The state of within-stand variation (WSV) in boreal, coniferous production forests and how it is dealt with in thinning operations is a scarcely researched topic. In the autumn of 2018, we surveyed a ...series of Norway spruce (Picea abies (L.) Karst) or Scots pine (Pinus sylvestris L.) dominated production stands scheduled for first commercial thinning from below. Here, we evaluate the potential causes of WSV in basal area, how WSV was addressed in the thinning operations, and finally how the stands and subsequent thinning practice conformed with the basal area target specified in the thinning guidelines. WSV in the yield attributes was defined as the dispersion in a stand attribute within a stand and quantified using the Qn scale estimator (a robust measure of dispersion). First, WSV in basal area at the time of first thinning was evaluated as a function of WSV in stem number and WSV in site index. Next, yield attributes before and after thinning were compared using paired t-tests, and the future development of WSV in basal area was evaluated using linear mixed-effects models. Finally, the thinning practice was evaluated before and after thinning by modelling the compliance with the basal area target as a function of stem number and dominant height, also using linear mixed-effects models. WSV in basal area appeared to be influenced by WSV in site index and WSV in stem number for Norway spruce, but not for Scots pine. Thinning reduced the WSV in basal area, standing volume, and stem number, while dominant height, quadratic mean diameter and basal area weighted mean height remained unaffected. At first thinning, compliance with the thinning guideline increased with increasing stem density and dominant height. However, moderate to high compliance with the basal area target in the thinning guidelines was only reached for plots with elevated dominant height (>15 m) in combination with high stem number (>2250 N ha-1). Thus, the recommended range in dominant height (12–14 m) for first thinning was generally exceeded, which may be attributed to the generally low stem number at the time of thinning. This study suggests that sub-optimal regeneration efforts and management of young forests can lead to WSV across a wide range of stand attributes, and likely also reductions in yield. Thinning decreased WSV in basal area, standing volume and stem number, however, the plots were heavily thinned to such a degree that it could potentially cause production losses.
•Within-stand variation (WSV) and thinning guide compliance were studied at first thinning in Scots pine and Norway spruce stands.•Higher WSV in basal area (BA) in Norway spruce stands (not Scots pine) with elevated WSV in site index and WSV in stem number (N).•Generally low to moderate compliance with the BA target within the recommended interval in dominant height (12 - 14 m).•Full compliance with thinning guides at dominant heights of 15 m for Scots pine and 17 m for Norway spruce for N > 2250 ha−1.•Thinning reduced WSV in standing volume, BA and N, but maintained WSV in dominant height, mean height and quadratic mean diameter.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•We explored the potential of bi-temporal ALS data for site index estimation.•Species-specific site index models were developed using NFI and ALS data.•ALS estimated height and height increment were ...key predictors of site index.•Validation checks indicate that the functions seem suitable for their purpose.•Nationwide site index maps are provided at a resolution of 12.5 × 12.5 m.
