article id 480, category Commentary
Category: Research article
article id 410, category Research article
Degree of previous cutting in explaining the differences in diameter distributions between mature managed and natural Norway spruce forests. Silva Fennica vol. 38 no. 4 article id 410. https://doi.org/10.14214/sf.410
The degree of naturalness was assessed in 37 mature (stand age 80 198 yrs) Norway spruce dominated stands located in southern Finland by measuring the number (0 610 ha–1) and basal area (0 33 m2 ha–1) of cut stumps. The Johnson’s SB distribution was fitted for living spruce trees to describe the dbh-frequency and basal area-dbh distributions. Regression models were constructed for predicting the parameters of the SB distribution using traditional stand parameters (median diameter, basal area, stem number) and the cut stump variables (number, basal area). Stump variables improved the models and enabled to explain the differences in diameter distributions between stands with varying intensity of past cutting. Model for basal area-dbh distribution was more accurate than dbh-frequency model in terms of regression statistics, but less accurate in terms of generated stand variables. The number and basal area of cut stumps seem to be useful and simple measures of stand naturalness which have potential uses in stand modelling and biodiversity-oriented forestry planning.
article id 409, category Research article
Equilibrium curves and growth models to deal with forests in transition to uneven-aged structure – application in two sample stands. Silva Fennica vol. 38 no. 4 article id 409. https://doi.org/10.14214/sf.409
Stem number distributions in uneven-aged forests are assumed to be stable, if they follow special functions, e.g. de Liocourt’s reverse J-shaped breast height diameter distribution. These distributions therefore are frequently regarded as a target in all-aged forests. Intending to convert an even-aged forest or any other forest, not yet exhibiting this sort of equilibrium, towards a steady state forest, the question rises, how to choose an appropriate equilibrium curve and how to achieve this stem number distribution by an appropriate thinning and harvesting schedule. Two stands are investigated: One dominated by Norway spruce (Picea abies), having developed from a 120 year old even-aged stand 25 years ago, after several “target diameter thinnings”. The other one is a mixed species stand of Norway spruce, white fir (Abies alba), larch (Larix europea), common beech (Fagus silvatica), and Scots pine (Pinus sylvestris), having lost its typical uneven-aged structure 20 years ago. These stands were used, together with the distance independent individual tree growth model PrognAus, to reveal that 1) there are more than only one equilibrium curve per stand, 2) not every hypothesised equilibrium can be reached with any stand, 3) an equilibrium in stem number does not necessarily mean a stable species distribution, and 4) growth models provide an excellent help to decide between several equilibrium curves and harvesting schedules to reach them.
article id 408, category Research article
Natural development of stand structure in peatland Scots pine following drainage: results based on long-term monitoring of permanent sample plots. Silva Fennica vol. 38 no. 4 article id 408. https://doi.org/10.14214/sf.408
We studied the dynamics of stand structure on drained peatland sites in Scots pine dominated stands untreated with thinnings. The data consisted of consecutive stand measurements in 10 permanent sample plots where the monitoring periods varied from 29 to 66 years. We assumed that the stand’s structural development was driven by the natural processes of regeneration, growth, and mortality, all related to inter-tree competition within the stand. The DBH distributions of live and dead trees at different times of post-drainage stand development – smoothed by Weibull function – were analysed to characterise the change in stand structure. The initial uneven-sized structure of the natural, widely-spaced stands became more uneven during the first decades following drainage due to enhanced regeneration. Later, as stand density and mean tree size continuously increased, the DBH distributions approached bell-shaped distributions. Accordingly, the suppressed trees showed their highest mortality rate during the first decades, but the peak of the mortality distribution shifted to larger trees along stand succession. The change in structure was faster in southern Finland than in northern Finland. We assumed the changes in stand dynamics reflected increased inter-tree competition, initiated by enhanced site productivity and increased stand stocking resulting from the ditching operation.
article id 407, category Research article
Impacts of different thinning regimes on the yield of uneven-structured Scots pine stands on drained peatland. Silva Fennica vol. 38 no. 4 article id 407. https://doi.org/10.14214/sf.407
Drained peatlands in northern Europe comprise more than 10 million ha of forestland and thus constitute a considerable production potential in forestry. Much of this area consists of stands dominated by Scots pine and close to maturity regarding commercial thinning. The trees within these stands typically vary in terms of age, size, and growth rate. The impacts of silvicultural cuttings on these uneven-structured stands are inadequately known. We simulated the impacts of a control regime with no thinnings, and three different thinning regimes, involving different thinning intensities, on the development of fifteen pine-dominated stands in Finland. The simulations started from the first thinnings and were continued until regeneration maturity. The predicted total yields ranged from 244 to 595 m3 ha–1, depending on site and thinning regime. The highest total yields were observed for the control regime in which 18–38% of the yield was, however, predicted to self-thin by the end of the simulation. Thus, the differences in the yields of merchantable wood were fairly small among the compared regimes. However, the regimes involving thinnings generally needed less time than the control regime to reach regeneration maturity. The mean annual increment of total stem volume was at its highest in the control regime. The highest mean annual increment of merchantable wood was obtained in the regime involving two moderate thinnings, but excluding the most low-productive sites where thinnings did not increase the yield of merchantable wood.
article id 406, category Research article
Growth and recruitment after mountain forest selective cutting in irregular spruce forest. A case study in Northern Norway. Silva Fennica vol. 38 no. 4 article id 406. https://doi.org/10.14214/sf.406
During the last thirty years the interest for the use of selective cutting in the sub-alpine spruce forests of Norway has increased. However, there have been very few investigations on the post harvesting development after such cuttings. Four plots in irregular Norway spruce (Picea abies (L.) Karsten) dominated forests on semi-fertile sites in Northern Norway have been the subjects of a case study. We performed a reconstruction of the stand development by means of biometric assessments and ring widths measurements of all standing trees. Tree ages, stand structure, growth and recruitment were examined. Even though a hypothetical reverse J-curve for the present diameter distribution was identified, the four plots were even-aged. Growth reactions indicate that most of the present sawtimber trees were established after heavy dimension cuttings in the late 19th century. The recruitment situation is characterized as satisfying in one of four plots. The post harvesting mean volume increment on the plots have been about two thirds of the potential yield estimated from site indices and maximum mean annual increment in regular stands. Managing strategies for irregular spruce forest stands are briefly discussed.
