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• Presence of spruce litter alters vegetation development after clear-cut. • Spruce litter can be considered a degrading legacy after plantation removal. • By litter removal, early stage vegetation establishment can be enhanced. • Wildlife grazing can suppress the litter removal effect. Restoration of areas used for intensive even-aged Norway spruce (Picea abies Karst.) plantations often involves felling and subsequent spontaneous vegetation succession. However, the accumulated litter layer may hamper vegetation development, and thereby postpone recovery or even change the outcome. We studied effects of the litter layer on vegetation establishment during two seasons following a clear-cut of Norway spruce in Denmark. We experimentally assessed the response of multiple vegetation properties to litter removal, with and without wildlife exclusion by fencing, and in combination with sowing of trees, while fencing. Burning was tested as an alternative way to remove the litter layer. Vegetation establishment was poor, when the litter layer was intact, and cover developed slowly remaining below 10% after two years, irrespective of fencing. In contrast, litter removal and fencing together gave significantly faster recovery and reached nearly 60% mean cover. Vegetation cover was driven by few dominant species, especially the sedge Carex pilulifera. Species richness was similar in all treatments, but increased with sowing of trees. Fencing resulted in taller birch seedlings independently of litter removal, but enhanced by seedling density. Litter removal seemed to favor species with lighter seeds, lower specific leaf area (SLA) and lower Ellenberg N value, i.e. associated with relative infertile conditions. Disturbing the litter by burning seemed to have an effect comparable to mechanical removal, and could be a management alternative. Our results showed that a persistent litter layer after spruce plantation removal may hamper the initial vegetation establishment. Actively removing litter may serve as an additional restoration intervention to overcome this legacy. However, as grazing can keep this potential in check, wildlife exclusion may be necessary as well. To speed up recovery and diversify vegetation structure after spruce plantation removal, we suggest patchy disturbance of the litter, essentially combined with wildlife exclusion. [ABSTRACT FROM AUTHOR]

• Windthrow is a common disturbance regime in boreal and temperate forests. • Recovery of trees after windthrow was dominated by post storm regeneration. • Advanced regeneration was an important process for regeneration of shade tolerant tree species. • Salvage logging after windthrow pushed forests towards earlier successional stages. • Forests in the boreal and temperate biomes were in all cases recovering after windthrow. Wind is a natural disturbance factor in boreal and temperate forests having large ecological and economic consequences. We investigated recovery processes in forests severely damaged by windthrow, by conducting a systematic quantitative literature review of 34 case studies. We addressed three questions on forest ecosystem recovery: (1) Which forest regeneration processes dominate forest recovery after windthrow? (2) Which structures and processes enhance or impede forest recovery after windthrow? (3) Does salvage logging after windthrow influence forest recovery? Our analyses showed that the main focus of the reviewed studies was on post storm seedling regeneration and survival. Advanced regeneration from suppressed seedlings or saplings also played an important role in the studies, especially for shade tolerant species and in the boreal biome. Pits and mounds and coarse woody debris played an important role for the establishment of Picea sp., especially in the studies from the boreal biome, whereas in the temperate biome game interference and competition from ground vegetation seemed to be the most important influencing processes. Salvage logging mostly acted as a subsequent disturbance after the windthrow, pushing the forest ecosystem towards an earlier successional stage, hereby impeding recovery. In none of the studies however, did the windthrow nor the consequent salvaging halt recovery completely, confirming the resilience of forests as the dominant vegetation type in these biomes. Based on our results forest management implications are discussed. [ABSTRACT FROM AUTHOR]

In tropical forests, selective logging generates a significant reduction of above-ground carbon stocks, due to direct removal of a few large merchantable individuals, and the death of smaller injured or smashed trees following harvesting. Several studies have shown a strong correlation between logging intensity and a reduction of biodiversity, wood production, and biomass stocks. However, little is known about the long-term effects of logging on the main forest carbon (C) stocks in above and below-ground tree biomass, deadwood, litter, and soil. In this study we quantified C stocks in 28 0.25-ha plots located in a mixed Dipterocarp forest, Borneo, Indonesia, logged 16 years ago at different intensities ranging from 0 to 57% of initial biomass removed. We investigated the effect of logging intensity, topography, and soil variables on each C stock using linear mixed models. Sixteen years after logging, total C stocks ranged from 218 to 554 Mg C ha −1 with an average of 314 ± 21 Mg C ha −1 , of which more than 75% were found in live trees. Logging intensity was found to be the main factor explaining the variability in carbon stored in above- and below- ground biomass of tree DBH >20 cm and deadwood. Simultaneously, the proportion of deadwood increased with logging intensity reaching 13.5% of total C stocks in intensively logged plots (>20% removal of initial biomass). This study confirmed, therefore, the need to limit logging intensity to a threshold of 20% of initial biomass removal in order to limit the long-term accumulation of deadwood after logging, probably due to high post-logging mortality. With more than half of all Bornean forests already logged, accounting for total C post-logging is key to better assess the long-term carbon footprint of commercial logging in the region, and is a necessary step towards the development of C-oriented forest management in the tropics. [ABSTRACT FROM AUTHOR]

