Vegetation structure and decreased moth abundance limit the recolonisation of restored habitat by the European Nightjar

Nathalie Winiger,Raphaël Arlettaz,Alain Jacot,Pius Korner

doi:10.3897/rethinkingecology.3.29338

Abstract

Woodland ecosystems of Europe have undergone major transitions in the last centuries. Changes in land use and the loss of natural forest dynamics have often led to structurally poor, uniform and dense stands. Not surprisingly, open forest species relying on a heterogeneous stand structure have suffered dramatic population declines. The European Nightjar Caprimulguseuropaeus, a nocturnal insectivorous bird, has undergone such a decline in its main Swiss stronghold in Valais. Despite the species’ potential to colonize new sites and habitat restoration measures implemented since 2001, recolonisation of restored sites has not taken place, suggesting problems with the current habitat restoration strategy. In order to refine management recommendations, we compared habitat structure and moth abundance, a key Nightjar food source, at sites that are still occupied and at sites that had been abandoned but have recently been restored. Vegetation structure was more heterogeneous and moth abundance greater at occupied than at abandoned sites. More specifically, occupied sites harboured a greater coverage of bare ground, while abandoned sites exhibited a higher amount of regeneration and intermediate shrub layer. The occurrence of natural perches was also higher in occupied sites. Abandoned sites are thus characterised by lower prey abundance and denser vegetation cover, the combination of which is likely to lead to lower prey availability for hunting Nightjars. Restoration action would benefit from maintaining snags and dead branches and by targeting unproductive habitats characterised by mineral soils, thereby slowing down regeneration and shrub regrowth. For future successful management of Nightjar habitats, it seems thereby essential trying to find the balance between actions that allow opening the lower and mid-strata of the forest while sustaining high moth populations.

Highlights

European forest ecosystems have undergone substantial changes over the last few centuries (Nilsson 1997; McGrath et al 2015)
Some forest species might benefit from stand homogenisation (Paillet et al 2009; Fonderflick et al 2010), pioneer species will suffer, notably those depending on the early stages of the vegetation succession
An open habitat seems to be especially important, as evidenced by the high percentage of bare ground coverage found in occupied sites

Summary

Introduction

European forest ecosystems have undergone substantial changes over the last few centuries (Nilsson 1997; McGrath et al 2015). The changes in timber harvesting practices have led to a homogenisation of forest structures, which can have negative effects on biodiversity (Spiecker 2003). Awareness of the importance of sustainable forest management for biodiversity and ecosystem services only emerged within the last 20 years Natural hazards and disturbances are important drivers of natural forest ecosystems (Angelstam 1998; Kuuluvainen 2009; Kulakowski et al 2011): they create pioneer habitats whose natural successional stages harbour locally adapted faunal and floral communities (Angelstam 1998). Some forest species might benefit from stand homogenisation (Paillet et al 2009; Fonderflick et al 2010), pioneer species will suffer, notably those depending on the early stages of the vegetation succession

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Results

Conclusion