The long-term effects of logging residue removal on forest floor nutrient capital, foliar chemistry and growth of a Norway spruce stand

This study compared the nutrient capital of the forest floor, the nutrient status of trees, and the growth of a stand of Norway spruce (Picea abies L. (Karst.)) planted on a whole-tree harvesting treatment (needles left on site) with a conventional stem-only harvesting treatment 30 years after clearcutting. No significant treatment effects were detected in the amount of organic matter, the amounts of nutrients in the forest floor, or the concentrations of foliar nutrients. The results indicate that whole-tree harvesting with the needles left on the site did not reduce the long-term nutrient capital of the forest floor or the nutritional status of trees. Whole-tree harvesting significantly reduced the height of dominant spruce compared to stem-only harvesting, however the stem volume of dominant spruce did not differ between the harvesting treatments. The greater height growth of the dominant trees in the stem-only harvesting treatment could be attributed to indirect factors other than changes in site resource availability (e.g. protection against frost damage), and hence the effect of whole-tree harvesting on potential site productivity was inconclusive due to the confounding effect of site factors. In the whole-tree harvesting treatment, the total stem volume of the stand and, consequently, the actual site productivity, was lower when compared to stem-only harvesting due to the lower density of naturally regenerated seedlings.     

Biomass retention following whole-tree, energy wood harvests in central Maine: Adherence to five state guidelines

The expansion of the bioenergy industry in Maine has led to an increase in integrated roundwood and energy wood whole-tree harvesting. A better understanding of the amounts of logging residue left unrecovered on whole-tree harvested sites will enable the refinement of available forest residue estimates for Maine and the assessment of the potential effect of such harvesting on forest health. Several states have developed biomass harvesting guidelines in response to concerns generated from an expanding bioenergy industry. In this study downed wood and snags were inventoried on twelve sites in central Maine that had recently been whole-tree harvested for roundwood and energy wood. The percentage of harvested material retained as residue on the study sites was determined. On average, 45% of the energy wood generated during the harvest was left on site. This removal efficiency must be considered when developing forest residue availability estimates. Additionally, the volumes of logging residue were compared to measurable criteria from biomass and biodiversity guidelines of several states. We found that enough fine woody material (<15 cm diameter) remained on the harvest sites to meet the guideline criteria; however, the quantities of coarse woody material (≥15 cm diameter), large logs (≥38 cm dbh), and snags (≥25 cm dbh) were insufficient to meet the guideline criteria. These deficiencies likely resulted from prior forest practices rather than from the current energy wood removal. Retaining more trees of larger sizes in the future can address this concern.     

Tracing N, K, Mg and Ca released from decomposing biomass to new tree growth. Part II: A model system simulating root decomposition on clearfell sites

The decomposing roots of harvested trees are a potential source of nutrients for new trees on both conventional and whole-tree harvested clearfell sites. Roots contain significant reservoirs of nutrients, but little is known about the magnitude and rate of their release. The aim of this study was to use stable isotope techniques in a model system to trace nutrients released by decomposing roots. Labelled biomass was obtained by growing Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings with a generous or poor nutrient supply containing elevated ¹⁵N, ⁴¹K, ²⁶Mg and ⁴⁴Ca. Labelled trees were re-potted in sand and in two contrasting soils types to remove them from the enriched isotope supply. After re-potting, the labelled above-ground biomass was harvested, removed and used in a separate study described previously (Part I of II). In the study described here (Part II of II), new Sitka spruce seedlings were planted alongside the labelled root systems. A full destructive harvest was undertaken after one growing season. Enriched ¹⁵N, ⁴¹K, ²⁶Mg, and ⁴⁴Ca were recovered in the new seedlings in both sand and soils. The elevated amounts of ¹⁵N, ⁴¹K, ²⁶Mg and ⁴⁴Ca recovered in new seedlings indicate that nutrients released from decomposing roots can make a direct contribution to the growth of new trees on restock sites. The success of this model system will provide guidance for the application of similar techniques in field experiments.     

