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Highlights • Six-year-old Scots pine post-harvest stand was a modest carbon source. • Eddy covariance and C budgeting methods yielded similar results for the annual C balance. • Studied ecosystem will be able to turn into a C sink already before ten years after cutting. • Understorey vegetation contributed 57% to annual net primary production in studied stand. Abstract Clear-cutting is a conventional method of forest management which significantly changes carbon (C) cycling at the ecosystem level for a long time. Estimation of the interim period during which the ecosystem turns from a C source to a C sink is crucial for clarifying the environmental effects of management on forest C cycling. The current study provided new knowledge of C cycling in young pine stand and demonstrated the recovery of C sequestration of the forest ecosystem during the post harvesting period. We estimated the C balance in a 6-year-old Scots pine stand by using two different methods: carbon budgeting, for estimating annual net ecosystem production (NEP), and eddy covariance (EC), for estimating net ecosystem exchange (NEE). For C budgeting, the above- and belowground biomass production of the ecosystem, as well as the soil heterotrophic respiration efflux at the studied site was estimated. Annual NEE at the studied young forest ecosystem was 1.19 ± 0.36 t C ha−1, gross primary ecosystem production was 9.87 and total ecosystem respiration was 11.06 t C ha−1. Estimated NEE was in good accordance with the results of NEP (1.37 t C ha−1), which confirms the relevance of the C budgeting method. Increased annual woody biomass production is the main factor which induced the young Scots pine ecosystem to act as a C sink: annual C accumulation in tree biomass in a 6-year-old stand was 1.0 t C ha−1 but reached already 2.4 t C ha−1 in the following year. Assuming that the annual R h flux is of the same magnitude in the subsequent years, the ecosystem will become a C sink already during a short period after clear-cut. Annual soil respiration (R s) and heterotrophic soil respiration (R h) were 6.0 and 4.2 t C ha−1, respectively and the R h /R s ratio was 0.70. However, at this stage also the understorey vegetation contributed essentially to NEP, making up 56% of the annual C uptake accumulated in the plants. The methane flux and the leached C flux were negligible, 0.004 and 0.015 t C ha−1 yr−1, respectively. Our results demonstrate that well regenerated young Scots pine stand on a former clear-cut area will be able to turn into a C sequestering ecosystem already before ten years after cutting. [ABSTRACT FROM AUTHOR]

Highlights • Fine root production of trees was the most varying input flux of carbon to soil. • Understorey comprised up to 28% of total fine root production. • Annual soil respiration did not differ between pine and spruce dominated stands. • SOC pool was most affected by tree-derived above- and belowground litter production. Abstract Estimation of soil-related carbon (C) fluxes is needed to understand the dynamics of the soil organic carbon pool, to determine changes in the carbon balance and functioning of forest ecosystems, and to support climate change policies. The objective of the study was to analyse the variation in the most dynamic soil C input (tree and understory above- and belowground litter production) and output (soil respiration) fluxes, in addition to the forest floor, understory and fine root biomass stocks, in eight different Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) sites growing on mineral soils in Estonia. Further, the impact of soil C input and output fluxes on the soil organic carbon (SOC) pool was examined, and the net ecosystem production (NEP) of the stands was estimated. Fine root production (FRP) of the trees constituted 53% and 28% and needle litter constituted 25% and 28% of the total annual C input to the soil in the Norway spruce and Scots pine stands, respectively. The total FRP of the trees and the understory roots and rhizomes ranged from 211 to 1040 g m−2 yr−1, of which the understory comprised up to 28%. The mean annual soil respiration (Rs) rate was 5.7 ± 0.3 and 6.5 ± 0.3 Mg C ha−1 yr−1 in the pine and spruce stands, respectively, and did not differ significantly between the two groups of stands. The SOC pool of the studied stands depended significantly on both the above- and belowground C input fluxes. Tree-derived litter had the strongest effect on the SOC pool, while the Rh as the main soil C output flux showed no significant impact. The NEP ranged from 4.2 to −1.8 Mg C ha−1 yr−1 and demonstrated a strong negative correlation with stand age. The results affirm the importance of belowground as well as aboveground litter production on carbon accumulation in forest soils. [ABSTRACT FROM AUTHOR]

