Forest restoration to attract a putative umbrella species, the white‐backed woodpecker, benefited saproxylic beetles

David Bell,Joakim Hjältén,Christer Nilsson,Dolly Jørgensen,Therese Johansson

doi:10.1890/es14-00551.1

Abstract

Umbrella species are often spatially demanding and have limited ability to adapt to environmental changes induced by human land‐use. This makes them vulnerable to human encroachment. In Sweden, broadleaved trees are disadvantaged by forestry, and commercially managed forests are often deprived of dead wood. This has led to a situation where previously widespread top predators in saproxylic food webs, such as the white‐backed woodpecker (Dendrocopos leucotos), have become species of conservation concern. The white‐backed woodpecker is generally considered an umbrella species, and it has been linked to forests with large volumes of dead wood from broadleaved trees. In recent years, forest stands have been restored for the white‐backed woodpecker, but post‐treatment evaluations have rarely included other species that also occur in broad‐leaved forests (co‐occurring species). Many co‐occurring species are saproxylic beetles. In this study, we collected saproxylic beetles and environmental data in restored and commercially managed forests to evaluate if habitat restoration for the white‐backed woodpecker also benefited other species with similar habitat associations. We found that volumes of coarse woody debris were higher in restored than in commercially managed forests, and that a majority of man‐made snags and downed logs were created from birch trees (Betula spp.). Most spruce trees (Picea abies) were extracted during forest restoration, and this opened up the forest canopy, and created stands dominated by broadleaved trees. Many saproxylic beetles were more common in restored forests, and there were significant differences in species composition between treatments. These differences were largely explained by species traits. Effects of sun‐exposure were particularly important, but many beneficiary species were also linked to dead wood from broadleaved trees. Red‐listed saproxylic beetles showed a similar pattern with more species and individuals in restored sites. The white‐backed woodpecker is still critically endangered in Sweden, but important prey species are already responding to forest restoration at the stand level. We recognize that landscape‐level improvements will be required to bring the white‐backed woodpecker back, but also that the umbrella species concept can provide a useful framework for successful forest restoration as many co‐occurring saproxylic beetle species seemingly benefitted from restoration for the white‐backed woodpecker.

Highlights

Human land-use has changed forest ecosystems world-wide
Dead wood was created during forest restoration, and restored sites contained larger total volumes of lying coarse woody debris than commercially managed sites (Table 2)
Restoration efforts guided by the white-backed woodpecker created stands significantly different from those impacted by commercial forestry, as predicted in our first hypothesis

Summary

Introduction

Forest management often favors production of commercially important tree species at the expense of less profitable but in many cases ecologically important tree species. In Sweden, stand-level volumes of timber have increased with 40–80% since the 1950s (SLU 2012). The explanation for this is an increased production of conifers at the expense of broadleaved trees that are disfavored by modern forestry, e.g., during thinning. Commercial forests are denser and less permeable to sunlight. This has led to an impoverished fauna of species associated with sun-exposed conditions and broad-leaved trees (Gardenfors 2010). Broadleaved trees are disadvantaged when natural disturbance regimes, such as recurrent wildfires in upland forests and seasonal floods in riparian environments, are suppressed or altered (Linder et al 1997, Johansson and Nilsson 2002, Hellberg 2004)

Methods

Results

Conclusion