Whole-tree Harvesting Research Articles

Using Macronutrient Distributions within Trees to Define a Branch Diameter Threshold for Biomass Harvest in Sugar Maple-Dominated Stands

As the use of forest harvesting residues for energy production gains popularity, debate continues regarding the long-term sustainability of whole tree harvesting (WTH). This practice removes nutrient-rich twigs that only account for a small fraction of harvest residues, emphasising the need to develop nutrient-efficient alternatives to WTH. This study assessed N, P, K, Ca, and Mg distributions within sugar maple (Acer saccharum Marshall) and yellow birch (Betula alleghaniensis Britton) branches of various sizes in order to determine the branch diameter threshold that would represent the best compromise between the quantity of harvested biomass and nutrient losses that were generated. Quantities of nutrients that were exported with harvesting were then modelled at the stand level using different biomass harvest scenarios to explore what factors ultimately drove total quantities of nutrients exported with harvest. We found that the branch diameter threshold for biomass harvesting should be set at 2 cm for most nutrients in both tree species. An exception was Mg in yellow birch, for which the harvesting of branches larger than 10 cm would always generate larger nutrient export than gains in terms of biomass. At the stand scale, we provide evidence that the intensity of biomass harvest (i.e., the number of branch compartments harvested) is the principal factor responsible for the quantity of nutrient that is exported with harvesting.

The effect of salvage logging on surface fuel loads and fuel moisture in beetle-infested lodgepole pine forests

Widespread tree mortality from mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) outbreaks has prompted forest management activities to reduce crown fire hazard in the Rocky Mountain region. However, little is known about how beetle-related salvage logging and biomass utilization options affect woody surface fuel loads and fuel moisture dynamics. We compared these attributes in salvage-logged lodgepole pine (Pinus contorta var. latifolia Engelm. Ex S. Wats.) stands harvested using either biomass removal (whole-tree harvest) or biomass retention (bole only harvest) prescriptions with untreated MPB-infested stands. Both prescriptions roughly doubled 1-h and 10-h fuel loads compared to untreated forest. Biomass retention left ten times more 1000-h fuels compared to biomass removal prescription (28 vs 3Mgha−1). Overall, the woody fuel load was more than twice as high with biomass retention compared to biomass removal (60 vs 25Mgha−1). Fuel moisture content was lower in salvage logged units compared to untreated forest plots, but it did not differ among the biomass prescriptions. Fine (10-h) and heavy (1000-h) fuels dried to a critical ignition threshold 3–8weeks earlier in the two prescriptions, respectively, compared to the untreated forests. Salvage logging removes canopy fuels and crown fire hazard, but we found that depending on the amount of biomass retained it can both increase surface fuel load and decrease fuel moisture compared to untreated stands. In the coming years, snag fall will transfer crown to surface fuels in untreated beetle-killed stands adding coarse surface fuel loads surpassing those in treated stands.

Effect of Timber Harvest Intensities and Fertilizer Application on Stocks of Soil C, N, P, and S

The purpose of this study was to determine the stocks of available P and S, total N, and oxidizable C at depth in an Oxisol cultivated with Eucalyptus in Brazil following different timber harvest intensities and fertilizer application over 12 years. The harvest regimes considered were (i) conventional stem-only harvest (all forest residues were maintained on the soil); (ii) whole-tree harvest (only litter was maintained on the soil—all slash, stemwood, and bark were removed); and (iii) whole-tree harvest + litter layer removal. The site was planted in 2004 considering three timber harvest intensities, some with and some without N and P fertilization. In 2012 the experiment was reinstalled, and all the treatments were reapplied in the each plot. From 2004 to 2016, nutrient accumulation and soil N, P, and S stocks were assessed in the 0–20 cm layer. Also in 2016, soil N, P, S, and oxidizable C stocks were measured to 2 m depth. For each treatment, the net balance of N, P, and S were calculated from soil stocks and harvest outputs during two forest rotations. A reduction in all nutrient stocks was observed in the 0–20 cm layer for all treatments. For N, this reduction was 20% smaller in the stem-only harvest treatment and 40% higher when no N fertilizer was applied, when compared to other treatments. Stem-only harvest treatment was observed to reduce the loss of N, P, and S due to harvest by 300, 30, and 25 kg·ha−1, respectively, when compared to the whole-tree harvest + litter layer removal treatment.