Breakeven price of biomass from switchgrass,big bluestem,and Indiangrass in a dual-purpose production system in Tennessee

The objective was to determine the breakeven price for switchgrass (SG) (Panicum virgatum L.), a mix of big bluestem (Andropogon gerardii Vitman) and Indiangrass (BBIG) (Sorghastrum nutans L. Nash), and a combination of SG and BBIG (SG/BBIG) produced under three harvest treatments. Two-harvest treatments included a forage harvest at early boot (EB) and at early seedhead (ESH) plus a biomass harvest at fall dormancy (FD). The third harvest treatment was a single biomass harvest at FD. Mixed models were used to determine if there were differences in yield, crude protein, and nutrient removal for each of the native warm-season grass (NWSG) treatments at each harvest. The EB plus FD harvest system would be preferred over the ESH plus FD harvest system for all NWSG treatments. BBIG was the only NWSG treatment with a breakeven price for biomass that decreased with an EB harvest. For all three NWSG treatments, a producer would be better off harvesting once a year for biomass than twice for forage and biomass. The cost of harvesting and replacing the nutrients for the forage harvest was greater than the revenue received from selling the forage.     

Integrated harvesting of energy wood and pulpwood in first thinnings using the two-pile cutting method

In order to increase the harvesting volumes of energy wood and pulpwood from first thinnings, harvesting costs have to be reduced significantly. Metsäteho Oy studied the integrated harvesting of pulpwood and energy wood based on a two-pile method, where industrial roundwood (pulpwood) and energy wood fractions are stacked into two separate piles when cutting a first-thinning stand. The productivity and cost levels of the integrated, two-pile cutting method were determined, and the harvesting costs of the two-pile method were compared with those of conventional separate wood harvesting methods.In the time studies, when the size of removal was 50 dm³, the productivity in conventional whole-tree cutting was 6% higher than in integrated cutting. With a stem size of 100 dm³, the productivity of whole-tree cutting was 7% higher than in integrated cutting. The results indicated, however, that integrated harvesting based on the two-pile cutting method enables harvesting costs to be decreased to below the current cost level of separate pulpwood harvesting in first-thinning stands. The greatest cost-saving potential lies in small-sized (d_1.3 = 7-11 cm) first thinnings. The costs of forest haulage after integrated pulpwood and energy wood cutting were higher than those of separate wood harvesting because of lower removals in integrated harvesting. The results showed that when integrated wood harvesting is based on the two-pile cutting method, the removals of both energy wood and pulpwood should be more than 20-25 m³ ha⁻¹ at the integrated harvesting sites in order to achieve economically viable integrated procurement.     

Patterns and drivers of fuelwood collection and tree planting in a Middle Hill watershed of Nepal

The majority of residents in the rural Middle Hills of Nepal use fuelwood from public and private sources as their primary energy source. This study investigated fuelwood availability in accessed forests, amount of fuelwood collected, preferred tree species for fuelwood, contribution of public and private sources to total fuelwood consumption, and investment in tree planting on agricultural land. Fuelwood availability declined in the decades prior to 1990, but stabilized by 1990. Fuelwood from fifty-three species was collected from forests. Median annual per capita collection was 683 kg and predicted only by family size. Occupational castes (‘low castes’) did not show different harvesting rates than non-occupational castes and non-caste ethnic groups. Wealth was not associated with total fuelwood collection, probably because there was no fuelwood market. Most households collected fuelwood from a private source, namely trees planted on sloping, rain-fed agricultural land (bari), but this accounted for only a small portion of most households’ requirement. Bari landholding area and livestock holdings-typical measures of wealth-drove the decision to plant trees on bari land, and the number of trees that were planted. Bari-poor and landless households were consequently the most vulnerable to forest degradation, so the promotion of private fuelwood planting by large bari landholders could reduce pressure on forests and promote greater fuelwood availability for landless households. Support of community forestry emphasizing access for bari-poor and landless families could further decrease fuelwood vulnerability of poorer households.     

