Spatial distribution and functional significance of leaf lamina shape in Amazonian forest 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, Belem, 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, Colombia
- 12INDECOR, Facultad de Ciencias Forectales, Universidad de Los Andes, Venezuela
- *now at: Universidade Federal de Viçosa – UFV, Av. P. H. Rolfs, S/N. Centro Viçosa, MG, 36570-000, Brasil
- **Conceived the study, collected leaf data, undertook the analysis, and wrote manuscript.
- ***Orientated, reviewed and improved manuscript.
- ****Contributed data.
Abstract. Leaves in tropical forests come in an enormous variety of sizes and shapes, each of which can be ultimately viewed as an adaptation to the complex problem of optimising the capture of light for photosynthesis. However, the fact that many different shape "strategies" coexist within a habitat demonstrate that there are many other intrinsic and extrinsic factors involved, such as the differential investment in support tissues required for different leaf lamina shapes. Here, we take a macrogeographic approach to understanding the function of different lamina shape categories. Specifically, we use 106 permanent plots spread across the Amazon rainforest basin to: 1) describe the geographic distribution of some simple metrics of lamina shape in plots from across Amazonia, and; 2) identify and quantify relationships between key environmental parameters and lamina shape in tropical forests. Because the plots are not randomly distributed across the study area, achieving this latter objective requires the use of statistics that can account for spatial auto-correlation. We found that between 60–70% of the 2791 species and 83 908 individual trees in the dataset could be classified as having elliptic leaves (= the widest part of the leaf is on an axis in the middle fifth of the long axis of the leaf). Furthermore, the average Amazonian tree leaf is 2.5 times longer than it is wide and has an entire margin. Contrary to theoretical expectations we found little support for the hypothesis that narrow leaves are an adaptation to dry conditions. However, we did find strong regional patterns in leaf lamina length-width ratios and several significant correlations with precipitation variables suggesting that water availability may be exerting an as yet unrecognised selective pressure on leaf shape of rainforest trees. Some support was found for the hypothesis that narrow leaves are an adaptation to low nutrient soils. Furthermore, we found a strong correlation between the proportion of trees with non-entire laminas (dissected, toothed, etc.) and mean annual temperature once again supporting the well documented association that provides a basis for reconstructing past temperature regimes.