Impact of whole-tree harvest on soil and stream water acidity in southern Sweden based on HD-MINTEQ simulations and pH-sensitivity

The shift in major drivers of acidification from sulfur deposition to biological acidification has put the focus on the impact of biomass harvest for bioenergy on the acid base status of forests soils and surface waters. This paper presents a model-based assessment in which the impact of whole-tree harvest (WTH) is compared with that of no harvest at two different sulfur deposition levels by use of the HD-MINTEQ model. Additionally, the pH-sensitivity of 179 randomly selected boreal headwater streams was assessed. The results indicate that the exchangeable Ca2+ pool in humus and mineral soils (⩽B-horizon) is most affected by harvest. Concerning the pH, the WTH impact is restricted to shallow soils and for a much shorter period of time. The impact of WTH on the soil solution was primarily restricted to the recharge area and much less pronounced in the discharge area. Due to high buffering capacity of riparian soils and low pH-sensitivity of many headwater streams, the pH effects of WTH on surface waters will most probably be small, at least over a rotation period of several decades. Over time perspectives of multiple rotations, the pH effects are more uncertain due to a possible slow successive protonation of organic matter in the riparian zone. Another important aspect is the currently restricted availability of mobile anion charge balancing the acidity produced by tree growth. Therefore, the acidity is to a large extent arrested in the soil. At the current low S deposition levels, southwestern Sweden seems to be the least vulnerable region to further acid input due to high buffer capacity at low pH. The streams in central and northern Sweden are much more pH-sensitive, but restricted availability of mobile strong acid anions and large buffer capacity in the soils make them less vulnerable to WTH. The partly diverging results between experimental and model studies indicate that one or more processes (hydrological, chemical or biological) are not fully understood or that available data are lacking for a proper parameterization. Thus, the results from long-term WTH experiments are very important for understanding the processes involved as well as for improving and validating model predictions. We therefore encourage societal support of maintaining monitoring and research coupled to such experiments. For the future and for improving our current understanding of biogeochemical dynamics in forest ecosystems subjected to active forestry as well as for policy and management purposes, a mixture of experiments and models ought to be used.

Carbon and nitrogen pools and mineralization rates in boreal forest soil after stump harvesting

The use of forest-derived biomass has steadily increased in Finland and Sweden during the past decades leading to more intensive forest management practices in the region, such as whole-tree harvesting, both above- and belowground. Stump harvesting results in a direct removal of stump and coarse-root carbon (C) from the stand and can cause extensive soil disturbance, which has been suggested to increase C mineralization. In this study, the effects of stump harvesting on soil C and nitrogen (N) mineralization, and soil surface disturbance were studied in two different clear-felled Norway spruce (Picea abies) sites in Central Finland. The treatments were whole-tree harvesting (WTH, removal of stems and logging residues), and WTH and stump harvesting (WTH+S). Both sites, Honkola (2 stands) and Haukilahti (6 stands) were mounded. In both treatments, soil samples were taken from different soil layers down to a total depth of 20cm in the mineral soil from (i) mounds, (ii) undisturbed soil and (iii) pits. The sampling was performed 11–12years after treatments. Soil C and N mineralization rates were determined in laboratory incubation experiments. In addition, total C and N pools (gm−2) were estimated for each disturbance class and soil layer. Soil C and N pools had a tendency to be lower following stump harvesting, but no statistically significant treatment effect was detected. Stump harvesting increased soil mixing as indicated by a significant decrease in C concentration in the mound disturbance class. There was no significant effect of stump harvesting on soil C mineralization rates. A combination of mineralization rates and soil pool data showed that field C mineralization (g CO2-Cm−2yr−1) did not significantly differ between stands where stumps were removed or were retained. Further, stump harvesting did not seem to have any stimulating effect on soil CO2 efflux 11–12years after treatment.

Should harvest residues be left on site in peatland forests to decrease the risk of potassium depletion?

