High-intensity fires therefore should not be considered atypical when occurring in these forest types, and may in fact be essential for ensuring their perpetuation. For example, moist riparian areas and north-facing slopes tend to be less prone to frequent fires. Insect and disease organisms . Insects and disease organisms, including those that attack and sometimes kill patches of trees, are integral components of healthy forest ecosystems. For example, insects and disease organisms help decompose and recycle nutrients, build soils, maintain genetic diversity within tree species, generate snags and down logs required by wildlife and fish, and create diverse patterns of vegetation at both site and landscape scales.
Many wildlife species depend upon insect and disease organisms for food or for creation of habitat.
Dwarf mistletoe, a parasitic plant that has traditionally been regarded as a serious pest because it often causes a reduction in tree growth rates, provides a case in point. Root-decay fungi may kill individual trees, thereby creating gaps in the forest canopy. However, major insect and disease outbreaks that kill trees over relatively large areas do occur. Mountain pine beetle populations typically increase to epidemic levels when large, homogeneous areas of lodgepole pine mature and provide suitable food resources. Such examples demonstrate the danger of prematurely judging the effects of insects and pathogens solely on the basis of short-term tree mortality.