Boreal forest recovery in a changing climate : Case studies following clear-cutting and wildfire in Sweden
Islam, Md. Rafikul LU
(2026)
- Abstract
- Boreal forests play a crucial role in the global carbon cycle and currently act as an important carbon sink. At the same time, these forests are increasingly affected by intensive forest management and a changing disturbance regime driven by climate change. Clear-cutting has been the dominant harvesting method in managed boreal forests, while wildfire, although rare over the last century in Sweden, is projected to increase in frequency and severity under future climate conditions. Both disturbances greatly affect forest structure, carbon exchange, and long-term carbon storage, yet their combined interactions with climate change and management decisions remain poorly understood. In this thesis, I aimed to improve understanding of boreal... (More)
- Boreal forests play a crucial role in the global carbon cycle and currently act as an important carbon sink. At the same time, these forests are increasingly affected by intensive forest management and a changing disturbance regime driven by climate change. Clear-cutting has been the dominant harvesting method in managed boreal forests, while wildfire, although rare over the last century in Sweden, is projected to increase in frequency and severity under future climate conditions. Both disturbances greatly affect forest structure, carbon exchange, and long-term carbon storage, yet their combined interactions with climate change and management decisions remain poorly understood. In this thesis, I aimed to improve understanding of boreal forest carbon dynamics by examining carbon recovery at one clear‑cut and one wildfire-affected site in Sweden, providing detailed insights into how these two major disturbance types respond under current and future climate conditions. I focused on how disturbance type, forest management strategies (particularly regeneration choice), and climate interact to shape post-disturbance carbon budgets. To address these questions, I combined process-based ecosystem modelling using LPJ-GUESS with long-term eddy covariance (EC) measurements of carbon, water, and energy fluxes from managed boreal forests in Sweden. I further applied statistical and machine‑learning methods to analyse the drivers of carbon fluxes and their shifts following clear‑cutting.
Using a scenario‑based modelling approach with the LPJ‑GUESS dynamic vegetation model, I evaluated carbon recovery trajectories after clear‑cutting (Paper Ⅰ) and wildfire (Paper Ⅱ) under contrasting climate scenarios and management options, including monoculture plantations, mixed stands, and no‑management strategies. I first modelled the pre‑disturbance forest conditions and compared the simulations with in‑situ observations. These modelling studies were complemented by an empirical analysis of an actual stand replacing clear-cut at the Norunda ICOS site, where I quantified changes in ecosystem carbon exchange and identified shifts in the environmental controls of carbon fluxes using EC observations (Paper III).
The results highlighted that both post-disturbance management decisions and climate change play a major role in determining forest carbon recovery. At Norunda, Scots pine reforestation resulted in faster carbon recovery and higher carbon uptake in both the short- and long-term compared to Norway spruce or pine-spruce mixtures under moderate and high warming scenarios (Paper I). A possible reason could be that the LPJ‑GUESS model generally simulates higher growth for Scots pine compared to Norway spruce. Furthermore, modelling results indicated that including deciduous species with conifers, such as Scots pine mixed with European aspen or silver birch, led to faster recovery and higher carbon uptake than pure conifer stands or pine spruce mixtures under current, low-emission, and high-emission climate scenarios (Paper II). Warming accelerated carbon recovery and increased carbon uptake, likely driven by elevated temperatures and carbon fertilisation effects, with higher warming producing the largest gains. Transitioning from the current climate to any warming scenario resulted in greater increases in carbon uptake in both the short- and long-term. These findings provide useful insights for stand-scale forest management aimed at maximising carbon sequestration under a changing climate. However, the results are based on stand-level simulations and do not fully account for additional disturbances that could reduce or offset the positive effects of warming. Therefore, caution is needed when extrapolating these findings to landscape-scale forest management decisions.
The analyses further indicated relatively short carbon compensation point (CCP), the time after a clear‑cut or forest fire when reforestation has absorbed enough carbon to offset the initial carbon loss, which ranged 12 to 21 years across simulations at both the Norunda and Ljusdal sites (Paper Ⅰ and Paper Ⅱ). The carbon parity point was achieved when comparing clear-cut stands with uncut forest at Norunda (Paper Ⅰ), without knowing the fate of harvested carbon. In contrast, when harvested wood products were taken into account as stored carbon in short‑ and long‑lived products, the carbon parity point was not reached within this century. In this case, the carbon compensation point would likely be substantially longer than the CCP estimates that do not include the fate of harvested carbon. This underscores the need to consider both in-forest carbon dynamics and post-harvest wood-use pathways when evaluating forest-based climate mitigation strategies.
The empirical analysis further indicated that clear-cutting shifted ecosystem carbon exchange from being primarily biotically controlled to being dominated by abiotic drivers (Paper Ⅲ). Comparison of post-clear-cut eddy covariance observations with model simulations highlighted limitations in current modelling setup, particularly in representing early successional processes such as understory dynamics and early stand development following clear-cutting and wildfires. Additional limitations related to how wildfire processes were represented in Swedish boreal forests, including overestimated litter inputs and missing soil carbon consumption in the model. By combining modelling and empirical approaches, this thesis advances our understanding of boreal forest carbon dynamics under changing climate and disturbance regimes and offers insights relevant for developing climate-resilient forest management strategies.
(Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/c0a31a7e-feb0-48e4-8da7-1c523724a623
- author
- Islam, Md. Rafikul
LU
- supervisor
- opponent
-
- Professor Sitch, Stephen, University of Exeter, UK
- organization
- publishing date
- 2026
- type
- Thesis
- publication status
- published
- subject
- keywords
- Ecosystem modelling, forest management, Norway spruce, Scots pine, carbon fluxes, carbon recovery time, carbon compensation point, eddy covariance, environmental drivers
- pages
- 70 pages
- publisher
- Lund University
- defense location
- Världen Hall, Geocentrum I, Sölvegatan 10, Lund.