article id 405, category Research article
Regeneration process from seed crop to saplings – a case study in uneven-aged Norway spruce-dominated stands in southern Finland. Silva Fennica vol. 38 no. 4 article id 405. https://doi.org/10.14214/sf.405
The dynamics of spruce regeneration, from seed crop to saplings, was studied based on five permanent plots in uneven-aged, spruce-dominated, boreal forest stands, cut with single-tree selection in the beginning of the 1990’s. The annual fluctuation of the spruce seed crop was very similar in uneven-aged and even-aged stands. The correlation between seed crop and number of germinants was significant; but stem number, basal area or volume of the stand did not influence on seedling emergence. The effects of good seed crops were seen as peaks or an increase in the number of germinants and smallest seedlings. The mean number of ‘stabilised’ spruce seedlings (height 11 cm to 130 cm) varied from 6000 ha–1 to over 25 000 spruce seedlings ha–1 from one monitoring plot to another. On a monitoring plot the number of ‘stabilised’ spruce seedlings was stable over time. Neither stand basal area nor stand volume influenced the number of ‘stabilised’ spruce seedlings, but the height of these seedlings was higher on subplots with lower stand volume and smaller basal area. In this study the monitoring period, 5–10 years, was too short to obtain reliable figures for ingrowth, i.e. the transition of seedlings to the sapling stage (h > 130 cm). The adjusted mean ingrowth was 26 stems ha–1 year–1.
article id 404, category Research article
Survival and early seedling growth of conifers with different shade tolerance in a Sitka spruce spacing trial and relationship to understorey light climate. Silva Fennica vol. 38 no. 4 article id 404. https://doi.org/10.14214/sf.404
Alternative silvicultural systems to clearfelling are being adopted in Great Britain as a means of increasing the species and structural diversity of conifer plantation forests. One area where knowledge is lacking is the critical level of below-canopy light for survival and growth of young seedlings. This was investigated by planting seedlings of European larch Larix decidua (Mill.), Scots pine Pinus sylvestris L., Sitka spruce Picea sitchensis (Bong.(Carr.)), Douglas fir Pseudotsuga menziesii (Mirb.(Franco.)), and western hemlock Tsuga heterophylla (Raf. (Sarg.)) in a Sitka spruce plantation thinned to 3 different spacings. The incident light intensity beneath the canopy ranged from about 2 to over 60 per cent of full light. Planting in an adjoining open area provided an indication of growth under full light. Growth and survival of these seedlings were followed for 4 growing seasons. The highest seedling survival was found under the widest spacing and declined with closer spacing and lower light intensity. Only Douglas fir and western hemlock seedlings survived at the closest spacing, and in low percentages. The tallest seedlings of each species were found in the open grown conditions but survival was variable due to increased weed competition. Species-specific growth responses showed little difference under high light conditions but performance at low light was generally consistent with shade tolerance rankings in the literature except that Sitka spruce shade tolerance was slightly lower than expected. Minimum light requirements for these species increased from 10 to 30 per cent of full light with decreasing shade tolerance. Other studies of incident light in Sitka spruce plantations indicated that target basal areas in the range 25–30 m2 ha–1 are required if these light conditions are to be met, which suggests an irregular shelterwood system with frequent interventions should be favoured.
article id 420, category Research article
Cost-effective measures for diffuse load abatement in forestry. Silva Fennica vol. 38 no. 3 article id 420. https://doi.org/10.14214/sf.420
This paper theoretically and empirically analyzes the design of cost-effective diffuse load abatement in forestry. Harvesting with related forest regeneration and drainage maintenance increases nutrient leaching, while riparian buffer strips and adjustments in drainage maintenance technology can be used to prevent this leaching. By utilizing a two-period model it is shown that cost-efficiency requires the establishment of a buffer strip system and a reduction in both current harvesting, and in drainage maintenance – if practized – relative to the private optimum to reflect their effects on water pollution. A simulation analysis was conducted to assess the magnitudes of the decision variables of the theoretical model, as well as to evaluate alternative technologies for the implementation and use of buffer strips and for the adjustment of drainage maintenance. The results for a representative forest holding in the southern half of Finland show that it is possible to considerably reduce total phosphorus leaching with minor cost.
article id 419, category Research article
A comparison of one- and two-compartment neighbourhoods in heuristic search with spatial forest management goals. Silva Fennica vol. 38 no. 3 article id 419. https://doi.org/10.14214/sf.419
This study presents a comparison of the performance of four heuristic techniques with one- and two-compartment neighbourhoods in harvest scheduling problems including a spatial objective variable. The tested heuristics were random ascent, Hero, simulated annealing and tabu search. All methods seek better solutions by inspecting the neighbourhood solutions, which are combinations that can be obtained by changing the treatment schedule in one (one-compartment neighbourhood) or two (two-compartment neighbourhood) compartments. The methods and neighbourhoods were examined in one artificial and four real landscapes ranging from 700 to 981 ha in size. The landscapes had 608 to 900 stand compartments, and the examined planning problems had 2986 to 4773 binary decision variables. The objective function was a multi-objective utility function. The spatial objective variable was the percentage of compartment boundary that joins two compartments, both of which are to be cut during the same 20-year period. The non-spatial objectives were net incomes of three consecutive 20-year management periods and the remaining growing stock volume at the end of the third 20-year period. In another problem formulation, the total harvest of the first 20-year period was used as an objective variable together with the spatial objective. The results showed that a two-compartment neighbourhood was systematically and often clearly better than a one-compartment neighbourhood. The improvements were greatest with the simplest heuristics, random ascent and Hero. Of the four heuristics, tabu search and simulated annealing proved to be the best methods, but with a two-compartment neighbourhood the differences between methods were negligible.