Estimation of the carbon (C) storages and fluxes in different forest ecosystems is essential for understanding their C sequestration ability. The net ecosystem production (NEP) and the net primary production (NPP) in five downy birch ( Betula pubescens ) stands, aged between 12 and 78 years, growing on fertile well-drained Histosols, were studied. Drainage of swamp forests is a large-scale manipulation, which causes significant shifts at the ecosystems level, altering C and nutrient cycling a great deal. Young and middle-aged downy birch stands (12–30-year-old) acted as C sink ecosystems, accumulating 1.4–3.0 t C ha −1 yr −1 . In the 38-year-old stand NEP was roughly zero; annual C budget was almost in balance. The over-matured downy birch stand (78-year-old) acted as a C source emitting 0.95 t C ha −1 yr −1 . Annual woody biomass increment of the stand was the main factor which affected the forest to act as a C accumulating system. Although the highest heterotrophic respiration (Rh) values were measured in the middle-aged stands, mean soil C emission did not differ significantly between the studied stands. Annual total soil respiration (Rs) and Rh ranged from 7.4 to 8.8 t C ha −1 and 4.7 to 6.2 t C ha −1 , respectively. Soil temperature appeared to be the dominant driver of the soil CO 2 effluxes. Temperature sensitivity (Q 10 value) of respiration rates (3.0–5.5), as well as the Rh/Rs (0.6–0.7) varied irrespective of stand age. Both the annual aboveground litter (1.5–1.9 t C ha −1 yr −1 ) and fine root litter (0.9–1.5 t C ha −1 yr −1 ) input fluxes were quite similar for the studied stands. However, the annual organic C input into the soil via above- and belowground litter was smaller than the annual Rh efflux, indicating that continuous mineralization of the peat layer reduces the soil organic C pool. The main share of the C stock in the drained swamp downy birch stands was soil C; the storage of C accumulated in the woody biomass of the trees accounted for only 5–20% of the total C storage of the ecosystem. [ABSTRACT FROM AUTHOR]

Stumps of conifer trees are a prospective source of bioenergy and stump harvesting is a novel practice in forestry management in the Baltic and Nordic countries. However, as stump harvesting may cause possible environmental risks there has emerged a clear need for research focusing on sustainable forest management. Three Norway spruce ( Picea abies ) clear-cut areas on different soils in Estonia were selected for the present study. We analysed the effect of stump harvesting on net nitrogen mineralization (NNM) and on nutrient leaching. On dry and sandy Endogleyic Arenosol ( Oxalis site type), stump harvesting reduced the annul NNM flux significantly; 134 and 202 kg N ha yr −1 at the harvested and at the control site, respectively. In clear-cut area where Endogleyic Cambisol was dominating ( Hepatica site type), stump harvesting had no effect on NNM (92 vs 88 kg N ha yr −1 ). However, in a clear-cut area where the soil type was Endogleyic Albic Podzol ( Myrtillus site type), stump harvesting increased the total annual NNM flux: 102 vs 70 kg N ha yr −1 at the harvested and at the control site, respectively. Stump harvesting affected also the proportion of nitrification and ammonification processes in NNM. At the Myrtillys site type stump harvesting increased the annual nitrogen (N) leaching flux. One year after stump harvesting, leaching at the harvested site was 11.7 vs 4.5 kg N ha −1 yr −1 at the control site. In the second year N leaching decreased and the difference levelled off. Increased N leaching was induced by a larger amount of water; average N concentration of the harvested and control sites did not differ. Although at the Oxalis site N leaching was larger at the harvested than at the control site, the total annual leached N flux was small (∼2 kg N ha −1 ). At the fertile Hepatica site type treatment had no impact on N leaching, which was only ca 1 kg N ha −1 yr −1 . Phosphorus (P) leaching was very small in all study areas, being below 0.1 kg P ha −1 yr −1 . The effect of stump harvesting on annual NNM as well as on N leaching was soil specific and highly variable. Stump harvesting affected also the proportion of the nitrification and ammonification processes in total NNM. Considering the first short-term results obtained from different site types, we can conclude that harvesting of spruce stumps does not induce serious environmental hazards in relation of N cycling. [ABSTRACT FROM AUTHOR]

