From mixtures to monocultures: Bird assemblage responses along a production forest conifer-broadleaf gradient

Adam Felton,Per-Ola Hedwall,Renats Trubins,Jakob Lagerstedt,Annika Felton,Matts Lindbladh

doi:10.1016/j.foreco.2021.119299

Adam Felton, Per-Ola Hedwall + Show 4 more

Open Access

https://doi.org/10.1016/j.foreco.2021.119299

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Abstract

Increasing the prevalence of broadleaf trees in conifer-dominated production forests is a recommended means of improving habitat availability for broadleaf and mixed-forest species. The implications for biodiversity are often measured by contrasting broadleaf-conifer mixtures with conifer-dominated stands. However, few studies include broadleaf-dominated stands in these assessments. Here we contrasted the bird assemblages of even-aged production forests along a mixture gradient from Norway spruce (Picea abies) dominated, to birch (Betula spp.) dominated stands in southern Sweden. We conducted point count surveys of bird individuals exhibiting breeding behaviour within 30 stands varying from <0.5% to over 98.5% broadleaf by basal area. A total of 355 birds were detected, comprising 36 bird species, seven of which are classified as near threatened by the Swedish Red-list. Our results indicate i) a distinct shift in bird community composition linked to the percentage of broadleaf trees at stand and landscape scales, ii) significantly higher bird species richness, evenness, and abundance in stands with a higher proportion of birch, iii) higher bird abundance in birch-dominated stands than in mixtures, and iv) shifts in bird species guilds as related to stand basal area, the amount of shrubs in the understory, and quantities of dead wood. All of these results have implications for the ways in which production forest management could be altered to enhance avian diversity, and we discuss these with respect to the use of broadleaf versus mixed-species stands.

Highlights

Conserving forest ecosystems is critical to tackling global biodiver sity loss (Ceballos et al, 2017; IPBES, 2019)
Both protected forests and forests actively managed for the production of biomass and other goods and services are important for forest biodiversity (Lindenmayer and Franklin, 2002)
By increasing the proportion of broadleaf tree species in otherwise conifer-dominated stands, a wider range of bird species is likely to be supported by production forest habitats

Summary

Introduction

Conserving forest ecosystems is critical to tackling global biodiver sity loss (Ceballos et al, 2017; IPBES, 2019). Despite widespread reliance on managed production forests for meeting conservation goals (Brockerhoff et al, 2017), these environments often diverge from natural forest conditions and the habitat requirements of many native species This can be due to differ ences in the anthropogenic disturbance regimes employed, tree species composition provided, and forest structures retained (Felton et al, 2016a). Current trends indicate that reliance on intensively managed production forests will continue to increase this century (Warman, 2014; Payn et al, 2015), which will further increase the distinction between natural forest conditions and those found in many production forests Countering these trends, there is growing international awareness of the potential biodiversity and ecosystem service benefits from diversifying silviculture (Felton et al, 2020a). Less inten sive silvicultural practices can provide greater structural complexity, small-scale variability (Kuuluvainen et al, 2012) and tree species di versity (Pretzsch et al, 2017) than the even-aged monocultures commonly used by intensive forestry, with expected benefits to habitat availability, and forest biodiversity (Lindenmayer and Franklin, 2002; Gustafsson et al, 2020)

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