Sauli Valkonen

Effect of Betula pendula Admixture on Tree Growth and Branch Diameter in young Pinus sylvestris Stands in Southern Finland

The effects of a birch admixture on the height and diameter growth and maximum branch diameter in planted Scots pine stands was studied using models constructed with a data set from 13 stands of 9–16 yrs of age and 2–8 m dominant height on average sites on mineral soils in southern Finland. The density and height of the birch varied highly between and within stands. Simulated results indicated that the pines were capable of keeping up in height growth with birches that had originated from seed. Even a very high number of birches (10 000 stems ha−1) had virtually no effect on the height growth of the pines. The number of birches had a pronounced effect on the diameter growth and the maximum branch diameter in pine. Retention of a temporary birch component in young pine stands seems a feasible way of mitigating the adverse effects of low planting densities on the external quality of pine.

Ingrowth, survival and height growth of small trees in uneven-aged Picea abies stands in southern Finland

The purpose of the study was to analyse height growth, mortality, and ingrowth of individual small-sized trees in uneven-aged spruce-dominated stands. It was based on experimental data from 16 stands for a 15-year observation period including four measurements with a 5-year interval. In the data of this study, the heights of small-sized trees varied from 0.1 to about 9 m. Results showed that the growth of small trees was rather slow, particularly in the smallest size classes. With average growth rates it would take about 60 years for a freshly emerged spruce germinant to achieve 1.3 m in height. The stand density, site quality and selection cuttings affected the growth of small-sized spruces. Average five-year mortality rates for spruce, birch and pine were 17.0%, 40.9% and 33.9%, respectively. Annual ingrowth rates with the threshold height of 1.3 m for the three species were on average 30.4, 2.8 and less than 0.1 trees per hectare, respectively. Even if, a selection cutting of modest intensity (25% of basal area removed on average) seemed to have accelerated the growth of small spruces, it is recommended that more intensive harvestings be applied to enhance the survival and growth of small spruces. It is also concluded that shade intolerant species like birch and pine do not seem to be capable of developing into viable undergrowth in spruce selection stands with their current levels of stand density.

Effect of edge stands on the development of young Pinus sylvestris stands in southern Finland

Abstract The quantitative effect of pine-dominated edge stands in southern Finland on the density and growth of pine saplings was addressed in the study. The cumulative effect of a mature edge stand on the development of a pine sapling stand with variable cutblock sizes was also estimated. The data were acquired from 10 study sites with a Scots pine sapling stand with a current dominant height of 1–6 m and an adjoining middle-aged to mature edge stand dominated by Scots pine. Tree level models were constructed to describe and simulate the structure and development of the sapling stands. The results indicated that dividing an average regeneration area (2 ha) into smaller cutblock units (1.0–0.5 ha) appreciably increased the edge stand effect. Total stand volume growth was 6% lower on 1 ha cutblocks, and 31% lower on 0.5 ha blocks, than on 2 ha blocks.

Feasibility of silviculture for complex stand structures: designing stand structures for sustainability and multiple objectives

