Removal of timber harvest residues found to enhance wild bee diversity

Production of biofuels from renewable materials has expanded in recent years to include feedstocks such as timber harvest residues, such as logging slash and tree boles. The potential for increased removal of harvest residues has led to questions about environmental implications, including biodiversity responses.

Harvest residue removal has the potential to influence plant and animal communities associated with young forests as they develop following regeneration. Young forests are limited in availability in some regions and provide habitat for many species such as insect pollinators and saproxylic beetles that can be of high conservation priority.

Wild bees are among the most important pollinator group in many young forests because they occur in large numbers and feed on pollen and nectar; however, their responses to removal of harvest residues has not been widely studied.

Recently, investigators with Oregon State University assessed wild bee communities across a gradient of management intensity in which the extent of harvest residue removal and soil compaction were experimentally manipulated. The paper by James W. Rivers, Codey L. Mathis, Andrew R. Moldenke, and Matthew G. Betts was recently made available online by the journal GCB Bioenergy.

The authors report that abundance and richness of bees were greatest in the most intensive treatment. Based on these and other results, they conclude that exposing mineral soil through removal of harvest residue and other organic materials may create new nesting areas for ground‐nesting species within managed forest landscapes.

The abstract for the paper follows.

The use of timber harvest residue as an energy source is thought to have environmental benefits relative to food‐based crops, yet the ecological impact of this practice remains largely unknown. We assessed whether the abundance and diversity of wild bees (Apoidea) were influenced by the removal of harvest residue and associated soil compaction within managed conifer forest in western Oregon, USA. We sampled bees over two years (2014–2015) on study plots that were subjected to five treatments representing gradients in removal of harvest residue and soil compaction. We collected >7,500 bee specimens from 92 distinct species/morphospecies that represented five of the seven bee families. We trapped 3x more individuals in the second year of the study despite identical sampling effort in both years, with most trapped bees classified as ground‐nesting species. Members of the sweat bee family (Halictidae) comprised more than half of all specimens, and the most abundant genus was composed of metallic green bees (Agapostemon, 33.6%), followed by long‐horned bees (Melissodes, 16.5%), sweat bees (Halictus, 15.9%), and bumble bees (Bombus, 13.6%). In both years, abundance and observed species richness were greatest in the most intensive harvest residue treatment, with other treatments having similar values for both measures. Our study indicates that early successional managed conifer forest that has experienced removal of harvest residue can harbor a surprising diversity of wild bees, which are likely to have important contributions to the broader ecological community through the pollination services they provide.

Reference 

Rivers, J.W., C.L. Mathis, A.R. Moldenke, and M.G. Betts. 2018. Wild bee diversity is enhanced by experimental removal of timber harvest residue within intensively managed conifer forest. GCB Bioenergy. https://doi.org/10.1111/gcbb.12531