Energy Storage and the Balance of Producers and Decomposers in Ecological Systems

While some fraction of the solar energy fixed by producing plants is released by respiration of these plants and of animals, much of it is stored in dead organic matter until released by decomposing organisms, at rates which vary greatly from place to place. The general differential equation for the rate of change in energy storage is illustrated by models for build-up and decomposition of organic matter, particularly for litter in deciduous or evergreen forests. Equations have a useful place in estimating decay parameters. For the case of steady production and decay, the ratio of annual litter production, L, to the amount accumulated on top of mineral soil in a steady state, X/sub 88/, provides estimates of the decomposition parameter k. Estimates range from over 4 in certain tropical forests to less than 0.01 in subalpine forests. Decomposition rates for organic matter within mineral soils may range from near 0.01 to 0.001. Since it takes a period of about 3/k years before storage has attained 95% of its steady-state level, many ecosystems continue to show a positive net community production for centuries - perhaps long after changes in numbers and biomass of some species are reduced to minor fluctuations around a climax composition. On the other hand, the slow change in soil conditions may in some cases facilitate the introduction of new species after some delay during succession. The change in productivity or decomposition parameters controlled by these species may lead in turn to a series of later readjustments in energy storage and release, which modify litter and soil conditions. Modified microenvironments in turn may further alter the succession and climax. 29 references, 7 figures, 2 tables.