Ecological traps and habitat loss, stump extraction and its effects on saproxylic beetles

Abstract

Stump storage piles created at stump extraction are stored next to the extraction clear-cuts for 2years. These storage piles may become a trap for saproxylic insects (dependent on dead wood) if they attract many breeding individuals, whose offspring are killed at biofuel processing. Stumps in clear-cuts are also an important habitat for many species and these species could be negatively affected by habitat loss when stumps are extracted.In a field study, we therefore estimated the trap effect for the saproxylic beetle fauna in stump storage piles. We also estimated the habitat loss and population decrease that was the result of stump extraction. Beetle density and habitat amounts were estimated in stump storage piles, extraction clear-cuts, and ordinary clear-cuts. In each of eight (six for piles) replicates, beetles were sampled from ten Norway spruce Picea abies stumps, by means of bark sieving, in each habitat (220 stumps in total).Stump extraction reduced the P. abies stump volume by 76%. The concomitant decrease in beetle community abundance was 70%, a decrease from 9109 to 2692 beetles per hectare. A conservative estimate is that between 5.2% and 23.1% of the beetles “produced” at the stump extraction site were killed at stump pile removal. Our results indicated that the stump storage piles were a severe ecological trap for four individual species. However, a lower community density of beetles in stump storage piles compared to surrounding extraction clear-cuts, indicate that stump storage piles did not constitute a community-wide ecological trap.