Sufficiency of potassium (K) is one of the biggest concerns for forestry in boreal peatlands, since the rooting zone stores of K in thick peat soils are generally small and significant proportion of the K in ecosystem is bound in stand biomass. Increased demand for bioenergy may lead to intensified harvesting also in such forests. There is thus an urgent need to study the significance of the nutrients in harvest residues for the next-generation forest productivity. The specific questions in peatland forests are whether the harvest residues are an important source of K to the restock or whether the K in harvest residues is lost by leaching. We quantified K losses from drained peatland forests following management by clear-felling with stem-only harvesting (SOH), whole-tree harvesting (WTH) and whole-tree harvesting plus stump harvesting (WTHS). Calibration period – control area method and mixed modelling approach were used to analyze the ditch-outflow K-concentration and water-borne K-export data from 17 harvested and 5 control catchments in southern and central Finland. K concentrations and runoff were monitored for 1–2years before and 3–4years after treatment. Supplementary long-term data from one pair of harvested and non-managed catchments was used to assess the duration of the harvest impact on K export.Mean annual K concentrations in ditch outflow were higher after than before harvesting. The concentrations started to increase during the second or third post-harvest year, reaching the peaks of 1.1–2.2mgL−1 in WTHS, 0.8–1.7mgL−1 in WTH, and 1.0–1.9mgL−1 in SOH. The concentrations correlated positively with the amount of K in the surface peat. In nutrient-poor ombrotrophic sites, the K concentrations were higher for sites with shallower water-table level.Using the supplementary data, the impact of harvesting on K losses was estimated to last for about eight years. The overall estimated K loss was about 28kgha−1 from minerotrophic sites, and about 9kgha−1 from ombrotrophic sites. There was no significant difference in K losses between the harvest treatments SOH, WTH and WTHS, indicating that the K in harvest residues was largely retained onsite. The role of K losses induced by harvesting in the site K stores in drained peatland forests is discussed.

Integrated supply of stemwood and residual biomass to forest-based biorefineries

ABSTRACTThe demand for forest biomass as raw material for a wide range of products in the developing bioeconomy is expected to increase. Along with a constant pressure on forestry to increase its productivity, this development has led to the search for new procurement methods and new assortments. The present study assessed innovative supply chain practices, with a particular focus on the integrated supply of stemwood and residual tree parts. The assortments considered included tree sections, long tops, saw logs with stump cores and small whole trees from thinnings. The assessment included geographically explicit modelling of the supply chain operations and estimation of supply cost and energy use for three industrial locations in Northern Sweden. The innovative supply chains were compared to conventional, separate, harvest of stemwood and logging residues. We conclude that integrated harvest of tops and branches with stemwood assortments, as well as whole-tree harvest in early thinnings, has a significant potential to reduce the supply cost for the non-stemwood assortments. Stump wood generally remains the most expensive assortment. The energy use analysis confirms earlier research showing that the energy input is relatively small compared to the energy content of the harvested feedstock.ABBREVIATIONSBWT, bundled whole trees; CTL, cut-to-length; ET, energy thinning; FF, final felling; FT, first thinning; LR, logging residues; LT long tops; ORN, Örnsköldsvik; PCT, pre-commercial thinning; PL, pulpwood; RS, roughly delimbed tree sections; SEK, Swedish currency; SFA, Swedish Forest Agency; SL, sawlogs; SNFI, Swedish National Forest Inventory; SP, stumps; SPC stump core; ST, second thinning; STO, Storuman; UME Umeå; WT, whole small trees;

Short-term effects of whole-tree harvesting on understory plant species diversity and cover in two Norway spruce sites in southern Norway

ABSTRACTEffects of clear-cut harvesting on ground vegetation plant species diversity and their cover are investigated at two Norway spruce sites in southern Norway, differing in climate and topography. Experimental plots at these two sites were either harvested conventionally (stem-only harvesting) or whole trees including crowns, twigs and branches were removed (whole-tree harvesting), leaving residue piles on the ground for some months. We compare the number of plant species in different groups and their cover sums before and after harvesting, and between the different treatments, using non-parametric statistical tests. An overall loss of ground vegetation biodiversity is induced by harvesting and there is a shift in cover of dominant species, with negative effects for bryophytes and dwarf shrubs and an increase of graminoid cover. Differences between the two harvesting methods at both sites were mainly due to the residue piles assembled during whole-tree harvesting and the physical damage made during the harvesting of residues in these piles. The presence of the residue piles had a clear negative impact on both species numbers and cover. Pile residue harvesting on unfrozen and snow-free soil caused more damage to the forest floor in the steep terrain at the western site compared to the eastern site.

