Abstract
Abstract Land set aside for preservation of biodiversity often has low productivity. As biodiversity generally increases with productivity, due to higher or more diverse availability of resources, this implies that some of the biodiversity may be left unprotected. Due to a lack of knowledge on the species diversity and conservation value of low‐productivity habitats, the consequences of the biased allocation of low‐productivity land for set‐asides are unknown. We examined the conservation value of boreal low‐productivity forests (potential tree growth <1 m3 ha−1 year−1) by comparing assemblages of tree‐ and deadwood‐dwelling lichens and forest stand structure between productive and low‐productivity forest stands. We surveyed 84 Scots pine‐dominated stands in three regions in Sweden, each including four stand types: two productive (managed and unmanaged) and two low‐productivity stands (on mires and on thin, rocky soils). Lichen species richness was the highest in low‐productivity stands on thin soil, which had similar amounts and diversity of resources (living trees and dead wood) to productive unmanaged stands. Stands in low‐productivity mires, which had low abundance of living trees and dead wood, hosted the lowest lichen richness. Lichen species composition differed among stand types, but none of them hosted unique species. The differences in both species richness and composition were more pronounced in northern than in southern Sweden, likely due to shorter history of intensive forestry. Synthesis and applications. Boreal low‐productivity forests can have as high conservation value as productive forests, which should be reflected in conservation strategies. However, their value is far from uniform, and conservation planning should acknowledge this variation and not treat all low‐productivity forests as a uniform group. Some types of low‐productivity forest (e.g. on rocky soil) are more valuable than others (e.g. on mires), and should thus be prioritized in conservation. It is also important to consider the landscape context: low‐productivity forests may have higher value in landscapes where high‐productivity forests are highly influenced by forestry. Finally, although low‐productivity forests can be valuable for some taxa, productive forests may still be important for other taxa.
Highlights
Land of low productivity is over‐represented in areas set aside for biodiversity conservation (Fridman, 2000; Scott et al, 2001)
We examined the conservation value of boreal low‐productivity forests by comparing assemblages of tree‐ and deadwood‐ dwelling lichens and forest stand structure between productive and low‐productivity forest stands
We surveyed 84 Scots pine‐dominated stands in three regions in Sweden, each including four stand types: two productive and two low‐productivity stands
Summary
Land of low productivity is over‐represented in areas set aside for biodiversity conservation (Fridman, 2000; Scott et al, 2001). Gjerde et al, 2005; Honkanen, Roberge, Rajasärkkä, & Mönkkönen, 2010), and amounts of valuable substrates, such as large trees and dead wood, (Liira & Kohv, 2010; Nilsson et al, 2002) are generally higher in more productive forests This is consistent with the general hypothesis that diversity increases with productivity due to associated increases in resources (Abrams, 1995), and low‐productivity forests are, considered less valuable for biodiversity preservation (Cederberg, 1997). The number of red‐listed lichens has been found to increase with stand continuity (Marmor, Tõrra, Saag, & Randlane, 2011) Despite these indications, further knowledge of the importance of low‐productivity forests for biodiversity in managed forest landscapes is required. Following the general positive productivity–diversity relationship, the total species richness of lichens is the highest in the unmanaged productive forests due to high resource availability, that is, high amounts and diversity of living trees and dead wood. The patterns of species assemblages among stand types differ between regions due to regional differences in history of forest use and productivity
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