Integrated procurement of pulpwood and energy wood from early thinnings using whole-tree bundling

To increase the volume of energy wood and pulpwood harvested from early thinnings, their procurement costs will have to be significantly reduced. This can be done through the integration of pulpwood and energy wood procurement applying a newly-developed supply chain based on whole-tree bundling. In 2007, the first prototype of the bundle harvester capable of incorporating compaction into the cutting phase was launched. Cost savings, especially in primary and secondary transportation, can be achieved by increasing the load sizes by replacing undelimbed whole trees with bundles. The bundles can be hauled by a standard forwarder to the roadside storage area, from where they are transported by a standard timber truck to the pulp mill. Batches of bundles are then fed into a wood flow consisting of conventional delimbed pulpwood. Separation of the bundles into pulpwood and energy wood fractions does not take place until the wood reaches the debarking drum.In this feasibility study, the required productivity level of bundle harvesting (i.e., cutting and bundling) in Scots pine-dominated stands was assessed by comparing the total supply chain costs based on whole-tree bundling with those of the other pulpwood and energy wood supply chains by means of system analysis. The cost calculations indicated that whole-tree bundling enables the procurement costs to be reduced to below the current cost level of separate pulpwood and energy wood procurement in early thinnings. The greatest cost-saving potential lies in small-diameter (d_1.3 = 7-10 cm) first-thinning stands, which are currently unprofitable for conventional pulpwood procurement.     

Recovery and diversity of the forest shrub community 38 years after biomass harvesting in the northern Rocky Mountains

We investigated the long-term impact of biomass utilization on shrub recovery, species composition, and biodiversity 38 years after harvesting at Coram Experimental Forest in northwestern Montana. Three levels of biomass removal intensity (high, medium, and low) treatments combined with prescribed burning treatment were nested within three regeneration harvest treatments (shelterwood, group selection, and clearcut). Four shrub biomass surveys (pre-treatment, 2, 10, and 38 years after treatment) were conducted. Shrub biomass for all treatment units 38 years after treatment exceeded the pre-treatment level, and biomass utilization intensity did not affect shrub recovery (ratio of dry biomass at time t to pre-treatment biomass). Species composition changed immediately after harvesting (2 years); however, the species composition of treated units did not differ from the untreated control 38 years after harvesting. Biodiversity indices (Shannon’s and Pielou’s indices) also decreased immediately following harvesting, but recovered 10 years after harvesting. The responses of diversity indices over time differed among biomass utilization levels with the high-utilization level and unburned treatment producing the most even and diverse species assemblages 38 years after harvesting. Our results indicate the shrub community is quite resilient to biomass harvesting in this forest type.     

Harvesting productivity and costs when utilizing energywood from pine plantations of the southern Coastal Plain USA

For woody biomass to make a significant contribution to the United States' energy portfolio, harvesting contractors must economically harvest and transport energywood to conversion/processing facilities. We conducted a designed operational study in the Coastal Plain of North Carolina, USA with three replications of three treatments to measure harvesting productivity and costs when utilizing woody biomass. The treatments were: a conventional roundwood only harvest (control), an integrated harvest in which merchantable roundwood was delivered to mills and residuals were chipped for energy, and a chip harvest in which all stems were chipped for energy use. The harvesting contractor in this study typically delivers 2200–2700 t of green roundwood per week and is capable of wet-site harvesting. Results indicate that onboard truck green roundwood costs increased from 9.35 $ t⁻¹ in the conventional treatment to 10.98 $ t⁻¹ in the integrated treatment as a result of reduced felling and skidding productivity. Green energy chips were produced for 19.19 $ t⁻¹ onboard truck in the integrated treatment and 17.93 $ t⁻¹ in the chip treatment. Low skidding productivity contributed to high chip costs in the integrated treatment. Residual green biomass was reduced from 18 t ha⁻¹ in the conventional treatment to 4 and 3 t ha⁻¹ in the integrated and chip treatments, respectively. This study suggests that until energywood prices appreciate substantially, loggers are unlikely to sacrifice roundwood production to increase energywood production. This research provides unique information from a designed experiment documenting how producing energywood affects each function of a harvesting system.     

