Past
In the early twentieth century, forestry was one of the most important sectors in Norway and an agitated discussion about the perceived decline of forest resources due to over-exploitation was ...ongoing. To base the discussion on facts, the young state of Norway established
Landsskogtakseringen
– the world’s first National Forest Inventory (NFI). Field work started in 1919 and was carried out by county. Trees were recorded on 10 m wide strips with 1–5 km interspaces. Site quality and land cover categories were recorded along each strip. Results for the first county were published in 1920, and by 1930 most forests below the coniferous tree line were inventoried. The 2nd to 5th inventories followed in the years 1937–1986. As of 1954, temporary sample plot clusters on a 3 km × 3 km grid were used as sampling units.
Present
The current NFI grid was implemented in the 6th NFI from 1986 to 1993, when permanent plots on a 3 km × 3 km grid were established below the coniferous tree line. As of the 7th inventory in 1994, the NFI is continuous, and 1/5 of the plots are measured annually. All trees with a diameter ≥ 5 cm are recorded on circular, 250 m
2
plots. The NFI grid was expanded in 2005 to cover alpine regions with 3 km × 9 km and 9 km × 9 km grids. In 2012, the NFI grid within forest reserves was doubled along the cardinal directions. Clustered temporary plots are used periodically to facilitate county-level estimates. As of today, more than 120 variables are recorded in the NFI including bilberry cover, drainage status, deadwood, and forest health. Land-use changes are monitored and trees outside forests are recorded.
Future
Considerable research efforts towards the integration of remote sensing technologies enable the publication of the Norwegian Forest Resource Map since 2015, which is also used for small area estimation at the municipality level. On the analysis side, capacity and software for long term growth and yield prognosis are being developed. Furthermore, we foresee the inclusion of further variables for monitoring ecosystem services, and an increasing demand for mapped information. The relatively simple NFI design has proven to be a robust choice for satisfying steadily increasing information needs and concurrently providing consistent time series.
To increase the annual uptake of CO2 as well as the long‐term storage of carbon (C) in forests, the Norwegian government consider large‐scale replacements of native, deciduous forests with ...faster‐growing species like Norway spruce. To assess the effects of tree species change on ecosystem C and nitrogen (N) stocks and soil chemistry, we used a paired plot approach including stands of native downy birch and planted 45‐ to 60‐yr‐old Norway spruce. The birch stands were used as reference for the assessment of differences following the tree species change. We found significantly higher C and N stocks in living tree biomass in the spruce stands, whereas no significant differences were found for dead wood. The cover of understory species groups, and the C and N stocks of the aboveground understory vegetation were significantly higher in the birch stands. The tree species change did not affect the soil organic carbon (SOC) stock down to 1 m soil depth; however, the significantly higher stock in the forest floor of the spruce stands suggested a re‐distribution of SOC within the profile. There was a significant positive correlation between the SOC stock down to 30 cm soil depth and the total ecosystem C stock for the birch stands, and a negative correlation for the spruce stands. Significant effects of tree species change were found for C and N concentrations, C/N, exchangeable acidity, base saturation, and exchangeable Ca, K, Mg, Na, S, and Fe in the organic horizon or the upper mineral soil layer. The total ecosystem C stock ranged between 197 and 277 Mg/ha for the birch stands, and 297 and 387 Mg/ha for the spruce stands. The ecosystem C accumulation varied between 32 and 142 Mg/ha over the past 45–60 yr, whereas the net ecosystem C capture was considerably lower and potentially negative. Our results suggest that the potential to meet the governments' targets to increase C sequestration depend on the C debt incurred from the removed birch stands, the rotation length, and potentially also the susceptibility of the different stand types to future risk factors related to climate change.
