Harvey, Alan E.; Jurgensen, Martin F.; Larsen, Michael J. 1979. Role of forest fuels in the biology and management of soil. Gen. Tech. Rep. INT-GTR-65. Fort Collins, CO: U.S. Department of Agriculture, Forest Service. Rocky Mountain Research Station.
Microbial activities are the principal biological determinants of forest site quality. The energy source or substrate for most microbes is derived from soil organic matter (fuels). Microbial activities most critical to site quality are nitrification, dinitrogen fixation, decay, ectomycorrhizal symbiosis, and pathogensis. Research on these subjects supports the following conclusions.
The end product of nitrification, nitrate, is subject to leaching loss. Nitrification is increased by forest disturbances, particularly clearcutting and burning. In most cases, losses of nitrogen are small and short lived.
The quantities of nitrogen fixed in forest soil by symbiotic associations are dependent on the presence of host plants. Such hosts are sometimes scarce. Nonsymbiotic nitrogen fixers depend only on organic matter. Soil humus, decaying and decayed wood, are important sites for nonsymbiotic nitrogen fixation, particularly during dry periods or on dry sites.
Soil humus and decayed wood are also the principal substrates for ectomycorrhizal symbionts during dry seasons and on dry sites.
Decay of wood and other organic material contributes to soil development by cycling carbon and minerals. Products of decay provide sites for nitrogen fixation and ectomycorrhizal activity. Decay of newly formed residues, to a point where they function in these capacities, is a long-term process.
Removing or burning forest fuels can lead to increased feeder root disease. It can also create wound entry sites for decay in living trees. In some instances this provides active centers of nitrogen fixation. Infected wood in root disease centers is a potential source for inoculation and further spread of the diseases.
Adequate quantities of woody residue, and other soil organic matter sources, are critical to optimal forest growth. Except where wood constitutes potential for disease or intense wildfire or where it is replaced in relatively short time spans (warm, moist sites) it should be conserved. This is particularly true of marginal (dry or cold) sites. Excess accumulation or inadequate supplies of wood provides an opportunity for site protection and enhancement through fuel management.