Effects of Fire on Pollinating Insects

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.