- defense date
- 2026-04-28 13:00:00
- ISBN
- 978-91-8104-863-6
- 978-91-8104-862-9
- language
- English
- LU publication?
- yes
- id
- c0a31a7e-feb0-48e4-8da7-1c523724a623
- date added to LUP
- 2026-03-18 12:20:25
- date last changed
- 2026-03-31 03:23:52
@phdthesis{c0a31a7e-feb0-48e4-8da7-1c523724a623,
abstract = {{Boreal forests play a crucial role in the global carbon cycle and currently act as an important carbon sink. At the same time, these forests are increasingly affected by intensive forest management and a changing disturbance regime driven by climate change. Clear-cutting has been the dominant harvesting method in managed boreal forests, while wildfire, although rare over the last century in Sweden, is projected to increase in frequency and severity under future climate conditions. Both disturbances greatly affect forest structure, carbon exchange, and long-term carbon storage, yet their combined interactions with climate change and management decisions remain poorly understood. In this thesis, I aimed to improve understanding of boreal forest carbon dynamics by examining carbon recovery at one clear‑cut and one wildfire-affected site in Sweden, providing detailed insights into how these two major disturbance types respond under current and future climate conditions. I focused on how disturbance type, forest management strategies (particularly regeneration choice), and climate interact to shape post-disturbance carbon budgets. To address these questions, I combined process-based ecosystem modelling using LPJ-GUESS with long-term eddy covariance (EC) measurements of carbon, water, and energy fluxes from managed boreal forests in Sweden. I further applied statistical and machine‑learning methods to analyse the drivers of carbon fluxes and their shifts following clear‑cutting.<br/>Using a scenario‑based modelling approach with the LPJ‑GUESS dynamic vegetation model, I evaluated carbon recovery trajectories after clear‑cutting (Paper Ⅰ) and wildfire (Paper Ⅱ) under contrasting climate scenarios and management options, including monoculture plantations, mixed stands, and no‑management strategies. I first modelled the pre‑disturbance forest conditions and compared the simulations with in‑situ observations. These modelling studies were complemented by an empirical analysis of an actual stand replacing clear-cut at the Norunda ICOS site, where I quantified changes in ecosystem carbon exchange and identified shifts in the environmental controls of carbon fluxes using EC observations (Paper III).<br/>The results highlighted that both post-disturbance management decisions and climate change play a major role in determining forest carbon recovery. At Norunda, Scots pine reforestation resulted in faster carbon recovery and higher carbon uptake in both the short- and long-term compared to Norway spruce or pine-spruce mixtures under moderate and high warming scenarios (Paper I). A possible reason could be that the LPJ‑GUESS model generally simulates higher growth for Scots pine compared to Norway spruce. Furthermore, modelling results indicated that including deciduous species with conifers, such as Scots pine mixed with European aspen or silver birch, led to faster recovery and higher carbon uptake than pure conifer stands or pine spruce mixtures under current, low-emission, and high-emission climate scenarios (Paper II). Warming accelerated carbon recovery and increased carbon uptake, likely driven by elevated temperatures and carbon fertilisation effects, with higher warming producing the largest gains. Transitioning from the current climate to any warming scenario resulted in greater increases in carbon uptake in both the short- and long-term. These findings provide useful insights for stand-scale forest management aimed at maximising carbon sequestration under a changing climate. However, the results are based on stand-level simulations and do not fully account for additional disturbances that could reduce or offset the positive effects of warming. Therefore, caution is needed when extrapolating these findings to landscape-scale forest management decisions. <br/>The analyses further indicated relatively short carbon compensation point (CCP), the time after a clear‑cut or forest fire when reforestation has absorbed enough carbon to offset the initial carbon loss, which ranged 12 to 21 years across simulations at both the Norunda and Ljusdal sites (Paper Ⅰ and Paper Ⅱ). The carbon parity point was achieved when comparing clear-cut stands with uncut forest at Norunda (Paper Ⅰ), without knowing the fate of harvested carbon. In contrast, when harvested wood products were taken into account as stored carbon in short‑ and long‑lived products, the carbon parity point was not reached within this century. In this case, the carbon compensation point would likely be substantially longer than the CCP estimates that do not include the fate of harvested carbon. This underscores the need to consider both in-forest carbon dynamics and post-harvest wood-use pathways when evaluating forest-based climate mitigation strategies. <br/>The empirical analysis further indicated that clear-cutting shifted ecosystem carbon exchange from being primarily biotically controlled to being dominated by abiotic drivers (Paper Ⅲ). Comparison of post-clear-cut eddy covariance observations with model simulations highlighted limitations in current modelling setup, particularly in representing early successional processes such as understory dynamics and early stand development following clear-cutting and wildfires. Additional limitations related to how wildfire processes were represented in Swedish boreal forests, including overestimated litter inputs and missing soil carbon consumption in the model. By combining modelling and empirical approaches, this thesis advances our understanding of boreal forest carbon dynamics under changing climate and disturbance regimes and offers insights relevant for developing climate-resilient forest management strategies.<br/>}},
author = {{Islam, Md. Rafikul}},
isbn = {{978-91-8104-863-6}},
keywords = {{Ecosystem modelling; forest management; Norway spruce; Scots pine; carbon fluxes; carbon recovery time; carbon compensation point; eddy covariance; environmental drivers}},
language = {{eng}},
publisher = {{Lund University}},
school = {{Lund University}},
title = {{Boreal forest recovery in a changing climate : Case studies following clear-cutting and wildfire in Sweden}},
url = {{https://lup.lub.lu.se/search/files/245183697/Rafikul_Islam_-_WEBB.pdf}},
year = {{2026}},
}