Birch Stumps Research Articles

Trait-environment interactions of saproxylic beetles as a guide to biodiversity conservation strategies

Conservation of biodiversity requires in-depth knowledge of trait-environment interactions to understand the influence the environment has on species assemblages. Saproxylic beetles exhibit a wide range of traits and functions in the forest ecosystems. Understanding their responses to surrounding environment thus improves our capacity to identify habitats that should be restored or protected. We investigated potential interactions between ecological traits in saproxylic beetles (feeding guilds and habitat preferences) and environmental variables (deadwood, type and age of surrounding forest). We sampled beetles from 78 plots containing newly created high stumps of Scots pine and Silver birch in boreal forest landscapes in Sweden for three consecutive years. Using a model based approach, our aim was to explore potential interactions between ecological traits and the surrounding environment at close and distant scale (20 m and 500 m radius). We found that broadleaf-preferring beetle species are positively associated with the local broadleaf-originated deadwood and broadleaf-rich forests in the surrounding landscapes. Conifer-preferring species are positively associated with the local amount of coniferous deadwood and young and old forests in the surrounding landscape. Fungivorous and predatory beetles are positively associated with old forests in the surrounding landscapes. Our results indicate that both local amounts of deadwood and types of forests in the landscape are important in shaping saproxylic beetle communities. We particularly highlight the need to increase deadwood amounts of various qualities in the landscape, exempt older forests from production and to increase broadleaf-rich habitats in order to meet different beetle species’ habitat requirements. Trait responses among saproxylic beetles provide insights into the significance of broadleaf forest and dead wood as essential attributes in boreal forest restoration, which helps conservation planning and management in forest landscapes.

ЭКСПЛУАТАЦИЯ ПОЧВООБРАБАТЫВАЮЩИХ ОРУДИЙ В УСЛОВИЯХ НЕРАСКОРЧЕВАННЫХ ВЫРУБОК ЕВРОПЕЙСКОЙ ЧАСТИ РОССИИ: АНАЛИЗ ПРЕПЯТСТВИЙ В ВИДЕ ПНЕЙ И КОРНЕЙ

Felled and burnt areas are distinguished wide variety of soil and climatic conditions. Therefore, the choice of technological techniques and technical means of preparing the soil prior to planting forest crops depends on many factors. The composition of the former stand also has a significant influence on the choice of the method of tillage. If, after cutting clean point stands, there is an insignificant amount of soft-wooded deciduous species growth, then after cutting mixed spruce-deciduous stands, abundant growth appears on the cutting. The upper horizon of the soil turns out to be heavily filled with the roots of woody and shrubs vegetation. On freshly cutting site non stump grubbing, the frequency of encounter of the working bodies of tillage tools with stumps and roots varies quite widely, which requires studying the parameters of such obstacles. Data collection was carried out in the eLIBRARY and Scopus databases. Processing was carried out using the programs StatSoft Statistica 10 and Microsoft Excel. It was found that the height of the stumps is equal to or greater than their diameters and increases with increasing diameter for all tree species studied. With a diameter of stumps up to 24 cm, their average height is 22...27 cm, with 25...36 cm - 30...40 cm, with 61...72 cm - 70 cm. 51.8% birch stumps, 58.8% spruce and 77.1% aspen. The remaining stumps reach a height of 50 cm or more. On coppice felling, the maximum average height of stumps (29.3 cm) is observed in oak and ash. A smaller average height of stumps (21.0 cm) is observed in maple and linden. In the clearing, every tenth stump reaches a height of more than 40 cm, every fourth - more than 30 cm. In the clearing of old-growth seed oak forests, oak stumps have the highest average height (40.6 cm). Ash stumps have a slightly lower height (31.1 cm). For maple and linden, it is 22.6 cm. The height of every fifth stump is 40 ... 70 cm, every second - more than 30 cm. It is concluded that for all types of trees, the root system is horizontal at a depth of 0-30 cm. It is in this zone that tillage takes place.