Natural regeneration of Norway spruce (
Picea abies
(L.) Karst.) is a relatively common practice in Norway on medium to low site indices. However, seedling establishment is often hampered by rapid ...regrowth of competing vegetation in scarified patches. The aim of our study was to examine the effect of coordinating scarification towards an expected seed-fall, by studying germination and seedling establishment in scarified patches of different age (fresh, one- and two-year-old). The experiment was conducted in two stands in southeast Norway that were clear-cut in 2007. Scarification was applied to subplots in autumn 2008–2010. To simulate seed-fall, seeds were sown in fresh scarification patches in spring 2009–2011, in one-year-old patches in 2010 and 2011, and in two-year-old patches in 2011. Both germination and seedling survival were negatively affected by the age of the scarified patches. Germination was higher, and mortality lower, at the small fern woodland site, compared with the bilberry woodland site. Sowing in fresh patches also resulted in increased height and root collar diameter of the seedlings compared with sowing in older patches. It is likely that the competing vegetation both on the site and in the scarification patches affected the growth of the seedlings. In conclusion, the age of the scarified patches affected both germination and mortality, as well as early growth of the seedlings.
Root rot in Norway spruce (Picea abies (L.) Karst.) causes substantial economic losses to the forestry sector. In this study, we developed a probability model for decay at breast height utilizing ...18,141 increment cores sampled on temporary plots of the Norwegian National Forest Inventory. The final model showed a good fit to the data and retained significant relationships between decay and a suite of tree, stand and site variables, including diameter at breast height, stand age, altitude, growing season temperature sum (threshold 5°C), and vegetation type. By comparing model predictions with recorded decay at stump height in an independent data set, we estimated a proportionality function to adjust for the inherent underestimation of total rot that will be obtained by applying a probability model derived from increment cores sampled at breast height. We conclude that the developed model is appropriate for national and regional scenario analyses in Norway, and could also be useful as a tool for operational forestry planning. This would however require further testing on independent data, to assess how well the new model predicts decay at local scales.
Northern landscapes accumulate carbon in vegetation and soils while rivers transport significant amounts of land-derived carbon to coastal areas. Here, we quantify carbon sources and sinks in main ...ecosystems (forests, peatlands, mountains, agricultural areas, lakes) in Norway for 1990–2008, and compare riverine carbon transport with terrestrial carbon accumulation in Norway’s four major discharge areas. Mean annual carbon accumulation (6.0 ± 0.9 Tg C; 19 g C m⁻²) in terrestrial ecosystems balanced 40 % of national greenhouse gas emissions. The area-normalized terrestrial sink strength declined in the following order (in g C m⁻²year⁻¹): tree biomass (40 ± 3) > peatlands (19 ± 15) > forest soils (9 ± 1) ≫ lakes (2 ± 1) > mountains (0.5 ± 0.3), while agricultural soils were sources of carbon (−36 ± 74). The most precise estimate in the carbon balance was for tree biomass, because of the underlying forest inventory data. Poor data on land management and soil type in agricultural soils, and on (former) drainage and peatland type resulted in high uncertainty in carbon loss and uptake estimates in agricultural soils and peatlands, which impacted the uncertainty in total terrestrial carbon accumulation. Also, carbon losses from disturbance in organic soil types were poorly constrained. Riverine coastal inputs of land-derived organic carbon (OC) were 1.0 ± 0.1 Tg C year⁻¹(3.0 g C m⁻²year⁻¹), with highest area-specific riverine export in western (4.5 g C m⁻²year⁻¹) and lowest (1.7 g C m⁻²year⁻¹) in subarctic Norway. In west and middle Norway, river OC export was approximately equal to carbon accumulation in soils and wetlands, while it was 50 % of soil and wetland carbon accumulation in southeast and subarctic Norway. Lateral aquatic transport of carbon is not explicitly accounted for in forest soil carbon accumulation estimates, although aquatic fluxes represent a climate-dependent carbon loss from soil carbon pools. The lack of methods that adequately account for lateral fluxes in carbon balances adds considerable uncertainty to soil carbon sink estimates. Climate warming and associated changes in precipitation may result in substantial alterations of terrestrial and aquatic carbon fluxes, with uncertain implications for the terrestrial carbon sink of northern landscapes.
Climate change is increasing the severity and frequency of droughts around the globe, leading to tree mortality that reduces production and provision of other ecosystem services. Recent studies show ...that growth of mixed stands may be more resilient to drought than pure stands. The two most economically important and widely distributed tree species in Europe are Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.), but little is known about their susceptibility to drought when coexist.
This paper analyses the resilience (resistance, recovery rate and recovery time) at individual‐tree level using a network of tree‐ring collections from 22 sites along a climatic gradient from central Europe to Scandinavia. We aimed to identify differences in growth following drought between the two species and between mixed and pure stands, and how environmental variables (climate, topography and site location) and tree characteristics influence them.
