Comparison of ground disturbance of frozen peatland during stump harvesting using a stump drill and rake

ABSTRACT

Tree stumps could be a source of renewable energy, contributing to a reduced dependence on fossil fuels. In Finland, stumps are currently harvested when the ground is not frozen to avoid co-removal of large amounts of soil and stones. Hence, the machinery used for stump extraction is not operated year-round. On peatlands, stumps could potentially be harvested when the ground is frozen. However, peatlands are highly sensitive to ground disturbance. There is, therefore, a need to identify equipment that causes low ground disturbance. In this study, peatland ground disturbance at stump level caused by stump harvesting using either a stump drill or a conventional stump rake was evaluated and compared in winter conditions. Results show that the stump drill caused up to 90% less ground disturbance per harvested stump than the conventional stump rake, but harvested 32–53% of the stump wood. Additionally, the size and shape of the disturbed areas changed between the harvesting year and following year, indicating that frost heaving plays a role in filling holes caused by stump extraction. The stump drill also consumed similar time to the conventional stump rake when harvesting Scots pine stumps on mineral soils, but far more when harvesting Norway spruce stumps.     

Dynamics of soil C,N and Ca in four Swedish forests after removal of tops,branches and stumps as predicted by the Q model

Abstract

We used the Q model to examine the dynamics of carbon (C), nitrogen (N) and calcium (Ca) in the litter/soil system in different scenarios of harvesting intensities, S (stems only), SSl (stems and slash, i.e. tops, and branches including needles) and SSlSt (stems, slash and stumps including coarse roots). Empirical data from long-term field experiments in Sweden, two sites with Norway spruce and two with Scots pine with different levels of productivity, were used to calibrate the model against the stem-only treatment. The highest initial reduction in soil C, N and Ca stores was predicted for SSlSt, and the reduction was more pronounced at low productive sites than at the high productive ones. Most of the decline in soil C and Ca stocks was offset by the litter production in the following forest stand. N showed an initial phase of immobilisation in stumps and coarse roots, while N was immediately released from tops and branches, which contained N-rich needles. Removal of stumps and coarse roots in combination with slash resulted in a similar load of inorganic soil N as for the S treatment, whereas the SSl treatment with stumps left in the soil initially reduced the inorganic soil N pool.     

Evaluation of the biological control agent Rotstop in controlling the infection of spruce and pine stumps by Heterobasidion in Latvia

The biological control agent Rotstop^® composed of a suspension of spores of Phlebiopsis gigantea (Fr.) Jül. is widely used for protecting conifer stumps from aerial infection by Heterobasidion species. The efficacy of Rotstop application on Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) stumps was determined in several locations and at different seasons in Latvia. Mean efficacy in controlling natural infection by Heterobasidion spp. in spruce stumps was 64%, calculated on the basis of number of infected stumps, and 89%, calculated on the basis of area of infected wood on sample discs cut from the stumps. Corresponding proportions for pine were 82% and 95%. The results show that Rotstop can be successfully used for stump treatment in Latvia, although improved efficacy is desirable, particularly in spruce. A Latvian isolate of P. gigantea, selected from numerous isolates in preliminary tests, was included in one experiment and was shown to be as effective as the Rotstop isolate. In untreated spruce stumps Heterobasidion spp. and P. gigantea were present in the same stump three times more frequently than in untreated pine stumps. Heterobasidion spp. infection in untreated spruce stumps was low when P. gigantea covered more than 10% of stump dissection.     

Long-term effects of stump harvesting on soil properties and tree growth in Scots pine and Norway spruce stands

Abstract

Effects of stump harvesting on the properties of surface soil and on the density, structure and growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands were estimated in a field trial in western Finland. The experiment was established in 1977 and measured in 2010. Stems and logging residues were harvested after clear-cutting, and stumps were lifted and removed from half of the experimental area. Sixteen plots were planted with pine seedlings and 16 with spruce. The main effects of stump harvesting were improved survival of planted trees and an increase in natural regeneration. No clearly negative effects were noted in the stand development. Stump harvesting had no or minimal effects on the properties of the organic layer and those of the 0- to 10-cm mineral-soil layer. Soil properties did not differ between tree species. Pine production was higher on plots with stump removal compared to plots without soil treatment.     

