Fire may result in large losses of nitrogen from the soil but it has been 

 found that the nitrogen lost is in a form that is unavailable to plants. On 

 the other hand, fire simultaneously increases the level of mineralized 

 nitrogen that is available to plants. 



The abundance of bacteria in soil sharply declines immediately following fire 

 and then rapidly increases to above pre-fire levels within a few months. Only 

 those bacteria in the top 1 to 2 inches (3 to 5 cm) of soil are killed by 

 fires and repopulation from lower layers is rapid. The increased nutrients 

 and decreased acidity promote high bacterial populations. 



The abundance of fungi is related to temperatures, acidity, and nutrient 

 sources. High temperatures reduce spore viability but reintroduction from 

 areas around the burned areas is rapid. Changes in pH affects the species 

 composition of fungi present, since species have different preferences. 



For the most part, the soil fauna is not usually hurt by fires, because they 

 can escape underground. The major exceptions are the mites and collembolans . 

 The soil fauna are adversely affected by the loss of organic matter (humus), 

 which provides both food and habitat for soil organisms. The xeric conditions 

 on the forest floor following fire also are not conducive to soil organisms. 

 Data on the organisms that have been studied so far indicate that earthworms 

 are reduced significantly following fire, primarily because of the loss of 

 soil moisture; spiders are drastically reduced because they inhabit the 

 uppermost soil layers; centipedes and millipedes are reduced because of a lack 

 of prey populations; and mites and collembolans are reduced by high 

 temperatures but recover in 3 to 4 years. 



Most fires do not seem to cause a considerable amount of direct mortality to 

 vertebrates, since animals are able to escape severe temperatures by burrowing 

 underground, or by moving to residual patches that are not burned, or into 

 water, or simply by outrunning the fire. The indirect effects are more 

 important. On-site climate is modified by burns; air temperature extremes are 

 greater, air moisture is lower during the day, wind velocity is higher, and 

 snow depths are greater. Vegetation structure is the most important change 

 following forest fires. Fires rarely burn evenly and, thus, create a mosaic 

 of old and new habitats. Burns create edges and interspersion of habitats, 

 which are beneficial to species requiring a variety of resources. Fire also 

 alters the plant species available as food; grasses, herbs, woody shrubs, and 

 browse, particularly increase. In addition to the quantity, the quality of 

 food may be improved as well. A slight increase in the protein or nutrients 

 available may occur. 



INTERACTIONS WITH OTHER SYSTEMS 



Forest systems are important to other systems (primarily aquatic) as a source 

 of nutrients and energy, and as a moderating effect on the flow of water from 

 terrestrial to aquatic systems. Many of the brooks and streams that drain 

 forest habitats in Maine are relatively infertile and rely on nutrients and 

 organic matter inputs from forests, upon which a detritus-based trophic 

 structure is built (see chapters 6, 7, and 8, "The Riverine System," "The 

 Palustrine System," and "The Lacustrine System" respectively for more detailed 

 discussions). The output of nutrients and organic matter from Maine's forests 

 is not known but is currently being studied. 



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