Sustainable use of eucalypt biomass grown on short rotation coppice for bioenergy

Bioenergy is one of the alternatives to reduce the dependence of global energy on fossil fuels. The short rotation coppice (SRC) of eucalypt species appears as an interesting option for forest biomass production in a short time. However, the harvesting of whole trees (included the crown) in SRC systems has implications on sustainable land use. More information is required on the increase of biomass as renewable energy resource to achieve the sustainability of these crops. The main objective of this research was to evaluate the sustainable use of biomass from very high-density eucalypt plantations, managed at tropical conditions for bioenergy. To accomplish this objective, the tree was fractionated into three fractions: stem, branches, and leaves, and there was determination of the dry matter, energy yield, and nutrients export. This experiment used a short rotation coppice, a hybrid clone of Eucalyptus urophylla × Eucalyptus grandis, of 2 years old. According to the results obtained, the density planting and fertilization levels have a greater influence on the dry matter yield, energy yield, and nutrient exports. The higher density planting reaches mean values of 30.9 tonnes of dry matter per hectare (t DM ha−1) and 743.3 GJ ha−1. Considering the biomass yield and nutrients export of short rotation coppice of eucalypt, the higher density planting with the lower dose of fertilization is more indicative of sustainable use. The leaves have an important participation in nutrients export and should be retained in the soil of forest.

Long-term soil calcium depletion after conventional and whole-tree harvest

Whole-tree harvest (WTH) may compromise tree productivity and health and lead to soil and surface water acidification. The aim of this study was to assess the long-term change (up to circa 40years) in soil exchangeable calcium (Ca2+) pools following conventional (CH) and WTH at three Swedish coniferous sites. A second aim was to evaluate how well the results could be reproduced by the dynamic model MAGIC (Model of Acidification of Groundwater in Catchments). Soil Ca2+ pools (down to 20cm) decreased at all three sites from stand age 15–16 to 37–38years. The depletion ranged from 2.6 to 8.6kEqha−1 (26.5–52.7%) and 0.2 to 5.0kEqha−1 (2.3–49.1%) in the CH and WTH treatment, respectively. The presence of an interaction effect indicated that the main effect of time was not statistically significant at all three sites. Over the course of time, soil Ca2+ pools have also become more similar between the CH and WTH treatments, but the Ca2+ pools were still significantly lower (p<0.05) after WTH at stand age 37–38years. The measured declines in Ca2+ pools were generally greater than what has been found in other studies and were largely explained by high soil Ca2+ availability and high tree Ca2+ uptake, especially in the CH-plots, as indicated by the MAGIC mass balance budgets. Model simulations by MAGIC partly agreed with the measured data. However, the model exaggerated the soil Ca2+ losses between 1990 and 2013 (CH=3.6–9.9kEqha−1; WTH=3.0–8.3kEqha−1), especially at the spruce sites. Furthermore, MAGIC could not reproduce the rapid diminishing differences between CH and WTH. Uncertainties in model parameters, underestimated soil Ca2+ pools or biological feed-back mechanisms could explain this discrepancy. Until these have been resolved, interpretations of Ca2+ changes related to CH or WTH using dynamic modelling or mass balance budget calculations should be done with caution.

Impacts of forest harvesting on mobilization of Hg and MeHg in drained peatland forests on black schist or felsic bedrock.