Persistence of a biocontrol strain of Phlebiopsis gigantea in conifer stumps and its effects on within‐species genetic diversity

Fungal isolations and genetic fingerprinting were used to determine whether Phlebiopsis gigantea stump treatment against Heterobasidion annosum sl. using a single genotype (Rotstop) would affect the genetic diversity of P. gigantea populations. The survival time of P. gigantea was longer in Norway spruce (Picea abies) stumps compared to Scots pine (Pinus sylvestris) as no isolates were obtained from pine stumps 6 years after treatment, whereas in about half of the spruce stumps the fungus was still present. The usage of Rotstop did not seem to increase the occurrence of the fungus 5 years after the treatment in fresh (1‐year‐old) untreated stumps within the same forest stands. All the isolates from the 6‐year‐old treated spruce stumps were identical in genotype with the Rotstop‐strain, whereas all isolates from the fresh untreated spruce and pine stumps differed from it. Within the treated pine stand, the biocontrol usage seemed to have caused a slight reduction in genetic markers not related to Rotstop, but there were no statistically significant differences between the marker frequencies and the local natural population. Thus, Rotstop is not likely to cause any immediate threat to the genetic diversity of P. gigantea.     

The spreading of the S type of Heterobasidion annosum from Norway spruce stumps to the subsequent tree stand

The occurrence of Heterobasidion annosum in stumps and growing trees was investigated on 15 forest sites in southern Finland where the previous tree stand had been Norway spruce (Picea abies) infected by H. annosum, and the present stand was either Scots pine (Pinus sylvestris), lodgepole pine (Pinus contorta), Siberian larch (Larix siberica), silver birch (Betula pendula) or Norway spruce 8–53 years old. Out of 712 spruce stumps investigated of the previous tree stand, 26.3% were infected by the S group and 0.3% by the P group of H. annosum. The fungus was alive and the fruit bodies were active even in stumps cut 46 years ago. In the subsequent stand, the proportion of trees with root rot increased in spruce stands and decreased in stands of other tree species. On average, one S type genet spreading from an old spruce stump had infected 3.0 trees in the following spruce stand, 0.5 trees in lodgepole pine, 0.3 trees in Siberian larch, 0.05 trees in Scots pine and 0.03 trees in silver birch stand. Although silver birch generally was highly resistant to the S type of H. annosum, infected trees were found on one site that was planted with birch of a very northern provenance.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Quality,productivity and costs of spot mounding after slash and stump removal

Abstract

In Nordic countries, the harvesting of slash and stumps from regeneration areas for energy purposes has rapidly increased, and will increase further in the future. This development has unknown technoeconomic effects on soil scarification. This study investigated three spot mounding methods and factors affecting their quality, productivity and costs in regeneration areas after slash and stump removal. The methods were integrated stump lifting and spot mounding (INTE), separate excavator-based spot mounding (BLADE), and separate spot mounding by a continuously working mounding unit (CONT). The average quality of work was worst in INTE, while CONT was the most sensitive to stoniness. Average work times per spot mound were 4.1 and 3.1 times higher in INTE and BLADE, respectively, than in CONT. Altogether, the cost–quality ratio of CONT was better than that of the other methods, except in very small areas.     

Collembola in low stumps at clear-cuts. Is stump harvesting a threat?

Abstract

Stump harvesting as a way to increase wood biomass production in order to meet the European Union targets for reduced CO₂ emissions is starting up in Sweden. The knowledge about if and how Collembola species can use low stumps as a substrate is very limited. Stumps of three different ages (4, 14 and 75 years) were sampled to see if Collembola used the dead wood during the whole rotation period of a forest. Stumps of spruce, pine and birch were compared. Both the bark and the splint wood of the stumps were sampled. To determine whether the stump also influenced the nearby soil, the soil close to the stump were sampled as well as the soil further away. In total, five Collembola species that are known to prefer dead wood as a substrate were found in the stumps. Wood specialists were more dominating in young stumps, but occurred also in the oldest stumps. No preference was found for any specific tree species. Wood-living Collembola seem to be able to survive in low stumps for a whole rotation period, at least in low numbers. There is, however, a risk for extinction debt due to their low capacity for active long-distance dispersal.     

