Eduardo Martínez-García

Boreal forests, essential for carbon sequestration and multiple ecosystem services, are increasingly threatened by climate-induced water stress. This study investigates how increasing water limitation affects growth and intrinsic water-use efficiency ( i _WUE ) in Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies (L.) Karst) in southern Finland from 1990 to 2022. Tree-ring data on basal area increment (BAI) and carbon isotope discrimination (Δ ¹³ C) were collected from three sites per species, with Scots pine on mineral soils and Norway spruce on organic soils and under contrasting soil moisture conditions. The tree-ring records were combined with regional growth indices (GIs) from the Finnish National Forest Inventory (NFI) to enable broader inference across soil types. Our results indicate that water limitation intensified over the past decade, with pronounced growth declines after 2016 in Norway spruce, while Scots pine exhibited smaller reductions, evident at the site level from around 2009 but not resolved in the regional GI. Δ ¹³ C analyses indicated increased stomatal regulation in Scots pine and more limited physiological adjustment in Norway spruce after 2016, consistent with rising atmospheric moisture demand. Accordingly, i _WUE increased more strongly in Scots pine, whereas Norway spruce showed only modest changes despite a substantial growth decline. Interannual variability in growth and i _WUE was related both to vapour pressure deficit (VPD) and to the summer water balance, but their relative importance differed between species: VPD had the larger effect per standard deviation in Scots pine, whereas Norway spruce responded to atmospheric demand and to the summer water balance to a similar degree. In Norway spruce, growth after 2016 was significantly constrained by VPD, whereas Scots pine showed comparatively buffered growth responses and stronger increases in i _WUE . Soil-type effects were generally weak at the regional scale, but clearer patterns emerged along local moisture conditions. At the site level, both species tended to show greater negative post-change growth under drier conditions; however, Scots pine maintained higher mean growth on wetter sites, whereas Norway spruce showed higher mean growth under drier conditions. These contrasting growth–physiology responses indicate species-specific strategies in coping with increasing water limitation, with Norway spruce showing greater growth sensitivity and more limited physiological adjustment than Scots pine. Overall, boreal forest responses to drought appear to be structured primarily by species-specific physiological strategies, while being further modulated by local hydrological conditions. Accounting for both species differences and fine-scale variation in moisture availability will be critical for sustaining forest productivity and resilience under increasingly warm and water-limited climates in northern Europe, underscoring the need for site-adapted management that integrates species selection with local soil and moisture conditions.

Boreal forests, essential for carbon sequestration and multiple ecosystem services, face increasing pressure from climate-induced water stress. This study investigates how increasing water limitation affects growth and intrinsic water-use efficiency (iWUE) in Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies (L.) Karst) in southern Finland. We combined site-level tree-ring data on basal area increment (BAI) and carbon isotope discrimination (Δ¹³C) from three sites per species, representing contrasting soil moisture conditions (dry versus wet), with regional growth indices from the Finnish National Forest Inventory (NFI) spanning 1990–2022. Our results show that forests in southern Finland have become increasingly water-limited over the past decade. Site-level and NFI based growth decline post-2015 is pronounced in Norway spruce, indicating strong sensitivity to water limitation, while Scots pine exhibits only marginal reductions beginning around 2010. Δ¹³C analyses indicate increased stomatal regulation in Scots pine and, to a lesser extent, in Norway spruce after 2015, consistent with intensifying water limitations. iWUE derived from tree ring Δ¹³C increased more steeply Scots pine than in Norway spruce, suggesting weaker physiological adjustment in spruce to rising atmospheric moisture demand. Interannual variability in both growth and iWUE for both species was strongly correlated with the standardized precipitation-evapotranspiration index (SPEI) and vapor-pressure-deficit (VPD). Linear mixed-effects models confirm that Norway spruce growth sensitivity to VPD and SPEI intensified after 2015, whereas Scots pine showed consistent Δ¹³C responses and relatively buffered growth. These findings highlight the growing vulnerability of boreal conifers, particularly Norway spruce, to intensifying water stress. Sensitivity varied by soil type: Scots pine was more responsive on organic soils, while Norway spruce was more vulnerable on mineral soils. Species- and site-specific differences in water-use strategies underscore the importance of adaptive forest management, including species choice, site matching, and silvicultural planning, to support forest resilience and productivity under warmer, drier climate.