Grey alder is a wide spread tree species in the Baltic region and a promising species for short rotation forestry. The symbiotic dinitrogen (N 2 ) fixation ability makes this tree important for the regulation of nitrogen (N) cycle in forested areas. In a homogeneous 32-year-old natural grey alder stand (GAS) and an adjacent clear-cut (CC) in South-East Estonia (58°17′ N; 27°17′ E; set up in May 2011) we analyzed net nitrogen mineralization (NNM; with incubated bags), N leaching (with plate lysimeters), and nitrous oxide (N 2 O) fluxes (with static chambers). The total annual NNM did not intensify in the CC area: in the upper 0–20 cm soil layer the NNM was 169.9 and 157.0 kg ha −1 in the (GAS) and in the CC, respectively. In both cases, the share of nitrification was 100% and NNM intensity was the highest in July. During the snow-melt in April, both in the GAS and in the CC site the leaching of total N was up to 25 kg N month −1 , whereas in the rest of study period it was negligible in both sites. Harvesting slightly decreased N 2 O emission, however, it was low at both study sites (−0.55 to 19.75 and −0.77 to 7.43 kg N 2 O ha −1 yr −1 in the GAS and the CC, respectively). Management of grey alder stands by traditional silvicultural methods (clear-cuts) did not to increased hazardous N losses through leaching. [ABSTRACT FROM AUTHOR]

• Average annual litter flux was similar for studied pine, spruce and birch stands. • Both stand age and site quality index were significant factors affecting the annual litter flux. • No significant relationship was established between stand basal area and litter flux. • For all tree species, the relative proportion of needles or leaves from in total annual litter flux declined with stand age. • The effect of weather conditions on the annual litter flux was revealed in continuously studied stands. Canopy litterfall represents an essential aboveground flux in every forest ecosystem, affecting soil carbon and nutrient dynamics as well as soil fertility. However, despite the important role of the canopy litter flux in ecosysteḿs functioning and carbon sequestration, litterfall dynamics is still poorly studied in hemiboreal forests. The main aim of the current study was to estimate average annual litter fluxes in Scots pine, Norway spruce and birch (Betula pendula and Betula pubescens) stands, as well as to compile regional litter models for estimating the annual litter flux. The annual litter flux from a total of 33 pine, 15 spruce and 21 birch stands, with 85, 43 and 53 datapoints, respectively, was included in the study. Although the annual litter flux depended on site quality index and stand age, no significant relationship was established between stand basal area and litter flux. Average annual canopy litterfall was similar for the studied tree species, being 3.24 ± 0.14 for pine, 3.62 ± 0.16 for spruce and 3.22 ± 0.07 t ha−1 yr−1 for birch across the stands of different ages. For all studied tree species, the relative proportion of needles or leaves in the total annual litter flux declined with stand age, due to the increased share of twigs and other fractions in the litter of older stands. The developed models of the litter flux allow to estimate the annual litter production of the canopy for the studied tree species on the basis of site quality index and stand age. [ABSTRACT FROM AUTHOR]

Stump removal is a novel potential source of woody biomass for renewable energy in the Nordic and Baltic countries. In Estonia, a prospective resource of Norway spruce ( Picea abies ) stumps is available for bioenergy. The main aims of the present study were to estimate the biomass and volume of harvested spruce stumps; also to evaluate nutrient and carbon loss from a site due to stump removal; and to estimate the effect of stump harvesting on soil respiration. In this pilot study an allometric model was elaborated for estimation of the biomass and volume of harvested stumps. The volume of harvested spruce stumps reached up to 130 m 3 ha −1 and potential energy content amounted to 290 MW h ha −1 . The average calorific value of different stump and root fractions varied between 19.0 and 19.3 kJ g −1 and there was no significant difference between the stump fractions. The weighted average density of the harvested spruce stumps was 430 kg m −3 . Fertile automorphic forest types were selected for this pilot study and the nitrogen (N) storage removed from clear-cuts with stumps was not appreciable, being 1.2–4.4%, in comparison with soil N storages. Removed phosphorus (P) accounted for 8–28% of total soil lactate soluble P and removed potassium (K) accounted for 6–23% of the soil K storage. The loss of carbon (C) made up 11–33% of the soil C storage. However, the concentration of lactate soluble P evidently reflected the balance between solubilized and assimilated P in the soil rather than actual P limitation. Hence, at fertile sites stump removal does not caused considerable N and C depletion, however, removal of P and K may be appreciable compared with corresponding soil storage values. Stump harvesting did not increase soil respiration intensity. Total annual soil respiration at the Oxalis site type was 4.9 and 5.1 t C ha −1 yr −1 in the uprooted and control plots, respectively. At the Myrtillus site type the respective values were lower, 3.7 and 3.9 t C ha −1 yr −1 . Also soil heterotrophic respiration in the Oxalis site type was practically the same at the uprooted and control sites, being 3.3–3.2 t C ha −1 yr −1 . However, in the Myrtillus site type the values of the heterotrophic respiration efflux was higher from the control plots than from the uprooted plot, at 2.5 and 1.8 C ha −1 yr −1 , respectively. Norway spruce stumps are a potential bioenergy resource in Estonian forests and stump harvesting at fertile autotrophic sites does not cause problems in terms of depletion of nutrients and carbon from the ecosystem. [ABSTRACT FROM AUTHOR]

