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Local and regional environmental variation influences the growth of tropical trees in selection trials in the Republic of Panama

Park, Andrew, van Breugel, Michiel, Ashton, Mark S., Wishnie, Mark, Mariscal, Emilio, Deago, José, Ibarra, Diogenes, Cedeño, Norma, Hall, Jefferson S.
Forest ecology and management 2010 v.260 no.1 pp. 12-21
trees, tree growth, tropical forests, climatic factors, environmental factors, edaphic factors, tropics, topography, soil properties, soil texture, slope, equations, regression analysis, basal area, Panama
Native Neotropical trees are being increasingly planted for restoration purposes and timber production, but we lack species-specific data on growth responses to different regional climates and local environmental variation. We used regression trees and variance components to quantify the effects of within- and among-site environmental variation on the basal area (BA) of 21 Neotropical and two exotic tree species at three selection trials in the Republic of Panama. Sites represented distinct regional climates in which annual rainfall varied from 1100 to 2226mm, with dry seasons of 4.1-6.7 months. Local environmental variables included measures of slope steepness and position, soil texture, soil color, and indicators of soil condition, such as subsoil rockiness. Basal area in 17 species responded primarily to regional differences among sites, and explained between 32% and 72% of species BA. Low BA plots of most species were located in the driest site, while high BA plots were found in the two wetter sites (mean BA difference=117±20.6cm²). Local variables also influenced the growth of 12 species, with percent slope, soil texture at 5-10cm, subsoil rockiness and Munsell value from 20 to 50cm explaining between 0.2% and 24.5% of within-site variance in BA. For these variables, BA differences across adjacent branches of regression trees ranged from 59±23.4cm² (subsoil rockiness) to 176±45.9cm² (Munsell value). Our results support the growing evidence that local as well as regional environmental variation influences tree community composition, growth and survival in mature forests. Furthermore, the heterogeneity of responses to local variables among environmentally sensitive species allowed us to make some preliminary site and species-specific silvicultural recommendations. For site generalists, future research should extend the current trials to multiple sites within each regional climate to separate climatic influences from those of the local environment.