article id 418, category Research article
Testing a large-scale forestry scenario model by means of successive inventories on a forest property. Silva Fennica vol. 38 no. 3 article id 418. https://doi.org/10.14214/sf.418
Modellers of large-scale forestry scenario models face numerous challenges. Information and sub-models from different disciplines within forestry, along with statistical and mathematical methodology, have to be considered. The individual biological sub-models (i.e. models for recruitment, growth and mortality) applied in large-scale forestry scenario models are in general well documented and extensively evaluated. However, evaluations by means of full-scale comparisons of observed and predicted values for continuous forest areas, where the totality of the large-scale forestry scenario model including interactions between sub-models and other parts of the model, are considered, have rarely been seen. The aim of the present work was to test the totality of the Norwegian large-scale forestry scenario model AVVIRK-2000, and thereby evaluate the applicability of the model for use in management planning. The test was done by means of successive inventories and accurate recordings of treatments over a period of 30 years for a property comprising 78.5 ha forest-land. Seen in the perspective of management planning, the differences between observed and predicted values for potential harvest level, growing stock and growth were small, e.g. a difference between observed growing stock in year 2000 and growing stock in the same year predicted from 1970 of 2.6%. The model may therefore be applied for practical purposes without any fundamental changes or calibrations of the biological model basis. However, the present test should be seen as an example that failed to falsify the model, rather than a final validation. As long as the model is in practical use, further evaluations should continue and subsequent possible calibrations should be performed.
article id 417, category Research article
The effect of two bucking methods on Scots pine lumber quality. Silva Fennica vol. 38 no. 3 article id 417. https://doi.org/10.14214/sf.417
Modern harvesters are equipped with measurement and bucking optimization systems able not only to continuously measure the length and diameter of the stem but also to predict the profile of the unknown part of a stem and to calculate the optimal cross-cutting points for the whole stem. So far, tree-bucking optimization in the Nordic countries has been efficiently applied only with spruce because the quality of pine and birch varies much more both within a stem and between stems. Since limitations in the measuring equipment mean that the presence and position of grade limits as well as additional defects in the stem will normally have to be detected and estimated manually. Consequently, optimization works inefficiently because the harvester operator is continuously forced to disregard the cutting suggestions supplied by the harvester’s automatic system. This paper presents the outcome of research intended to define how change from the current quality bucking principle to automatic bucking affects lumber quality. The study is based on field experiments and test sawing data on 100 Scots pine (Pinus sylvestris) stems from southwestern Finland in 2001. Automatic bucking does not markedly lower the amount of good-quality lumber compared to quality bucking. Since automatic bucking inevitably leads to log distribution that matches the length requirements of customers better, it may be regarded as appropriate for these harvesting conditions.
article id 416, category Research article
Long-term impacts of forest harvesting related soil disturbance on log product yields and economic potential in a New Zealand forest. Silva Fennica vol. 38 no. 3 article id 416. https://doi.org/10.14214/sf.416
The effect of soil disturbance (litter removal, topsoil removal and compaction) from forest harvesting on the productivity, log product yields and economic potential of second-rotation Pinus radiata growing on a clay loam soil, was assessed in a long-term trial 21 years after planting. The results are projected forward to the expected harvest age of 28 years. Relative to control plots, average tree volume at 21 years was reduced by 8% in the plots where the litter had been removed and the topsoil had been compacted, and by up to 42% in the plots where the topsoil had been removed and the subsoil compacted. The “degree of compaction” did not have a significant effect on average tree volume in the plots where litter had been removed but did have a significant effect where the topsoil had been removed. Per tree economic potential was reduced to a greater extent (up to 60% loss in value) than average tree volume was reduced. This was largely due to changes in log product yield distribution. Projecting tree growth forward to the end of the rotation at age 28 indicated that the impacts of soil disturbance on tree growth, economic potential and log product yields are likely to be similar in relative terms to those found at age 21.
article id 415, category Research article
Stress intensity factor of wood from crack-tip displacement fields obtained from digital image processing. Silva Fennica vol. 38 no. 3 article id 415. https://doi.org/10.14214/sf.415
Stress intensity factor of radiata pine (Pinus radiata) in Tangential-Longitudinal opening mode was determined from crack-tip displacement fields obtained from digital image correlation in conjunction with orthotropic fracture theory. For lower loads, experiments agreed with the linear elastic fracture theory but for higher loads, stress intensity factor and load relationship was nonlinear. For 41% of the specimens tested, tip-displacement based stress intensity factor agreed with that based on the ASTM standard formula for lower loads but deviated for higher loads closer to failure. The tip displacement plots showed that the nonlinear behaviour is due to large displacements which we attributed to large plastic deformations and/or micro-cracking in this region. The other 59% specimens showed a similar trend except that the crack-tip based stress intensity factor was consistently higher than the value obtained from the standard formula. The fracture toughness from tip displacements was larger than the standard values for all specimens and the two were related by a logarithmic function with an R2 of 0.61. The study also established that fracture toughness increases with the angle of inclination of the original crack plane to the Radial Longitudinal plane.
article id 414, category Research article
Variation in forest fire ignition probability in Finland. Silva Fennica vol. 38 no. 3 article id 414. https://doi.org/10.14214/sf.414
We examined climate-caused spatio-temporal variation of forest fire ignition probability in Finland based on empirical ignition experiments and 37 years of meteorological data from 26 meteorological stations scattered across Finland. First, meteorological data was used in order to estimate the variation in forest fuel moisture content with the model of the Finnish forest fire risk index. Second, based on data from empirical ignition experiments, fuel moisture content was linked with forest fire ignition probability. In southern Finland average forest fire ignition probability typically peaks in late May and early June, whereas in the northern part of the country the peak occurs at the end of June. There was a three-fold difference in the average annual ignition probability between the north-eastern part (3%) and south-western part of the country (9%). The observed differences in fire ignition probability suggest that the characteristics of the natural fire regime also vary considerably in the southern versus the northern part of the country.