Soil respiration after slash and stump removal in three clear-cut areas with patch scarification and mounding

We studied the soil carbon dioxide respiration (R_s) at three clear-cut mesic forest sites in south, central and north central Finland, which had been treated with different intensities of stump lifting and slash removal and then patch mounded and planted with spruce. The follow-up period after the initial calibration lasted for five consecutive years. Throughout the study the R_s remained at fairly steady levels according to the study site and soil disturbance level. Based on a split-plot test using the general linear model there were no significant differences in the R_s between the different stump and slash removal treatments at the three study sites, but unaffected and moderately affected soil surfaces had significantly higher R_s than mounds and wheel ruts. We conclude that the removal of stumps and slash have minor direct effects on R_s, but large indirect effects through soil disturbance.     

Temporal changes in functional diversity of culturable bacteria populations in Sitka spruce stumps

Changes in culturable aerobic bacterial communities of Sitka spruce stumps between 1 and 10 years old were investigated by isolating from the top 55 mm of the stumps. High numbers of bacteria were recovered from 15 mm below the surface of 1‐ and 2‐year‐old stumps, particularly in the sapwood, after which numbers dropped by an order of magnitude. Proportions of colony‐forming units (cfu) capable of degrading cellulose and chitin increased with stump age, whereas siderophore producers decreased. Colony‐forming units were grouped on the basis of 13 phenotypic characteristics, including colony form and colour, Gram stain, heat tolerance, siderophore production and production of various enzymes. Four groups of bacteria were identified; the proportions of the three Gram‐negative groups varied with stump age. A quadratic relationship between bacterial diversity and stump age was detected using the Shannon–Weaver diversity index. Bacterial diversity was higher 15 mm below the stump surface than in deeper sampling points. The results are discussed in terms of the possible influence of prokaryotic organisms on the development of decay communities in Sitka spruce stumps.     

Effectiveness of treatment of Norway spruce stumps with Phlebiopsis gigantea at different rates of coverage for the control of Heterobasidion

The natural establishment of the root and butt rot causing fungus Heterobasidion annosum s.l. on Norway spruce (Picea abies) thinning stumps treated with Phlebiopsis gigantea was investigated on seven sites in southern Sweden. The trees were cut during summertime and the stumps were treated with different patterns simulating the effect of mechanical stump treatment with a single‐grip harvester. Sampling was conducted 3 and 12 months after treatment. At both samplings, the best control was obtained when 100% of the stump surface was covered by P. gigantea: in contrast, untreated control stumps showed the highest incidences of H. annosum s.l. infection at both sampling times. However, 30 and 26% of the fully covered stumps at the first and second samplings, respectively, were diseased, and question the efficacy of treating Norway spruce stumps with this biological control agent in Sweden.     

Phosphorus and base cation accumulation and release patterns in decomposing Scots pine,Norway spruce and silver birch stumps

Tree stumps are integral constituents of managed forest ecosystems, but their role in nutrient cycling is poorly understood. We studied phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) dynamics in decomposing Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and silver birch (Betula pendula) stumps in southern Finland in a chronosequence of 0-, 5-, 10-, 20-, 30- and 40-year-old clear-cut areas. Along with the decomposition of pine and spruce stumps, the amount of P in stumps increased, but K and Ca were released, and the amount of Mg initially decreased and then increased. All nutrients, except K, accumulated in birch stumps during the first ten years, but were released thereafter. After 40 years of decomposition, pine and spruce stumps contained 180% and 202% of their initial amounts of P, respectively. In addition, the amounts of Mg were larger than the initial amounts in 40-year decomposed pine (126%) and spruce (202%) stumps. In contrast, birch stumps lost 64% and 75%, respectively, of their initial amounts of P and Mg over a 40-year period. The stumps of all the species were found to release K and Ca. Pine, spruce and birch stumps lost 48%, 64% and 87% of their initial amount of K, and 49%, 35% and 42% of their initial amount of Ca, respectively, during the 40-year period. The results indicate that decomposing stumps of the major tree species in Fennoscandian forests are long-term nutrient pools and they serve as P sinks, thus potentially reducing P leaching after clear-cutting.     

