Stand characteristics and dead wood in urban forests: Potential biodiversity hotspots in managed boreal landscapes

• Published in: Landscape and urban planning Vol. 201; p. 103855
• Main Authors: Korhonen, Aku, Siitonen, Juha, Kotze, D. Johan, Immonen, Auli, Hamberg, Leena
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2020
• ISSN: 0169-2046; 1872-6062
• DOI: 10.1016/j.landurbplan.2020.103855

•Living tree structure and dead wood were measured in urban spruce stands.•Urban forests were compared to rural managed and semi-natural forests.•Living stands in urban forests were structurally diverse and rich in old trees.•Biodiversity value of urban forests could be developed by retaining more dead wood. Urban forests are usually not intensively managed and may provide suitable environments for species threatened by production forestry. Thus, urban forests could have the potential of enhancing biodiversity both within cities and at a larger landscape scale. In this study, we investigated stand structures of boreal urban forests to assess them in terms of naturalness and biodiversity conservation potential. We sampled two types of urban spruce-dominated stands: random urban stands as representatives of average urban forests, and valuable urban stands known to host high polypore richness and assumed to represent urban biodiversity hotspots. Urban forests were compared to rural forests with different levels of naturalness. Living and dead trees and cut stumps were measured from all studied stands. Urban forests had generally diverse living tree structures with abundant large-diameter trees. Random urban forests had more dead wood (median 10.1 m3 ha−1) than production forests (2.7 m3 ha−1) but still considerably less than protected, former production forests (53.9 m3 ha−1) or semi-natural forests (115.6 m3 ha−1). On the other hand, valuable urban forests had relatively high median volume of dead wood (88.2 m3 ha−1). We conclude that the combination of diverse stand composition and the presence of old-growth characteristics in boreal urban forests form a strong baseline from which their biodiversity value can be further developed, e.g. by leaving more fallen or cut trees to form dead wood. We propose that urban forests could become significant habitats for biodiversity conservation in the future.