We found that both the timing and duration of drought drive the different responses between species and compositions. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time than Scots pine. Mixtures provided higher drought resistance for both species compared to pure stands, but the benefit decreases with the duration of the drought. Especially climate sensitive and old trees in climatically marginal sites were more affected by drought stress.
Synthesis. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change. However, if future droughts become longer, the advantage of mixed stands could disappear which would be especially negative for Norway spruce.
Mixtures of Scots pine and Norway spruce provided higher drought resistance for both species compared to pure stands, but the benefit decreases with drought duration. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change.
The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with ...species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas.
Here, we used a unique dataset of 261 stands combining pure and two‐species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests.
We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between‐species asynchrony in mixtures in comparison to monocultures.
Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies.
Resumen
Las cada vez más frecuentes perturbaciones en masas forestales monoespecíficas en todo el mundo, son una muestra de su inestabilidad bajo el cambio climático. Numerosos estudios indican que la estabilidad temporal de la productividad aumenta con la riqueza de especies, aunque los fundamentos ecológicos de esta relación se han estudiado principalmente en experimentos de diversidad de especies. Para una gestión adecuada de los ecosistemas forestales, es necesaria una mejor comprensión del efecto de la mezcla de especies en la estabilidad temporal de la productividad y de cómo esta se ve modificada por las condiciones climáticas.
En este trabajo usamos una base de datos única de 261 masas monoespecíficas y mixtas de dos especies a largo de un amplio rango de condiciones climáticas para examinar el efecto de la mezcla de especies en el nivel y estabilidad temporal de la productividad. Las mezclas estudiadas son combinaciones de dos especies entre cuatro de las especies forestales más relevantes en Europa. Se utilizan modelos de ecuaciones estructurales para explorar la influencia directa e indirecta del clima, el mayor crecimiento en mixtas que en puras (overyielding), la asincronía entre especies y el efecto aditivo (estabilidad temporal esperada según el crecimiento de las dos especies en las masas puras) en la estabilidad temporal en masas mixtas.
Los resultados muestran que añadiendo solo una especie a las masas monoespecíficas el nivel (overyielding: +6%) y la estabilidad temporal (+12%) del crecimiento aumentan significativamente. Se ha identificado que la temperatura tiene un efecto clave en la desestabilización del crecimiento, que puede ser mitigado en parte por la mezcla de especies. Se confirma que la asincronía, a través del efecto aditivo y de la interacción de especies (que modifica la asincronía entre especies en masas mixtas con respecto a la de las masas monoespecíficas), es el principal factor que explica la mayor estabilidad temporal en masas mixtas.
Síntesis y aplicaciones. Este estudio revela las propiedades emergentes asociadas a la mezcla de dos especies, que resultan en sistemas de producción eficientes y estables. Se identifica el impacto negativo de las temperaturas en la estabilidad temporal de la productividad y cómo el efecto estabilizador de la mezcla de dos especies puede contrarrestar este impacto. El nivel y la estabilidad temporal del crecimiento estudiados en este trabajo son fundamentales en los servicios ecosistémicos ligados al nivel y el ritmo del crecimiento forestal. Los resultados subrayan que la mezcla de dos especies puede ser una realista y efectiva solución climática basada en la naturaleza, que contribuya a cumplir los objetivos climáticos de la EU.
This study highlights the emergent properties associated with mixing two‐species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies.
•The study based on 90 mature Scots pine stands along a productivity gradient across Europe.•Growth partitioning became more asymmetric and structuring with increasing site quality.•Mortality ...eliminated predominantly small trees with increasing site quality.•We found the highest size variation on poor sites and the lowest on rich sites.•As a result stand structure became more homogeneous with increasing site quality.
Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we revealed how the stand structure is determined by site quality and results from site-dependent partitioning of growth and mortality among the trees. We based our study on 90 mature, even-aged, fully stocked monocultures of Scots pine (Pinus sylvestris L.) sampled in 21 countries along a productivity gradient across Europe. A mini-simulation study further analyzed the site-dependency of the interplay between growth and mortality and the resulting stand structure. The overarching hypothesis was that the stand structure changes with site quality and results from the site-dependent asymmetry of competition and mortality.