article id 413, category Research article
Inorganic and organic phosphorus fractions in peat from drained mires in northern Finland. Silva Fennica vol. 38 no. 3 article id 413. https://doi.org/10.14214/sf.413
Soil samples from 15 eutrophic, 26 herb-rich, 15 tall-sedge, and 11 low-sedge drained peatland sites were analysed for easily soluble and aluminum, iron, and calcium bound phosphorus (P) using the Chang and Jackson sequential fractionation method. Compared to earlier investigations, where only total and easily soluble P contents (e.g. NH4OAc or dilute H2SO4 extractable P) in peat have been analysed, significantly higher differences between sites were observed. The eutrophic sites were characterized by four to six-fold greater Ca-bound organic P and two to three-fold greater Ca-bound inorganic P contents than on the other three site type groups, whereas the average Al-bound inorganic P content of the eutrophic sites was only one-third of that at the other site types. Substantial differences between sites were also observed for Fe-bound inorganic P, i.e. two to four-fold greater Fe-P contents were measured at the herb-rich sites compared with the other three site type groups. The stand volume growth in the 67 studied drained peatland sites correlated significantly with Al-bound organic P and Fe-bound inorganic and organic P. The study showed that a detailed fractionation and discrimination of different forms of soil P is important in increasing the understanding of the relationship between P availability and vegetation community types and stand growth on drained peatlands.
article id 412, category Research article
Nutrient distribution in Picea likiangensis trees growing in a plantation in West Sichuan, Southwest China. Silva Fennica vol. 38 no. 3 article id 412. https://doi.org/10.14214/sf.412
We measured nutrient distribution of Picea likiangensis (Franchet) E. Pritzel var. balfouriana trees growing in a plantation by field investigations, sample tree and plot harvest in West Sichuan, Southwest China. Based on the results in this study, the total biomass of plant compartments in plantation ecosystem was 114 829.1 kg ha–1. Tree, shrub, herb, bryophyte and litter layers accounted for 93.9%, 0.9%, 0.02%, 0.04%, 5.2%, respectively. The total biomass of tree layers was 107 817.1 kg ha–1. Needles, branches, stem wood, stem bark and roots accounted for 13.2%, 19.7%, 42.3%, 10.0% and 14.8%, respectively. The concentration of the nutrients was generally highest in the actively growing parts of the trees (e.g. needles) and lowest in the structural and not actively growing parts (e.g. stem wood). On the other hand, the concentrations of N, P, K and Mg were generally higher in the current year needles and branches than in the older needles and branches. These nutrient concentrations were also higher in the upper stem wood and bark than in the lower stem wood and bark, and in small roots than in large roots, whereas the opposite patterns were observed for the concentration of Ca in these compartments. The results will be helpful in understanding the nutrient behavior in a highly productive forest plantation and thereby providing decisive information for their sustainable management.
article id 430, category Research article
Objectives and motivations of small-scale forest owners; theoretical modelling and qualitative assessment. Silva Fennica vol. 38 no. 2 article id 430. https://doi.org/10.14214/sf.430
Forest management changes with societal change, and it has been debated if economic development in society places material objectives in a less preferable position: it is assumed this is also the case as regards forest management. The aims of this study were to propose a theoretical model for empirical studies of objectives and motivations within this field and to depict motivations and objectives of small-scale forest owners in Sweden. Comparative literature studies were undertaken and qualitative methodology was used for the empirical studies. Firstly, to depict general trends among forest owners, interviews with professional foresters were conducted. Secondly, forest owners throughout Sweden were interviewed to compare the results of the interviews with the professional foresters on the motivations and objectives of small-scale forest owners. Within the literature, there were no consistent views on the subjective grounds for owning and managing small-scale forest estates. The proposed theoretical model originated from the cultural concept. Sets of interpretive and normative qualities were seen as underlying people’s actions, and such sets were related to basic values. The ‘objectives’ were clustered into groups creating four clusters i.e. ‘motivations’. The four motivations depicted were: Conservation; Utilities; Amenities and Economic Efficiency. The empirical results highlighted that the objectives and motivations of forest-owners covered a broad field and a move towards conservation interests was indicated. The theoretical model presented here is suggested a suitable tool for both depicting the motivations and objectives of forest owners and for making future comparisons.
article id 429, category Research article
Optimizing the supply chain strategy of a multi-unit Finnish nursery company. Silva Fennica vol. 38 no. 2 article id 429. https://doi.org/10.14214/sf.429
This paper introduces a capacitated mixed integer programming (CMIP) model for solving an integrated production-distribution system design problem (PDSDP) in the seedling supply chain management (SCM) of a multi-unit Finnish nursery company. The model was originally developed from a strategic perspective in which a company desires to evaluate the expansion or closure of its facilities. Nevertheless, the model is also used for solving operational and tactical level problems by applying applicable constraints. The data were collected from the company studied. The results proved that economies of scale could be exploited in seedling production more than the company does today; Compared to the company’s current supply chain strategy with 5 nursery units producing seedlings, when other supply chain strategies were applied the number of nursery units decreased by 2–4 units, and cost savings in the supply chain varied from 11.3% to 21.3%.
article id 428, category Research article
Effects of three harvesting work methods on Harwarder productivity in final felling. Silva Fennica vol. 38 no. 2 article id 428. https://doi.org/10.14214/sf.428
During the last ten years interest in the harwarder has increased, however, studies have concentrated on effects of technical improvements on machine productivity. It has been noted that there is a large potential to increase the productivity through development of suitable work methods. To find efficient work patterns for a harwarder with a turnable loading area, three different harvesting methods were studied in final felling. Three work methods were used. Method 1: the harwarder drove backwards into the stand making a strip road, strip road trees were felled and left on the ground, on the way out of the stand the harwarder cut and processed the trees on both sides of the machine directly into the loading area. Method 2: the harwarder drove forward along the edge of the cut, cutting and processing trees directly into the loading area. Method 3: the harwarder drove forward into the stand and cut and processed strip road trees and trees standing on both sides of the machine directly into the loading area. The most efficient work method was method 2 where the productivity was 13.0 m3 u.b. per E0h (cubic metre under bark per effective hour). The productivities for method 1 and 3 were 12.1 and 11.9 m3 u.b. per E0h, respectively. In addition to work method harwarder productivity was shown to be dependent on load volume, average tree size and hauling distance. The only work elements significantly affected by work methods were processing and movement during processing. The operator had only a few weeks to get used to the machine and even less time to practise on the work methods. Thus, it is probable that the productivity for the studied methods will increase with increasing work experience. Furthermore, as only three work methods were studied, there are still untested work methods. The potential to further improve harwarder work methods is considerable.
