Reed, C.C. 1995. Insect responses to prairie management. Final report submitted to the Minnesota Department of Natural Resources. 74 pp.
This report summarizes published and unpublished information on the effects of burning, grazing and haying on prairie insects. The presettlement tallgrass prairie was maintained by wildfire and grazing by native herbivores. Changes in the prairie since settlement are based in massive habitat loss, species loss and fragmentation. Prairie remnants are isolated and in some cases have been grazed, hayed, invaded by woody plants and by alien weeds, and protected from fire: all these factors influence their insect communities. Genetic changes may accompany fragmentation.
Studies of the effects of a single burn on insect communities frequently produce inconsistent results, but generally spiders leave the burned area; millipedes tend to be more numerous on burned areas compared to unburned controls; collembola populations are reduced on burned areas; grasshoppers emerge earlier on burned areas and are generally well adapted to burning; Hemiptera and Homoptera are initially reduced in population but tend to invade recently burned areas where the vegetation is regrowing; beetles, Lepidoptera and flies vary among families in their responses to burning; ants tend to survive burning well except for above-ground nesters. Few statistically significant observations were made on other insect groups.
Studies of managed areas indicate that burning causes mortality among many species, and that recolonization from unburned areas is necessary to reestablish populations. Prairie obligate Lepidoptera and leafhopper populations are reduced on sites burned annually, while prairie obligate Orthoptera increase in abundance and species richness on annually burned sites. Many insect species are attracted to recently burned areas or to areas burned one or two years previously. Insects use sites in a very patchy manner; usually any species uses only a fraction of any site, and is absent from some suitable sites. Grazing and haying have received little study as conservation methods.
Site history influences the response of any site to management: the effects of a burn persist for several years, and over the long term species are lost from a site or persist on it in response to local conditions including management. Insect species vary in their responses to management based on their life history (those which pass a dormant period underground are likely to be fire tolerant), mobility and host specificity.
Many areas require additional research: basic biology of prairie insect species and their responses to management, characteristics of sites showing high insect species richness, identification of prairie obligate species, and larger issues of insect population biology on a regional scale are among the most urgent.
Management recommendations differ among authors, with botanists generally urging frequent and thorough burns to enhance prairie vegetation and butterfly specialists urging minimal if any burning to prevent mortality among butterflies. There is no single management program to protect all insects: a three year burn cycle leaving ample unburned areas at any time is recommended for conservation of fire tolerant and intolerant species on midwestern tallgrass sites. Sites should be monitored to determine the effects of management.