The concepts of ‘from homogeneity to heterogeneity’, ‘from simplicity to complexity’, and ‘from an agricultural system to a natural disturbance-based system’ are widely recognized in alternative silviculture. Stand structure is closely related to microclimate, cycling of materials, quality and quantity of wildlife habitat, and other ecological functions. Therefore, stand structure determines the sustainability and resilience of forest ecosystems. Most forest services, such as timber production, wildlife conservation, maintenance of aesthetics, and hydrological values, are stand structure dependent. These services are influenced by the manipulation of stand structure. Silviculture that maintains complex stand structure and continuous crown cover over time is termed multi-aged forestry (O’Hara 1996), close-to-nature forestry (Mlinsek 1996) or continuous-cover forestry (Garfitt 1995). This type of silviculture is being widely advocated to meet changing social demands, from economic profit to environmental services. Integrating complexity into silviculture prescription is therefore believed to improve the resilience and adaptability of managed forests (Puettmann et al. 2008). Achieving a silvicultural system for complex stand structures requires close, diligent control of overstory stock and canopy coverage to ensure successful seedling regeneration and growth. Therefore, a more complex silvicultural system is generally more expensive and labour intensive, or requires more advanced techniques. How can we feasibly build up forest ecosystems with complex stand structures from both the ecological and economic points of view? To help solve this question, we organized the Sixth Workshop of the Uneven-Aged Silviculture Group (IUFRO) in Shizuoka from 24 to 27 October 2008. The workshop was entitled ‘Feasibility of silviculture for complex stand structures, designing stand structures for sustainability and multiple objectives’. Ten papers presented at this workshop are included in this special issue, which we believe will promote future studies and practices for sustainable forest management. Studies on long-term dynamics of stand structures in uneven-aged stands provide us with a feasible basis for integrating complexity into silviculture. Three papers included in this issue show the result of stand structure dynamics in the long term after operations. Lähde et al. (2010) compare stand volume increments over 17 years among three alternative unevenand even-sized management approaches. Klopcic and Boncina (2010) show a difference in growth pattern in long-term growth of silver fir– European beech in single-selection forests in Slovenia. Deal et al. (2010) report on growth 50 years after partial harvesting of western hemlock–Sitka spruce stands in southeast Alaska and compare this with newly regenerating stands following clear-cutting, and uncut old-growth stands. Mimicking natural disturbance systems is recognized as an efficient silviculture approach for complex stand structures. Information on the response of stand structure to natural disturbance will provide tools and models for manipulating uneven-aged managed stands. We include here four examples of how information on natural H. Mizunaga (&) Faculty of Agriculture, Shizuoka University, Ohya 836, Suruga, Shizuoka 422-8529, Japan e-mail: mizunaga@agr.shizuoka.ac.jp

Models for the establishment and height development of naturally regenerated Pinus sylvestris in Finnish Lapland

Abstract The study focused on constructing models for the establishment and seedling height development of naturally regenerated seedling stands in the natural regeneration of Scots pine by the seed-tree method in Lapland, northern Finland. Modelling was used to describe the dynamics of the regeneration process and to analyse the principal ecological factors and management activities influencing regeneration success. Models for the density of seedling stands were developed with the generalized linear mixed model method. The most significant variables affecting seedling establishment were elevation, time since the establishment cutting, the interaction of forest site type and site preparation, and stoniness. The results indicated that the average stocking level tends to remain unsatisfactory on moist, fertile site types without site preparation. Seedling height development was modelled as a function of age using the linear mixed model. Age explained 97% of the variance of seedling height. Other independent variables in the model were effective temperature sum, site preparation and the presence or absence of seed trees.

Damage to saplings in mechanized selection cutting in uneven-aged Norway spruce stands

Abstract Damage to 0.5–2.5 m saplings in selection cuttings in uneven-aged Norway spruce stands was studied in three stands in Finland. Harvest removals were 96–122 m3ha−1 or 32–41% of initial basal area. Harvesting was carried out with one-grip harvester and forwarder in March–April 2007. The strip road network had been established in previous cuttings. Before harvesting, trees higher than 2.5 m were measured and mapped with coordinates. Saplings 0.5–2.5 m were measured on circular sample plots of 10 m2 on a square grid, where line and plot intervals were 7.07 m. Trees to remove were selected with a computerized tree selection procedure and marked before cutting. Factors affecting the probability and severity of injury to an individual sapling were studied with logistic regression models. Percentage of injured saplings was 17.6, 29.8, and 61.0%, depending on study stand. Stem breakage was the most common type of injury. Distance of the sapling from the nearest strip road, sapling height, harvested basal area within 25 m of the sapling, and the distance to the nearest remaining tree were statistically significant factors in the model of the probability of injury. In the model for the severity of injury, only the distance from the nearest strip road and the sapling height were significant. Saplings near strip roads were vulnerable during both cutting and forwarding, and they often ended up under slash or logs. Development in working methods and machinery are potentially effective in reducing sapling damage in selection cuttings.