Forest harvesting, especially when intensified harvesting method as whole-tree harvesting with stump lifting (WTHs) are used, may increase mercury (Hg) and methylmercury (MeHg) leaching to recipient water courses. The effect can be enhanced if the underlying bedrock and overburden soil contain Hg. The impact of stem-only harvesting (SOH) and WTHs on the concentrations of Hg and MeHg as well as several other variables in the ditch water was studied using a paired catchment approach in eight drained peatland-dominated catchments in Finland (2008-2012). Four of the catchments were on felsic bedrock and four on black schist bedrock containing heavy metals. Although both Hg and MeHg concentrations increased after harvesting in all treated sites according to the randomized intervention analyses (RIAs), there was only a weak indication of a harvest-induced mobilization of Hg and MeHg into the ditches. Furthermore, no clear differences between WTHs and SOH were found, although MeHg showed a nearly significant difference (p = 0.06) between the harvesting regimes. However, there was a clear bedrock effect, since the MeHg concentrations in the ditch water were higher at catchments on black schist than at those on felsic bedrock. The pH, suspended solid matter (SSM), dissolved organic carbon (DOC), and iron (Fe) concentrations increased after harvest while the sulfate (SO4-S) concentration decreased. The highest abundances of sulfate-reducing bacteria (SRB) were found on the sites with high MeHg concentrations. The biggest changes in ditch water concentrations occurred first 2years after harvesting.

Can increased weathering rates due to future warming compensate for base cation losses following whole-tree harvesting in spruce forests?

Whole-tree harvesting, i.e. harvesting of stems, branches and tops, has become increasingly common during recent decades due to the increased demand for renewable energy. Whole-tree harvesting leads to an increase in base cation losses from the ecosystem, which can counteract recovery from acidification. An increase in weathering rates due to higher temperatures is sometimes suggested as a process that may counteract the acidifying effect of whole-tree harvesting. In this study the potential effect of increasing temperature on weathering rates was compared with the increase in base cation losses following whole-tree harvesting in spruce forests, along a temperature gradient in Sweden. The mechanistic model PROFILE was used to estimate weathering rates at National Forest Inventory sites at today’s temperature and the temperature in 2050, as estimated by two different climate projections. The same dataset was used to calculate base cation losses following stem-only and whole-tree harvesting. The calculations showed that the increase in temperature until 2050 would result in an increase in the base cation weathering rate of 20–33 %, and that whole-tree harvesting would lead to an increase in base cation losses of 66 % on average, compared to stem-only harvesting. A sensitivity analysis showed that moisture changes are important for future weathering rates, but the effect of the temperature change was dominating even when the most extreme moisture changes were applied. It was concluded that an increase in weathering rates resulting from higher temperatures would not compensate for the increase in base cation losses following whole-tree harvesting, except in the northernmost part of Sweden.

Long-term effect of whole tree biomass harvesting on ground cover vegetation in a dry Scots pine stand

Long-term (47 years) effect of experimental whole tree harvesting (WTH) with a heavy soil scarification on ground cover vegetation was assessed in a dry nutrient-poor Scots pine ( L.) stand in Latvia. Neighbouring conventionally managed young (10 years) and mature (119 years) stands of the same type were used for comparison. Higher species richness was observed in the WTH stand compared to conventionally managed young and mature stands (24, 18 and 16 species, respectively), likely due to the profound disturbance. The Shannon diversity index was higher in the young than in the WTH and mature stands (2.36, 1.77 and 1.63, respectively); still, the composition and structure of ground cover vegetation in WTH was more similar to the mature stand. Nevertheless, the occurrence of oligotrophic species in the WTH stand suggested decreased soil nutrient content and potential development of different plant community. Hence, such method might be considered for restoration of oligotrophic stands. Nevertheless, the period of 47 years appeared sufficient for the ground cover vegetation to recover after the WTH.Pinus sylvestris

Elemental Ratios in Foliage and Soil of a Jeffrey Pine Stand Subjected to Thinning and Burning Restoration Practices

Forest thinnings accomplished through cut-to-length and whole-tree harvesting followed by a prescribed underburn were assessed for their influences on mineral nutrition in eastern Sierran Jeffrey pine (Pinus jeffreyi Grev. & Balf.). As derived from foliar elemental concentrations determined at six samplings distributed over three growing seasons, molar Ca/Al, Mg/Al, K/Al, Ca/Mn, Mg/Mn, and K/Mn were generally higher in the unthinned treatment and lower in burned stand portions. Conducted under drought conditions, the driest phase of the study resulted in lower Ca/Al, Mg/Al, and K/Al and higher Ca/Mn and Ca/Zn when averaged across treatments. Foliar K/Mn, K/Zn, and K/Cu were generally lower in the early portion of the growing season compared to the late portion. At mid growing season, Mg/Al, K/Al, Mg/Mn, K/Mn, K/Fe, K/Zn, and K/Cu were higher in young needles while Ca/Al, Ca/Fe, Mg/Fe, Ca/Zn, Ca/Cu, and Mg/Cu were so in older ones. At mid study, soil Ca/Fe was higher in the unthinned treatment generally and especially in its unburned portion while K/Cu was higher overall in burned stand portions, most especially in the unthinned treatment. These findings provide insight into the interrelationships of base cations and metallic elements in forest nutrition as influenced by restoration practices.

