Experimental Decomposition of Litter from the Tamaulipan Cloud Forest: A Comparison of Four Simple Models

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Abstract
Four differential equation decomposition models were postulated, based on different assumptions of the behavior of the decomposition rare (1/X.cntdot.dX/dt): Model 1, rate constant; Model 2, rate decreasing linearly as a function of the remaining litter fraction; Model 3, rare decreasing nonlinearly as a function of the remaining litter fraction; and Model 4, litter formed by two fractions, each having a constant decomposition rate but varying in proportion with time (thus the overall rate will also vary with time). The models were tested against dry-weight data from three contrasting litter types from the Tamaulipan [Mexico] cloud forest: leaves of Liquidambar styraciflua, fruits of Prunus serotina, and branch segments of L. styraciflua. All three types were incubated in litter bags at constant temperature (30.degree. C) and 100 percent relative humidity. Subsets of four replicates were collected, dry-weighed, and discarded at increasing intervals for three months. Model 1 (the negative exponential) consistently gave the worst fit to the data. The best fits were obtained from Models 3 and 4, showing the high intrinsic heterogeneity of litter and, consequently, the variability of the relative decomposition rates.