GUYAFOR: a network of research permanent plots of tropical forests in French Guiana

GUYAFOR, a network of forest research permanent plots, is dedicated to long term studies in forest dynamics and biodiversity. Forest plots have been established in French Guyana from the late 60's to recent years by Cirad, ONF and CNRS. From 2000, they are progressively integrated in the GUYAFOR network with standardized protocols for both tree inventories and environmental characterization. The network includes 45 plots distributed on 10 sites mainly in the coastal area.157 800 trees above 10 cm dbh are monitored within 235 ha at regular intervals (2 to 4 years). Undisturbed forests are monitored on all sites. Forests subjected to different logging treatments are also monitored on four sites (Paracou, Organabo, Risquetout and Montagne Tortue), providing a unique feature to this network. Recent works carried out on the Guyafor network include studies to understand patterns of tree biological diversity at specific, functional and evolutionary levels and studies on the effects of logging practices on the carbon cycle. (Résumé d'auteur

A trait database for Guianan rain forest trees permits intra- and inter-specific contrasts

International audienceWe present a plant trait database covering autecology for rain forest trees of French Guiana. The database comprises more than thirty traits including autecology (e.g., habitat associations and reproductive phenology), wood structure (e.g., density and tension characteristics) and physiology at the whole plant (e.g., carbon and nitrogen isotopes) and leaf level (e.g., specific leaf area, photosynthetic capacity). The current database describes traits for about nine hundred species from three hundred genera in one hundred families. For more than sixty species, data on twelve morphological and ecophysiological traits are provided for individual plants under different environmental conditions and at different ontogenetic stages. The database is thus unique in permitting intraspecific analyses, such as the effects of ontogenetic stages or environmental conditions on trait values and their relationships

Performance Trade‐Offs Among Tropical Tree Seedlings In Contrasting Microhabitats

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117031/1/ecy20058692461.pd

Current knowledge of general patterns of biomass dynamics after logging in Amazonian forests

Sustainable management of tropical forests for timber production has been proposed as a potential tool for the conservation of large areas of tropical forest. The key is to identify practices that promote repeated extraction of forest goods (timber and non timber forests products) without compromising important forest services (e.g., biodiversity and carbon). Currently, 350 million hectares of tropical moist forests worldwide are designated as production forests, about a quarter of which is managed by rural communities and indigenous people. Yet general management guidelines remain elusive, in large part because not only harvesting practices but also forest types vary broadly both within and among regions. For example, the Amazon region shows a strong east-west gradient in both floristic composition and forest dynamics. This paper presents a literature review of our present knowledge of the biomass dynamics of tropical forests in the Amazon after logging. The objectives are (i) to disentangle the mechanisms behind different types of responses in different forests; and (ii) to propose research priorities to improve forest management guidelines so that they better reflect the gradient of forest types across the region. (Résumé d'auteur

Microhabitat associations and seedling bank dynamics in a neotropical forest

We conducted a rigorous test of tropical tree seedling microhabitat differentiation by examining microhabitat associations, survival and growth of established seedlings of ten tropical tree species representing a four-factor gradient in seed size. Eight microhabitat variables describing soil and light conditions were measured directly adjacent to each of 588 seedlings within twelve 10×100 m belt transects at Paracou, French Guiana, and at 264 reference points along the transects. From these measurements, we defined three principal components describing soil richness, soil softness and canopy openness. Six of ten species (in 9 of 30 total cases) were distributed non-randomly with respect to microhabitat along at least one principal component. However, few species demonstrated clear microhabitat specialization. All shifts in distribution relative to reference points were in the same direction (richer, softer soil). Furthermore, of 135 pairwise comparisons among the species, only 7 were significantly different. More than three-fourths of all seedlings (75.3%) survived over the 2-year monitoring period, but survival rates varied widely among species. In no case was the probability of survival influenced by any microhabitat parameter. Relative height growth rates for the seedlings over 2 years varied from −0.031 cm cm −1  year −1 ( Dicorynia guianensis , Caesalpiniaceae) to 0.088 cm cm −1  year −1 ( Virola michelii , Myristicaceae). In only 4 of 30 cases was height growth significantly associated with one of the three principal components. Because the conditions in this study were designed to maximize the chance of finding microhabitat differentiation among a group of species differing greatly in life history traits, the lack of microhabitat specialization it uncovered suggests that microhabitat partitioning among tropical tree species at the established seedling stage is unlikely to contribute greatly to coexistence among these species.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47708/1/442_2004_Article_1691.pd

Trait‐based community assembly pattern along a forest succession gradient in a seasonally dry tropical forest

We aimed to determine the important functional dimensions that may drive forest succession and community assembly patterns in dry tropical forests. We investigated whether there were patterns in specific functional strategies during succession in the dry tropical forests of the Florida Keys, whose unique physical setting includes nutrient‐stressed, salt‐stressed, and water‐limited environments. The study, which focused on ten traits, determined the leading trait dimensions by which species differentiate from one another in the study area. The general patterns of trait covariation at individual sites and among species were analyzed using principal component analysis. Trait niche overlap indices were calculated for all species sampled across all plots. Evidence for/against likely community assembly processes was tested using the coefficient of heterogeneity to determine whether variation within and among five key traits was clustered, random, or evenly distributed across young, old, or all measured forest stands. A combination of plant architecture, wood density, and three leaf traits (specific leaf area, leaf phosphorus, and leaf nitrogen) comprised a key set of functional traits that are important for understanding the community assembly process in dry tropical forest. Older forest stands were dominated by species with low specific area, low leaf nitrogen content, dense wood, and deeper and narrower canopies. Trees of old forests had leaves with lighter carbon isotope composition, suggesting that such individuals were making more efficient use of scarce water. Tests of trait distributions showed significant clustering across forests of all ages. When individual trait distributions in old stands were tested, they displayed either randomly or evenly distributed traits across trait niche space, indicating that resource partitioning was predominant in shaping community composition. Physical traits of trees in young communities are associated with resource acquisitive strategies, while old communities are dominated by species with traits that enhance survival in environments defined by competition or chronic resource scarcity

Within-individual variation of trunk and branch xylem density in tropical trees

Premise of the study: Wood density correlates with mechanical and physiological strategies of trees and is important for estimating global carbon stocks. Nonetheless, the relationship between branch and trunk xylem density has been poorly explored in neotropical trees. Here, we examine this relationship in trees from French Guiana and its variation among different families and sites, to improve the understanding of wood density in neotropical forests. Methods: Trunk and branch xylem densities were measured for 1909 trees in seven sites across French Guiana. A major-axis fit was performed to explore their general allometric relationship and its variation among different families and sites. Key results: Trunk xylem and branch xylem densities were significantly positively correlated, and their relationship explained 47% of the total variance. Trunk xylem was on average 9% denser than branch xylem. Family-level differences and interactions between family and site accounted for more than 40% of the total variance, whereas differences among sites explained little variation. Conclusions: Variation in xylem density within individual trees can be substantial, and the relationship between branch xylem and trunk xylem densities varies considerably among families and sites. As such, whole-tree biomass estimates based on non- destructive branch sampling should correct for both taxonomic and environmental factors. Furthermore, detailed estimates of the vertical distribution of wood density within individual trees are needed to determine the extent to which relying solely upon measures of trunk wood density may cause carbon stocks in tropical forests to be overestimated