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

doi:10.1016/j.foreco.2022.120448

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

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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 language	English
Article number	120448
Number of pages	11
Journal	Forest Ecology and Management
Volume	521
Early online date	3 Aug 2022
DOIs	https://doi.org/10.1016/j.foreco.2022.120448
Publication status	Published - 1 Oct 2022
Externally published	Yes

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

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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title = "Intimate mixtures of Scots pine and Sitka spruce do not increase resilience to spring drought",

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.",

keywords = "Global change ecology, Resilience, Extreme drought, Pinus sylvestris, Picea sitchensis, Mixed forests",

author = "Ovenden, {Thomas S} and Perks, {Mike P} and Forrester, {David I} and Maurizio Mencuccini and Jazz Rhoades and Danielle Thompson and Stokes, {Victoria J} and Jump, {Alistair S}",

note = "This work was funded by Forest Research, the Scottish Forestry Trust and the University of Stirling. We thank Stephen O{\textquoteright}Kane, Alistair MacLeod, Sean Thomson, Colin Smart, Duncan Williams from Forest Research{\textquoteright}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.",

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AU - Ovenden, Thomas S

AU - Perks, Mike P

AU - Forrester, David I

AU - Mencuccini, Maurizio

AU - Rhoades, Jazz

AU - Thompson, Danielle

AU - Stokes, Victoria J

AU - Jump, Alistair S

N1 - 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.

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N2 - 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.

AB - 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.

KW - Global change ecology

KW - Resilience

KW - Extreme drought

KW - Pinus sylvestris

KW - Picea sitchensis

KW - Mixed forests

U2 - 10.1016/j.foreco.2022.120448

DO - 10.1016/j.foreco.2022.120448

M3 - Article

SN - 0378-1127

VL - 521

JO - Forest Ecology and Management

JF - Forest Ecology and Management

M1 - 120448

ER -

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

Abstract

Bibliographical note

Data Availability Statement

Keywords

UN SDGs

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