Mechanized Thinning, Prescribed Fire, and Needle Age Influences on the Mineral Nutrition of Jeffrey Pine: Elemental Concentrations in Foliage and Soil

Forest thinnings using cut-to-length and whole-tree harvesting approaches followed by prescription underburning were assessed for their influences over multiple growing seasons on the mineral nutrition of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) on a Sierran site. Specifically examined were foliar and soil elemental concentrations encompassing macronutrients and micronutrients plus Al. Foliar N was higher in thinned stand subunits initially before transitioning to a relatively elevated concentration in the burned portion of either the cut-to-length or wholetree subunits, while higher foliar S in the burned cut-to-length treatment combination was evident in the last two of the six sampling periods. Foliar Mn was usually higher in the burned whole-tree combination while B and Al were often higher in burned stand portions but with less specificity regarding thinning treatment. At mid growing season, N, P, K, S, Fe, and Cu were higher in young needles while Ca, Mn, and Al were so in older ones. Near mid study, mineral soil Ca was higher in the unthinned subunit while Mg, Fe, Mn, Zn, and Cu were higher in unburned stand portions.

Changes in forest floor and soil nutrients in a mixed oak forest 33 years after stem only and whole-tree harvest

Vegetation, forest floor, and soils were resampled at a mixed oak site in eastern Tennessee that had been subjected to stem only (SOH), whole-tree harvest (WTH), and no harvest (REF) 33years previously. Although differences between harvest treatments were not statistically significant (P<0.05), average diameter, height, basal area and biomass were 8–18% lower in the WTH than in the SOH treatment 33years after harvest whereas they differed by 2% 15years after harvest. In contrast to results 15years post-harvest, total forest floor mass and nutrient contents were twofold greater in the WTH than in the SOH treatment at 33years post-harvest, due largely to differences in Oa horizon mass. Soil total C concentrations increased significantly (P<0.05) over the first 15years post-harvest in both harvest treatments. Decreases in soil C between 15 and 33years post-harvest were not statistically significant. Soil total N increased significantly in both harvest treatments over the first 15years post-harvest. Consistent decreases in soil total N occurred in the WTH treatment between years 15 and 33 post-harvest that bordered on statistical significance whereas total N was stable over that time period in the SOH treatment. The increases and decreases in soil N content cannot be explained by any known processes of N inputs or outputs. Harvest treatment effects on both Ca2+ and Mg2+ observed at 15years post-harvest are still observable and significant at 33years post-harvest, although decreases between 15 and 33years were found. Treatment effects and changes in soil exchangeable Ca2+ and Mg2+ are consistent with known inputs from decomposing logging residues, inputs from atmospheric deposition, and increments in forest floor and vegetation. No treatment effects were found for soil extractable P, but steady decreases over time were found. No treatment or time effects were found for soil exchangeable K+.

Carbon storage and nutrient mobilization from soil minerals by deep roots and rhizospheres

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.

Response of soil nutrient content, organic matter characteristics and growth of pine and spruce seedlings to logging residues