Over the past century, extensive areas of northern peatlands have been drained for forestry. Today, concerns about their role as significant sources of greenhouse gases (GHG) have sparked growing interest in peatland rewetting as a climate mitigating strategy. However, empirical evidence for rewetting effects on ecosystem carbon (C) and GHG balances is still limited, particularly for minerogenic boreal peatland forests. Rewetting of peatland forests also involves decisions about tree harvest, which can have important but understudied consequences for the C cycle. In this study, we quantified tree growth and estimated carbon dioxide (CO ₂ ) and methane (CH ₄ ) fluxes in both peatland areas and ditches over 2 years before (2019–2020) and after (2021–2022) rewetting a low‐productive, minerogenic peatland forest in boreal Sweden. We also assessed effects of tree removal during rewetting by comparing harvest and non‐harvest areas. Our results suggest that the peatland forest was, on average, C‐neutral at the ecosystem‐scale during the drained years. After rewetting, the harvested area became a C source (79 g C m ⁻² year ⁻¹ ), while the treed area acted as a small C sink (−24 g C m ⁻² year ⁻¹ ), with the difference due to diverging responses in net CO ₂ exchange. Furthermore, CH ₄ emissions doubled after rewetting, resulting in a two‐ to threefold increase in total GHG emissions (expressed in CO ₂ equivalents) over both 20‐ and 100‐year timeframes. While ditches functioned as significant CO ₂ sinks and moderate CH ₄ sources during the drained years, they became CO ₂ ‐neutral and CH ₄ emission hotspots after being infilled. Altogether, our findings suggest that rewetting low‐productive boreal peatland forests may have a negative short‐term climate impact. However, rewetting without tree harvest considerably meliorates ecosystem C and GHG balances. Overall, our study highlights the importance of tree harvesting decisions and the need for a deeper understanding of rewetting as a climate mitigation strategy.

Over the past century, extensive areas of northern peatlands have been drained for forestry. Today, concerns about their role as significant sources of greenhouse gases (GHG) have sparked growing interest in peatland rewetting as a climate mitigating strategy. However, empirical evidence for rewetting effects on ecosystem carbon (C) and GHG balances is still limited, particularly for minerogenic boreal peatland forests. Rewetting of peatland forests also involves decisions about tree harvest, which can have important but understudied consequences for the C cycle. In this study, we quantified tree growth and estimated carbon dioxide (CO2) and methane (CH4) fluxes in both peatland areas and ditches over two years before (2019-2020) and after (2021-2022) rewetting a low-productive, minerogenic peatland forest in boreal Sweden. We also assessed effects of tree removal during rewetting by comparing harvest and non-harvest areas. Our results suggest that the peatland forest was, on average, C-neutral at the ecosystem-scale during the drained years. After rewetting, the harvested area became a C source (79 g C m-2 yr-1), while the treed area acted as a small C sink (-21 g C m-2 yr-1), with the difference due to diverging responses in net CO2 exchange. Furthermore, CH4 emissions doubled after rewetting, resulting in a two- to threefold increase in total GHG emissions (expressed in CO2 equivalents) over both 20- and 100-year timeframes. While ditches functioned as significant CO2 sinks and moderate CH4 sources during the drained years, they became CO2-neutral and CH4 emission hotspots after being in-filled. Altogether, our findings suggest that rewetting low-productive boreal peatland forests may have a negative short-term climate impact. However, rewetting without tree harvest considerably meliorates ecosystem C and GHG balances. Overall, our study highlights the importance of tree harvesting decisions and the need for a deeper understanding of rewetting as a climate mitigation strategy.

Boreal forests, essential for carbon sequestration and multiple ecosystem services, face increasing pressure from climate-induced water stress. This study investigates how increasing water limitation affects growth and intrinsic water-use efficiency (iWUE) in Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies (L.) Karst) in southern Finland. We combined site-level tree-ring data on basal area increment (BAI) and carbon isotope discrimination (Δ¹³C) from three sites per species, representing contrasting soil moisture conditions (dry versus wet), with regional growth indices from the Finnish National Forest Inventory (NFI) spanning 1990–2022. Our results show that forests in southern Finland have become increasingly water-limited over the past decade. Site-level and NFI based growth decline post-2015 is pronounced in Norway spruce, indicating strong sensitivity to water limitation, while Scots pine exhibits only marginal reductions beginning around 2010. Δ¹³C analyses indicate increased stomatal regulation in Scots pine and, to a lesser extent, in Norway spruce after 2015, consistent with intensifying water limitations. iWUE derived from tree ring Δ¹³C increased more steeply Scots pine than in Norway spruce, suggesting weaker physiological adjustment in spruce to rising atmospheric moisture demand. Interannual variability in both growth and iWUE for both species was strongly correlated with the standardized precipitation-evapotranspiration index (SPEI) and vapor-pressure-deficit (VPD). Linear mixed-effects models confirm that Norway spruce growth sensitivity to VPD and SPEI intensified after 2015, whereas Scots pine showed consistent Δ¹³C responses and relatively buffered growth. These findings highlight the growing vulnerability of boreal conifers, particularly Norway spruce, to intensifying water stress. Sensitivity varied by soil type: Scots pine was more responsive on organic soils, while Norway spruce was more vulnerable on mineral soils. Species- and site-specific differences in water-use strategies underscore the importance of adaptive forest management, including species choice, site matching, and silvicultural planning, to support forest resilience and productivity under warmer, drier climate.