In the present study the chronosequence approach was applied to the analysis of the dynamics of the growth of 2-45-year-old grey alder stands (Alnus incana) growing at fertile sites as well as the dynamics of carbon (C) and nitrogen (N) accumulation in woody biomass and in the soil. A new yield table was elaborated for natural grey alder stands growing at fertile sites. The average growing stock and increment of grey alder stands were lower than those presented in earlier yield tables compiled in Estonia or in the other Baltic or Nordic states. It can be explained by an uneven spatial distribution of trees in natural grey alder stands; because of this, the production of different alder stands of the same age was highly variable. However, some stands were characterised by remarkably high production, which indicates the high growth potential of this tree species. The bulk maturity of grey alder stands is achieved at the age of 12-13 years. However, the recommendable optimal harvesting age of grey alder stands could be 20-25 years, as annual woody biomass increment was high even after the age of 20 years. The average stemwood density found in this study was 396 ± 3.6 kg m³ and the average density of the branches was 460 ± 2.9 kg m³. Regarding of CN accumulation in the stands, different land use histories demonstrated different patterns. First-generation grey alder stands growing on previously non-forested lands accumulated effectively C and N in the soil. The average increase of the C pool in the 10 cm topsoil layer was in the range 1.1-1.2 t ha-1 yr-1 in young stands and 0.97-0.84 t ha-1 yr-1 in older stands. In the case of second-generation grey alder stands the soil C pool in young and old stands was of same magnitude and these stands accumulated C mainly in woody biomass. The share of the soil C pool in middle-aged and old grey alder stands was roughly two times as large as the C storage accumulated in the above-ground woody biomass of the trees. The average N accumulation in first-generation grey alder stands of the age of 14-35 years was 74 kg N ha-1 yr-1. Also a significant acidifying effect of alders on the soil pH status was revealed. The study confirmed that grey alder has the potential to be a high yielding tree in short-rotation forestry for woody biomass production. Grey alder stands serve as efficient forest ecosystems accumulating C both in biomass and in the soil. However, previous land use history plays an essential role in this respect. [ABSTRACT FROM AUTHOR]

Highlights: [•] The fine root live/dead ratio decreased with stand age. [•] Ectomycorrhizal biomass per basal area varied between 8 and 14kgm−2. [•] Root to shoot ratio of 21% is reasonable for silver birch stands. [•] Belowground part of a stand acts as a significant carbon sink. [ABSTRACT FROM AUTHOR]

Abstract: Short-rotation energy forestry is one of the potential ways for management of abandoned agricultural areas. It helps sequestrate carbon and mitigate human-induced climate changes. Owing to symbiotic dinitrogen (N2) fixation by actinomycetes and the soil fertilizing capacity and fast biomass growth of grey alders, the latter can be suitable species for short-rotation forestry. In our study of a young grey alder stand (Alnus incana (L.) Moench) on abandoned arable land in Estonia we tested the following hypotheses: (1) afforestation of abandoned agricultural land by grey alder significantly affects the soil nitrogen (N) status already during the first rotation period; (2) input of symbiotic fixation covers an essential part of the plant annual N demand of the stand; (3) despite a considerable N input into the ecosystem of a young alder stand, there will occur no significant environmental hazards (N leaching or N2O emissions). The first two hypotheses can be accepted: there was a significant increase in N and C content in the topsoil (from 0.11 to 0.14%, and from 1.4 to 1.7%, respectively), and N fixation (151.5kgNha−1 yr−1) covered about 74% of the annual N demand of the stand. The third hypothesis met support as well: N2O emissions (0.5kgNha−1 yr−1) were low, while most of the annual gaseous N losses were in the form of N2 (73.8kgNha−1 yr−1). Annual average NO3–N leaching was 15kgNha−1 yr−1 but the N that leached from topsoil accumulated in deeper soil layers. The soil acidifying effect of alders was clearly evident; during the 14-year period soil acidity increased 1.3 units in the upper 0–10cm topsoil layer. [Copyright &y& Elsevier]