Cutlink Cleaning Head with a Spreading Feature for Biological Sprout Control

The ability of deciduous trees to sprout efficiently after cutting is problematic in young forests where the target is to cultivate coniferous trees for industry. Since the use of chemicals has been restricted, new alternatives are needed. One potential and environmentally friendly option is biological sprout control that is based on the use of a white-rot fungus, Chondrostereum purpureum (Pers. Ex Fr.) Pouzar. This method has been efficient in earlier investigations when performed manually, but efficient, fully mechanized devices which are able to cut and treat stumps with a fungus are still unavailable. Therefore, the efficacy of biological sprout control conducted with a Cutlink cleaning head equipped with a spreading feature was studied in two young Norway spruce (Picea abies (L.) H. Karst.) forests in central Finland.Sample plots for the control (cutting deciduous saplings only) and fungal treatment (cutting and spreading fungal inoculum on fresh stump surfaces) were established, and the ability of the Cutlink cleaning head in preventing sprouting of silver and downy birch (Betula pendula Roth and B. pubescens Ehrh., respectively) in the sample plots was investigated for two years.In the near vicinity of cultivated Norway spruce, the proportion of cut deciduous saplings varied from 50–60% after the Cutlink operation. The average mortality of silver and downy birch stumps in the fungal treatment plots was ca. 40%, while stump mortality in the control, i.e., cutting only, was only ca. 13%, after two years. Stump mortality increased up to 73% if the stumps did not include old branches, i.e., the stump was cut to a low enough height.These results confirmed that the Cutlink cleaning head is a potential tool in young stand management operation but further development will be needed in working methods in order to achieve lower stump heights (no branches on the stump) and also to increase the proportion of cut saplings.

Rainstorm effects on the biocontrol efficacy of the decay fungus Chondrostereum purpureum against birch sprouting in boreal forests

In forest regeneration areas, alongside roads and railways, under electric power lines and above gas pipe lines, there is a need for regular sprout control. A biocontrol method against broadleaved sprouting with formulations including the decay fungus Chondrostereum purpureum (Pers. Ex Fr.) Pouzar has been shown to be effective. Yet, heavy rain during spreading of this fungal inoculum on freshly cut stumps may affect the efficacy of the treatment, i.e., stump mortality during the following years. Thus, we performed an experiment where freshly cut birch stump surfaces (Betula pendula Roth and Betula pubescens Ehrh.) were treated with fungal inoculum under heavy irrigation and without it. Furthermore, two different adjuvants which aimed to fix the fungal inoculum to freshly cut stumps during irrigation and to protect against solar radiation were tested. Our results revealed that the artificial rainstorm treatment caused a delay in the efficacy of C. purpureum, but after three growing seasons, there was no significant difference in the mortality of birch stumps treated under irrigation or without it (stump mortalities 74 and 86%, respectively). Adjuvants did not improve the efficacy in stumps treated under irrigation nor in those treated without irrigation.Key Points• Heavy rain delayed the sprout control efficacy of a fungus Chondrostereum purpureum.• Final efficacy of formulations was the same in wet and dry conditions.• No additional adjuvants are needed to improve formulations.

The biocontrol efficacy of Chondrostereum purpureum is not sensitive to prevailing environmental conditions in boreal forests

Sprouting of deciduous trees is problematic in forest regeneration areas, alongside roads and railways, under electric power lines and above gas pipe lines. A decay fungus Chondrostereum purpureum is a potential biocontrol agent against sprouting of deciduous trees. However, before this method can be utilized in practice, the effects of environmental factors on the efficacy of the fungus, i.e., its ability to cause stump mortality, should be understood. Thus, in this study, the effects of environmental factors on the efficacy of C. purpureum in controlling birch stump sprouting were investigated. Fungal inoculum was spread on 342 freshly cut birch (Betula pendula and B. pubescens) stumps at 17 sites, which were thereafter used to investigate the effects of solar radiation, temperature, precipitation, and soil properties on the efficacy of C. purpureum treatment. In the control plots, 318 birches were cut but no fungal inoculum was spread on their freshly cut stumps. The results revealed that solar radiation had no effect on the mortality of treated birch stumps, but an increasing proportion of hot days after the fungal treatment and an increase in precipitation within one week prior to the treatment reduced the mortality rate of stumps by the end of the first growing season following stump treatment. Furthermore, an increase in precipitation after the treatment and high soil moisture were also related to an increase in stump mortality. However, these effects were only temporary as by the end of the second growing season only precipitation that has occurred prior to the treatment had slight effect on birch stump mortality, while other investigated environmental conditions, i.e., proportion of hot days, amount of precipitation after the treatment and soil moisture, had no effect. Furthermore, application of the fungal inoculum immediately after cutting was essential for efficient sprout control. Even a delay of 15–30 min has significantly reduced stump mortality rates. Taken together, this study revealed that the presented method of biological stump sprouting control is not very sensitive to the investigated environmental conditions, suggesting that it can be used also during hot and rainy periods as long as requirement for a minimal delay between the cutting of trees and stump treatment is considered.