Boreal forests, essential for carbon sequestration and multiple ecosystem services, face increasing pressure from climate-induced water stress. This study investigates how increasing water limitation affects growth and intrinsic water-use efficiency (iWUE) in Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies (L.) Karst) in southern Finland. We combined site-level tree-ring data on basal area increment (BAI) and carbon isotope discrimination (Δ¹³C) from three sites per species, representing contrasting soil moisture conditions (dry versus wet), with regional growth indices from the Finnish National Forest Inventory (NFI) spanning 1990–2022. Our results show that forests in southern Finland have become increasingly water-limited over the past decade. Site-level and NFI based growth decline post-2015 is pronounced in Norway spruce, indicating strong sensitivity to water limitation, while Scots pine exhibits only marginal reductions beginning around 2010. Δ¹³C analyses indicate increased stomatal regulation in Scots pine and, to a lesser extent, in Norway spruce after 2015, consistent with intensifying water limitations. iWUE derived from tree ring Δ¹³C increased more steeply Scots pine than in Norway spruce, suggesting weaker physiological adjustment in spruce to rising atmospheric moisture demand. Interannual variability in both growth and iWUE for both species was strongly correlated with the standardized precipitation-evapotranspiration index (SPEI) and vapor-pressure-deficit (VPD). Linear mixed-effects models confirm that Norway spruce growth sensitivity to VPD and SPEI intensified after 2015, whereas Scots pine showed consistent Δ¹³C responses and relatively buffered growth. These findings highlight the growing vulnerability of boreal conifers, particularly Norway spruce, to intensifying water stress. Sensitivity varied by soil type: Scots pine was more responsive on organic soils, while Norway spruce was more vulnerable on mineral soils. Species- and site-specific differences in water-use strategies underscore the importance of adaptive forest management, including species choice, site matching, and silvicultural planning, to support forest resilience and productivity under warmer, drier climate.

Boreal forests, essential for carbon sequestration and multiple ecosystem services, face increasing pressure from climate-induced water stress. This study investigates how increasing water limitation affects growth and intrinsic water-use efficiency (iWUE) in Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies (L.) Karst) in southern Finland. We combined site-level tree-ring data on basal area increment (BAI) and carbon isotope discrimination (Δ¹³C) from three sites per species, representing contrasting soil moisture conditions (dry versus wet), with regional growth indices from the Finnish National Forest Inventory (NFI) spanning 1990–2022. Our results show that forests in southern Finland have become increasingly water-limited over the past decade. Site-level and NFI based growth decline post-2015 is pronounced in Norway spruce, indicating strong sensitivity to water limitation, while Scots pine exhibits only marginal reductions beginning around 2010. Δ¹³C analyses indicate increased stomatal regulation in Scots pine and, to a lesser extent, in Norway spruce after 2015, consistent with intensifying water limitations. iWUE derived from tree ring Δ¹³C increased more steeply Scots pine than in Norway spruce, suggesting weaker physiological adjustment in spruce to rising atmospheric moisture demand. Interannual variability in both growth and iWUE for both species was strongly correlated with the standardized precipitation-evapotranspiration index (SPEI) and vapor-pressure-deficit (VPD). Linear mixed-effects models confirm that Norway spruce growth sensitivity to VPD and SPEI intensified after 2015, whereas Scots pine showed consistent Δ¹³C responses and relatively buffered growth. These findings highlight the growing vulnerability of boreal conifers, particularly Norway spruce, to intensifying water stress. Sensitivity varied by soil type: Scots pine was more responsive on organic soils, while Norway spruce was more vulnerable on mineral soils. Species- and site-specific differences in water-use strategies underscore the importance of adaptive forest management, including species choice, site matching, and silvicultural planning, to support forest resilience and productivity under warmer, drier climate.