Allocation of five macroelements and quality of fuels derived from Norway spruce wood obtained by thinning operations

The use of forest biomass for energy production is growing in Europe and biomass energy plants market is constantly increasing. However, there is the need to define the environmental sustainability issues dealing with the emerging renewable energy scenario. In particular, the polluting emissions (i.e. PMx, NO_x and ozone) caused by the biomass combustion heavily impact on the air quality. In this context, the elemental characterization of the wood and the element allocation in the different tree organs, can provide important information about the quality of the derived wood fuels and give hints about the choice of the most appropriate combustion technique and/or the right wood fuel for a given combustion technique. Moreover, since elements have different concentrations in the different plant tissues, the preventive knowledge of the elements allocation can lead to the identification of the best harvesting strategy aimed at producing wood fuel with the lowest possible ash forming elements and environmental impact.This work focuses on the allocation in three tree compartments (foliage, branches and stem) of five important macroelements (K, Mg, Ca, N and P) in Norway spruce (Picea abies), and points out the possible effects of different harvesting strategies and tree age on the quality of the wood fuels. Results suggest that the Stem Only Harvesting is preferable to Whole Tree Harvesting system in terms of prevention of mineral content loss, as well as is preferable to avoid forest biomass from young trees because of the poorer fuel quality of the wood chips.     

The characteristics of whole-tree fuel stocks from silvicultural cleanings and thinnings

The fuel properties of small-sized whole-tree fuel stocks were studied in roadside and in-stand storages. The significance of pile cover, season and storage site on moisture content and heating value of Scots pine (Pinus sylvestris) and pubescent birch (Betula pubescence) fuel stocks were observed.When the fuel stocks are placed in a well-ventilated location moisture content may be lowered below the 40% mark during one summer period. Covering the piles will give up to 6% units lower moisture content in comparison with non-covered piles. The most benefit is gained from covering during snow melting in spring and the least in midwinter when the snow is dry.Multi-tree harvested stemwood with no limbs seasoned equally well as the whole trees both in roadside and in-stand trials. This is because the processing of multi-tree bunches caused some debarking to take place. As a result, the transpiration drying capability of whole trees was equalized by the evaporation of moisture via the open wood surface. Both assortments reached moisture contents below 30% in in-stand conditions during one summer's seasoning.The effective heating values of neither birch nor pine showed significant changes. However, heating value deviated with the composition of the fuel stock. The presence or absence of crown material was a factor.The microbial counts of mesophilic fungi in whole-tree fuel stocks were only 1% of that found in logging residues. The counts of thermo-tolerant fungi were still much smaller. Leaving the Scots pine piles uncovered will increase the number of mesophilic fungal spores and bacteria.     

The effect of cutting back willow after one year of growth on biomass production over two harvest cycles

Trials were conducted on four separate but adjacent blocks of willow at a site near Carlow, Ireland in which willow, after one growing season, was either coppiced or left to grow. Each of the four randomised complete block design trials contained a different willow genotype (Endeavor, Resolution, Terra nova and Tordis). Coppicing had no adverse effect on stool mortality but significantly increased the number of stems per stool from 2.0 to 3.3. The average, median and maximum diameters of stems from non-coppiced stools were significantly greater than those of stems from coppiced stools. Biomass from non-coppiced treatments was significantly greater than that from coppiced treatments both one year after coppicing (4.3 Mg/ha [coppiced]; 9.3 Mg/ha [non-coppiced]) and two years after coppicing (12.6 Mg/ha [coppiced]; 20.8 Mg/ha [non-coppiced]). Both coppiced and non-coppiced treatments were harvested two years after coppicing and left to grow for an additional two years. After this two year period, there was no significant difference in stem numbers per stool, stem diameter and biomass yield between the coppiced and non-coppiced treatments. All willow genotypes responded in a similar way to coppicing. The results suggest that the omission of the coppicing operation after one year of growth may increase biomass yield at the first harvest without compromising yield at the second harvest.     

Reducing the establishment costs of short rotation willow coppice (SRC) – A trial of a novel layflat planting system at an upland site in mid-Wales

Two mechanical planting systems, the traditional Turton Step planter and a prototype layflat planter, were compared for the planting and establishment of short rotation willow coppice (SRC) at an upland site in Mid-Wales. Planted during March 2000, both plots were monitored for three seasons and after this establishment phase monitoring continued for the layflat planted plot until year three of a second rotation. Establishment parameters of stem density, survival rates and estimated biomass yields of a range of willow varieties during the first three years growth were greater for the layflat planted willows than step planted. At the first harvest (4 growing seasons), layflat planted willows achieved mean yields of 6.22 odt ha^?1 yr^?1, three years into the second rotation estimated yields ranged from 1.99 odt ha^?1 yr^?1 to 12.34 odt ha^?1 yr^?1 (mean of 8.14 odt ha^?1 yr^?1). Since layflat planting has been shown to reduce planting costs by up to 48%, and yields achieved were equivalent to traditionally planted SRC, it is clear that this method of planting could provide an economic alternative to the traditional step planter. It is recommended that further trials take place using new varieties available, particularly to investigate stem density/thinning effects and harvesting time, and also to test recent modifications to the planter which allow adjustable planting depth for planting under drier soil conditions.     