Fuel quality of Norway spruce stumps – influence of harvesting technique and storage method

Abstract

The interest in using stump biomass as a biofuel has recently increased in Sweden. The uneven consumption of wood fuel during the year creates a need for storage. This study examined the properties of stump biomass and how they vary at two sites in Sweden depending on harvesting technique, storage method and storage period. Norway spruce stumps, extracted using three different stump harvesting heads (Pallari, Rotary Cutter and Aalto), were stored in windrows or heaps. After 3 months, stumps stored in heaps were gathered into windrows. The fuel quality parameters moisture content (MC), ash content (AC) and calorific value (CV) were evaluated on five occasions in the period May 2008–September 2009. After 16 months of storage, the MC in all treatments had decreased to <25% (wet basis). Average AC decreased from 3.8% to around 1% (dry basis), whereas CV marginally increased. Stumps split during harvesting dried better than those harvested in one piece. The influence of storage method was minimal, although initial storage in heaps allowed better drying in the stumps harvested in one piece. In general, fuel quality improved in all treatments after storage.     

Decomposition of stump and root systems of Norway spruce in Sweden—A modelling approach

The demand for quantifying the biomass of stumps and roots and the carbon stored therein is related to aspects of biodiversity, site productivity, atmospheric carbon cycling issues, and the demand for bioenergy. This, in turn, creates a need to develop high-quality tools for estimating biomass and carbon-equivalents in the ground. The objective of this study was to develop decomposition functions for quantifying the remaining dry weight of the biomass of individual stumps and their associated roots in Norway spruce (Picea abies (L.) Karst.). The negative exponential model was chosen for this purpose, combined with a chronosequence approach, involving 99 stumps and their roots from three sites in Sweden. The results showed a relative decay rate of 4.6% annually for stump and root systems. Based on this rate, the time required for the loss of 50% (t_0.5) and 95% (t_0.95) of the wood is 15 and 64 years, respectively. Although there are many variables that affect decomposition, residual studies indicated that the remaining biomass could be predicted fairly accurately on the basis of the independent variables stump diameter and time.     

Effect of planting Scots pine around Norway spruce stumps on the spread of Heterobasidion coll.

Management of a Norway spruce stand planted on a site infected by Heterobasidion coll. is problematic because the fungus spreads vegetatively from the colonized stumps of the previous generation to the new seedlings. Growing of mixed stand with more resistant tree species has been suggested to decrease the economic losses caused by butt rot in Norway spruce trees. The mechanistic simulation model Rotstand describing the spread of Heterobasidion coll. in coniferous stands of southern Finland was used to study the effect of planting Scots pines around colonized clear‐felling stumps of Norway spruce of the previous generation. Planting of Scots pines in clusters around colonized stumps markedly decreased the butt rot of Norway spruce trees at the age of 20 years and at clear felling. If the same number of Scots pines were planted randomly, the effect was weak. When the average diameter of colonized clear‐felling stumps was 30 cm, a Scots pine circle with a radius of 3 m resulted in the highest soil expectation value (SEV) at 2% discounting rate, whereas with 40‐cm stump diameter, a 4‐m radius produced the highest SEV. When the proportion of Heterobasidion parviporum in the old colonized stumps was 50% instead of 95%, planting pines around colonized stumps still clearly decreased the butt rot at the age of 20 years and in final felling.     