Fine roots (diameter ≤ 2 mm) contribute significantly to the forest carbon cycle and are essential for resource acquisition from the soil. We conducted a study to assess the relationships between tree and ground vegetation fine root biomass and tree species diversity (monocultures compared to 2–5 species mixtures), conifer proportion and other site factors (stand basal area, soil carbon stocks and C:N ratio) in the six major European forest types, boreal forest in Finland, temperate forests in Poland, Germany and Romania, thermophilous deciduous forests in Italy, and Mediterranean forests in Spain. We sampled the fine roots of trees and ground vegetation to the depth of 20 cm in the mineral soil and allocated the fine root biomass to individual tree species using near-infrared reflectance spectroscopy (NIRS). We did not find any general positive effects of tree species diversity on the fine root biomass of trees or ground vegetation across the forest types and tree species combinations. However, our results suggest that tree fine root biomass increases with tree species diversity in pure broadleaf forests, but not in pure conifer forests. Species diversity explained 7% of the variation in tree fine root biomass in the broadleaf stands. The narrow tree species diversity gradient (1–2 species) in the conifer forests compared to the broadleaf forests (1−4) may have decreased the probability of conifer species combinations with below-ground functional traits conducive to over-yielding. Some evidence of diversity-mediated changes in the vertical rooting patterns of broadleaf trees and ground vegetation were found within the entire organic and 0–20 cm mineral soil layer although the weighted mean depth of fine root biomass was not affected. Negative diversity effects were found in the organic layer and positive diversity effects in the 0–10 cm mineral soil layer for broadleaf tree fine root biomass. Diversity effects were negative for ground vegetation fine root biomass in the 0–10 cm mineral soil layer. There was a general positive effect of conifer proportion on total fine root biomass in the organic layer, but not in the mineral soil layers. In general conifer proportion and site factors explained more of the variation in tree fine root biomass than tree species diversity. More research covering the annual variation in fine root biomass and deeper soil layers is needed before recommending managing species-rich forest for increasing below-ground biomass and carbon pools. [ABSTRACT FROM AUTHOR]

Dedicated energy poplar plantations have a high biomass production potential in temperate regions, which may be further increased by improved management practices. The aim of this study was to investigate the effects of fertilization on short rotation forest poplar established on former arable land. We examined the effects on biomass production, net nutrient uptake in stems and branches, nutrient leaching fluxes and changes to the nutrient budgets calculated as inputs minus outputs. An experiment was carried out in four stands of different development stages, the establishment (EST), canopy-closure (CC), pre-thinning (PT), and late aggradation (LAG) stage. After fertilizing with NPK12-5-14 corresponding to 120 kg ha −1 of N we measured the biomass production during three years and analysed biomass samples to assess the net nutrient uptake in stems and branches. We estimated nutrient leaching based on water fluxes modelled with CoupModel and soil solution analyses and calculated the nutrient budgets. Fertilization effects depended on the stage of stand development, but were inconsistent in time. The biomass production increased in EST in the first year after fertilization and in PT in the third year after fertilization, relative to the control. There were no effects in CC and LAG. Nitrogen leaching at 0.9-m depth ranged between 3 and 14 kg ha −1 yr −1 in the control plots of EST and PT and it was negligible in the CC stand. Nitrogen leaching doubled in EST in the year of fertilization with values up to 28 kg ha −1 yr −1 and it tripled in PT in the second year after fertilization, compared to the control. Budgets of N, P and K were negative in all unfertilized and some fertilized treatments, indicating that fertilization may be required to adequately sustain soil nutrient supply in the long term, as large amounts of nutrients will be removed when the biomass is harvested. [ABSTRACT FROM AUTHOR]

