What determines forest litter decomposition? Global trends and local variance

Abstract

Global patterns in forest leaf litter decomposition has been studied for decades. The result has been the formulation of a range of models relating organic matter decay rate to climatic and litter-specific factors. It is now commonly accepted that the prime factor determining the litter decomposition rate on a global scale, is actual evapotranspiration (AET). However, this main effect can be seriously modified by the chemical composition of organic matter itself, resulting in large variance at local scales. Among leaf litter components, the lignin concentration, content of water-soluble compounds, concentration of nitrogen and some other nutrients have been indicated by different authors as the major determinants of litter decomposition rate. Unfortunately, our understanding of the factors regulating the decomposition is still far from satisfactory as indicated by the failure of existing models to predict properly litter decay rate in many cases. These include especially ecosystems from outside the temperate climate, such as boreal and wet tropical forests. The existing models still cannot explain the large differences in litter decomposition rates between species, even within reasonably wellstudied temperate forests. My article presents several reasons for the problem of finding satisfactory litter decomposition models. The most important reason is the bias in studies towards temperate ecosystems, high inter-correlations between chemical characteristics of litter and soil, and the lack of properly designed studies on very broad geographic scales.