Attacks of bark‐ and wood‐boring coleoptera on snow‐broken conifers over a two‐year period

The attacks of bark‐ and wood‐boring Coleoptera on broken conifer stems after severe snow‐breakage in early 1988 were studied in autumn 1988 and 1989. The study included twelve stands in the county of Värmland in central Sweden differing in age and edaphic conditions. The tops on the ground as well as the remaining rooted stem stumps of 94 Picea abies and 61 Pinus sylvestris were inspected. The presence of living branches on the stumps strongly influenced the incidence of insect attack. All stumps without branches were attacked during the two‐year period, whereas only a few spruce stumps with more than ten branches and no pine stumps with more than five branches were attacked. On spruce stumps, the most frequently encountered Coleoptera were all scolytids, i.e. the species Pityogenes chalcographus, Hylurgops palliatus, and the genera Polygraphus, Dryocoetes, and Trypodendron. On pine stumps, Tomicus piniperda was the most common species. Most of the spruce tops and virtually all pine tops were attacked during the two‐year period, and most of these attacks occurred during the first summer. P. chalcographus, Dryocoetes, and weevils of the genus Pissodes were the most frequent Coleoptera on spruce tops. On pine tops, the dominant insects belonged to the genera Pissodes and Pityogenes.     

Two studies to assess the risk to Pinus sylvestris from Heterobasidion spp. in southern Sweden

Abstract

Pine stumps are not being treated against Heterobasidion spp. in Sweden. To determine whether they should be, the frequency of stump infections and the species of Heterobasidion involved were investigated in nine newly thinned pure Scots pine (Pinus sylvestris L.) stands in southern Sweden. The incidence of Heterobasidion was measured in roots of standing Scots pine in another 15 stands. Infections by both H. annosum (Fr.) Bref. s.s. and H. parviporum Niemelä & Korhonen were numerous in stumps six months after a summer thinning. The pathogen, mostly H. annosum, was found in 44 of 60 sampled root systems, from 14 of the 15 stands. Twenty of the infected pines were assessed as healthy on the basis of crown symptoms while 24 trees had defoliated crowns. Infected root systems were most frequent among trees with thin crowns in stands on former agricultural land, where previous thinnings had been carried out during the growing season when airborne spores are plentiful. The study suggests that stump treatment may be a profitable way to reduce disease development in Scots pine monocultures on sandy soils as well as in mixtures with Norway spruce [Picea abies (L.) Karst.] on any soil.     

Sprouting characteristics of a subtropical evergreen broad-leaved forest following clear-cutting in Okinawa,Japan

This study explores the sprouting characteristics of an evergreen broad-leaved forest after clear-cutting based on a survey of 1,893 stumps of 62 tree species in Okinawa, Japan. The sprouting capabilities of the stumps varied among tree species. The stumps of 60 species could produce sprouts, while those of the other two species could not. In 10 of the sprouting species, the mean sprout-stem number was higher than 4.0 stems per stump; nine sprouting species showed low sprouting capabilities. Additionally, Castanopsis sieboldii and Schima wallichii, the dominant species, exhibited high sprouting capabilities. Further, the sprouting capabilities varied with stump diameter at breast height (DBH). Stumps with a larger DBH tended to have a higher mean number of sprout stems per stump, higher DBH, and higher tree height than the smaller stumps. The forest stands regenerated by sprouting might recover into a tree community similar to that before clear-cutting.     

Decomposition of stumps in a chronosequence after clear-felling vs. clear-felling with prescribed burning in a southern boreal forest in Finland

The wood bulk density, bark mass and decomposition rate constants of cut stumps of the main European boreal tree species were assessed along a 40-year chronosequence of clear-felled sites with and without prescribed burning. Using the single exponential model, the annual decomposition rate constants k of above-ground stumps were calculated as 0.048, 0.052 and 0.068 year⁻¹ for Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula sp.), respectively. Bark decomposed faster than wood and bark fragmentation increased the rate of decomposition. There was a significant negative effect of burning on decomposition rate for pine wood, and for pine and spruce bark but not for spruce and birch wood or for birch bark. The decomposition of bark of all species was slower with larger diameter stumps but only slightly slower in the case of birch wood. Our results suggest (i) using different decomposition rate constants for wood and bark, (ii) taking into account fragmentation as it greatly increases the volume loss, and (iii) adjusting of k in carbon dynamics studies on burned sites. Such refinements to estimates of coarse woody debris decomposition constants could aid in identification of ecosystems and management scenarios necessary to maximize carbon storage and conserve biodiversity. Prescribed burning for restoration purposes decreases decomposition rates and consequently ensures longer persistence of stumps for maintaining biodiversity in intensively managed forests.