Wildfires Influence Abundance, Diversity, and Intraspecific and Interspecific Trait Variation of Native Bees and Flowering Plants Across Burned and Unburned Landscapes

Laura A Burkle,Jonathan A Myers,Michael P Simanonok,J Simone Durney,R Travis Belote

doi:10.3389/fevo.2019.00252

Laura A Burkle, Jonathan A Myers + Show 3 more

Open Access

https://doi.org/10.3389/fevo.2019.00252

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Abstract

Wildfire regimes are changing in the western United States, yet we have little basic understanding of how wildfires influence native bees, the resources they depend on for food and nesting, or the traits that influence their interactions with plants. In burned and unburned areas in Montana, USA, we investigated the abundance and diversity of native bees, floral and nesting resources, nesting success, and traits of flowers and bees. In two of the three localities studied, burned areas, including areas that burned with high-severity wildfires, supported higher density and diversity of native bees and the flowers they depend on for food and larval provisioning. Burned areas also had more bare ground for ground-nesting bees and more available coarse woody debris for cavity-nesting bees than unburned areas. Moreover, cavity-nesting bees were completely unsuccessful at nesting in artificial nesting boxes in unburned areas, while nesting success was 40% in burned areas. Mean bee intertegular distance (a trait strongly correlated with tongue length, foraging distance, and body size) was similar between burned and unburned areas. However, wildfires influenced both interspecific and intraspecific trait variation of bees and plants. Intraspecific variation in bee intertegular distance was higher in unburned than burned areas. Both interspecific and intraspecific variation in floral traits important for interactions with pollinators were generally higher in burned than unburned areas. Thus, wildfires generally increased the density and species diversity of bees and flowers as well as trait variation at both trophic levels. We conclude that wildfires – even large, high-severity wildfires – create conditions that support native bees and the resources they need to flourish, but that unburned areas maintain trait variation in landscape mosaics with heterogeneous fire conditions.

Highlights

Among the many threats posed to biodiversity by global environmental change, changes to natural disturbance regimes are likely to have some of the most profound impacts on animals and plants and the ecosystem services they provide (Hessburg et al, 2015; Johnstone et al, 2016)
interspecific variation in plant traits was generally greater than their intraspecific variation across plots
though the relative effects of wildfire were of similar magnitude between bees and plants

Summary

Introduction

Among the many threats posed to biodiversity by global environmental change, changes to natural disturbance regimes are likely to have some of the most profound impacts on animals and plants and the ecosystem services they provide (Hessburg et al, 2015; Johnstone et al, 2016). Despite the importance of wildfires in natural ecosystems, neither ecologists nor land managers fully understand how or why wildfire affects biodiversity and ecosystem services across complex landscapes that vary in environmental conditions (Burkle et al, 2015) This lack of understanding is true for native bees, which provide pollination services essential to the recovery of plant communities in post-fire landscapes (e.g., Potts et al, 2006; Van Nuland et al, 2013; Heil and Burkle, 2019). Wildfires can open forest canopies and increase space and resources for understory flowering plants, and native bees are attracted to burned areas with abundant floral resources (e.g., Van Nuland et al, 2013) Such increases in bee and floral abundance and diversity tend to peak soon (1–5 years) after fire (Potts et al, 2003a). Fire can subsequently affect the interactions between bees and flowering plants (Peralta et al, 2017)

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