article id 427, category Research article
Logging versus fire: how does disturbance type influence the abundance of Pinus strobus regeneration? Silva Fennica vol. 38 no. 2 article id 427. https://doi.org/10.14214/sf.427
Eastern white pine (Pinus strobus) has decreased in abundance over the past century throughout the Great Lakes Region of North America, but the relative constraints placed on recruitment under contrasting disturbance regimes are not well understood. The objectives of this study were to determine the extent to which white pine could invade areas recently disturbed by fire or logging (within 10–28 years), and assess the relative limitations placed on recruitment by seed supply, microsite habitat, and competition. We compared white pine regeneration on 61 sites disturbed by fire or logging that were adjacent to intact mature stands that provided a seed source. White pine seedling and sapling densities declined with increasing distance from a seed source, and the rate of decrease was determined by the interaction between seed supply and variation in number and quality of safe sites. For a given combination of seed source and site, white pine seedlings were three times more abundant on burned than logged sites. White pine seedlings grew into the sapling size class more often on burned than logged sites due to lower shrub cover on burned sites. At 25 years after disturbance, regeneration densities of white pine sufficient to achieve eventual future dominance occurred up to 80 m and 20 m from the edge of mature white pine stands after fire and logging, respectively. To attain a similar level of white pine stocking after disturbance, three to four times as many patches of mature white pine need to be left after logging than after fire.
article id 426, category Research article
Cambium dynamics of Pinus sylvestris and Betula spp. in the northern boreal forest in Finland. Silva Fennica vol. 38 no. 2 article id 426. https://doi.org/10.14214/sf.426
Wood formation dynamics of pine and birch along a south-north transect in Finnish Lapland were determined by the pinning technique. For all trees at all sites a more or less sigmoid shape of the wood formation intensity is characteristic with a slow beginning, a faster growth in the middle and a decreasing activity towards the end of the vegetation period. Wood formation of pine started at sites 1–3 (southern sites) in the second week of June and at sites 4 and 5 (northern sites) only in the last week of June, whereas wood formation ended within the first half of August. Wood formation of birch started in the second half of June and ended around the beginning of August. First cells were laid down by pine and birch when the temperature sum had reached the level of 85 to 90 degree days and 110 to 120 degree days, respectively. The intensity of wood formation in pine was highest in July, in birch within two weeks in the middle of July. Wood formation in pine lasted for about seven weeks at the southernmost and about six weeks at the northernmost site. In birch, the duration of wood formation was about five weeks at the southernmost site and around three weeks at the other sites.
article id 425, category Research article
Allocation of above-ground growth in Pinus sylvestris – impacts of tree size and competition. Silva Fennica vol. 38 no. 2 article id 425. https://doi.org/10.14214/sf.425
The effect of tree age, size and competition on above ground growth allocation was studied with 69 Pinus sylvestris trees. Competition was described by tree-level indicators (needle density, crown ratio and height-diameter ratio). The stem, branch and needle growth were determined by stem and branch radial increments and tree level biomass analysis. Combined growth of compartments was strongly correlated with needle mass. Furthermore, tree age, size and competition indicators affected the allocation of growth among the compartments. The allocation of growth to stem and needle increased with tree age and size while the allocation of growth to branch decreased. The increasing crown ratio increased allocation of growth to branches. The combined growth of the components and separate growth of needles, branches and stem were related to needle mass. However, competition and tree size were significant additional explanatory variables when the stem, branch and needle growth were estimated according to needle mass. The growth efficiency increased with relative tree height and decreased with increasing needle density.
article id 424, category Research article
Stem straightness and compression wood in a 22-year-old stand of container-grown Scots pine trees. Silva Fennica vol. 38 no. 2 article id 424. https://doi.org/10.14214/sf.424
The distribution of compression wood in relation to eccentric growth and development of stem straightness was studied in a 22-year-old Scots pine (Pinus sylvestris L.) stand in central Sweden that was established with container-grown seedlings. Stem straightness was measured on the same 440 trees in 1986 and 1997. The number of stems with straight base sections increased from 60% in 1986 to 89% in 1997. Measurements of 72 sample trees in 2001 showed that 96% of the trees had developed straight stem bases. External geometry data of the logs was obtained with a Rema 3D log scanner. A sub-sample of 16 trees was randomly selected for analysis of compression wood distribution and eccentricity measurements. From each tree, 11 discs were cut at every 60 cm along the stem. All discs, except one, contained compression wood. Compression wood and pith eccentricity was most pronounced near the stem base but not significantly correlated to basal sweep. Severe compression wood content was correlated to pith eccentricity and bow height. In general, correlations were better for the basal sections of the logs. Even though most trees were straight, they contained large amounts of compression wood. It is evident that eccentric growth and compression wood formation play major roles in the development of stem straightness. In several stems, a spiral compression wood distribution pattern was found. Reasons for this are discussed.
article id 423, category Research article
Effects of repeated slash removal in thinned stands on soil chemistry and understorey vegetation. Silva Fennica vol. 38 no. 2 article id 423. https://doi.org/10.14214/sf.423
The increased interest in harvesting logging residues as a source of bio-energy has led to concerns about the potentially adverse long-term impact of the practice on site productivity. The aim of this study was to examine the effects on soil chemistry (pH, C, N and AL-extractable P, K, Ca and Mg) in three different soil layers (FH, 0–5 cm and 5–10 cm mineral soil) and understorey vegetation after the second removal of logging residues in whole-tree thinned stands. The study was performed at four different sites, established in the period 1984–87, representing a range of different climatic and soil conditions: a very fertile Norway spruce (Picea abies (L.) Karst.) site in south-western Sweden and three Scots pine (Pinus sylvestris L.) sites located in south, south-central and central Sweden. The effects of whole-tree thinning on soil chemistry and understorey vegetation were generally minor and variable. Across all sites the concentrations of Ca and Mg were significantly lower when slash was removed.