Recent advancements in remote sensing of forests have demonstrated the capabilities of three-dimensional data acquired by airborne laser scanning (ALS) and, consequently, have become an integral part of enhanced forest inventories in Northern Europe. In Sweden, the first national laser scanning revolutionised forest management planning through low-cost production of large-scale and spatially explicit maps of forest attributes such as basal area, volume, and biomass, compared to the earlier practice based on field survey data. A second scanning at the national level was launched in 2019, and it provides conditions for the estimation of height growth and site index. Accurate and up-to-date information about site productivity is relevant for planning silvicultural treatments and for the prognosis of forest status and development over time. In this study, we explored the potential of bi-temporal ALS data and other auxiliary information to predict and map site productivity by site index according to site properties (SIS) of Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.) in even-aged stands in Sweden. We linked ground survey data of SIS from more than 11,500 plots of the Swedish National Forest Inventory (NFI) to bi-temporal ALS data to predict and map site index using an area-based method and two regression modelling strategies: (1) a multiple linear regression (MLR) model with an ordinary least-squares parameter estimation method, and (2) a non-parametric random forests (RF) model optimised for hyper-parameter tuning. For model development, permanent plots were used, whereas the validation was done on the temporary plots of the Swedish NFI and an independent stand-level dataset. Species-specific models were developed, and the root mean square error (RMSE) metric was used to quantify the residual variability around model predictions. For both species, the MLR model gave precise and accurate estimates of SIS. The RMSE for SIS predictions was in the range of 1.96 – 2.11 m, and the relative RMSE was less than 10 % (7.68 – 9.49 %) of the reference mean value. Final predictors of site index include metrics of 90th percentile height and annual increment in the 95th percentile height, altitude, distance to coast, and soil moisture. Country-wide maps of SIS and the corresponding pixel-level prediction errors at a spatial resolution of 12.5 m grid cells were produced for the two species. Independent validations show the site index maps are suitable for use in operational forest management planning in Sweden.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Ozone (O3) enters plants through the stomata, passes into the intercellular air space and is decomposed in cell walls. Two factors that affect the O3 level in the intercellular air space are the ...stomatal conductance and the concentration of biogenic volatile organic compounds (BVOCs). Stomatal conductance controls the O3 flux into the air space and the intercellular BVOCs react with the O3. Therefore, the intercellular air space serves as a place where O3 defense can occur, but it has received relatively little attention. This study aimed to explore potential plant-defense against O3 in the intercellular air space by measuring the stomatal conductance and intercellular BVOC concentrations of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Seedlings of both species were exposed to two levels of O3, ambient (15 nmol mol−1) and 80 nmol mol−1 (dropping to an ambient level at night), in plant growth chambers for five days in both spring and summer. We found that O3 decreased stomatal conductance in both species and in both seasons, which can lower the O3 flux into the intercellular air space. Intercellular BVOC concentrations were decreased in spring while increased in summer for both species in response to O3. This suggests that the BVOC protection in the intercellular air space is only of consequence in summer. These results demonstrate the potential for BVOCs to provide intercellular O3 defense in both species, but with seasonal variation.
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•Potential intercellular defense responses to O3 stress were studied in conifers.•Plants decreased stomatal conductance in spring and summer for defense against O3.•Plants had decreased intercellular BVOC concentrations in response to O3 in spring.•Intercellular BVOC concentrations increased only in summer for defense against O3.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Time after cutting, trunk diameter, southern and western location, and spruce compared pine and deciduous trees increased the probability of pendulous lichens.•There was no significant difference ...between the different continuous cover forestry (CCF) methods, but in southern and western parts of the study area, small gap cutting maintained pendulous lichen slightly more than selective cutting.•CCF-stands maintained more pendulous lichens than normal managed young thinning stands, but less than mature managed even-aged stands.•To reconcile forestry and reindeer husbandry, larger trees should be retained, the cutting cycle should be kept long, or the lichen-rich areas should be excluded from logging.
Competition for land use between forestry and reindeer husbandry has been debated in northern Finland, particularly due to the possible adverse effects of forestry on the availability of forage resources for reindeer. In an attempt to achieve a better reconciliation of these land uses, as well as to promote multiple forest use, we studied the effects of 37 stand-, plot-, and tree-level variables on pendulous lichens (Alectoria sp., Bryoria sp. and Usnea sp.), and compared two methods of continuous cover forestry (CCF) on pendulous lichen occurrence in Finnish Lapland.
The main findings of the study indicate that the number of years after cutting, and the trunk diameter increase the probability of pendulous lichen occurrence. The highest probability of pendulous lichen occurrence by tree species was achieved in Norway spruce (Picea abies (L) Karst), and by area, in the southern and western parts of the study area. Of the two CCF methods studied – small gap cutting and selection cutting – the former was slightly more successful in maintaining pendulous lichens, especially in southern and western Lapland. In addition, the ground lichen coverage indicating the degree of xeric features of the stand reduced the probability of pendulous lichen occurrence. Furthermore, we compared our data with reference material, and found that the CCF stands of the present study maintained more pendulous lichens than managed young thinning stands, but less than managed mature even-aged forests.