Tracing N, K, Mg and Ca released from decomposing biomass to new tree growth. Part I: A model system simulating harvest residue decomposition on conventionally harvested clearfell sites

It is necessary to assess the effects of removing nutrient-rich harvest residues (brash) from clearfell sites because there is a growing market for this brash as bioenergy. The aim of this study was to use stable isotope techniques in a model system to trace nutrients released by decomposing brash. Labelled biomass was obtained by growing Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings with a generous or poor nutrient supply containing elevated ¹⁵N, ⁴¹K, ²⁶Mg, and ⁴⁴Ca. This biomass was used in two subsequent studies. In this study (Part I of II), the above-ground biomass was harvested and placed on soil in a pot containing a newly planted seedling. Soils from two forests, Ae and Teindland, of contrasting nutritional status were used. A full destructive harvest was undertaken after one growing season. Enriched ¹⁵N, ⁴¹K, ²⁶Mg, and ⁴⁴Ca were recovered in the new seedlings. The percentage contribution from labelled biomass to new tree growth was small, but discernible. The N contribution from labelled biomass to new trees was greater in Ae soil, but the base cation contribution was greater in Teindland soil. Results are discussed with reference to the initial nutrient concentrations of each soil. The elevated ¹⁵N, ⁴¹K, ²⁶Mg and ⁴⁴Ca in new seedlings indicate that nutrients in brash can make a direct contribution to new tree growth. The success of this model system will provide guidance for the application of similar techniques in field experiments.     

Effects of delayed winter harvest on biomass yield and quality of napiergrass and energycane

Napiergrass (Cenchrus purpureus (Schumach.) Morrone) and energycane (Saccharum hyb.) are perennial grasses that are well-suited for biomass production in the southeastern USA. The purpose of this study was to determine the effects of delayed winter harvest on biomass yield and quality of these grasses. The study was conducted on two adjacent sites near Midville, GA. Each site used a split-plot design with four replications, with species as the main plot, and harvest times (December, January, or February) as sub-plots. Dry matter (DM) yields were measured by mechanical harvesting, and a sample of biomass was taken from each harvest for determination of ethanol production by simultaneous saccharification and fermentation (SSF). Biomass moisture, N, P, K, and ash mass fractions were also measured. Energycane DM yields were stable from December (46.8 Mg ha⁻¹) to January (42.9 Mg ha⁻¹), but then declined (36.8 Mg ha⁻¹), while napiergrass yields declined sharply from December (47.0 Mg ha⁻¹) to January (35.0 Mg ha⁻¹). Napiergrass moisture mass fraction was reduced by an average of 18% in February harvests compared to December. Mass fractions of N, K, and ash tended to decrease with later harvesting, but sometimes increased due to changes in biomass composition. Delaying harvest of napiergrass from December to January reduced N removal by an average of 144 kg ha⁻¹, while delaying harvest of energycane to February reduced N removal by an average of 54 kg ha⁻¹. In SSF, later-harvested energycane produced less ethanol per unit of DM while napiergrass was less affected by harvest date.     

Management alternatives of energy wood thinning stands

Energy wood thinning has become a feasible treatment alternative of young stands in Finland. Energy wood thinnings have been carried out mainly in stands where precommercial thinning has been neglected and the harvesting conditions for industrial wood thinning are difficult. Despite of its positive effects on harvesting costs and on renewable energy potential, whole-tree harvesting has been constantly criticized for causing growth loss. In this paper, the profitability of energy wood thinning was studied in 20 Scots pine-dominated stands where energy wood thinning was carried out. The growth of the stands after thinning was predicted with the help of Motti-stand simulator. Entire rotation time of the stands was simulated with different management alternatives. The intensity of first thinning and recovery level of logging residues varied between alternatives. In order to attain acceptable harvesting conditions, industrial wood thinning had to be delayed. The effect of energy wood thinning on subsequent stem wood growth was almost the same as in conventional thinning. Whole-tree harvesting for energy proved to be profitable alternative if the stumpage price is around 3€ m⁻³, the interest rate is 3% or 5% and the removal of pulpwood is less than 20 m³ ha⁻¹. If the harvestable pulpwood yield is over 20 m³ ha⁻¹, integrated harvesting of industrial and energy wood or delayed industrial wood harvesting becomes more profitable.     

