Models that Describe Litter Decomposition
The graphs for accumulated litter mass loss vs time form different patterns, which may be described using a few simple mathematical functions. Generally we may state that litter may decompose completely or leave a stabilized residue, which may decompose v
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Models that Describe Litter Decomposition
9.1 Introduction Models serve a variety of functions for ecologists, but all ecological models are abstract representations of biological systems expressed in either mathematical or symbolic terms. Models may serve as hypotheses to be tested, or as tools to predict behavior of the ecosystem or one or more of its subsystems. In a concise review, Moorehead et al. (1996) distinguished three groups of decomposition models. Some models are empirical and most of these are statistically based. For example, regression models relate parameters in a system. These models are useful for identifying or indicating the strength of hypothesized relationships, but cannot, by themselves, reveal causality. Empirical models are often useful for prediction, but they are, or at least should be, limited to the range of data from which they were developed. Extrapolation, however tempting, can be misleading. Mechanistic models are another general class of models. They are often analytical in nature, using a system of equations to describe complex processes. Such models have proven very useful for gaining insight into ecosystem behavior, and for developing and testing general theories. A third group of models is simulation models. They are created to simulate the behavior of a system, in a way that allows researchers to manipulate initial conditions, or other aspects of the model, to investigate potential outcomes. Simulation models may use a combination of mechanistic and empirical components to achieve their goal. Ecosystem simulation models often include a decomposition submodel. In reality, models are often hybrids of these types. Empirical or data-based models may be based on a mechanistic understanding of processes. From a different perspective, theoretical (theory-based) models can be made more specific by validation with experimental data, and by using data to determine parameters. Simulation models often use such hybrids to enhance their ability to predict. One of the challenges facing those who model decomposition is the large number of factors that influence the rates and patterns of litter decomposition. Thus, a single model or a relatively simple approach would not likely give a generally applicable description of the decomposition process. Factors that influence decomposition can B. Berg and C. McClaugherty, Plant Litter, DOI: 10.1007/978-3-642-38821-7_9, Springer-Verlag Berlin Heidelberg 2014
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9 Models that Describe Litter Decomposition
be highly interactive, variable, and even hard to measure. These factors include microbial ingrowth, climate, variation in weather between years and different levels of nutrients, heavy metals, and lignin/AUR. Considering the complexity of the decomposition process, we should expect a set or system of functions, each specific for different litter types and conditions. Such a set of functions in relation to litter type and ecosystem remains to be established. In this chapter, we simply describe empirical functions that have been found to
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