Diptera in clear-felling stumps like it dry

ABSTRACTWhen stumps on clear cuts are harvested for bioenergy, retention of a share of them is recommended to mitigate environmental issues. To maximise benefits for the diversity of saproxylic beetles, retention should be done in dry positions. Saproxylic dipterans are usually thought to be associated with wetter wood substrates. We therefore hypothesised that dipterans would benefit from other recommendations. We tested that by rearing out insects from spruce and birch stumps sampled in clear fellings, and received a material of 866 individuals of 24 Diptera taxa. Among six Diptera species tested statistically, one was associated with dry stumps when comparing within spruce, and the total abundance of dipterans was higher in dry spruce stumps than in wet. No parameter (total species number, species number per stump, total abundances and abundances of individual species) showed a higher value for wet stumps than for dry. We conclude that there are several Diptera species that frequently use stumps, of which a large share was earlier regarded as very rare. For those, our hypothesis was falsified, as the affinities to dry stumps seem similar as for beetles and the same recommendations could be used.

The potential of the decay fungus Chondrostereum purpureum in the biocontrol of broadleaved tree species

Abstract The ability of the decay fungus Chondrostereum purpureum to grow within birch (Betula pendula and Betula pubescens), aspen (Populus tremula), rowan (Sorbus aucuparia) and willow (Salix caprea) stumps or root systems is unknown, although such information would be crucial in understanding its impact on the vegetative growth of broadleaved trees, their ecology and potential biocontrol. Saplings of these tree species were cut and inoculated with the fungus. After 3 months, 47, 14, 0 and 0% of birch, aspen, rowan and willow stumps, respectively, were dead, and C. purpureum was frequently present within the stumps of all species. In more than half of the birch stumps investigated, the fungus had penetrated into the roots unlike in the other tree species. Our results indicate that C. purpureum can utilize the woody material of birch better than that of other species, and that penetration into the roots is needed to kill the host.

Ways to use silver birch Betula pendula Roth regeneration in sites considered for stand conversion due to decline of Norway spruce Picea abies (L.) H. Karst. in the Silesian Beskid Mountains

Abstract One of the tree species appearing after a decline of Norway spruce Picea abies (L.) H. Karst. in the Silesian Beskid Mountains is Silver Birch Betula pendula Roth. Therefore our study was aimed at evaluating this birch regeneration and the dynamics of changes resulting from experimental cutting. Measurements and inventories of trees were conducted on research plots located in a ten-year old birch regeneration site with either no cutting, partial cutting (50%) or clear cutting (100%) of birch. We observed an introduction of biocenotic species (rowan, willow, aspen) as well as the target species (spruce, fir, beech) under the birch canopy. Fir and beech were also planted, because of their slow natural regeneration. The clear cut treatment caused a great number of sprouts growing from birch stumps, reaching a height of about 2 m over 3 years, resulting in competition with the regeneration of other species. Partial cutting did not cause such a drastic amount of sprouting. Furthermore, we found that only the spruce height increment is significantly less under a birch canopy compared to open space. The obtained results indicate a necessity to adjust the density and species composition of regenerating tree species under a birch canopy, avoiding complete removal of the first generation birch cover and the need to moderately thin out birch.

Mycobionta of birch and birch stump roots and its possible effect on the infection by Armillaria spp. I.

<i>Zygorhynchus moelleri</i> was the dominating species on/in roots of 2 year-old stumps of the 49 year-old birches. <i>Trichoderma viride</i> was more frequently found in the fine roots of living birches than in the fine roots of stumps though its population increased in thick roots of stumps. Occasionally the fungus also occurred on the surface of fine roots of stumps. <i>Z. moelleri</i> is known to produce indole 3-ethanol and indole-3 acetic acid which stimulate the growth of <i>A. ostoyae</i> rhizomorphs and phenoloxidizing enzymes which play an important role in the degradation of the wood. It seems that the accumulation of <i>Z. moelleri</i> and absence of bigger populations of <i>T. viride</i> on/in roots of 2-year-old stumps of the 49 year-old birches may result in an increase of their susceptibility to <i>Armillaria</i> infection.

