Rune Halvorsen

Average temperatures are rising more rapidly in high-latitude and alpine regions than elsewhere, leading to a gradual compression of the alpine bioclimatic zone due to the upward shift of the tree- and forest lines (TFLs). While most studies on TFL dynamics indicate advance, the rate at which regional and local treelines respond to climate warming remains uncertain. Furthermore, not every empirical TFL is determined by climate alone; edaphic conditions, species traits, and, in particular, land use, affect tree growth and distribution. In many regions, domestic grazing and other forms of traditional mountain summer farming have historically depressed forest lines. Previous research has been limited by the comparison of data sampled with mixed methods and poor temporal data coverage. Additionally, there is still a lack of studies accounting for time-lags, thus including data spanning a long time. In this study, we used consistently remapped in situ measurements of mountain birch (Betula pubescens ssp. czerepanovii) in Norway, dating from 50 to 130 years back, to: (1) document the rate of TFL change; (2) understand the impact of land use and climate change on regional TFL dynamics; and (3) discuss regional aspects and quality components of the data. We find that Norwegian TFLs are advancing at rates exceeding 0.5 m yr−1, primarily driven by climate change for TLs and land use for FLs. Still, the rates of TFL change vary considerably between regions, likely due to stochastic disturbances (e.g. snow avalanches, insect outbreaks, pests, landslides, rockfalls). We highlight the need for better quantification of time lags in treeline responses and for consistent definitions and methodologies when assessing long-term TFL dynamics in boreal–alpine ecotones.

Average temperatures are rising more rapidly in high-latitude and alpine regions than elsewhere, leading to a gradual compression of the alpine bioclimatic zone due to the upward shift of the tree- and forest lines (TFLs). While most studies on TFL dynamics indicate advance, the rate at which regional and local treelines respond to climate warming remains uncertain. Furthermore, not every empirical TFL is determined by climate alone; edaphic conditions, species traits, and, in particular, land use, affect tree growth and distribution. In many regions, domestic grazing and other forms of traditional mountain summer farming have historically depressed forest lines. Previous research has been limited by the comparison of data sampled with mixed methods and poor temporal data coverage. Additionally, there is still a lack of studies accounting for time-lags, thus including data spanning a long time. In this study, we used consistently remapped in situ measurements of mountain birch (Betula pubescens ssp. czerepanovii) in Norway, dating from 50 to 130 years back, to: (1) document the rate of TFL change; (2) understand the impact of land use and climate change on regional TFL dynamics; and (3) discuss regional aspects and quality components of the data. We find that Norwegian TFLs are advancing at rates exceeding 0.5 m yr−1, primarily driven by climate change for TLs and land use for FLs. Still, the rates of TFL change vary considerably between regions, likely due to stochastic disturbances (e.g. snow avalanches, insect outbreaks, pests, landslides, rockfalls). We highlight the need for better quantification of time lags in treeline responses and for consistent definitions and methodologies when assessing long-term TFL dynamics in boreal–alpine ecotones.

Average temperatures are rising more rapidly in high-latitude and alpine regions than elsewhere, leading to a gradual compression of the alpine bioclimatic zone due to the upward shift of the tree- and forest lines (TFLs). While most studies on TFL dynamics indicate advance, the rate at which regional and local treelines respond to climate warming remains uncertain. Furthermore, not every empirical TFL is determined by climate alone; edaphic conditions, species traits, and, in particular, land use, affect tree growth and distribution. In many regions, domestic grazing and other forms of traditional mountain summer farming have historically depressed forest lines. Previous research has been limited by the comparison of data sampled with mixed methods and poor temporal data coverage. Additionally, there is still a lack of studies accounting for time-lags, thus including data spanning a long time. In this study, we used consistently remapped in situ measurements of mountain birch (Betula pubescens ssp. czerepanovii) in Norway, dating from 50 to 130 years back, to: (1) document the rate of TFL change; (2) understand the impact of land use and climate change on regional TFL dynamics; and (3) discuss regional aspects and quality components of the data. We find that Norwegian TFLs are advancing at rates exceeding 0.5 m yr−1, primarily driven by climate change for TLs and land use for FLs. Still, the rates of TFL change vary considerably between regions, likely due to stochastic disturbances (e.g. snow avalanches, insect outbreaks, pests, landslides, rockfalls). We highlight the need for better quantification of time lags in treeline responses and for consistent definitions and methodologies when assessing long-term TFL dynamics in boreal–alpine ecotones.