Abstract: The effect of land use type on the dynamics and annual rate of net nitrogen mineralization (NNM) in a naturally generated silver birch stand and in a grassland, both on abandoned agricultural land, was assessed in situ in the upper 0–20cm soil layer using the method of buried polyethylene bags. Annual NNM rate in the birch stand (156kgNha−1 year−1) was higher than in the grassland (102kgNha−1 year−1); in both cases NNM covered a major part of the plants annual nitrogen demand. The rate of NNM in the upper 0–10cm soil layer in the birch stand (99kgNha−1 year−1) exceeded the respective rate of NNM in the grassland (51kgNha−1 year−1) roughly two times. In the grassland the rates of NNM in the 0–10 and 10–20cm layers were equal; in the birch stand NNM in the 0–10cm layer was 1.7 times higher than in deeper 10–20cm layer. The intensity of daily NNM in the upper 0–10cm soil layer in the birch stand was the highest in June and in the grassland in May, 776 and 528mgkg−1 Nday−1, respectively. In our study no significant correlation was found between NNM and the environmental factors monthly mean soil temperature, soil moisture content and pH. The share of net nitrification in NNM in the birch stand and in the grassland was similar, 60% and 63%, respectively. In the deeper topsoil layer (10–20cm) net nitrification made up a significantly higher proportion in NNM in the grassland than in the birch stand, 58% and 35%, respectively; this may increase nitrogen leaching from the deeper soil layers. Most probably, more intensive NNM did not lead to higher N leaching or emission losses from ecosystems in the birch stand compared with the grassland because an essential amount of nitrogen is retained in tree biomass. [Copyright &y& Elsevier]

Abstract: During the last decade, more than 400000ha of agricultural land was abandoned in Estonia. Such areas are often characterized by rapid natural afforestation with silver birch, which has led to an increase both in the woodland area and in the area of silver birch stands. However, many bioenergetic aspects related to birch stands growing on arable land are still poorly understood. The main aim of the present study was to investigate the above-ground biomass production, nutrient (NPK) accumulation, and foliar characteristics of young silver birch stands on abandoned agricultural land. Five 8-year-old stands of silver birch growing on different soil types were included in the study. The density of the studied stands varied from 3060 to 36200 trees per ha and their above-ground biomass varied from 6.0 to 22.9tDMha−1. The largest share in the above-ground biomass of the birches (59–80%) was from the stems. The mean stem mass of the birches ranged from 0.29 to 1.79kg, and the mean total above-ground biomass ranged from 0.36 to 3.03kg. The leaf area index for the studied stands varied from 1.21 to 4.64m2 m−2, being the highest for the stand of medium density. Mean single leaf area varied from 9.4±0.2 to 15.4±0.3cm2, leaf weight per area varied from 61.1±0.4 to 77.5±0.5gm2, and specific leaf area varied from 13.2±0.1 to 16.8±0.1m2 kg−1. However, no significant differences were found between stand density and the foliar characteristics. There was a strong positive correlation between soil nitrogen concentration and leaf nitrogen concentration (R=0.92); regarding phosphorus concentration, the corresponding correlation was weak (R=0.52) and regarding potassium concentration, no significant correlation was found. The amount of nitrogen accumulated in the above-ground part of the silver birch stands varied between 42.4 and 145.8kgha−1, the amount of phosphorus, between 5.9 and 27.9kgha−1, and the amount of potassium, between 7.2 and 78.6kgha−1. The N:P:K ratios for the foliage were comparable. It is evident that the proportion of nitrogen and phosphorus are close to optimum, while the N:K ratio was lower than optimum value in all cases. [Copyright &y& Elsevier]