The aim of this study was to determine the effects of different amounts of logging residues on soil properties and growth of Scots pine and Norway spruce seedlings 10years after clear-felling. The field experiments consisted of two Scots pine and four Norway spruce experiments. The treatments, on three replicate 8m∗8m plots in all field experiments, were whole-tree harvesting, i.e. harvesting all the above-ground biomass with no logging residue left on the site (R0), stem-only harvesting, leaving logging residues on the site (R1), and stem-only harvesting with double the amount of logging residues left on the site (R2). In the R1 treatment the amount of logging residue in the spruce stands was 39–54Mgha−1 dry mass and in the pine stands, 11–18Mgha−1 dry mass. Over all sites, logging residues had no consistent effects on seedling growth, amounts of soil carbon and nutrients or organic matter characteristics. In some spruce experiments, however, logging residues increased the average diameter, height and height growth (last three years), as well as the number of seedlings, stem volume and biomass. In pine experiments, logging residues had no effect on tree or stand characteristics. In one pine experiment the amounts of exchangeable base cations increased, and there were also changes in the quality of organic matter: the C/N ratio decreased, and NH4–N, microbial biomass N and C mineralization increased due to residues. In the spruce experiments and the other pine experiment, the effect of logging residues on the soil properties measured was slight. Logging residues did not affect NO3–N concentrations or rates of net nitrification, which in most soils were both negligible. Seedling height and height growth correlated strongly and positively with net N mineralization and its ratio to microbial biomass N. All in all, logging residues improved tree and stand characteristics generally in spruce stands, but the effects on soil properties and processes, if any, occurred mostly in one pine stand. This poor correspondence may point to other changes brought on by the logging residues, such as changes in physical environment or decreased competition with ground vegetation, being more important for seedling growth than nutrient status was.

Strong negative impacts of whole tree harvesting in pine stands on poor, sandy soils: A long-term nutrient budget modelling approach

Global environmental changes such as climate change, overexploitation and human population growth increase the interest in woody biomass from forests as a resource for green energy, chemistry and materials. Whole Tree Harvesting (WTH) can provide additional woody biomass, mainly for bioenergy, by harvesting parts of the crown not harvested under conventional Stem-Only Harvesting (SOH). However, WTH also increases nutrient export, potentially depleting soil nutrients and threatening future stand productivity. Here we assess the impacts of WTH in Corsican pine stands (Pinus nigra ssp. Laricio var. Corsicana Loud.) with a rotation period of 48years on poor, sandy soils in Belgium. We performed a detailed nutrient budget assessment before and after thinnings and clear-cuts under scenarios of WTH and modelled the long-term changes in ecosystem nutrients under both WTH and SOH. Our results demonstrate a strong immediate impact of WTH on aboveground nutrient stocks (mainly in clear-cuts). In clear-cuts with WTH, half of the base cations (calcium, potassium, magnesium) in the trees and forest floor were exported. The amount of available cations in the soil is not sufficient to immediately compensate for this export. Only one fourth of the amount exported were available for biota in the top 50cm of the soil. We also modelled long-term development of ecosystem nutrients (available nutrients in the soil and nutrients in trees and forest floor) and found that the available soil calcium, potassium and phosphorus stocks are insufficiently replenished by deposition and weathering to sustain WTH on the long term. We found no indications of potential depletion of ecosystem cations and phosphorus for the next ten rotation periods under SOH management. Our results thus support a less intensive management in pine stands on poor, sandy soils, for instance, by adopting SOH and/or longer rotation periods.

Logging operations in pine stands in Belgium with additional harvest of woody biomass: yield, economics, and energy balance

Due to the enhanced demands for woody biomass, it is increasingly relevant to assess possibilities to harvest forest residues in addition to logs. Here, eight strategies for whole-tree harvesting from clearcuts and early thinnings of pine (Pinus nigra Arnold) stands in northern Belgium are evaluated. A detailed cost analysis using the machine-rate method was conducted along with scenario and sensitivity analyses of the variables affecting the harvesting cost. On average, we found much higher revenue for logs than for wood chips from forest residues. In clearcuts, a mobile chipper was more profitable than a roadside chipper. On the other hand, the harvesting cost of logs was higher for early thinnings than for clearcuts. However, the revenue remained higher than for chips, making the separate harvesting of logs and chips more cost effective than chipping whole trees. In the latter case, an excavator, a forwarder, and a roadside chipper were more cost effective than a harvester, a tractor with trailer, and a mobile chipper, respectively. Harvest of additional woody biomass required limited energy input compared with processing and intercontinental transportation of wood pellets. However, at present, we find very small profits from local additional biomass harvests. The low and fragmented forest cover and important sustainability issues further impede the development of a viable production sector in this region.