First, we show that Scots pine stands structure across Europe become more homogeneous with increasing site quality. The coefficient of variation and Gini coefficient of stem diameter and tree height continuously decreased, whereas Stand Density Index and stand basal area increased with site index.
Second, we reveal a site-dependency of the growth distribution among the trees and the mortality. With increasing site index, the asymmetry of both competition and growth distribution increased and suggested, at first glance, an increase in stand heterogeneity. However, with increasing site index, mortality eliminates mainly small instead of all-sized trees, cancels the size variation and reduces the structural heterogeneity.
Third, we modelled the site-dependent interplay between growth partitioning and mortality. By scenario runs for different site conditions, we can show how the site-dependent structure at the stand level emerges from the asymmetric competition and mortality at the tree level and how the interplay changes with increasing site quality across Europe.
Our most interesting finding was that the growth partitioning became more asymmetric and structuring with increasing site quality, but that the mortality eliminated predominantly small trees, reduced their size variation and thus reversed the impact of site quality on the structure. Finally, the reverse effects of mode of growth partitioning and mortality on the stand structure resulted in the highest size variation on poor sites and decreased structural heterogeneity with increasing site quality. Since our results indicate where heterogeneous structures need silviculture interventions and where they emerge naturally, we conclude that these findings may improve system understanding and modelling and guide forest management aiming at structurally rich forests.
Past: In the early twentieth century, forestry was one of the most important sectors in Norway and an agitated discussion about the perceived decline of forest resources due to over-exploitation was ...ongoing. To base the discussion on facts, the young state of Norway established Landsskogtakseringen - the world's first National Forest Inventory (NFI). Field work started in 1919 and was carried out by county. Trees were recorded on 10 m wide strips with 1-5 km interspaces. Site quality and land cover categories were recorded along each strip. Results for the first county were published in 1920, and by 1930 most forests below the coniferous tree line were inventoried. The 2nd to 5th inventories followed in the years 1937-1986. As of 1954, temporary sample plot clusters on a 3 km × 3 km grid were used as sampling units.Present: The current NFI grid was implemented in the 6th NFI from 1986 to 1993, when permanent plots on a 3 km x 3 km grid were established below the coniferous tree line. As of the 7th inventory in 1994, the NFI is continuous, and 1/5 of the plots are measured annually. All trees with a diameter ≥5 cm are recorded on circular, 250 m2 plots. The NFI grid was expanded in 2005 to cover alpine regions with 3 km x 9 km and 9 km x 9 km grids. In 2012, the NFI grid within forest reserves was doubled along the cardinal directions.Clustered temporary plots are used periodically to facilitate county-level estimates. As of today, more than 12C variables are recorded in the NFI including bilberry cover, drainage status, deadwood, and forest health. Land-use changes are monitored and trees outside forests are recorded.Future: Considerable research efforts towards the integration of remote sensing technologies enable the publication of the Norwegian Forest Resource Map since 2015, which is also used for small area estimation at the municipality level. On the analysis side, capacity and software for long term growth and yield prognosis are being developed. Furthermore, we foresee the inclusion of further variables for monitoring ecosystem services, and an increasing demand for mapped information. The relatively simple NFI design has proven to be a robust choice for satisfying steadily increasing information needs and concurrently providing consistent time series.
Age trends of phenotypic, environmental, and additive genetic variance and heritability were estimated for overall density and its components earlywood and latewood densities and latewood proportion. ...The objective was to acquire information for both individual and cumulated rings from ring number 3 to 12 counted from the pith. Age-age correlations were calculated for cumulated density traits only. The wood density data were obtained with X-ray analysis of increment cores from 47 open-pollinated families of Norway spruce (Picea abies (L.) Karst.). The families had earlywood and latewood with significant differences in density for individual and cumulated rings and consequently for overall density. The latewood proportion had significant family variation for cumulated rings but not for all individual rings. Large fluctuations in environmental variance caused fluctuations in heritability estimates for successive rings. A strong decrease in environmental variance for all cumulated traits, especially from ring 3 to 5, resulted in a steady increase in heritability estimates. The latewood density had the highest heritability estimates and latewood proportion the lowest for both individual and cumulated rings. Overall density and the cumulated components at cambial age 12 showed strong genetic correlations with their respective traits at all younger ages.
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