The dynamics and annual rate of net nitrogen mineralization in a grey alder plantation growing on abandoned agricultural land was assessed in situ using the method of buried polyethylene bags. Nitrogen mineralization was assessed in the upper 0–10 and 10–20 cm soil layers, where 47.5 and 26.3% of the fine roots, respectively, were situated. Net nitrogen mineralization was the highest in May and September, 314 and 306 mg kg−1 N per day, respectively. Annual net nitrogen mineralization and net nitrification in the upper 0–10 cm soil layer were estimated as 84 and 87 kg ha−1 per year, respectively. Annual net nitrogen mineralization in the upper 0–20 cm soil layer was estimated as 141 kg ha−1, which accounted for 62% of the annual nitrogen used by trees and the understorey vegetation. Among various environmental factors related to mineralization, pH played a significant role. [Copyright &y& Elsevier]

In 1999, the area of abandoned agricultural land in Estonia formed 223,000 ha which is partly perspective for afforestation with grey alder, the most rapidly growing indigenous tree species. The production and nutrient (NPK) accumulation of a grey alder short-rotation plantation on former agricultural land was investigated. The production of above-ground biomass was estimated during 5 years after the establishment of the stand. In the fifth year after planting, the biomass of the above-ground part of the plantation was 15.9 t DM ha−1 and above-ground biomass production was 6.4 t DM ha−1 per year. In the fourth year after planting, the biomass of the below-ground part was 2.7 t DM ha−1, which accounted for 18% of total biomass. The biomass of the nodules was estimated at 169±76 kg DM ha−1 and the biomass of fine roots (d<2 mm) at 550±105 kg DM ha−1. Of fine roots 73.8% and all nodules were located in the upper 0–20 cm soil layer. In the fourth year after establishment, the amount of nitrogen introduced in the soil through leaf litter was 59.6 kg ha−1. As the site represented abandoned farm land, the pool of total soil nitrogen was relatively large (2.64 t ha−1 in the 0–20 cm layer). However, concerning phosphorus, the positive effect of grey alders was significant. While in the first year after planting the concentration of lactate soluble phosphorus in the 0–20 cm layer was 22.53 mg kg−1, then in the following years it was more than twice as high, varying from 47.2 to 59.7 mg kg−1. After the fifth year the amount of nitrogen accumulated in above-ground biomass was 147.1 kg ha−1, that of phosphorus 21.3 kg ha−1 and that of potassium 42.6 kg ha−1. Most of accumulated nitrogen and potassium (38.9 and 37.6%, respectively) was located in the leaves and most of phosphorus (61.0%) in the wood. [Copyright &y& Elsevier]

• Positive effect of stump removal on the height growth of the trees was revealed. • Stump removal had no effect on the nutritional status of the needles of young trees. • Positive trend of stump removal on twig and needle parameter revealed. • Stump removal had no effect on the spread of Heterobasidion sp., Armillaria sp. • The main causal agent of root rot on all the sampling sites was H. parviporum. Stumpwood as a resource of renewable bioenergy has considerable potential in the Nordic and Baltic countries. So far, however, it has largely been left unutilised in Estonia. This study reports the results of the height growth, needle and twig traits, and Heterobasidion sp. and Armillaria sp. infection in emerging Norway spruce (Picea abies) stands after stump harvesting. After six and eight growing seasons, a significant positive effect of stump harvesting on the height growth of the trees was revealed, compared to control plots with no ground preparation. In one study site stump harvesting was revealed to have a positive effect on the morphologic parameters of twigs and needles, while no differences were noted in the other two sites. The nutrient content of the needles was similar between the treatments across all study sites. Stump harvesting had no effect on the spread of Heterobasidion sp. and Armillaria sp. in the new forest generation. Root infections in young trees with Heterobasidion sp. were detected as early as within two growing seasons from planting. The infection was most severe in the Hepatica site type stand, where 90% of the trees in the previous forest generation had been infected by Heterobasidion sp. In the two other stands studied, where the share of infected trees in the previous generation had been 26% and 16%, Heterobasidion sp. was significantly less widespread. The main causal agent of root rot on all the sampling sites was H. parviporum , but the presence of Armillaria sp. was also remarkable. [ABSTRACT FROM AUTHOR]

