A comparison of avian diversity in spruce monocultures and spruce-birch polycultures in southern Sweden

Abstract

The replacement of some spruce monocultures with stands composed of planted Norway spruce (Picea abies) and naturally regenerated birch (Betula spp.) has a range of potential benefits, but the implications for biodiversity are generally unknown. Here we conduct a paired replicated study in southern Sweden of the avian biodiversity found within Norway spruce monocultures, and within Norway spruce stands possessing approximately 20% birch. Our research leads us to three findings. First, avian diversity was significantly higher in the spruce–birch polycultures. Second, spruce–birch polycultures exclusively attracted broadleaf-associated bird species and retained the majority of conifer-associated bird species found in the spruce monocultures. Third, avian biodiversity within the spruce–birch polycultures did not incorporate threatened taxa. We suggest that in addition to the apparent benefits for stand level diversity, widespread use of spruce–birch polycultures could provide a means of softening the matrix for broadleaved-associated species, while concurrently providing an increased broadleaf base from which future conservation actions could be implemented. Our results are relevant to multi-use forestry, and recent policy initiatives by forest certification agencies which aim to increase broadleaf-associated biodiversity within conifer-dominated production forest landscapes.