Roots mobilize nutrients via deep soil penetration and rhizosphere processes inducing weathering of primary minerals. These processes contribute to C transfer to soils and to tree nutrition. Assessments of these characteristics and processes of root systems are important for understanding long-term supplies of nutrient elements essential for forest growth and resilience. Research and techniques have significantly advanced since Olof Tamm’s 1934 “base mineral index” for Swedish forest soils, and the basic nutrient budget estimates for whole-tree harvesting systems of the 1970s. Recent research in areas that include some of the world’s most productive and intensively managed forests, including Brazil and the USA, has shown that root systems are often several meters in depth, and often extend deeper than soil is sampled. Large amounts of carbon are also sometimes stored at depth. Other recent studies on potential release of nutrients due to chemical weathering indicate the importance of root access to deep soil layers. Nutrient release profiles clearly indicate depletion in the top layers and a much higher potential in B and C horizons. Reviewing potential sustainability of nutrient supplies for biomass harvesting and other intensive forest management systems will advance understanding of these important ecosystem properties, processes and services relevant for management. [ABSTRACT FROM AUTHOR]

Abstract: A field trial was carried out in 1995 to study the effect of fertilization at planting on the survival, growth, and nutrition of tree seedlings planted on Andisol soils at two sites in South Iceland. Nine fertilizer treatments were tested on three tree species Betula pubescens Ehrh., Larix sibirica Ledeb. and Picea sitchensis (Bong.) Carr. After six growing seasons, seedlings provided with controlled-release-fertilizer (Osmocote®: 25g per seedling) or smaller amounts of easily soluble nitrogen–phosphorus fertilizer (e.g. 1.2g N per seedling and 1.4g P per seedling) showed significantly improved survival and growth. Larger amounts of N increased mortality during the first year. Fertilized trees were less subject to frost heaving than untreated trees. In the year following application of NPK fertilizer the effect was insignificant on the foliar concentration of macronutrients of the fertilized seedlings, compared to control seedlings. It is concluded that fertilization during afforestation in Iceland and other areas in the world with similar climatic and soil properties could make the difference between plantation success or failure. [Copyright &y& Elsevier]

The aim of this study was to assess the effect of the N, P and K status on frost sensitivity of Norway spruce needles in a fertilization experiment situated in a nutrient poor 29-year-old Picea abies stand in western Denmark. The relative difference in frost sensitivity among trees was assessed by an index of injury, based on conductivity measurements of ion leakage from needles. Despite fertilization, all trees indicated N, P and K deficiency. The foliage, collected in late winter, was generally not very frost sensitive, but foliage from trees with the lowest K and P status were more sensitive to frost, and the current year needles were more sensitive than the second and third year needles. The advancement of bud burst was assessed in May. Trees with a relatively high N concentration in the current year needles had a more advanced bud burst than trees with a lower N concentration, increasing the risk for frost damage by a temperature backlash. [Copyright &y& Elsevier]

The influence of various fertilization treatments on the availability of N and P in the forest floor was studied in a Danish Norway spruce (Picea abies (L.) Karst.) stand. The treatments included fertilization with N alone in two doses, N combined with lime and other essential nutrients, and lastly lime and nutrients other than N. We tested the hypotheses that fertilization with N alone would increase the availability of N and P in forest floors, and that fertilization with N in combination with lime and other nutrients would further increase N and P availability. Extractable and mineralizable NH4–N, NO3–N, and PO4–P 2 and 3 years after application of fertilizers were the indicators of N and P availability. Microbial activity as reflected by basal respiration rates was not affected by any of the fertilization treatments. The extractable and mineralizable amounts of N both indicated that N fertilization did not increase the availability of N in forest floors. Combined fertilization with N and other essential nutrients including lime reduced N availability, and application of lime and other nutrients than N resulted in the lowest N availability of all treatments. Nitrification rates were, however, increased after application of the highest amount of N and after application of lime. The replication over 2 years showed a consistent pattern, and treatment responses mainly occurred in the LF layer of forest floors. Phosphorus availability increased following liming and fertilization with nutrients other than N; this occurred in the H layer of forest floors.The results did not support the hypothesis that N fertilization increases N availability in the forest floor. There was also no evidence of a sustained positive effect on N availability of combined fertilization with N, lime, and other nutrients. In fact, N availability was reduced by the application of other nutrients and lime, whereas the study suggests that this treatment may positively affect P availability in a longer-term perspective. [Copyright &y& Elsevier]

Abstract: Ambitious targets for reducing emissions of carbon dioxide have created a demand for renewable sources of energy. Short rotation coppice (SRC) willow has the potential for meeting part of this demand. In this study, an experiment including four commercial clones of willow grown on two different soil types in northern Denmark is reported. Annual biomass production was estimated after the first and second growing season in the first rotation using a non-destructive method and total biomass production was measured by harvesting of the willow after the second growing season. The non-destructive method showed a large increase in annual biomass production from the first to the second growing season. Based on the harvested willow, average annual biomass production of the four clones ranged from 5.2 to 8.8 odt ha−1 yr−1 with a significant effect of both soil type and clone. The interaction between clones and soil types was also significant, indicating that different clones may be better suited for different soil types. On average, estimates of annual biomass production obtained by non-destructive estimation exceeded those obtained by destructive methods by 1.2 odt ha−1 yr−1. This bias indicates a need to revise commonly used methods for assessment of biomass production in SRC willow. [Copyright &y& Elsevier]

