Intimate mixtures of Scots pine and Sitka spruce do not increase resilience to spring drought

Thomas S Ovenden*, Mike P Perks, David I Forrester, Maurizio Mencuccini, Jazz Rhoades, Danielle Thompson, Victoria J Stokes, Alistair S Jump

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
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Abstract

Understanding how we can increase the resilience of forest systems to future extreme drought events is increasingly important as these events become more frequent and intense. Diversifying production forests using intimate mixtures of trees with complementary functional traits is considered as one promising silvicultural approach that may increase drought resilience. However, the direction and magnitude of the drought response of mixed-species stands relative to monospecific stands of the same species can vary with species identity, relative abundance and levels of competition in a focal tree's immediate neighbourhood. Using a long-term experiment where tree-level mortality and the neighbourhood composition of each tree was known, we assessed the radial growth response of 24-year-old Scots pine (Pinus sylvestris) and Sitka spruce (Picea sitchensis) trees in intimately mixed and monospecific stands to a short-duration, high-intensity spring drought in Scotland. Mixing proportions included 25:75, 50:50 and 75:25 of P. sylvestris and P. sitchensis. At the species level, Scots pine was more drought resistant and resilient than Sitka spruce, while Sitka spruce showed higher recovery. Surprisingly, neither pre-drought tree size nor neighbourhood competition were significantly associated with resistance or resilience to drought, and trees of both species within monospecific stands showed higher recovery and resilience than trees growing in mixed stands. Our study suggests intimate mixtures of these two species may not be an effective way to mitigate the negative impacts of future extreme spring drought events. Given that these two species comprise almost 70% of coniferous forests in the UK, our results highlight the pressing need to better understand their vulnerability to drought and the conditions under which intimate mixtures of these species could be beneficial or detrimental. Such knowledge is essential if we are to enable forest managers to effectively plan how to adapt these forests to the challenges of a changing climate.
Original languageEnglish
Article number120448
Number of pages11
JournalForest Ecology and Management
Volume521
Early online date3 Aug 2022
DOIs
Publication statusPublished - 1 Oct 2022
Externally publishedYes

Bibliographical note

This work was funded by Forest Research, the Scottish Forestry Trust and the University of Stirling. We thank Stephen O’Kane, Alistair MacLeod, Sean Thomson, Colin Smart, Duncan Williams from Forest Research’s Technical Support Unit along with Daniela Thiele from Crown Estate Scotland and both Michael Bell and Salvatore Bonomo from Forest Research for their invaluable help during fieldwork. We are also grateful to Jack Forster, Toni-kim Clarke and Bill Mason of Forest Research for their technical support and guidance. Finally, we would like to thank all of the reviewers for their constructive comments.

Data Availability Statement

Data will be made available on request.

Keywords

  • Global change ecology
  • Resilience
  • Extreme drought
  • Pinus sylvestris
  • Picea sitchensis
  • Mixed forests

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