Mycobionta of birch and birch stump roots and its possible effect on the infection by Armillaria spp. II.

This paper presents the differences in size and structure of mycobionta communities occurring in soil and on/i n roots of a 30 year-old birch and its stumps 2 years after cutting of the trees. Special attention was paid to the occurrence of <i>Zygorhynchus moelleri</i> and <i>Trichoderma viride</i>. The first species due to the metabolites produced may presumably stimulate the infection by <i>Armlllaria</i>. The second species is a well-known antagonist of <i>Armillaria, Z. moelleri</i> accounted only for 2.6, l.3 and 9.l % of the total number of isolates in rhizoplane as well as in the fine and thick roots of stumps, respectively. <i>Trlchodcrma viride</i> and <i>T. virens</i> were present in roots of Hve birch and its stumps only occasionally. The relatively big population of <i>Mycelium radicis atrovirens</i>- particularly in the fine roots of stumps is attributed to their high vitality and relatively lower level of root decomposition. It seems that the rate of stump root decomposilion does not favour their colonization by <i>Z. moelleri</i> and its supposed contribution in enhancing the infection by <i>Armillaria</i> might not be so distinct as on stumps of 49-year-old birches.

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

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.

Nutrient concentrations in stumps and coarse roots of Norway spruce, Scots pine and silver birch in Sweden, Finland and Denmark

The objective of this study was to evaluate the concentrations of nutrients in stumps and coarse roots in Norway spruce, Scots pine and silver birch in Sweden, Finland and Denmark, and to assess how nutrient concentrations vary with site characteristics, stand age and root size. Concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na) in spruce, pine and birch stumps were assessed in eight sites across Scandinavia.Nutrient concentrations were higher in birch than in spruce and pine. In Sweden and Finland, the nutrient concentrations were generally higher at the southern sites than at the sites located in the northern part of the countries, except for P. For all nutrients, concentrations were significantly higher in the bark of the stump and roots than in the wood. Furthermore, nutrient concentrations increased significantly with decreasing root diameter. This study did not demonstrate any correlations with stand age.Further studies are needed to provide a broader picture of how the stump nutrient contents vary with site characteristics and forest management practices to provide a better foundation for nutrient balance calculations when setting up recommendations for stump removal.

Saproxylic insect fauna in stumps on wet and dry soil: Implications for stump harvest

An increasing demand for bioenergy has stimulated interest in harvesting of tree stumps after felling operations. To reduce the amount of soil disturbance, it is recommended to retain stumps in wet areas. We wanted to evaluate if that strategy is beneficial also for saproxylic (wood-living) insects, which will have less habitat to breed in at stump harvest, and therefore also need mitigation. We tested if stumps in wet positions on a clear-cut harbour fewer species and a different assemblage of saproxylic insects than do stumps in dry positions. Insects were reared out from wood pieces taken from 100 stumps (50 Norway spruce, Picea abies and 50 birch, Betula spp.) sampled in pairs: one stump from wet and one from dry soil in each pair. In the lab 2201 individuals representing 49 beetle and 6 moth species were encountered. Fewer species were found in spruce stumps on wet soil than on dry soil, both when measured per stump or as an accumulated value over all stumps within the categories. No difference was detected between the number of species found in wet and dry birch stumps. However, three beetle species that live mainly in birch were more common in dry stumps than in wet. No species showed an association with wet stumps. We conclude that stumps in wet positions form an inferior habitat to stumps in dry positions, and that this should be considered when making recommendations concerning the harvesting of stumps for bioenergy.

Interaction between Chondrostereum purpureum and Phlebiopsis gigantea in mixed suspensions and their biocontrol efficacy in spruce logs and birch stumps

As the same machinery might be used in applying biocontrol agents Chondrostereum purpureum and Phlebiopsis gigantea to tree stumps, we studied whether the efficacy of one agent is affected by traces of the other present in the treatment suspension. Our results revealed that the same machinery can be used for both biocontrol agents.

