Monday, November 13, 2006
112-5
Canopy and Soil N and P in a Tropical Forest Across Temperature and Precipitation Gradients.
Travis Idol, Univ of Hawaii, 1910 East West Rd, Honolulu, HI 96822 and Patrick Baker, Monash Univ, School of Biological Sciences, Building 18, Victoria 3800, Australia.
Environmental conditions are hypothesized to control forest structure and function in predictable ways, but few natural gradients exist to test these hypotheses within single forest types. We utilized gradients of precipitation and elevation/temperature in Hawaiian forests dominated by the native N-fixing tree Acacia koa in order to investigate relationships of soil nutrient availability and leaf and canopy nutrient content. As expected, stand basal area, leaf N and P concentration, and canopy N and P content were greater in sites with higher temperature and precipitation. Soil N availability was uniformly high at all sites, but P availability decreased with temperature at the mesic site. Leaf mass per area decreased with temperature and precipitation, resulting in relatively constant leaf N per unit leaf area and canopy N per unit basal area. Canopy P increased with soil P at two of the three locations studied and was not constant per unit stand basal area. These results suggest that A. koa has the capacity to adjust leaf N concentration in order to maintain relatively constant N content per unit leaf area over broad environmental gradients. However, soil P availability may limit the ability of A. koa to adjust leaf P content to changes in climatic conditions. Adjustments in A. koa P use efficiency, therefore, may be necessary for it to maintain optimal productivity across environmental gradients. Despite past research identifying water as the most limiting resource for A. koa productivity, this study suggests there are complex interactions of water, temperature, and nutrients that influence forest structure and function. Single-resource investigations are likely to be insufficient to adequately describe or predict forest dynamics.
Handout (.pdf format, 2328.0 kb)