polinomial de segundo orden presentó la mejor bondad de ajuste. El Po de los árboles fue de 73.4 % ± 7.92 %, el área de copa fue de 49.3 m2/árbol, el Asa fue de 36.2 m2/árbol, el NPa fue de 83 árboles. Conclusiones: La producción de vainas frescas/árbol en el S. spectabilis presenta un potencial en la disponibilidad de alimento para los rumiantes o la producción de semillas. El potencial de producción de vainas en u arreglos silvopastoriles podría ser de 2.72 t/ha, y 1.64 t/ha de vainas secas, esto muestra la importancia del árbol de producción de vainas y la contribución nutricional para los ecosistemas secos.

Plant diversity patterns in neotropical dry forests and their conservation implications.

Seasonally dry tropical forests are distributed across Latin America and the Caribbean and are highly threatened, with less than 10% of their original extent remaining in many countries. Using 835 inventories covering 4660 species of woody plants, we show marked floristic turnover among inventories and regions, which may be higher than in other neotropical biomes, such as savanna. Such high floristic turnover indicates that numerous conservation areas across many countries will be needed to protect the full diversity of tropical dry forests. Our results provide a scientific framework within which national decision-makers can contextualize the floristic significance of their dry forest at a regional and continental scale.