In the wider context of heathland restoration, we investigated how field scale experimental acidification with sulphur (sulfur) affected soil biodiversity, fertility and function over a period of 17 years. A field experiment was conducted in the Isle of Purbeck, England, using ferrous sulphate and elemental sulphur as acidifying agents. We tested the effects of acidification on soil fertility, plant communities, litter decomposition, microbiology (including fungi bacteria and actinomycetes), arbuscular and ericoid mycorrhizal colonisation, and soil fauna (including earthworms, nematodes, rotifers and tardigrades). We found that elemental sulphur had a considerable and persistent effect on soil pH, lowering it to levels found in the surrounding reference acid grassland and heathland sites. A newly adapted heathland restoration index based on soil chemistry, found that elemental sulphur was by far the most successful treatment leading to soil conditions similar to the heathlands. Overall, acidification caused a loss of base cations and an increase in toxic aluminium compounds. Consequently the more mesotrophic components of soil biology were reduced by acidification during the course of the experiment. This transformed the soil biological system into one typical of acid grasslands and heathlands. Concomitant litter decomposition was similarly inhibited by acidification, with the microbiota more strongly hindered in acidified soil than the macroscopic fauna. Acidification resulted in a reduction in nematode and rotifer abundance and earthworm biomass. The vegetation community was also strongly modified by the elemental sulphur treatments and, where grazing was restricted, soil acidification allowed a restored heathland community to endure. Arbuscular mycorrhizal colonisation of grasses was reduced where heather plants were established, while ericoid mycorrhizas had developed sufficient populations in the acidified pastures to match the colonisation rate in the native heathlands. • Soils amended with elemental sulphur were strongly acidified compared with controls • The biota of the acidified treatments was considerably altered • Only microbial litter mass loss was significantly different between treatments • Control plots had the most litter loss, acidified plot were significantly lower • Heathland vegetation communities emerged after sulphurous acidification [ABSTRACT FROM AUTHOR]

Highlights • Phosphorus (P) pool in 23 forest soils was 0–4 Mg ha−1 by dilute HNO 3 extraction. • Soil texture and pH were ambiguous predictors for nutrient release. • In Al-Fe oxide buffered soils base cation loss is not reflected by a clear pH decline. • Soil test methods can predict the ability to recover from P and base cation depletion. • Mapping of soils can aid the monitoring of sustainable biomass harvest and regrowth. Abstract The long-term carrying capacity for biomass production is highly dependent on available soil resources. A soil test method for potential nutrient release capability was applied to 23 Nordic and Baltic forest soil profiles. The soils had coarse (10), medium (12) and fine (1) soil texture and most were podsolising. Extraction with dilute (0.1 M, 1:50 sample:solution ratio) nitric acid for 2 h was followed by 48 h and 168 h of extraction in soil samples from pedogenetic horizons. Dilute nitric acid solution was replaced after each step and release of mineral nutrient elements in solution was determined. C-horizon nutrient release (µmol g−1 fine earth, 0–218 h) was negatively correlated with mean annual temperature (MAT 0.5–8.5 °C) and for potassium (K) also mean annual precipitation (MAP 523–1440 mm y−1) suggesting a gradient in the mineralogy of the parent material that sediment transports during Pleistocene glaciations have not distorted. In B-horizons of sandy parent materials with felsic mineralogy cumulative nutrient release was positively correlated with pH and with Al and Fe release suggesting accumulation and stabilisation of nutrients in pedogenic products. E-horizons had less nutrient release capability than C-horizons, indicating a more weathered state of E-horizon parent material. Soil formation due to mineral dissolution and leaching of base cations and the gradient in parent material origin and weathering state both affected the observed pattern of nutrient release. On soils with very low mineral P resources (e.g. <250 kg P ha−1 to 50 cm) by repeated dilute acid extraction, harvest of nutrient rich biomass will not be sustainable. However, it can't be concluded that sites with high P availability by 0.1 M HNO 3 can support an intensive harvest without compensation of P (and Ca) by fertilisation. Due to buffering of removed base cations in B-horizons, nutrient export with biomass may not be traceable as pH decline at decadal time scale. Therefore, the direct measurement of nutrient stocks by the extraction procedure (or other similar assessment of nutrient reserves by strong acid) is suggested as indicative for the mineral weathering capability of forest soils to recover from P and base cation depletion by biomass harvest. [ABSTRACT FROM AUTHOR]