Control efficacy of stump treatment and influence of stump height on natural spore infection by Heterobasidion spp. of precommercial thinning stumps of Norway spruce and birch

An alternative precommercial thinning technique results in trees being cut higher up the stem compared to the normal method using a brush saw. The aims of this study were to investigate if primary infection of Heterobasidion spp. on precommercial thinning stumps of Norway spruce and birch is influenced by stump height and to test the control efficacy of stump treatment with Phlebiopsis gigantea on precommercial thinning stumps of Norway spruce. Small Norway spruce and birch trees were felled on five sites in southern Sweden and their stumps subjected to natural spore infection. For each species, two treatments of stump height were created: 15 and 100 cm. Half of the Norway spruce stumps were treated with P. gigantea. After two months, 896 stumps were sampled and infection by Heterobasidion spp. was quantified. The height of stumps did not significantly influence infection frequency or size of infection on either tree species. Untreated Norway spruce stumps had an infection frequency of 55% while 31% of the treated stumps were infected. The control efficacy of stump treatment in terms of reduced relative infected area was 61–65%. The area occupied by Heterobasidion spp. on birch stumps was generally small, on average 0.4 cm2 per infected stump, although 15% of the stumps were infected. The risk of primary infection in Norway spruce dominated stands should be considered when precommercial thinning is conducted but the control efficacy and economy of stump treatment warrants further investigation before practical recommendations can be made.

Stump decomposition rates after clear-felling with and without prescribed burning in southern and northern boreal forests in Finland

The high importance of stumps for biodiversity, carbon and nutrient cycling requires narrowing the uncertainties in their decomposition rate assessment. We estimated the stump decomposition rates of the main European boreal tree species along a chronosequence of 0-, 5-, 10-, 20-, 30-, 40- and 50-year-old clear-felled sites with and without prescribed burning in southern and northern Finland. Estimation was done based on the bulk density and mass loss of above- and below ground wood and bark. The factors explaining the variation in mass loss during decomposition in decreasing order of importance were: stump part > tree species > vegetation zone > stump size > prescribed burning. In northern sites, stump turn-over time ( t 95) was 153, 104 and 100 years for Scots pine ( Pinus sylvestris), Norway spruce ( Picea abies) and birch ( Betula sp.), respectively. The decomposition rates of above- and below ground wood did not differ from each other. In southern sites, where only the above-ground parts of stumps were studied, the turn-over time was 61, 56 and 43 years for pine, spruce and birch, respectively. In southern sites, the wood and bark of all tree species decomposed faster compared to those in northern sites, except for charred pine wood. Burning slowed down the decomposition of un-fragmented parts of pine and spruce bark in all sites and pine wood in southern sites (mean bark cover 32%). It also facilitated the decomposition of birch wood in northern sites (mean bark cover 78%) and increased bark fragmentation. Decomposition of birch bark in northern sites and birch wood in southern sites was slower for larger diameter stumps. Pine and spruce bark as well as birch bark in southern sites showed the opposite tendency since the size effect was dominated by the effects of fragmentation and burning. The bark of pine and spruce decomposed faster than the wood, whereas birch bark decomposed more slowly than birch wood. Bark fragmentation accelerated mass loss in all cases except for birch stumps in northern sites. Decomposition factors are interrelated and their relative importance should be taken into account when up-scaling the species-specific decomposition rate constants. Refinements to decomposition rate estimates could aid in management scenarios to maximize carbon and nutrient storage and ensure the availability of stumps for maintaining biodiversity in intensively managed forests.

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.

