Wild bee diversity is enhanced by experimental removal of timber harvest residue within intensively managed conifer forest

Abstract

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.

Relative bee abundance varies by collection method and flowering richness: Implications for understanding patterns in bee community data

“…We found that seasonal variation of bee richness in pan traps stayed relatively stable at both higher and lower levels of floral richness compared to bee composition in nets. This may be because pan traps can detect bees regardless of floral resource availability, including when there is a complete absence of vegetation (Rivers et al., 2018), whereas netting relies heavily on the availability of flowers from which the collector can sample (Cane et al., 2000; Gibbs et al., 2017; Nielsen et al., 2011).…”

“…Abundance of bees in pan traps is often used as a proxy measure of abundance in a given habitat (Rivers et al., 2018) and to estimate community composition (Mallinger et al., 2016; O'Connor et al., 2019; Smith DiCarlo et al., 2020; Westphal et al., 2008). Our work shows that this relationship is complex and that pan traps are potentially problematic for community metrics that rely on abundance measurements.…”

Frequent prescribed fires favour ground‐nesting bees in southeastern U.S. forests

“…Given such low capture rates across studies, this approach requires either numerous traps or many days of sampling to yield adequate data. Capture rates appear to vary regionally and among ecosystems, with the highest reported rates (0.62 and 0.27) coming from agricultural areas in California (Sardiñas et al ., 2016a; Sardiñas et al ., 2016b) and the lowest published rates (0.01) coming from harvested forests in Oregon (Rivers et al ., 2018). The rate of capture in this study (0.05) is quite similar to rates (0.04 and 0.05) previously reported from Florida (Cope et al ., 2019).…”

The impacts of bioenergy pine plantation management practices on bee communities

“…We found that harvesting plantation woody debris correlated with higher bee abundances but on a per-individual basis, and species richness and community evenness were markedly lower. This is perhaps unsurprising, given that coarse woody debris has been associated with wood-nesting bee diversity in other managed forests (Rivers, Mathis, Moldenke, & Betts, 2018;Rodríguez & Kouki, 2017). Physical soil disturbance from the collection of debris may also impact ground nesters (Vázquez, Alvarez, Debandi, Aranibar, & Villagra, 2011).…”