The vulnerability of insects and other invertebrates to fire depends on their location at the time of fire. While adult forms can burrow or fly to escape injury, species with immobile life stages that occur in surface litter or aboveground plant tissue are more vulnerable. However, aboveground microsites, such the unburned center of grass clump, can provide protection (Robbins and Myers 1992). Soil also protects most soil macrofauna and pupae of many insects from fire. The level of protection depends on depth of the organism and depth of heat penetration, which in turn depend on duff consumption (Schmid and others 1981).

Fire may be beneficial for invertebrates. At least 40 species of arthropods are attracted to fires (Evans 1971), alerted by stimuli including heat, smoke, and increased levels of carbon dioxide. Many use burned trees for breeding, and when the larvae hatch, they feed on the burned trees. Insect abundance above ground decreases immediately after fire in prairies but then increases as fresh, young plant growth becomes available (Robbins and Myers 1992). Fire can also have a positive effect on soil mesofauna. For example, an August understory burn in South Carolina forest reduced the soil mesofauna as measured the day after fire, but annually burned plots had generally higher populations of soil mesofauna than did plots that had not been burned in 3 years or more (Metz and Farrier 1971).

Seasonality of fire no doubt interacts with phenology for many invertebrates. Research is needed on fire effects at all stages of insect life cycles, even though larval stages may be more difficult to track than adult stages (Pickering 1997).

For more information on fire effects on invertebrates, see:

• Fire Effects on Pollinating Insects
• Fire Effects on Aquatic Macroinvertebrates
• Fire Effects on Soil Macroinvertebrates

Pollination is a key process that occurs within forest communities, with some plants depending on only one insect species for pollination (Kevan 1975). Insects are the most important pollinators of plants in most habitats. Folkerts et al. (1993) showed that nearly 75% of all plants in a longleaf pine habitat were pollinated by insects. Because insects are responsible for the bulk of plant pollination, they can have significant effects on the overall plant community. Most pollinating insects will visit and obtain pollen/nectar from numerous plant species. Bees, such as the common honeybee and bumblebees, are considered to be the most common and important type of insect pollinator. However, butterflies, flies such as hoverflies and beeflies, and beetles can also be good pollinators. Due to the importance, conservation of pollinators in forested areas should be considered in land management decisions. The following discussion summarizes what little is currently known about how fire or other forest management practices affect pollinators.

Fire can affect various insect populations in southeastern forests both positively and negatively. Pollinating insects, such as butterflies and bees, could be negatively affected either directly by fire mortality or indirectly by limiting floral resources (pollen and nectar) (Hermann et al., 1998). In prairie regions, certain butterfly species have been negatively affected by fire, with their abundance depending on the number of generations/year, mobility, location during fires, and the response of food plants to fire (Swengel 1996).

However, fire may also greatly enhance pollinating insect habitat by creating and maintaining floral resources and/or nesting sites. If applied properly, periodic burnings can help maintain plant diversity, protect some plant species from diseases, and allow perennial grasses and herbaceous plants to grow (Kerstyn and Stiling 1999). Fire is also important for inducing flowering in many plants (Brewer and Platt, 1994). The majority of bee species are solitary and nest underground or in existing holes in wood or stems. Some pollinators (i.e. ground nesting bees) find nesting sites by looking for patches of bare ground. Fire and possibly other management techniques may enhance and fashion nesting sites by removing litter and exposing bare soil.

Effects of Fire Surrogates on Pollinators

While prescribed burning is the most common method of hazardous fuel reduction in the southern United States, mechanical or chemical "fire surrogates" are being investigated because of the increasing human populations in and around forested areas. These alternatives to fire, such as mechanical thinning and herbicide use, could also impact pollinators. The amount of sunlight received and the locality of plants may be extremely important in determining a plant’s chances for being pollinated by insects (Beattie 1971). Prescribed burns and other alternatives will undoubtedly affect the amount of sunlight reaching the forest floor and change the locations and diversity of understory plants. Plants may actually compete for insect pollinators, which also may help in determining plant community structure (Heithaus 1974, Pleasants 1983, Levan and Anderson 1970). Therefore, changes in insect pollinator abundance and diversity are expected with changes in plant communities. However, exactly what consequences fire and these alternative management practices will have on pollinators are still under investigation.