Abstract: Owing to its ability to produce large amounts of biomass in a short period of time, grey alder can be considered to be a prospective tree species for short-rotation forestry (SRF) in Eastern Europe and the Nordic countries. Relatively scanty data is available about grey alder yield and growth dynamics. Seven yield-tables from six countries and several published studies have been included in this review. The main aim of the review was to sum up and analyze published data; to evaluate the potential for biomass production and to summarize the existing relevant knowledge for giving recommendations about the optimal principles on managing alder stands. According to different yield-tables, the mean annual increment (MAI) of 20-year-old stands varied from 2.56 m3 ha−1 to 4.75 m3 ha−1 (dry matter). In favourable conditions, the growth of alder stands can be rapid and biomass production high. The highest woody biomass of annual production reported in literature amounts to 17 t ha−1 y−1. A rotation length of 15…20 years is recommended by the majority of authors. The rotation period is longer in northern countries (Norway, Finland) than in southern countries. According to yield-tables, it coincides with the start of the decrease in MAI in most cases. Approximately 60 t ha−1–90 t ha−1 of stemwood can be produced during one rotation. The density of the natural grey alder stand is typically very high. The optimal initial density of grey alder may not exceed 10,000 ha−1 in the case of plantations and the optimal number of trees per hectare before harvesting should range between 3000 ha−1 and 6000 ha−1. [Copyright &y& Elsevier]

Carbon (C) budgets were compiled for silver birch chronosequence stands by synthesizing the above- and belowground C pools and fluxes with the aim to assess the impact of age on stand C sequestration and cycling. The fine root ( d < 2 mm) biomass, production, turnover rate and longevity of 13-, 32- and 45-year-old silver birch stands were determined by the ingrowth core method. Fine root production after the third year from the installation of cores was 0.89, 1.44 and 1.31 t ha −1 year −1 in the pole, middle-aged and premature silver birch stands, respectively. Soil respiration ( R s ) was measured during the two growing seasons of 2010 and 2011; the trenching method was used to estimate the contribution of heterotrophic respiration ( R h ) to total soil respiration. Soil temperature was the driving environmental factor of the temporal variation of R s and R h . Stand age affected significantly respiration rates. Annual R s was 6.2, 9.7 and 8.2 t C ha −1 and annual R h was 2.97, 4.21 and 3.61 t C ha −1 in the pole, middle-aged and premature silver birch stands, respectively. The annual contribution of R h to R s was similar in each stand ranging from 0.43 to 0.48. Total annual net primary production (NPP) of the ecosystems of 7.4, 7.9 and 8.5 t C ha −1 year −1 was estimated in the pole, middle-aged and premature stands. After balancing the C input and output fluxes in the silver birch stands of different development stages, it appeared that they all acted as effective C sinks. Net ecosystem production (NEP) was 4.4, 3.7 and 4.9 t C ha −1 year −1 in the pole, middle-aged and premature stands, respectively. In the premature stand the second layer of the spruce contributed significantly to the increased C input. The annual organic C input into the soil through above- and belowground litter occurred to be of the same magnitude as C loss via annual heterotrophic respiration. Thus, annual increment of woody biomass in fertile silver birch stands reflects annual organic C sequestration in the ecosystem. Among the studied stands, estimated NEP values were the lowest in the middle-aged stand and the highest in the oldest stand, indicating non-linear relationship between stand NEP and stand age. [ABSTRACT FROM AUTHOR]

Abstract: The two alder species, black alder (Alnus glutinosa (L.) Gaertn.) and grey alder (Alnus incana (L.) Moench) are known to be pioneer species in the succession of new land areas, and important tree species in renewable biomass production, the restoration of post-mining sites and riparian forest ecosystems. We analyzed the influence of soil physico-chemical characteristics (soil water content, pHKCl, total N, soluble P, organic matter content, C and N ratio, and elemental content) on bacterial community structure based on pyrosequencing analysis of the 16S rRNA gene V2 and partly V3 region in two black and two grey alder stand soils with different management histories. The analyses revealed clear differences in all the measured chemical characteristics of studied soils. All the studied stands also had distinct soil bacterial communities, and the number of shared species was low. In all stands species from phylum Proteobacteria were dominant, and the next phyla by percentage were Bacteroidetes and Actinobacteria. At the family level, Chitinophagaceae and Bradyrhizobiaceae species dominated. The obtained bacterial community Inverted Simpson''s diversity indices showed no difference between the studied sites. The alder species did not affect soil bacterial community structure. Distance-based regression analysis indicated that soil pH value, water content, soluble phosphorus concentration and also total boron, cadmium, and aluminium content were related to the variation of soil bacterial community structure in alder stand soils. The results of this study emphasize the importance of soil geomorphological properties in addition to soil physical and chemical characteristics in the formation of soil bacterial community structure during restoration of exhausted open mining areas, management of abandoned agricultural lands, and short rotation forests with different alder species. [Copyright &y& Elsevier]