article id 422, category Research article
Export of dissolved organic carbon, nitrogen and phosphorus following clear-cutting of three Norway spruce forests growing on drained peatlands in southern Finland. Silva Fennica vol. 38 no. 2 article id 422. https://doi.org/10.14214/sf.422
The effect of clear-cutting on the concentrations of dissolved organic carbon (DOC), organic nitrogen (DON), NH4+, NO3–, and P in outflow water from three productive, Norway spruce dominated drained peatlands (RCC, VCC-1, VCC-2) were studied. Changes in runoff and transport loads (concentration x runoff) at two of the catchments during the frost-free period are also presented. Approximately 40% of the area was cut at RCC and VCC-2, and 72% at VCC-1. The volume removed was 250 m3 ha–1 at RCC, 259 m3 ha–1 at VCC-1, and for VCC-2, 317 m3 ha–1. The mean annual increase in outflow concentrations of DOC during the first four years after clear-cutting was 9.0 mg l–1 at RCC, 22.8 mg l–1 at VCC-1 and 8.4 mg l–1 at VCC-2. Corresponding increases in the forms of nitrogen were: 0.23, 0.51 and 0.16 mg DON l–1; 0.06, 0.31 and 0.04 mg NH4+-N l–1; and 0.05, 0.12 and 0.22 mg NO3–-N l–1. Clear-cutting did not significantly (p > 0.05) increase P concentrations. The increase in non-frost season runoff over the first three years after clear-cutting was 107 mm at RCC and 207 mm at VCC-1. The export loads of DOC during the non-frost season increased by 80 kg ha–1 at RCC and by 184 kg ha–1 at VCC-1 over the first three years. Corresponding increases for the other studied solutes were: 1.78 and 3.98 kg DON ha–1; 0.39 and 1.49 kg NH4+-N ha–1; 0.45 and 0.48 kg NO3–-N ha–1, and 0.09 and 0.06 kg P ha–1. The study demonstrated that clear-cutting may significantly increase the export of DOC and different forms of nitrogen from drained productive peatlands while only small increases in phosphorus export may occur.
article id 439, category Research article
Microfibril angle and density patterns of fertilized and irrigated Norway spruce. Silva Fennica vol. 38 no. 1 article id 439. https://doi.org/10.14214/sf.439
Two Norway spruce nutrient optimisation trials, one in the north of Sweden and one in the south, were used to study the effects of intensive growth and fertilization on wood density and microfibril angle. Three different treatments and a control were available; daily irrigation, daily liquid fertilization and solid fertilization. The nutrient optimisation was based on foliage analysis and the solid fertilization essentially comprised the same amount of nutrients but was applied annually in solid form. Measurements of density and microfibril angle (MFA) were performed using X-ray diffraction. Growth rate, expressed as a transformation of annual ring width, was very important at the southern site when the effect of cambial maturation had been taken into account. Effects of both fertilization and irrigation remained strong and significant for density, and irrigation was a significant factor explaining MFA. At the northern site distance from pith was the dominant factor but the effect of growth rate was also strong and the treatment effect was significant for both density and MFA. The combination of higher MFA and decrease in density for fertilized trees resulted in a lower calculated strength of the wood. An over 100% increase in ring width only corresponded to approximately a 20% decrease in wood density and the production of wood dry matter was hence increased by treatments.
article id 438, category Research article
Cell wall thickness and tangential and radial cell diameter of fertilized and irrigated Norway spruce. Silva Fennica vol. 38 no. 1 article id 438. https://doi.org/10.14214/sf.438
Two Norway spruce nutrient trials were used to evaluate the effects of fertilization and irrigation on transverse tracheid dimensions. Three different treatments and a control (C) were used; daily irrigation (I), daily liquid fertilization (IL) and an annual solid fertilization (F). The nutrient optimisation was based on foliage analysis and both liquid and solid fertilization essentially comprised the same amount of nutrients but the latter was applied annually in solid form. The cell measurements; cell wall thickness, radial and tangential cell widths, were obtained using image analysis (SilviScan at CSIRO, Melbourne, Australia). Mean annual cell wall thickness was decreased by fertilization (F and IL) on both sites whereas no effect of the irrigation on wall thickness could be detected. Radial cell width was increased by treatment at Flakaliden but at Asa the effect of irrigation and fertilization was reversed when the data structure i.e. development from pith and out and annual ring width was taken into account. Tangential cell width was not significantly affected by treatment at Flakaliden. At Asa fertilization caused a small increase on tangential cell width. Ring width was positively affected by treatment and is an important factor explaining the effects on primarily cell wall thickness and radial cell width.
article id 437, category Research article
Comparison of short-wood forwarding systems used in Iberia. Silva Fennica vol. 38 no. 1 article id 437. https://doi.org/10.14214/sf.437
Time studies were conducted to quantify the productivity and the operational cost of mechanized wood extraction in the Iberian Eucalyptus plantations. The key objectives were: to determine the significant variables that influence machine productivity and extraction costs in shortwood transport within the forest and to find the basis for optimization of shortwood transport with respect to Eucalyptus forest stands. Three machines were selected for study, each representative of the different log forwarding regimes that are used in Iberia and that could be extended to most of Southern Europe. These were: 1) a modified articulated dumper, 2) a purpose-built forwarder and 3) a farm tractor paired to a twin-axle forestry trailer. It was observed that the productivity and the cost of shortwood extraction may vary from 6 to 15 fresh tonnes/SMH and 3.5 to 6.5 Euro/fresh tonne, respectively. It was estimated that the optimal extraction route network covered approximately 10% of the forest surface. It was also observed that the modified dumper is the most-productive unit, and given its higher speed (> 5 km/h) and larger payload (16 tonnes), it is the economic choice for extraction distances in excess of 1000 m. However, it also generates the most severe rutting, hence it should be used with caution. For extraction distances below 1000 m, the light purpose-built forwarder compares favourably with the modified dumper, while generating less than half the site disturbance. The tractor-trailer combination is economically inferior to the modified dumper and the light forwarder, and should be regarded as a complement to the main extraction fleet and where short-haul operations are required. Under the assumptions of the study, light forwarders (8-tonne payload) may become competitive with heavier ones when road density is at least 6 m/ha, so that extraction distance does not exceed 1 km. This study provides a model for estimating the productivity and the cost of timber forwarding under varying conditions.