Average temperatures are rising more rapidly in high-latitude and alpine regions than elsewhere, leading to a gradual compression of the alpine bioclimatic zone due to the upward shift of the tree- and forest lines (TFLs). While most studies on TFL dynamics indicate advance, the rate at which regional and local treelines respond to climate warming remains uncertain. Furthermore, not every empirical TFL is determined by climate alone; edaphic conditions, species traits, and, in particular, land use, affect tree growth and distribution. In many regions, domestic grazing and other forms of traditional mountain summer farming have historically depressed forest lines. Previous research has been limited by the comparison of data sampled with mixed methods and poor temporal data coverage. Additionally, there is still a lack of studies accounting for time-lags, thus including data spanning a long time. In this study, we used consistently remapped in situ measurements of mountain birch (Betula pubescens ssp. czerepanovii) in Norway, dating from 50 to 130 years back, to: (1) document the rate of TFL change; (2) understand the impact of land use and climate change on regional TFL dynamics; and (3) discuss regional aspects and quality components of the data. We find that Norwegian TFLs are advancing at rates exceeding 0.5 m yr−1, primarily driven by climate change for TLs and land use for FLs. Still, the rates of TFL change vary considerably between regions, likely due to stochastic disturbances (e.g. snow avalanches, insect outbreaks, pests, landslides, rockfalls). We highlight the need for better quantification of time lags in treeline responses and for consistent definitions and methodologies when assessing long-term TFL dynamics in boreal–alpine ecotones.

Fungi are key players in nearly all ecosystems, contributing to ecological dynamics through diverse ecosystem services. They are versatile and can have complex life cycles across hosts or substrates. Although environmental DNA approaches have advanced our understanding of fungal distributions at broad spatial scales, in‐depth explorations at fine spatial scales across substrates within ecosystems remain scarce. Here, we provide a comprehensive assessment of fungal diversity and ecology in boreal forests by characterising fungal communities across 26 substrates spanning major ecological compartments such as soil, plant tissues, fungal sporocarps and aquatic habitats in three forests. Fungal community composition is highly structured by substrate, with comparatively weaker effects of geographic site, resulting in clear community partitioning across boreal forest strata, from forest floor to canopy. Nearly half of the detected fungal taxa were restricted to a single substrate, implying a high degree of specialisation. Soils act as reservoirs of fungal diversity, while plants host less diverse but more specialised fungal communities. Aerial and aquatic substrates supported dynamic, likely dispersal‐driven fungal assemblages, while tree‐related substrates contributed substantially to overall ecosystem diversity, including large fractions of unexplored diversity. By characterising the mycobiome across a wide range of substrates, we provide an ecosystem‐level perspective on fungal diversity in the boreal forest, highlighting the importance of considering the full breadth of fungal diversity beyond well‐studied substrates to accurately assess and conserve fungal biodiversity.

Average temperatures are rising more rapidly in high-latitude and alpine regions than elsewhere, leading to a gradual compression of the alpine bioclimatic zone due to the upward shift of the tree- and forest lines (TFLs). While most studies on TFL dynamics indicate advance, the rate at which regional and local treelines respond to climate warming remains uncertain. Furthermore, not every empirical TFL is determined by climate alone; edaphic conditions, species traits, and, in particular, land use, affect tree growth and distribution. In many regions, domestic grazing and other forms of traditional mountain summer farming have historically depressed forest lines. Previous research has been limited by the comparison of data sampled with mixed methods and poor temporal data coverage. Additionally, there is still a lack of studies accounting for time-lags, thus including data spanning a long time. In this study, we used consistently remapped in situ measurements of mountain birch (Betula pubescens ssp. czerepanovii) in Norway, dating from 50 to 130 years back, to: (1) document the rate of TFL change; (2) understand the impact of land use and climate change on regional TFL dynamics; and (3) discuss regional aspects and quality components of the data. We find that Norwegian TFLs are advancing at rates exceeding 0.5 m yr−1, primarily driven by climate change for TLs and land use for FLs. Still, the rates of TFL change vary considerably between regions, likely due to stochastic disturbances (e.g. snow avalanches, insect outbreaks, pests, landslides, rockfalls). We highlight the need for better quantification of time lags in treeline responses and for consistent definitions and methodologies when assessing long-term TFL dynamics in boreal–alpine ecotones.