Effect of timing of precommercial thinning on the consumption of working time in Picea abies stands in Finland

The effect of the timing of precommercial thinning on the productivity of work was examined in young Norway spruce [Picea abies (L.) Karst.] stands in southern Finland. The common problem of large variation between sample plots in time studies was avoided by introducing a new approach based on a combination of stand measurements, tree-ring analysis and existing work productivity functions. The results indicated that a 2 year delay in the precommercial thinning of a stand was enough to cause an increase of 10-42% in the consumption of working time at a mean height of 1.5-3.1 m. At a later thinning, at a mean height 4.1-7.2 m, the increase was 8-24%. The development of the stand up to the first commercial thinning was not significantly influenced by a 2 year delay in the late precommercial thinning.

Regeneration and tree growth dynamics of Picea abies, Betula pendula and Betula pubescens in regeneration areas treated with spot mounding in southern Finland

Abstract This study addresses the dynamics of young stands established in areas of southern Finland which have been site prepared with spot mounding and planted with Norway spruce. The principal attributes investigated were the density of natural birch on the major soil surface types associated with the method (mounds, patches and undisturbed soil) and the growth rate of the planted spruces compared with natural birches. The study material included 18 regeneration areas treated with spot mounding and planted with Norway spruce container seedlings, around three, six or nine growing seasons before measurement. Rather than permanent plots that would have constituted a genuine time series, the data collected for the study originated from a sample of stands of different ages. The results indicated that there were comparatively few birches on the mounds after 3 years, but greater average densities were evident at 6 and 9 years than on the patches and undisturbed soil. Compared with methods such as patch scarification and disc trenching, the observed delay in the emergence of birch probably gives spruce a competitive advantage during the most susceptible, earliest stages of development in spot mounding.

Natural regeneration in patch clear-cutting in Picea abies stands in Southern Finland

Abstract The success of natural regeneration on patch clear-cuts in Norway spruce stands in Southern Finland was examined in terms of stocking and tree height. The experiment was established in mature spruce stands in the submesic Myrtillus (MT) site type. In each of the eight study sites, three plots were treated with clear-cutting and planting, clear-cutting with partial tree retention and planting, and patch clear-cutting without site preparation, respectively. In three of the study sites, one plot with patch clear-cutting and site preparation was established. Each plot was 1 ha, out of which three patches of 40×40 m were clear-cut in the patch treatments. 10–11 years after cutting, the patches had on average 1316 crop trees ha–1, of which 91% were spruces. Some 27% of the stands were up to the target stocking level (≥1600 ha−1), and 36% were at least satisfactory (≥1300 ha−1). Site preparation did not yield greater stocking levels on patches, but that result is ambiguous due to a difference in initial stocking. The average spruce tree height in the patches (0.76 m) was much smaller than in the case of clear-cutting and planting (2.42 m). In conclusion, the patches had been restocked tolerably well with spruce and birch for practical purposes during the 10- to 11-year period, but the regeneration process had been very slow compared to clear-cutting and planting.

Forest management inspired by natural disturbance dynamics (DISTDYN) – a long-term research and development project in Finland

A large-scale and long-term research and development project Forest management inspired by natural disturbance dynamics (DISTDYN) was initiated in Finland in 2009. The aim is to examine how variation in spatial and temporal scales of felling affects forest structure and biota. Harvesting methods applied in this project include selection, gap, partial and clear felling with variable retention. Rehabilitation is also applied as dead wood is intentionally increased while harvesting. The motivation of the project lies in the growing interest in using natural disturbances as an inspiration of forest-ecosystem management and in the recognition that mid- to small-scale disturbances are a characteristic feature of unmanaged Fennoscandian forests. The effects of felling methods are studied at the stand scale. However, a unique aspect of the project is the focus on landscape-scale impacts of different harvesting alternatives by comparing ca. 150-ha landscape units with varying harvesting regimes. Overall, the project aims at creating a long-lasting multidisciplinary research infrastructure. It also addresses core issues of forest-ecosystem management, including ecological, timber-production, economic and socio-cultural performances of alternative harvesting practices.