Silvicultural practices, forest age, forest type, and large-scale regional factors influencing numbers of American burying beetles, Nicrophorus americanus (Coleoptera: Silphidae)

Abstract

The federally threatened American burying beetle, Nicrophorus americanus previously occurred throughout much of eastern North America but now is self-sustaining only on an eastern island and along the western edge of the historic range. The beetle occurred on landscapes managed by Weyerhaeuser Company for timber production, providing an opportunity to evaluate possible effects of silvicultural practices on the species. For 1997–2007, fluctuating densities were low on these lands in southeastern Oklahoma and southwestern Arkansas. We recaptured 23.0% of individuals (all within same year), 27.4% of those at different sites (1.40 km mean distance moved; longest 4.25 km). Comparable surveys at Fort Chaffee, Arkansas (185 km north) and Camp Gruber, Oklahoma (209 km north-northwest) during 1998–2004 demonstrated for Weyerhaeuser-Chaffee near-perfect correspondence in beetle densities expressed as percentage change from previous year but no relationship for Weyerhaeuser-Gruber. The species regionally may be bivoltine with Weyerhaeuser and Chaffee sampled in the second generation and Gruber in the first. The close Weyerhaeuser-Chaffee association indicates numbers were influenced substantially by non-local factors, although given the data in hand we were unable to demonstrate association of climatic factors with beetle relative densities or density changes. No clear-cutting effect on beetle densities was demonstrated. Increases occurred 2 years after a partial cut compared to the prior year. Beetles used pole (13–29 years old) and mature (30–50) sites less often than expected and sapling (5–12) and delayed-harvest (> 50) sites more frequently. For delayed-harvest sites, beetles frequented hardwood (≥ 75% hardwood) less than pine (≥ 75%) or mixed hardwood-pine sites. There were differences relative to stand age and type, but large-scale regional factors probably influenced numbers more than silvicultural practices. Low numbers in southeastern Oklahoma, coupled with substantial year-to-year fluctuations, elevated extirpation risk. Extirpation in the study area likely occurred in 2006 or shortly thereafter, possibly influenced by increases in red imported fire ants, Solenopsis invicta.

Implications for insect conservation

Our study highlights that multiple factors influence numbers of the American burying beetle. Our findings suggest it would be fruitful for investigators to devote further attention to broader regional factors that affect year-to-year variation in such numbers. Silvicultural practices can affect beetle numbers in positive or negative ways, influences that fluctuate through the various stages involved in managing forested landscapes.