Some Bees Just Want to See The Prairie Burn
Primary Source: Brokaw, Julia, et al. “Prescribed fire increases the number of ground‐nesting bee nests in tallgrass prairie remnants.” Insect Conservation and Diversity, vol. 16, no. 3, 2023, pp. 355–367, https://doi.org/10.1111/icad.12628.
Prescribed burning is a method of mediating grassy ecosystems. In the American midwest, indigenous tribes used slow-burning, low-intensity fires to keep woody plants from encroaching onto the prairie ecosystem for millenia, maintaining grazing lands for herbivores. While European settlers abandoned this practice, in recent years prescribed burning has become a widely recognized land management practice. However, while the effects of prescribed burns on vegetation are well understood, more research is being done into its effects on other organisms in the ecosystems in which it is utilized. One such study, a collaboration between researchers in Minnesota and Pennsylvania, sought to understand how prescribed fires may affect the prairie’s bee population within the year of the fire.
Purveying the Prairie
Other, similar studies have already noted that areas of the prairie ecosystem in which prescribed burns were applied that year had higher populations of bees compared to areas that had not been burned that year. Additionally, they have found that most of the species of bees in the burned areas are ground-nesting bees as opposed to stem-nesting bees, which theoretically makes sense given the lack of woody plants and access to open, dry ground for nesting provided by prescribed burns. However, these studies leave much to be desired in terms of conclusiveness. While more bees may have been sampled in burnt areas compared to unburned areas, nothing in these studies rules out the possibility of these bees having nested in the area before the prescribed burn was applied. If this were the case, it would mean that the noted difference in population is unrelated to the prescribed burns.
It was for this reason that the researchers of this study utilized a novel method of determining which bees sampled had nested within the year of the prescribed fire. For each specimen, the researchers scored based on species, sex, wing wear, and mandible wear. Independent observers were then to determine the specimen ‘worn’ or ‘unworn’ based on the presence of frayed wings or worn-down mandibles, both of which would indicate recent nesting. For social bee species, all individuals of the same species were presumed to come from the same nest to avoid inflating the estimated number of nests. Meanwhile, for solitary bee species, the presence of a nest was determined by the presence of a ‘worn’ female. Additionally, the researchers measured various factors known to affect nesting habits of bees, such as vegetation cover, percentage of bare ground, and slope, for both burned and unburned areas.
Buzzing Results
The researchers found that, as expected, areas which had been burned had a significantly higher estimated number of nests than unburned areas. Additionally, the percentage of bare ground was significantly higher in burned areas, despite both areas in which prescribed burns were applied that year and areas which were not burned having comparable vegetation cover, number of flowers, and number of flower-species. This implies that, as theorized from previous studies, prescribed fires produce more ideal nesting conditions by increasing the percentage of bare ground and decreasing the ground moisture.
While this study confirms what was already theorized, the novel method in which the researchers accounted for a previously overlooked shortcoming is a fantastic example of advancement in environmental science. Whereas previous studies simply used the general bee population as a proxy for bee nesting, this study considered the actions involved in nesting and found more fitting proxies. Additionally, this research serves as an excellent reminder into the cascading effects that human land management can have on the same ecosystems we strive to protect. While the effects in this case were beneficial ones, negative consequences can quickly compound just as much, if not more-so, as it did in the very same ecosystem during the infamous and disastrous Dust Bowl.
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