Can burning benefit insects in isolated prairies?

Research Brief for Resource Managers Release: July 2014

Contact: Tracy L. Hmielowski

Phone: 608-890-4713

Email: [email protected]

Can burning benefit insects in isolated prairies? Ron Panzer. 2002. Compatibility of prescribed burning with the conservation of insects in small, isolated, prairie reserves. Conservation Biology 16:1296-1307.

There is some concern that burning of fragmented prairie remnants will have a negative impact on invertebrate populations. Evidence from existing literature on the effects of fire varies, with findings that some species benefit while others do not. Given that there are thousands of invertebrates that inhabit prairies, looking at the response of a limited suite of species can add to the difficulty of making the best decisions for managing these ecosystems. Additionally, few studies attempt to follow species for multiple years post-fire, and there is limited understanding of long term impacts of fire on insect populations. To address this lack of data, Ron Panzer conducted a study to examine species responses across a wide geographic area for multiple years. Panzer surveyed remnant prairie sites in Wisconsin, Illinois, and Indiana from 1992 to 1997, looking at the differences in invertebrate populations in burned and unburned sites. Sites were burned multiple times throughout the study, typically in March or April. Insects were sampled throughout the five years of the study, using a variety of methods to maximize the species represented in the data set. Additionally, continued monitoring of populations post fire provided insight into how long it may take for insect populations to recover following burns.

Tallgrass Prairie and Oak Savanna Fire Science Consortium Joint Fire Sciences Program

Management Implications  Annual fires may not allow a long enough recovery time for a minority subset of prairie insects  Burning every 2-3 years may balance concerns over insect recovery with other conservation goals (e.g., plants, birds)  Remnant dependent insects recover at the same rate as remnant independent insects The response of individual species to fire was consistent across sites and years. For all insects surveyed (151 species representing 33 families and 7 orders) 26% responded positively to fire, 34% neutral, and 40% responded negatively immediately post-fire. Negative effects were more common for remnant dependent species (i.e., only found on prairie remnant sites) (54%) than remnant independent species (27%). Two-hundred of the negatively impacted populations, representing 70 species, were tracked for at least one year post-fire. After two years 163 populations, representing 66 species, were considered to be recovered, and 68% of these populations recovered within 1 year. Recovery times were similar for remnant dependent and independent species, and similar for species with varying methods for dispersal (e.g., wings vs no wings). The 37 populations which were not tracked to recovery were the result of unplanned fires or low sample size and cannot be attributed to the prescribed fires. Additional resources online http://www.tposfirescience.org

This study suggests that the negative impacts of prescribed fire on the subset of remnant dependent insect species that are sensitive to fire may be short lived. The author did recognize that in this study not all species could be sampled, and that some populations or species may be negatively impacted and unable to recover. However, sampling all invertebrates in prairies is virtually impossible. Panzer also cautioned against making assumptions about the response of species based on observations of other species in the same genus, as closely related species were observed to respond differently to fire.

Tallgrass Prairie and Oak Savanna Fire Science Consortium Joint Fire Sciences Program

This study supports managing prairie remnants with frequent fire to maintain overall ecosystem health. Fire return intervals of 2-3 years should provide sufficient time for recovery of the majority of prairie insects. However, it is also important to not burn an entire isolated site in a given year as recovery of some species may require recolonization from nearby un-burned areas.

Additional resources online http://www.tposfirescience.org