Variations in coastal redwood forest decomposition and productivity along an environmental gradient

Coastal redwood forests are a critical natural and economic resource for the State of California and the United States, yet little is known about the biogeochemical cycles that sustain these forests.  Here we report the results of a decomposition experiment utilizing coastal redwood (Sequoia sempervirens) needles at three sites arrayed along a temperature and moisture gradient in California.  At each site we monitored decay of three types of litter (“home-site”, common source, and control) for 24 months using standard litterbag techniques.  Environmental data, including air, litter, and soil temperature, litter and soil moisture, relative humidity and precipitation were collected continuously throughout the experiment.  Monthly litterfall for each site was also examined during the 24-month experiment so we could relate decomposition to above-ground productivity.  We found no significant difference in decomposition rate constants (k) for the home-site litter at each of the three sites (0.34 < k < 0.37), but common and control litters decomposed more rapidly in the cooler, wetter, northern site than in the warmer, drier, southern site (respectively, k = 0.39 and k = 0.28 for common litter, k = 0.34 and k = 0.12 for control litter).  Similar to the pattern observed for decomposition rates, estimates of forest productivity were greater in the cooler and wetter northern site compared to the two southern sites.  The analysis of litter quality (C:N, %N and lignin) from the litter bags used at each site is currently underway and will be related to the decomposition rates of the three litter types and to site conditions.  Our study is among the first to monitor ecosystem properties of redwood forests, and will improve our understanding of environmental regulation on the biogeochemical cycles in these forests.