Increasing the amount of dead wood by creation of high stumps has limited value for lichen diversity

Aino Hämäläinen,Thomas Ranius,Joachim Strengbom

doi:10.1016/j.jenvman.2020.111646

Abstract

Artificial creation of dead wood in managed forests can be used to mitigate the negative effects of forestry on biodiversity. For this to be successful, it is essential to understand the conservation value that the created dead wood has in comparison to naturally occurring dead wood, and, furthermore, where in the landscape addition of dead wood is most beneficial, i.e. how landscape composition influences species occurrence on dead wood. We examined these questions by surveying epixylic lichens on artificially created high stumps of Scots pine (Pinus sylvestris) in 3–17 years old clear-cuts. We compared lichen assemblages on high stumps to those on other types of pine dead wood in mature forests, and examined how stump age, the amount of dead wood at the clear-cuts, and landscape composition at 500 m - 2.5 km scale influenced the assemblages. In comparison to other dead wood types, high stumps hosted lower lichen richness and less variable assemblages containing mainly common generalist species. Species richness increased with stump age, whereas dead wood amount and landscape composition were not important; only the total amount of forests in the landscape had a minor positive effect. We conclude that at the studied timescale high stumps of Scots pine are not particularly valuable for epixylic lichens and provide a poor substitute for naturally occurring dead wood in mature forests, although their value may increase with age. Furthermore, directing dead wood creation to specific stands or landscapes does not appear beneficial for lichen biodiversity, given the minor effect of landscape composition found at scales below 2.5 km.

Highlights

Intensive forest management leads to changes in the structure and dynamics of forests, including a drastic decrease in the structural rich ness that is important for maintaining forest biodiversity (Franklin et al, 1997; Gauthier et al, 2015)
We examined the assemblages of epixylic lichens on high stumps and assessed whether they are affected by the surrounding forest stand and landscape
The stands were selected so that the surrounding landscapes had a gradient in the amount of protected forests and unmanaged low-productivity forests

Summary

Introduction

Intensive forest management leads to changes in the structure and dynamics of forests, including a drastic decrease in the structural rich ness that is important for maintaining forest biodiversity (Franklin et al, 1997; Gauthier et al, 2015). The decrease of dead wood, in turn, has led to a decline of species dependent of it, estimated to comprise 20–25% of all forest-dwelling species in European boreal forests (Siito nen, 2001) Restoration forestry, such as artificial creation of dead wood, is often suggested as a practice to compensate for losses and enhance biodiversity (Halme et al, 2013). Dead wood volumes can be increased for example through girdling of living trees to create snags (Walter and Maguire, 2005), or retention of residual dead wood created during harvest (Doerfler et al, 2017) Another widely used method is to create so-called high stumps by cutting living trees at height of 3–5 m (Stokland et al, 2012). They are commonly used for example in Sweden, where the forest certification standards FSC and PEFC that together cover over 60% of the country’s managed forests (Swedish Forest Agency, 2019), require creation of high stumps at all clear-cut stands (Anonymous, 2010, 2016)

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