Spatial trends in leaf size of Amazonian rainforest trees
1School of Geography and the Environment, Oxford University, UK
2Dept. of Plant Ecology and Biodiversity, Utrecht University, The Netherlands
3Earth and Biosphere Institute, School of Geography, University of Leeds, UK
4Museo Noel Kempff Mercado, Santa Cruz, Bolivia
5Museu Paraense Emilio Goeldi, Belém, Brazil
6Instituto National de Pesquisas Amazônicas, Manaus, Brazil
7Center for Applied Biodiversity Science, Conservation International, Washington, DC, USA
8Herbario Vargas, Universidad Nacional San Antonio Abad del Cusco, Cusco, Perú
9Herbario Nacional del Ecuador, Quito, Ecuador
10Center for Tropical Conservation, Duke University, Durham, USA
11Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, Bogotá DC, Colombia
*Conceived the study, collected leaf data, undertook the analysis, wrote manuscript.
**Developed the idea, reviewed and improved manuscript.
Abstract. Leaf size influences many aspects of tree function such as rates of transpiration and photosynthesis and, consequently, often varies in a predictable way in response to environmental gradients. The recent development of pan-Amazonian databases based on permanent botanical plots has now made it possible to assess trends in leaf size across environmental gradients in Amazonia. Previous plot-based studies have shown that the community structure of Amazonian trees breaks down into at least two major ecological gradients corresponding with variations in soil fertility (decreasing from southwest to northeast) and length of the dry season (increasing from northwest to south and east). Here we describe the geographic distribution of leaf size categories based on 121 plots distributed across eight South American countries. We find that the Amazon forest is predominantly populated by tree species and individuals in the mesophyll size class (20.25–182.25 cm2). The geographic distribution of species and individuals with large leaves (>20.25 cm2) is complex but is generally characterized by a higher proportion of such trees in the northwest of the region. Spatially corrected regressions reveal weak correlations between the proportion of large-leaved species and metrics of water availability. We also find a significant negative relationship between leaf size and wood density.