Assemblages of flower-visiting insects in clear-cuts are rich and dynamic

Per Milberg,Karl-Olof Bergman,Victor Eriksson

doi:10.14411/eje.2021.019

Abstract

Clear-cuts in production forests provide an open, sunny environment, with an abundance of nectar, as well as exposed soil and woody debris. This makes them a potential habitat for several groups of insects that typically use open habitats like grassland, including those species that visit flowers. In the current study, we used colour pan traps to catch flower-visiting species. Study sites were selected according to age (2-8 yrs since clear-cut) and land-use history (forest or meadow 150 yrs ago). We caught and identified solitary bees (395 specimens belonging to 59 species), social bees (831/16), other Hymenoptera (367/66), Syrphidae (256/31), and beetles (Lepturinae & Cetoniinae; 11,409/12). Age of the clear-cut strongly affected species composition as well as several groups and species, with most species caught mainly in the younger clear-cuts. Flower abundance statistically affected several groups and species, but inferring causation is difficult due to the flower-richness bias in pan trap catches. Bare soil and woody debris were important for the insect assemblage sampled, while bare rock was not. Although the majority of the insects caught were forest species, about one third of the species were associated with open, agricultural sites and hence seem to be able to locate and exploit resources in clear-cuts.

Highlights

Production forests cover vast tracts of land and are habitats for many organisms
When production systems are based on native vegetation they may support a large proportion of native fauna and flora (Bergner et al, 2015; Hanula et al, 2016; Rivers et al, 2018) and since the areas affected are large, potential habitats that may be created by forestry practices are important for understanding population dynamics of species at the landscape scale (Bergman et al, 2018)
In total 13,258 insects belonging to 184 species were identified

Summary

Introduction

Production forests cover vast tracts of land and are habitats for many organisms. When production systems are based on native vegetation they may support a large proportion of native fauna and flora (Bergner et al, 2015; Hanula et al, 2016; Rivers et al, 2018) and since the areas affected are large, potential habitats that may be created by forestry practices are important for understanding population dynamics of species at the landscape scale (Bergman et al, 2018).Today, many production forests are subject to clear-cutting, i.e. all or most trees in an area are removed. Other insect groups that exploit clear-cuts include bees and wasps (Fye, 1972; Cartar, 2005; Romey et al, 2007; Pengelly & Cartar, 2010; Rubene et al, 2015; Westerfelt et al, 2015, 2018; Heneberg et al, 2016; Roberts et al, 2017; Johansson et al, 2020), hoverflies (Makino et al, 2006; Deans et al, 2007; Berglund & Milberg, 2019; Johansson et al, 2020), and flower-visiting beetles (Makino et al, 2006; Berglund & Milberg, 2019). Compared with mature forests, there are more pollinators in clear-cuts (Nielsen & Totland, 2014) and higher densities of bees and hoverflies (e.g. Makino et al, 2006; Deans et al, 2007; Romey et al, 2007; Proctor et al, 2012; Roberts et al, 2017; Rodríguez & Kouki, 2017; Amos, 2019)

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