article id 436, category Research article
Thinning response and growth trends of seeded Scots pine stands at the arctic timberline. Silva Fennica vol. 38 no. 1 article id 436. https://doi.org/10.14214/sf.436
Growth patterns and reactions of Scots pine (Pinus sylvestris L.) to thinning in extremely harsh climatic conditions were studied in two seeded Scots pine stands located on the arctic timberline. Coniferous trees usually do not form closed stands at the timberline, but occur only in scattered tree groups. The trial was established in two stands in 1985–1986 when the trees were at an age of 47 and 56 years and an average dominant height of 6.0–6.9 m. The trial was remeasured in 1998. The thinning treatments reduced the stem number for five different levels; final density of 300, 550, 800, 1050, and 1300 stems ha–1 and unthinned. The experiment had a randomised block design with four replications in each stand. The increased growing space provided by thinning accelerated diameter growth after a delay of 2–3 years. The differences between the radial growth of the thinning treatments were very clear during the whole 13- to 14-year observation period. Annual increment of the mean diameter was regularly the higher, the larger the spacing. Dominant diameter was less influenced by treatments. There were no significant differences in dominant height between any of the treatments. Both basal area and volume were regularly the greater the higher the stem number was. Even a relatively light thinning had a distinct positive effect on tree growth, i.e. not carrying out thinning resulted in a production loss of merchantable wood. According to the results, seeded stands on the arctic timberline can grow surprisingly well in favourable conditions and reach a dominant height of 12–14 m in 100 years and a mean annual increment of 1.0–1.5 m3 ha–1 y–1 over a rotation period of 130–160 years. Based on increment figures and thinning reactions, a spacing of ca. 1000 stems ha–1 can be recommended.
article id 435, category Research article
Potential yield, return, and tree diversity of managed, uneven-aged Douglas-fir stands. Silva Fennica vol. 38 no. 1 article id 435. https://doi.org/10.14214/sf.435
The effects of different management regimes on uneven-aged Douglas-fir stands in the Pacific Northwest of the United States were predicted with a simulation model. Management alternatives were defined by residual stand structure and cutting cycle. The residual stand structure was set by basal area–diameter-q-ratio (BDq) distributions, diameter-limit cuts (assuming concurrent stand improvement), or the current diameter distribution. Cutting cycles of 10 or 20 years were applied for 200 years. The current diameter distribution was defined as the average of the uneven-aged Douglas-fir stands sampled in the most recent Forest Inventory and Analysis conducted in Oregon and Washington. Simulation results were compared in terms of financial returns, timber productivity, species group diversity (hardwoods vs softwoods), size class diversity, and stand structure. Other things being equal, there was little difference between 10- and 20-year cutting cycles. The highest financial returns were obtained with either a 58.4 cm diameter-limit cut, or a BDq distribution with 8.4 m2 of residual basal area, a 71.1 cm maximum diameter, and a q-ratio of 1.2. Using the current stand state as the residual distribution was the best way to obtain high tree size diversity, and high species group diversity. Several uneven-aged regimes gave net present values comparable to that obtained by converting the initial, uneven-aged stand to an even-aged, commercially thinned, plantation.
article id 434, category Research article
Contrasting tree-ring data with fire record in a pine-dominated landscape in the Komi Republic (Eastern European Russia): recovering a common climate signal. Silva Fennica vol. 38 no. 1 article id 434. https://doi.org/10.14214/sf.434
For the period 1420–1960 we contrasted fire events reconstructed at 14 sites distributed over a 50 km x 50 km area in the central part of the Komi Republic (European Russia) with a set of tree-ring width chronologies of Scots pine (Pinus sylvestris L.), developed for the same area. Our aim was to infer common climatic information contained in tree-ring variables and independently dated fire events with the help of a superposed epoch analysis. The strongest weather–growth link was shown for the latewood width, which was positively correlated with the temperature in April–May and July–August of the current growth season and with previous year precipitation in July–August. Earlywood width was positively affected by previous year precipitation in May and November. The relationship between yearly ring variables and multiple-site fire events was dependent on the seasonal timing of fire events as recorded in the scars. In years with early-season fires (which made up 37% of all fires dated with seasonal resolution) total ring width was significantly narrower. In years with late-season fires (63%) total ring width, earlywood, and latewood width were significantly wider. Years with late-season fires tended to be associated with local highs of the latewood width chronologies over 1400–1960, which implied a link between decadal-scale climate variation and fire regime of the area.
article id 433, category Research article
Variation in soil nutrient concentrations and bulk density within peatland forest sites. Silva Fennica vol. 38 no. 1 article id 433. https://doi.org/10.14214/sf.433
The within-site variability of soil characteristics on sites with different soil types remains poorly quantified, although this information is crucial for the success of research on soil properties, and especially for monitoring soil properties over time. We used coefficients of variation and multilevel variance component models to examine the within-site variation of soil (0–30 cm) mineral nutrient concentrations (P, K, Ca, Mg, Fe, mg g–1; Mn, Zn, mg g–1) and bulk density (kg m–3) on boreal deep-peat sites. We then evaluated the reliability of the site-level estimates (sample means) obtained using different sampling intensities (numbers of samples per site). Our 11 sites represented a single original site type within the oligotrophic nutrient level. Two of the sites were undrained while the rest had been drained for forestry at different points in time. Overall, P concentrations showed the smallest and Mn concentrations the largest within-site variation. The sampling depth contributed more than 50% of the total variance in all other characteristics except the concentrations of P and Fe, and bulk density. The variance proportions of peatland basin, site (within basin), and sampling location (within site) varied by sampling depth for most soil characteristics. The estimates obtained when using a certain number of samples per site were always more reliable for the 0–30 cm layer’s composite samples than for any single 10-cm layer at any depth sampled. On average, it was found that between 4 (P) and some 200 (Mn) samples per site would be needed for the estimates to have a theoretical 10% maximum deviation.
