Throughfall volume and chemistry as affected by precipitation volume, sapling size, and defoliation intensity

Throughfall and stemflow are important components of hydrologic processes in forests, but relative con-tributions of multiple factors, including precipitation volume, plant size, and folivory (leaf removal by defoliators), onthroughfall/stemflow have not been reported. This paper reports the relative influences of precipitation volume (0-230L m-2), sapling size (1.4-6.7 cm diameter at root collar; 0.07-0.45 kg calculated dry foliage mass), and manipulatedfolivory (0-20% foliage removal) on throughfall volume and N, K, and Ca fluxes as evaluated with stepwise multipleregression in a young Douglas-fir (Pseudotsuga menziesii [Mirb.J Franco) ecosystem.
Precipitation volume explained most variation in throughfall volume (R2 = 0.81). Folivory and sapling size each hadsignificant but minor effects on throughfall volume and nutrient fluxes. These data indicate that folivore effects, whilesignificant, are masked by precipitation in this wet ecosystem. Wider ranges in sapling size and folivory and/or drierconditions likely would improve interpretation of their influence on throughfall volume and chemistry.
Key words: throughfall, nutrient cycling, defoliation, nitrogen, potassium, calcium, conifer, ecosystem, forest, plantation.