Pining for diversity: Does greater tree species diversity enhance the resilience of associated biodiversity and ecosystem functioning in Pinus sylvestris forests?

Pinus sylvestris is widely distributed in the Northern Hemisphere. In the UK it forms the dominant tree in native pine forests and is the only native conifer of economic significance. P. sylvestris is threatened by a range of diseases and climate change. We assess if tree species diversification will provide resilience for P. sylvestris-associated biodiversity and how diversification would alter ecosystem functioning related to decomposition rates and nutrient cycling. Collating existing records, we found 1589 species that use P. sylvestris for either feeding or living in/on in the UK. This included 199 fungi and 16 invertebrate species that only use P. sylvestris, together with 12 lichens that only use the Pinus genus. Forty-seven other tree species were assessed for their suitability to support these P. sylvestris associated species. Using the data with the highest confidence, the maximum percentage of non-obligate species that could be hosted by any other alternative tree species was 15 %, 11 % of species used only one other tree species and 23 tree species would be required to support 41 % of species. The importance of Betula pubescens/pendula, Quercus petraea/robur, Fagus sylvatica and Picea abies in supporting P. sylvestris associated species is highlighted. An extensive literature review revealed that diversification with native broad-leaved trees could lead to more rapid nutrient cycling while diversification with other conifers (non-natives) would maintain a more similar nutrient cycling. We conclude that tree species diversification within the UK’s P. sylvestris forests will only provide enhanced resilience for a limited suit of associated biodiversity.