Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 43°S to 68°N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region- or biome-scale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity.

Dead organic matter is an important structural and functional element in natural forests, but its quantity, quality, and spatial distribution are greatly modified by intensive harvesting and management through forestry. From the perspective of conflicts with biodiversity, the most important changes are associated with reductions in the abundance of snags, cavity trees, and coarse-woody debris, all of which are well known as critical habitat elements for a wide range of indigenous species. Changes in the depth and quality of the forest floor of managed stands are also important for some species and guilds of wildlife. Resolution of this conflict between forestry and biodiversity will require the design and implementation of management systems that accommodate the critical habitat qualities associated with dead organic matter, particularly with large-dimension deadwood and cavities. This goal may be most effectively achieved by an integrated strategy that involves (i) basing forest-management planning on shifting-mosaic habitat models of stand harvesting and replacement, designed to ensure a continuous availability of sufficient areas of stands old enough to sustain habitat features associated with dead organic matter, along with (ii) the provision of protected areas of mature and older growth forest, associated with riparian buffers, deer yards, and nonharvested ecological reserves and other kinds of protected areas. The protected areas are necessary to accommodate those elements of biodiversity that cannot tolerate the conditions of managed stands.Key words: biodiversity, managed forests, plantations, old-growth forests, coarse-woody debris, cavity trees, snags.

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