GLOBAL LITTER PRODUCTION, POOLS, AND TURNOVER TIMES - ESTIMATES FROM MEASUREMENT DATA AND REGRESSION-MODELS

Systematic and compatible databases to quantify composition, distribut ion, and turnover times of carbon in global litter were developed and evaluated. The study employs an integrated approach, estimating relate d litter pools and fluxes using a variety of data-based and model-base d techniques. The analysis includes direct estimates and indirect, or proxy, estimates of litter production and pools; steady-state turnover times are estimated from the two. Proxies for litter production inclu de net primary productivity and root respiration-soil respiration rela tionships. In addition to implementing a suite of regression models, > 1100 published measurements of litter components, along with site char acteristics, were integrated into a baseline data set and used to esti mate litter production and pools. Historically, global estimates of li tter production have ranged from 75 to 135 Pg dm/yr; several estimates from this study suggest values in the middle of this range, from 90 t o 100 Pg dm/yr. The estimate of aboveground litter production from the compiled measurements, 39 Pg dm/yr, includes mainly forest, woodland, and wooded grassland; other grassland, shrubland, and xeromorphic com munities that occupy similar to 25% of the ice-free land surface are u nrepresented in the present compilation. Aboveground litter production may be 5-10 Pg dm/yr higher with the inclusion of these ecosystems, a nd the total, including belowground production, may approach 90-110 Pg dm/year. Two novel production estimates derived from soil-and root-re spiration relationships are 93 Pg and 100 Pg dm/yr. These estimates ha ve the major advantage of accounting. for both aboveground and belowgr ound litter; the latter is rarely included and can account for a subst antial fraction of total production. Production of coarse woody detrit us may add similar to 12 Pg dm/yr to the fine litter total. The global litter pool has previously been estimated at similar to 100 to 400 Pg dm. The fine litter pool estimated here from the measurement compilat ion is 136 PE dm. Although this partial estimate includes ecosystems c overing just under half the ice-free land surface, it encompasses fore sts and woodlands which have the largest pools. Inclusion of the remai ning ecosystems may add similar to 25 Pg, raising the total to similar to 160 Pg dm. An additional similar to 150 PE dm is estimated for the coarse woody detrital pool. Global mean steady state turnover times o f litter estimated from the pool and production data range from 1.4 to 3.4 years; mean turnover time from the partial forest/woodland measur ement compilation is similar to 5 years, and turnover time for coarse woody detritus is similar to 13 years. By encompassing spatial distrib ution, composition, and magnitude, along with numerous field measureme nts, this integrated approach has begun to yield compositional and eco system constraints on modeled global and regional litter fields and NP P allocation schemes in ecosystem models.