Comparative analysis of harvesting machines on an operational high-density short rotation woody crop (SRWC) culture: One-process versus two-process harvest operation

Short rotation woody crops (SRWCs) are being studied and cultivated because of their potential for bioenergy production. The harvest operation represents the highest input cost for these short rotation woody crops. We evaluated three different harvesting machines representing two harvesting systems at one operational large-scale SRWC plantation. On average, 8 ton ha⁻¹ of biomass was harvested. The cut-and-chip harvesters were faster than the whole stem harvester; and the self-propelled harvester was faster than the tractor-pulled. Harvesting costs differed among the harvesting machines used and ranged from 388 € ha⁻¹ to 541 € ha⁻¹. The realized stem cutting heights were 15.46 cm and 16.00 cm for the tractor-pulled stem harvester and the self-propelled cut-and-chip harvester respectively, although a cutting height of 10 cm was requested in advance. From the potential harvestable biomass, only 77.4% was harvested by the self-propelled cut-and-chip harvester, while 94.5% was harvested by the tractor-pulled stem harvester. An increase of the machinery use efficiency (i.e. harvest losses, cost) is necessary to reduce costs and increase the competitiveness of biomass with other energy sources.     

Energy trade-offs between intensive biomass utilization, site productivity loss, and ameliorative treatments in loblolly pine plantations

Loblolly pine plantations are the most important source of forest products in the US and the slash remaining after conventional harvest represents a significant potential source of bioenergy. However, slash removal in intensive harvests might, under some circumstances, reduce site productivity by reducing soil organic matter and associated nutrients. Two complimentary studies in the Gulf Coastal Plain of the southeastern US were designed to test whether harvest intensity (level of biomass removal) could have a negative long-term impact on site productivity. Harvesting tree crowns in addition to the merchantable bole had a negative impact (18%) on pine biomass accumulation by age 7–10 years on 15 of 19 research blocks. Sites at risk of harvest-induced reductions in productivity were relatively unproductive prior to harvest and had low soil phosphorus (P) concentrations. Intensive harvesting, fertilization, and chemical control of non-crop vegetation were all energy efficient; the additional biomass energy gained through these practices was two-orders of magnitude greater than the energy needed to conduct the activities. Harvest of slash for bioenergy in the Gulf Coastal Plain of the southeastern US has the potential to reduce productivity on infertile soils, but fertilization has the potential to restore and even improve productivity on those sites in an energy-efficient way.     

Reed canary grass yield and fuel quality in Estonian farmers’ fields

Reed canary grass (Phalaris arundinacea) is one of the possible raw materials for bioenergy production in northern Europe. Its cultivation is favoured because its high productivity and local origin. However, problems with the biomass quality for combustion have been reported. Usually delayed harvest in spring is suggested to improve the quality and decrease the moisture content of biomass. On the other hand, the feasibility of spring harvest depends on local climatic conditions and may cause yield losses. In current paper we studied reed canary grass fields in Estonia locating on different soil types and cultivated with various varieties. The influence of several fertilisation schemes on biomass yield was analysed. Our results indicated that production was higher on mineral soils than on the organic soil of abandoned peat extraction sites. Even different types of fertilisation did not increase the production on organic soils to the level comparable to those on mineral soils. Among studied varieties ‘Venture’ had the highest production. The highest yield per area was obtained late in the autumn (12.7 t d.w. per ha and 7.2 t d.w. per ha on mineral and organic soils, respectively). By spring the amount of biomass had decreased in all studied sites. Due to wet soil some of the fields remained unharvested, the others had high yield losses during practical harvesting. The chemical analyses did not reveal significant differences in the composition of biomass between late autumn and spring. Therefore we conclude that late autumn harvest should be preferred in local climatic conditions.