Abstract: A facility for free air humidity manipulation (FAHM) was established to investigate the effect of increased air humidity on trees’ performance and their canopy functioning with respect to rising air humidity predicted for Northern Europe. The FAHM system enables air relative humidity (RH) to be increased up to 18 units (%) over the ambient level during mist fumigation, depending on the wind speed inside the experimental stand. Water was dispersed inside 14×14m experimental plots in the form of mist with an average particle size of 50μm from June to August in 2008, and from May to September in 2009. The average increase in RH was 7 units (%) over the whole period of humidification in 2008 (P <0.05). The average diurnal stem sap flux density per unit projected leaf area (F) in silver birch (Betula pendula Roth.) trees was 24.8% (P <0.05) and 27.2% (P <0.01) higher in control (C) plots compared to humidification (H) plots during misting in 2008 and 2009, respectively. However, the difference between C and H plots was statistically insignificant (P >0.05) in silver birch on the days without misting. In hybrid aspen (Populus tremula L.× P. tremuloides Michx.) the average difference in F between C and H plots was 61.1% (P <0.001) during mist fumigation in the summer of 2009. Nevertheless, the difference was considerable (38.8%; P <0.001) also on the days without misting, reflecting the impact of plant inner factors on F as a result of long-term acclimation to fumigation. The leaves of silver birch in a humidified plot demonstrated up to 2.4°C lower (P <0.05) leaf temperature (T L) compared to the control plot in 2009. The decline in T L decreased the humidity gradient between leaf and air by about 1/3, whereas 2/3 of the effect was caused directly by changes in air humidity in the leaf boundary layer. Our preliminary data suggest that the FAHM experimental facility enables water fluxes through a deciduous tree canopy to be reduced and this effect is attributable both to the increased air humidity and decreased leaf temperature. Changes in these two basic factors may create considerable differences in the physiology, anatomy and nutrition of a whole tree, also affecting forest functioning in the light of global climate change. [Copyright &y& Elsevier]

Abstract: Mining activities create wastelands that require reclamation. The relief of abandoned opencast oil shale mining area is rugged, and the mining spoil is extremely stony and alkaline (pH 8), with low N and organic content. Planting of fast-growing deciduous tree species such as silver birch (Betula pendula) on post-mining area is the best means to accelerate the development of a new forest ecosystem in such harsh conditions. A chronosequence of silver birch stands (1, 2, 3, 5, 29, 40 years old) was investigated to reveal changes in bulk soil (S) and rhizosphere (R) properties, in rhizosphere effect on bacterial activity and diversity, and in fine-root morphological adaptations in relation to stand development. The rhizosphere effect on bacterial activity was measured as a rhizosphere/soil (R/S) ratio and on species diversity as a similarity (%) between rhizosphere and bulk soil bacterial communities. Bacterial species diversity was determined by denaturing gradient gel electrophoresis (DGGE) technique and was expressed as Shannon diversity index. Biolog EcoPlates were used to determine the summed activity of cultivable bacteria in rhizosphere and bulk soil. Short-root morphological parameters were measured using WinRHIZO™ Pro. Soil pH and available P concentration decreased logarithmically, and N% and organic matter concentration increased linearly with increasing stand age. During the first 30 years of stand development SIR increased an order, from 0.18 to 1.90mgCg−1. Bulk soil bacterial diversity increased logarithmically with stand age. The bacterial diversity was higher in rhizosphere than in bulk soil. Rhizosphere effect on bacterial activity was low a year after planting, increased more than two times in the next 2 years, and decreased thereafter rapidly with stand age. Rhizosphere effect, indicating plant support to rhizosphere microbial communities, was highest when soil conditions were still poor, but trees had already overcome the transplant shock. All short-root morphological parameters showed certain trends with age. Specific short-root length varied between 56 and 313mg−1 and decreased logarithmically with stand age and soil improvement. The fastest changes in short-root morphology, rhizosphere effect, and soil pH occurred during the early development of silver birch stands – in the first 5 years; P nutrition and N use efficiency improved simultaneously. Rhizosphere effect and short-root morphological adaptation have an important role in soil and stand development on oil shale post-mining area, and silver birch is a promising tree species for reclamation of alkaline mining spoil. [Copyright &y& Elsevier]