This study shows that in order to better reconcile forestry and reindeer husbandry in a reindeer herding area, the larger trees should be saved, and the cutting cycle should be kept as long as possible. In addition, lichen-rich areas should be excluded from logging, and the access of reindeer to those areas should be secured. Of the two CCF methods studied, small gap cutting could be a viable method in reconciling forestry and reindeer husbandry, as well as the multiple use of forests, in that it allows to keep at least parts of the forest intact for a longer period of time, which advances the growth of pendulous lichens. Selection cutting, in turn, affects the whole area, and removes the large trees, which are advantageous for pendulous lichens.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Seedling establishment is a crucial step in boreal forest rotation forestry.•Outplanted conifer seedlings were supplied with organic or inorganic n fertilizer.•Survival, growth, and fungal ...communities on roots and soil were assessed.•Planting position had largest effect on seedling performance.•Fungal community composition determined largely by priority effects.
Forestry in Sweden largely relies on planting genetically improved seedlings after clear-cutting, and high survival and early growth of planted seedlings is vital for stand establishment, economic viability, and carbon sequestration. Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) are the two most important tree species in Swedish forest stands and both are associated with a variety of ectomycorrhizal fungi. While seedlings are generally not fertilized at outplanting, previous results have shown that fertilization with arginine phosphate can increase root growth and seedling survival. However, it is not clear how this affects fungal community composition on the roots of growing seedlings. In a planting experiment sampled after one and two growing seasons, we found that planting position had the largest effects both on seedling performance and on fungal community composition and provide insight into the early stages of fungal community succession on planted Norway spruce and Scots pine seedlings. Fungal taxa present on seedlings before planting persisted on seedling roots, while some degree of novel colonization by site indigenous taxa was observed. Fertilization modified the relative abundance of some fungal taxa but did not lead to significant changes in overall community composition. In terms of seedling performance, ammonium nitrate led to increased mortality while arginine phosphate improved root growth.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Tree size, competition, and local topography have largest effect on height growth.•Consistent height growth patterns over large environmental gradient.•Competition can be depicted well by indices ...based on basal area and light.•Accurate and robust, yet relatively simple models of regeneration development.
In managed mountain forests, height growth of Norway spruce (Picea abies (L.) Karst) regeneration is a decisive factor for the gap-filling process, especially when the silvicultural goal is to provide continuous protection against natural hazards such as snow avalanches or rockfall. For the planning of management interventions, robust predictions on height growth of regeneration at the scale of forest gaps are thus needed. However, there is a lack of such data for trees of intermediate sizes, and existing studies fail to cover large environmental gradients. The goal of our study is to identify the key factors that influence height growth of Norway spruce regeneration in small gaps of spruce-dominated forests in the Swiss Alps. Furthermore, we assess whether there are site-specific differences of height growth or whether it follows a similar pattern along a large gradient of temperature (i.e., along elevation) and of water and nutrient availability (i.e., among different phytosociological site types) within the upper montane and subalpine vegetation belts. On 124 plots, >2′000 observations of annual height increments of Norway spruce regeneration (10 cm tree height to 12 cm stem diameter) in gaps were collected. Using linear mixed effects models and cross-validation for model selection, we identified the best variable combinations to predict annual height growth. Consistently across the entire gradient, the most important factors were 1) the positive effect of tree size, 2) the negative effect of competition by the surrounding stand, and 3) local topography. We found site-specific differences in height growth patterns such as gap size and therefore direct radiation being the most important competition measure in subalpine sites, as opposed to diffuse radiation in high montane sites. However, the pooled model for the entire environmental gradient allowed for predictions of regeneration height growth with similar explanatory power as the more specific models while containing comparable effect sizes. Furthermore, competition can be equally well expressed by metrics based on basal area measurements as by metrics derived from hemispherical photography. Based on these relatively simple models, accurate and robust predictions of the development of Norway spruce regeneration in gaps of managed mountain forests are possible.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Summary
Carbon (C) exuded via roots is proposed to increase under drought and facilitate important ecosystem functions. However, it is unknown how exudate quantities relate to the total C budget of a ...drought‐stressed tree, that is, how much of net‐C assimilation is allocated to exudation at the tree level.
