PARENT SESSION
Oral Session #94: Nutrient Cycling.
Presiding: R. Yanai
Thursday, August 8. 1:00 PM to 3:45 PM. Grand Ballroom East, Radisson.
Sphagnum colonization and nutrient accumulation in a Hawaiian montane forest.
Vitousek, Peter*,1, Hotchkiss, Sara2, Ku, Teh-Lung3, Luo, Shangde3, 1 Stanford University, Stanford, CA2 University of Wisconsin-Madison, Madison, WI3 University of Southern California, Los Angeles, CA
ABSTRACT- Nutrient limitation can be driven by imbalances between: 1) the supply of and demand for nutrients within an ecosystem; 2) sources and sinks; and 3) inputs and outputs. These levels of control interact, but the first level is dominant on monthly, the second on decadal, and the third millenial and longer time scales. Supply/demand and input/output balances have been characterized on developmental sequences across the Hawaiian Islands, but source/sink dynamics are poorly known. Generally intermediate-aged sites along these sequences are fertile and productive, but forests on intermediate-aged Kohala Mountain are low in N in particular. Sphagnum palustre forms extensive mats in wet forest and bogs there, but not elsewhere in Hawai'i. Although Sphagnum is native, its widespread dominance appears to be a recent, following stand-level disturbance. We used 210Pb and 137Cs to determine when Sphagnum arrived in 11 sites, and to measure rates of C, N, and P accumulation. Sphagnum accumulated 2200, 45, and 2.7 g m-2 of C, N, and P respectively in several decades, and annual production and nutrient uptake by Sphagnum in one site were 140, 1.4, and 0.08 g m-2 yr-2 of C, N and P. Annual accumulation of N was equivalent to ~ 30% of the quantity cycling in nearby forests, a sink that could substantially reduce N availability.
KEY WORDS: hawaiian islands, sphagnum palustre, nitrogen, phosphorus