Abstract ID: 672

Branch xylem density patterns across Amazonia

There is increasing evidence showing that wood density is a plant trait that reflects physiological options of trees in response to the environment and to their evolutionary heritage. We studied the density of the functional xylem, Dx, for branches from the upper crown of an average of 20 trees > 10 cm DBH, selected at random in each of 80 1ha permanent plots across the Amazonia. We divided the Amazon basin into 13 geographical regions each one containing between two and 14 permanent plots (sites). Dx was measured for 1466 trees representing 503 species. Measured values ranged from 240 kgm−3 for a Brosimum parinarioides (Moraceae) from Tapajos in West Para, Brazil to 1130 kgm−3 for an Aiouea sp. (Lauraceae) from Caxiuana, Central Para, Brazil. A partitioning of the total variance in the dataset showed that geographic location and plot accounted for 33% of the variation with species identity accounting for an additional 27%; the remaining “residual” 40% of the variance may be accounted by tree to tree variation such as tree height and diameter, branch age, measuring error and unexplored reasons. Differences among plots appear to be related to site factors rather than differences in species composition, as evidenced by significant intraspecific variation among plots. For example Rinorea guianensis a species belonging to the relatively high density family Violaceae varied from 580 kg cm-3 in Cuzco Amazonico, South Peru to 1079 kg m-3 in Caxiuana, Central Pará, Brazil and Virola callophylla an species belonging to the low density Myristicaceae family varied from 410 kg m-3 in Jatun Sacha, Ecuador to 791 kg m-3 in Caxiuana. Variations of xylem density at plot level can be explained by the effects of physical and chemical properties of soils and climate. For instance, high density sites tend to have high proportions of either sand or clay, low pH, P, K, a larger dry season, higher mean temperature, lower annual mean precipitation and lower altitude. Although branch xylem density has a clear genetic component, it also shows a broad plastic response to soils and climate among Amazonian trees.

Session:  Biodiversity - Permanent plot networks for inventory of biodiversity and carbon stocks: integrating taxonomic and ecosystem objectives.

Presentation Type:  Oral