We calculated the proportion of daily C assimilation allocated to root exudation during early summer by collecting root exudates from mature Fagus sylvatica and Picea abies exposed to experimental drought, and combining above‐ and belowground C fluxes with leaf, stem and fine‐root surface area.
Exudation from individual roots increased exponentially with decreasing soil moisture, with the highest increase at the wilting point. Despite c. 50% reduced C assimilation under drought, exudation from fine‐root systems was maintained and trees exuded 1.0% (F. sylvatica) to 2.5% (P. abies) of net C into the rhizosphere, increasing the proportion of C allocation to exudates two‐ to three‐fold. Water‐limited P. abies released two‐thirds of its exudate C into the surface soil, whereas in droughted F. sylvatica it was only one‐third.
Across the entire root system, droughted trees maintained exudation similar to controls, suggesting drought‐imposed belowground C investment, which could be beneficial for ecosystem resilience.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
DNA methylation plays important roles in many biological processes, such as silencing of transposable elements, imprinting, and regulating gene expression. Many studies of DNA methylation have shown ...its essential roles in angiosperms (flowering plants). However, few studies have examined the roles and patterns of DNA methylation in gymnosperms. Here, we present genome-wide high coverage single-base resolution methylation maps of Norway spruce (Picea abies) from both needles and somatic embryogenesis culture cells via whole genome bisulfite sequencing. On average, DNA methylation levels of CG and CHG of Norway spruce were higher than most other plants studied. CHH methylation was found at a relatively low level; however, at least one copy of most of the RNA-directed DNA methylation pathway genes was found in Norway spruce, and CHH methylation was correlated with levels of siRNAs. In comparison with needles, somatic embryogenesis culture cells that are used for clonally propagating spruce trees showed lower levels of CG and CHG methylation but higher level of CHH methylation, suggesting that like in other species, these culture cells show abnormal methylation patterns.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
•Effects of species interaction were studied in a mature mixed beech-spruce forest.•A broad spectrum of parameters was included at organ (leaf, fine root, ECM), tree and stand scale.•Mixture with ...beech exacerbated soil water accessibility for spruce.•Exacerbated soil water accessibility in mixture did not increase drought susceptibility of spruce.•Group-wise mixture appears to buffer putatively negative effects of beech competition on spruce.
Mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) frequently over-yield, when compared to respective monospecific stands. Over-yielding is attributed to enhanced resource uptake efficiency through niche complementarity alleviating species competition, for example through enhanced root stratification in mixture. Under severe and frequent summer drought, however, water limitation may become crucial in modifying the prevailing competitive interaction in mixed beech-spruce forests. We hypothesize, therefore, that under drought (H I) inter-specific interaction with beech reduces water accessibility for spruce more than intra-specific conditions, thus (H II) exacerbating drought susceptibility of spruce in terms of reduced photosynthesis and stem growth. Reactions at the organ (leaf, fine root), tree and stand scale were analysed in a mature forest with beech-spruce group mixture. Under inter-specific conditions spruce’s fine-root production and depth of water uptake (assessed via δ18O of xylem water) shifted to shallow, drought-prone soil horizons, in agreement with H I. Overall, lowered fine root production and ramification along with a reduction in long-distance explorative ectomycorrhizal types resulted in decreased soil exploitation in spruce when growing together with beech. Spruce’s drought sensitivity was exemplified by a distinct decrease in stomatal conductance, net CO2 uptake rate and stem growth during periods of water limitation. Notwithstanding, species interaction effects were absent in leaf gas exchange and stem diameter growth, during a six-week summer drought period in 2013 as well as in the extremely dry year of 2003, hence rejecting H II. Based on results from soil moisture measurements and water uptake depth, we interpret the conflicting findings for H I and H II to result from: (i) seasonal shifts between positive (during spring drought) and negative (during summer drought) effects of beech neighbourhood on soil water availability for spruce, possibly overriding each other in their effect on annual stem diameter growth and (ii) the group-wise mixture pattern, where spruce is exposed to competition with beech only along group edges, i.e. laterally only, so that the putatively adverse beech effect on water accessibility stays limited. Our results suggest, compared to single tree mixture, group-wise mixture of beech and spruce to be a favourable silvicultural option in the face of climate change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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