Forces required to vertically uproot tree stumps

Stumpwood attracts renewed interest due to increased use of forest biomass for bioenergy. In Nordic countries stumps are generally uprooted with crawler excavators, which have strong cranes (ca. 400 kNm gross lift torque), but are not designed for moving in forest terrain. Their use is based on practical experience with available and tested machine types rather than thorough examinations of requirements, partly due to limited knowledge of force requirements for uprooting of stumps. Therefore, in this work mean and maximum forces required to vertically uproot stumps of Norway spruce (Picea abies) and birch (Betula spp.) were quantified together with the effects of various soil types and uprooting methods. The used excavator’s crane-mounted uprooting device enabled comparisons between usage of solely crane force, and a method in which preparatory loosening forces were applied prior to crane force. Uprooting stumps in single pieces proved difficult; 61% split unintentionally. Force requirements were similar across tree species, increasing curve-linearly with stump diameter, and stumps uprooted in a single piece required more force than split stumps. Preparatory loosening reduced crane force requirements and, surprisingly, less force was required to uproot stumps from a mesic, till soil than from a moist, finer-textured soil. No stump required more than 60 kN crane force and functions for maximum force requirements indicate that powerful harvesters and forwarders (gross crane lifting capacity of 273 and 155 kNm, respectively) should be able to uproot all stumps with ≤ 61 cm and ≤ 32 cm diameter, respectively, in one piece. Larger stumps could be managed if it is acceptable that stumps are split before uprooting.

Carbon and nitrogen release from decomposing Scots pine, Norway spruce and silver birch stumps

Stumps are the largest coarse woody debris component in managed forests, but their role in nutrient cycling is poorly understood. We studied carbon (C) and nitrogen (N) dynamics in Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and silver birch (Betula pendula) stumps, which had decomposed for 0, 5, 10, 20, 30 and 40 years after clear-cutting in southern Finland. Carbon and N were released significantly faster from birch stumps than from conifer stumps. In 40 years, conifer stumps lost 78% and birch stumps 90% of their initial C. In contrast, the amount of N in stumps increased, indicating that external N accumulated in the stumps. After 40 years of decomposition, the amount of N was 1.7 and 2.7 times higher than the initial amount in pine and spruce stumps, respectively. Nitrogen was released from birch stumps, but only after they had decomposed for 20 or more years. On average, 59% of N stored in birch stumps was released during 40 years. The results indicate that the stumps of the major tree species in Fennoscandian forests are long-term C and, especially, N pools which serve as N sinks, thus potentially diminishing N leaching into ground water and watercourses after harvesting. This suggests that the removal of stumps for bioenergy production may markedly affect the nutrient status and nutrient cycling of boreal forests.

The efficacy and potential risks of controlling sprouting in Finnish birches (<em>Betula</em> spp.) with the fungal decomposer <em>Chondrostereum purpureum</em>

Sprouting of fast-growing broad-leaved trees causes problems in young coniferous stands, under power transmission lines and along roads and railways. Public opinion and the Finnish Forest Certifi cation System oppose the use of chemical herbicides to control sprouting, which means that most areas with problems rely on mechanical cutting. However, cutting is a poor control method for many broad-leaved species because the removal of leaders can stimulate the sprouting of side branches and cut stumps quickly re-sprout. In order to be effective, cutting must be carried out frequently but each cut increases the costs, making this control method increasingly diffi cult and expensive once begun. As such, alternative methods for sprout control that are both effective and environmentally sound represent a continuing challenge to managers and research biologists. Using biological control agents to prevent sprouting has been given serious consideration recently. Dutch and Canadian researchers have demonstrated the potential of the white-rot fungus Chondrostereum purpureum (Pers. ex Fr.) Pouzar as a control agent of stump sprouting in many hardwoods. These fi ndings have focused the attention of the Finnish forestry community on the utilization of C. purpureum for biocontrol purposes. Primarily, this study sought to determine the effi cacy of native C. purpureum as an inhibitor of birch stump sprouting in Finland and to clarify its mode of action. Additionally, genotypic variation in Finnish C. purpureum was examined and the environmental risks posed by a biocontrol program using this fungus were assessed. Experimental results of the study demonstrated that C. purpureum clearly affects the sprouting of birch: both the frequency of living stumps and the number of living sprouts per stump were effectively reduced by the treatment. However, the treatment had no effect on the maximum height of new sprouts. There were clear differences among fungal isolates in preventing sprouting and those that possessed high oxidative activities in the laboratory inhibited sprouting most effi ciently in the fi eld. The most effective treatment time during the growing season was in early and mid summer (May–July). Genetic diversity in Nordic and Baltic populations of C. purpureum was found to be high at the regional scale but locally homogeneous. This natural distribution of diversity means that using local genotypes in biocontrol programs would effectively prevent the introduction of novel genes or genotypes. While a biocontrol program using local strains of C. purpureum would be environmentally neutral, pruned birches that are close to the treatment site would have a high susceptibility to infect by the fungus during the early spring.