Litter dynamics in two Sierran mixed conifer forests. I. Litterfall and decomposition rates

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Abstract
Litterfall and decomposition rates. Can. J. For. Res. 18: 1127-1135. Litterfall was measured for 4 years and leaf litter decomposition rates were studied for 3.6 years in two mixed conifer forests (giant sequoia - fir and fir-pine) in the southern Sierra Nevada of California. The giant sequoia - fir forest (GS site) was dominated by giant sequoia (Sequoiadendron giganteum (Lindl.)Buchh.), white fir (Abies concolor Lindl. and Gord.), and sugar pine (Pinus lambertiana Dougl.). The fir-pine forest (FP site) was dominated by white fir, sugar pine, and incense cedar (Calocedrus decurrens (Torr.) Florin). Litterfall, including large woody debris < 15.2 cm in diameter, at the GS site averaged 6364 kg .cntdot. ha-1 .cntdot. year-1 compared with 4355 kg .cntdot. ha-1 .cntdot. year-1 at the FP site. Compared with other temperate coniferous forests, annual variability in litterfall (as computed by the ratio of the annual maximum/minimum litterfall) was extremely high for the GS site (5.8:1) and moderately high for the FP site (3.4:1). In the GS site, leaf litter decomposition after 3.6 years was slowest for giant sequoia (28.2% mass loss), followed by sugar pine (34.3%) and white fir (45.1%). In the FP site, mass loss was slowest for sugar pine (40.0%), followed by white fir (45.1%), while incense cedar showed the greatest mass loss (56.9%) after 3.6 years. High litterfall rates of large woody debris (i.e., 2.5-15.2 cm diameter) and slow rates of leaf litter decomposition in the giant sequoia - fir forest type may result in higher litter accumulation rates than in the fir-pine type. Leaf litter times to 95% decay for the GS and FP sites were 30 and 27 years, respectively, if the initial 0.7-year period (a short period of rapid mass decay) was ignored in the calculation. A mass balance approach for total litterfall (< 15.2 cm diameter) decomposition yielded lower decay constants than did the litterbag study and therefore longer times to 95% decay (57 years of the GS site and 62 years for the FP site).