article id 432, category Research article
Comparison of methods for estimation of needle losses in Scots pine following defoliation by Bupalus piniaria. Silva Fennica vol. 38 no. 1 article id 432. https://doi.org/10.14214/sf.432
In 1996, ca. 7000 hectares of pine forests at Hökensås in SW Sweden were defoliated by the pine looper, Bupalus piniara (L.) (Lepidoptera. Geometridae). Following an aerial damage survey using CIR (colour infra red) photography, and estimation of pupal densities in the soil, ca 4000 ha of the most defoliated pine stands were sprayed in early August 1997 with Bacillus thuringiensis var. kurstaki. The control operation was succeessful but probably redundant, as no further defoliation occurred in unsprayed reference areas. In order to assess defoliation levels in different damage classes for later growth loss studies, 47 circular study plots were laid out in pine stands representing different damage and age classes. The remaining foliage was recorded for each tree using the following classes: 0, 10, 30, 50, 70, 90 and 100%. The defoliation levels in 1996 were estimated by disregarding the 1997 needle age class. Thirteen ca. 40-year-old sample trees representing different damage classes were felled, and the remaining foliage of all branches was estimated by needle age class using the above-mentioned scale. One branch in each of the whorls 1996, 1991, 1986 and 1981 was sampled and its needle dry weight was determined. The sample branch data confirmed the field observations that virtually no additional defoliation took place in 1997. The damage classes estimated from the CIR-pictures only agreed with the field damage estimates at the higher end of the damage scale. In contrast, the field estimate correlated well with plot means derived from tree-wise estimates (R2 = 0.93), and with with the calculated needle biomasses per tree (R2 = 0.90). Thus, the field damage classification was supported by the more detailed defoliation estimates, and hence forms a relevant basis for later growth loss studies.
article id 431, category Research article
Reduced simple ratio better than NDVI for estimating LAI in Finnish pine and spruce stands. Silva Fennica vol. 38 no. 1 article id 431. https://doi.org/10.14214/sf.431
Estimation of leaf area index (LAI) using spectral vegetation indices (SVIs) was studied based on data from 683 plots on two Scots pine and Norway spruce dominated sites in Finland. The SVIs studied included the normalised difference vegetation index (NDVI), the simple ratio (SR), and the reduced simple ratio (RSR), and were calculated from Landsat ETM images of the two sites. Regular grids of size 1 km2 with gridpoints placed at 50 m intervals were established at the sites and measurements of LAI using the LAI-2000 instrument were taken at the gridpoints. SVI-LAI relationships were examined at plot scale, where the plots were defined as circular areas of radius 70 m around each gridpoint. Plotwise mean LAI was computed as a weighted average of LAI readings taken around the gridpoints belonging to the plot. Mean LAI for the plots ranged from 0.36 to 3.72 (hemisurface area). All of the studied SVIs showed fair positive correlation with LAI but RSR responded more dynamically to LAI than did SR or NDVI. Especially NDVI showed poor sensitivity to changes in LAI. RSR explained 63% of the variation in LAI when all plots were included (n = 683) and the coefficient of determination rose to 75% when data was restricted to homogeneous plots (n = 381). Maps of estimated LAI using RSR showed good agreement with maps of measured LAI for the two sites.
Category: Review article
article id 411, category Review article
Stand dynamics modelling approaches for multicohort management of eastern Canadian boreal forests. Silva Fennica vol. 38 no. 4 article id 411. https://doi.org/10.14214/sf.411
The objective of this paper is to discuss approaches and issues related to modelling stand dynamics for multi-cohort forest management in eastern Canadian boreal forests. In these forests, the interval between wildfires can be rather long, and the development of natural forest stands may include the establishment, growth and mortality of several cohorts of trees. Later cohorts are characterised by increasing structural complexity, including spatial heterogeneity and irregular tree size distribution. A multi-cohort forest management framework has been proposed to maintain this complexity, and associated biodiversity, on the landscape. Multi-cohort forest management planning requires forecasts of the development of stands with complex structure in response to silvicultural treatment and to natural disturbance, but current stand dynamics models in the region are applicable mainly to even-aged mono-specific stands. Possible modelling approaches for complex stands include i) the adaptation of current whole-stand growth and yield models, ii) distance-independent, empirically-derived individual-tree models, such as the USDA Forest Service Forest Vegetation Simulator, and iii) distance-dependent, empirically-derived or process-oriented individual-tree models. We conclude that individual-tree models are needed because observational data for fitting whole-stand models are not available for the full array of silvicultural treatments and natural disturbances encompassed by multi-cohort forest management. Predictive accuracy is a concern with individual-tree models, and the incorporation of coarse-scale constraints into these models is a promising means to control error.
Category: Research note
article id 421, category Research note
Effect of thawing duration and temperature on field performance of frozen-stored Norway spruce container seedlings. Silva Fennica vol. 38 no. 3 article id 421. https://doi.org/10.14214/sf.421
Increasing use of frozen storage in nurseries at northern latitudes calls for thawing methods that are safe, economical and easy to apply on a large scale. The easiest and most economical method would be to thaw seedlings in the same boxes they were stored in. However, doing this safely requires more knowledge about how long and at what temperatures seedlings should or can be kept in the boxes without reducing field performance. In this study, 1-yr-old frozen-stored Norway spruce (Picea abies (L.) Karst.) container seedlings were thawed for 4, 8 or 16 days at 4 or 12 °C in cardboard boxes before planting on a reforestation site and on experimental field in mid-June. Some seedlings were also planted on these locations after thawing for only 7 hours at 12 °C in order to separate frozen root plugs. We found some evidence that planting seedlings after short thawing periods (7 hours at 12 °C and 4 days at 4 °C), under which conditions the root plugs remain completely or partly frozen, has a negative effect on field performance of Norway spruce seedlings. Thawing over a 4-8 day period in cardboard boxes at ca. 12 °C appears to ensure complete thawing of the root plugs and unaffected field performance, but is short enough to prevent the growth of mould.