[Show abstract][Hide abstract] ABSTRACT: Secondary forests cover large areas of the tropics and play an important role in the global carbon cycle. During secondary forest succession, simultaneous changes occur among stand structural attributes, soil properties, and species composition. Most studies classify tree species into categories based on their regeneration requirements. We use a high-resolution secondary forest chronosequence to assign trees to a continuous gradient in species successional status assigned according to their distribution across the chronosequence. Species successional status, not stand age or differences in stand structure or soil properties, was found to be the best predictor of leaf trait variation. Foliar δ(13)C had a significant positive relationship with species successional status, indicating changes in foliar physiology related to growth and competitive strategy, but was not correlated with stand age, whereas soil δ(13)C dynamics were largely constrained by plant species composition. Foliar δ(15)N had a significant negative correlation with both stand age and species successional status, - most likely resulting from a large initial biomass-burning enrichment in soil (15)N and (13)C and not closure of the nitrogen cycle. Foliar %C was neither correlated with stand age nor species successional status but was found to display significant phylogenetic signal. Results from this study are relevant to understanding the dynamics of tree species growth and competition during forest succession and highlight possibilities of, and potentially confounding signals affecting, the utility of leaf traits to understand community and species dynamics during secondary forest succession.
PLoS ONE 01/2014; 9(2):e86042. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The spatial distribution of individuals is a fundamental property of most species and constitutes essential information for the development of restoration and conservation strategies, especially for endangered plant species. In this paper we describe the spatial distribution of different size classes of the endangered tropical tree Guaiacum sanctum and the effect of canopy cover on spatial aggregation. Adult G. sanctum were located and mapped in a 50 ha plot in Palo Verde National Park, Costa Rica. Seedlings, saplings and juveniles were mapped to the nearest centimetre and permanently marked in three 50 x 50 m subplots. Within each subplot spatial aggregation was assessed using Ripley's K statistic and canopy opening readings were performed every 5 m using a densitometer. Kriging spatial interpolation and Monte Carlo simulations were used to determine if average canopy cover differed among size classes. Individuals of G. sanctum were spatially aggregated at all size classes with seedlings being the most frequent size class in all subplots. Seedlings were found predominantly in areas with significantly higher canopy cover. In contrast, juveniles were more likely found in areas with higher light availability. The high number of seedlings, saplings, and juveniles relative to adults suggests that populations of G. sanctum in PVNP are expanding. Light availability and canopy structure are important factors shaping the spatial distribution of this species. The contemporary demographic structure of G. sanctum is dependent on forest gap dynamics and changes in human disturbance during the past 25 years.
Revista de biologia tropical 09/2013; 61(3):1521-33. · 0.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: War and civil conflict have been shown to contribute directly to increased wildlife poaching and environmental degradation, especially in developing countries. The Democratic Republic of Congo (DRC) suffered heightened political instability that intensified during its first (1996–1997) and second (1998–2003) civil wars. Ground-based observations reported severe impacts on wildlife from increased human reliance on bushmeat as well as evidence of human populations moving deeper into interior forests to escape conflict. Both were observed in the study area comprised of forests in and around Luo Scientific Reserve located in northern DRC, where studies on wild bonobos (Pan paniscus) have been conducted since 1973. Using Landsat TM and ETM + satellite imagery, we employed an automated classification tree algorithm developed specifically for Central Africa to monitor wartime patterns of human migration and resource use in the study area. We analyzed and compared primary forest loss and degradation rates across two decades (1990–2010). Annual rates of primary forest loss occurring during the 1990–2000 decade were over double the rates of the mainly post-war 2000–2010 decade, indicating higher human pressure on the forests during wartime. Maps and analyses of peripheral forests occurring around the edges of forest clearings illustrated an increased prevalence of small, scattered clearings during the war. We also found evidence showing there was likely less human pressure on interior forests after the wars ended. We demonstrate the utility of satellite-based remote sensing techniques for monitoring human access in interior forests and examining wartime links to observed declines in wildlife.
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