Decomposers and Consumers 



Of the total energy fixed by green plants (net primary production), some is 

 stored in the conununity as woody tissue and the rest is used by the consumer 

 and decomposer organisms of the system. More energy flows through the 

 detrital pathway (decomposers) than the grazing pathway (consumers) in forest 

 systems. For example, in a mature stand of northern hardwoods in New 

 Hampshire 99% of the nonwoody net production passed through the detrital 

 pathway (Bormann and Likens 1979). In addition, much of the energy that flows 

 through the grazing pathway ultimately ends up in the detritus food chain 

 (e.g., feces and dead animals). The importance of the detrital chain is often 

 overlooked, however, because the animals comprising the grazing pathway are 

 more important and more visible to people. 



Decomposers . There are two major groups of decomposer organisms: the 

 soil microflora, which include bacteria, fungi, and protozoa, and the soil 

 invertebrates, which include nematodes, earthworms, mites, snails, isopods, 

 springtails, dipteran larvae, Enchytraeidae, diplopods, and coleopteran larvae 

 (Edwards et al. 1970). Decomposers break down the organic matter and release 

 nutrients, which are absorbed by plants. The actual chemical decomposition is 

 accomplished by the microorganisms (bacteria, fungi, and protozoans), which 

 possess enzymes necessary to hydrolize cellulose and lignin. This process is 

 aided by the soil invertebrates (primarily earthworms, enchytreaid worms, 

 diplopods, isopods, dipteran larvae, collembolas, and mites), which consume 

 the litter and break it down mechanically. This increases the surface area 

 that is exposed to further invasion by microorganisms and is considered the 

 most important contribution to litter breakdown (Edwards et al. 1970). Very 

 little chemical change takes place in the litter as it passes through soil 

 invertebrates. These organisms receive their nourishment from the microflora 

 and other small invertebrates that are gleaned from the litter. After litter 

 breakdown soil invertebrates also serve to mix the organic material into the 

 soil and form soil aggregates. 



The soil invertebrates form the base of an entire food chain consisting 

 primarily of predaceous invertebrates but also small mammals (moles, shrews, 

 and voles), birds, reptiles, and amphibians. 



Rate of decomposition . Temperature, moisture, pH, and type of litter 

 determine the rate of decomposition. Decomposition is most rapid in a warm, 

 moist environment. In acid soils, common to coniferous forests, fungi are the 

 dominant decomposers, whereas in neutral or alkaline soils (most common in 

 hardwood stands) bacteria are the most abundant decomposer organisms. In acid 

 soils fewer soil invertebrates are present to break down and mix organic 

 matter and, as a result, decomposition is slower than in neutral and alkaline 

 soils (see "Soils," below). 



Woody tissue (branches and trunks) may take several decades to decompose 

 completely, whereas leaves, fruits, and buds usually decay completely in a few 

 years. Leaves of yellow birch, sugar maple, and beech are 95% decomposed in 

 5, 9, and 11 years respectively (Bormann and Likens 1979). 



Consumers . Consumer organisms include herbivores (primary consumers), 

 insectivores , and carnivores (secondary or higher level consumers). In forest 

 systems important primary consumers are insects and other invertebrates, 



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