Along many streams, natural riparian vegetation has been replaced by agricultural fields or plantations resulting in ecosystem alterations due to changes of the interactions across the land-water ecotone. We studied the effect of restoration interventions by removing a dense spruce plantation in a 25 m wide zone along a 4 km section of a headwater stream. Water discharge, nutrient and total organic carbon concentrations were unaffected by the intervention, which only involved 0.7% of the catchment area. Focusing on the oxygen dynamics within several sections of the stream revealed that the stream water was generally oxygen under-saturated both before and after the restoration reflecting the dominance of heterotrophy over photoautotrophy typical of small streams. Oxygen saturation was tightly coupled to water discharge, with anoxia or hypoxia developing during low summer flow, and levels just below saturation during high autumn-spring flow at low temperature and low metabolism. Stream-near felling increased incident irradiance and reduced the duration and extent of summer hypoxia despite unaltered discharge, temperature and concentration of total organic carbon. Increased incident irradiance was accompanied by higher oxygen saturation in open sections compared to control sections with intact tree cover. Diel oxygen changes followed incident irradiance during low summer flow, while alterations at high winter flow were caused by changes in temperature-dependent oxygen solubility and high reaeration. In conclusion, we show that anoxic or hypoxic oxygen levels occur in warm, low-flow summer periods and this stress is reduced when intense shading from spruce plantation is removed and in-stream oxygen production is stimulated. [ABSTRACT FROM AUTHOR]

Given the key role of belowground biota on forest ecosystem functioning, it is important to identify the factors that influence their abundance and composition. However, the understanding of the ecological linkage between tree diversity and belowground biota is still insufficient. Here we investigated the influence of tree diversity (richness, True Shannon diversity index, functional diversity) and identity (proportion of evergreen leaf litter and leaf litter quality) on earthworm species richness and biomass at a continental and regional scale, using data from a Europe-wide forest research platform (FunDivEUROPE) spanning six major forest types. We found a marked tree identity effect at the continental scale, with proportion of evergreen leaf litter negatively affecting total earthworm biomass and species richness, as well as their biomass per functional group. Furthermore, there were clear litter quality effects with a latitudinal variation in trait-specific responses. In north and central Europe, earthworm biomass and species richness clearly increased with increasing litter nutrient concentrations (decreasing C:N ratio and increasing calcium concentration), whereas this influence of litter nutrients was absent or even reversed in southern Europe. In addition, although earthworms were unaffected by the number of tree species, tree diversity positively affected earthworm biomass at the continental scale through functional diversity of the leaf litter. By focusing on tree leaf litter traits, this study advanced our understanding of the mechanisms driving tree identity effects and supported previous findings that litter quality, as a proxy of tree identity, was a stronger driver of earthworm species richness and biomass than tree diversity. [ABSTRACT FROM AUTHOR]

Earthworms have a significant influence on the structure, composition and functioning of forest ecosystems, but in spite of their role as ecosystem engineers, little is known on the factors controlling their distribution across European forests. Optimised sampling techniques, as well as more advanced statistical tools and geographical information systems have facilitated studies at the landscape scale. But these, and even larger-scale studies, are scarce due to data limitations, taxonomic inconsistencies and practical issues in linking existing databases. In this continental-scale field-based study we used boosted regression tree modelling to identify and evaluate the relative importance of environmental factors explaining earthworm incidence (presence/absence) and abundance (density and biomass) in European forests. To parameterise our models earthworms were sampled in six forest landscapes along a latitudinal gradient from the boreal north to the Mediterranean south in spring or autumn of 2012, together with several environmental variables. Earthworms were sampled using a combined method of mustard extraction and hand sorting of litter and a soil monolith, after which they were weighed and identified to functional group (epigeic, endogeic and anecic). We found that litter- and soil-related variables best explained earthworm incidence and biomass in European forests, leaving only a minor role to climate-related variables. Among the litter related variables, understory vegetation played an important role in explaining earthworm incidence and abundance. The relative importance of explanatory variables differed between models for incidence, density and biomass and between earthworm functional groups. Our results suggested that threshold values for soil C:N ratio, forest floor pH and understory plant biomass and plant nutrient concentrations have to be attained before earthworms can occur. Beyond these threshold values, variables like soil C:N ratio, tree litter C:P ratio and forest floor mass further explain earthworm biomass. Mechanisms behind these observations are discussed in the light of future earthworm distribution modelling at continental scale. [ABSTRACT FROM AUTHOR]