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In the northern boreal region, tree growth, timber yields and economic returns are low, meaning low regeneration costs are the basis of profitable forestry. If natural regeneration is successful, it may be favoured over expensive planting or seeding. We studied the regeneration success and early growth of Scots pine in gaps in terms of seedling density and height 10 years after gap cuttings in central Finnish Lapland. Three gap sizes (diameters of 20, 40, and 80 m) were studied on patch scarified xeric and sub-xeric sites in six random blocks and a total of 18 replicates of each. The number of pine seedlings was high across the gap sizes. The proportion of empty regeneration plots (size 5 m2) was ∼ 2%. Site preparation substantially increased the number of seedlings. The growth of seedlings was faster in larger gaps, but a high proportion of exposed mineral soil decreased it. The results suggest that all studied gap sizes regenerated naturally well, and that soil scarification exposing 10–20% of the surface area or even less can be enough to achieve regeneration goals. Gaps of a diameter of 40 m or more are required to achieve an optimal balance between seedling density and growth. [ABSTRACT FROM AUTHOR]

The influence of thinning on growth, development, and yield of a spruce understory and a pine overstory was examined based on an experiment including five stands in southern Finland. Two thinning intensities (regular and heavy) were applied to the pine overstory. They were combined with four treatments in the spruce understory: total removal, retention of 800 and 1600 stems ha−1, and untreated. The plots were remeasured at 5-year intervals during the monitoring period of 10–15 years. The results indicated that thinning of the pine overstory significantly promoted the diameter growth of the spruce understory trees throughout the 10–15-year study period without notable delay, and height growth with a substantial lag during the first 5-year period. The influence was swifter and greater with heavier thinning. Thinning of the understory did not influence the height growth of the dominant understory spruces or the growth of the overstory. Complete removal of the understory resulted did not consistently influence growth of the overstory. It was concluded that a spruce understory seemed to thrive and grow relatively well under an overstory of pine, but repeated thinnings in the overstory were required to sustain understory vitality and growth in a prolonged two-storied situation. [ABSTRACT FROM AUTHOR]

The objective of the study was to examine the success of regeneration in gaps of variable size in pine-dominated stands in terms of seedling density. It was based on an experiment in central Lapland containing circular clear-cut gaps of 20, 40 and 80 m in diameter on typical sub-xeric and xeric pine sites with site preparation (patch scarification). The observation period covered the first five years after cutting. The average number of seedlings that had emerged after gap cutting was about 22 000 ha−1 for pine and 7 000 ha−1 for birch. The proportion of regeneration sample plots without any pine seedlings was less than 10%. The seedling density diminished constantly with greater distance from the edge stand but indicating sufficient density up to the largest gap size in the study (diameter 80 m, area ca. 0.5 ha). Site preparation promoted regeneration remarkably, and we conclude that successful regeneration would be achieved in most cases with soil scarification exposing just 10-20% of the soil surface. [ABSTRACT FROM AUTHOR]

• Natural regeneration was highest when tree density was low and mineral soil exposed. • With site preparation more trees can be retained, maintaining the same seedling number. • Seedling growth was low in denser stands and negligible in unthinned control stands. In northern boreal region the growth of forests is slow, and yield and profit are low, which is why low reforestation costs are important for profitable forestry. If natural regeneration is successful, expensive artificial forest regeneration (planting or direct seeding) can be avoided. In this study, we look at the impact of overstory density and site preparation on natural regeneration and seedling growth of Scots pine. Study stands were established in different parts of Northern Finland and in each stand following treatments: 50, 150 and 250 trees ha−1 or unthinned control, where the stand density was ≥ 250 trees ha−1, were randomly allocated to experimental plots. In addition, site preparation (disc trenching, 4000–5000 m ha−1) was carried out on two experimental plots in which tree density was either 50 or 150 trees ha−1. In the experimental stands seedling number, age and growth were monitored for 11 years. Monitoring revealed that the number of seedlings increased with decreasing tree density. Average seedling height growth was very low or even non-existent in the unthinned control and in the densest (250 trees ha−1) treatment, but increased when the density of trees decreased. The highest seedling number and the highest growth were achieved when the tree density was 50 trees ha−1 and the soil was prepared to expose mineral soil. Achieving e.g. 2000 seedlings ha−1, would need about 40% exposition of mineral soil. The required low tree density implies that not only seed supply from seed trees and site preparation is important for regeneration success in northern boreal Scots pine forests but also the reduction of competition by mature trees. [ABSTRACT FROM AUTHOR]

The study focused on the success of regeneration on patch cuts in spruce-dominated stands in terms of stocking and tree height. It was based on an experiment in the Kainuu region in northern Finland. The experimental design included 8 stands with 58 clearcut patches of variable size (0.09–0.37 ha), on which either natural regeneration without site preparation or site preparation and planting of Scots pine was applied. A regeneration survey was conducted 13–15 growing seasons after treatments. Patches without site preparation had been restocked quite well from natural seed sources. The average number of trees was about 11,000 ha−1, of which 1700 ha−1 crop trees. With site preparation and planting, the stocking levels were also very high, 25,000 and 2100 ha−1, respectively. One hundred percent of the planted patches and 75% of the naturally regenerated patches had an acceptable density. Restocking was equally good across the range of patch sizes. Tree growth had been somewhat slower in the smallest patches than in the largest ones in the range. Natural regeneration was capable of yielding good regeneration results in most patches, especially when site preparation was applied. Stocking levels and height development were higher yet in the planted patches. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The purpose of the study was to examine the effect of retained Scots pine (Pinus sylvestris L.) trees in the context of even-aged management systems on height, diameter growth, and branching of individual Scots pine seedlings and seedling stands in Southern Finland. A modeling and simulation approach was applied. Empirical models were constructed using data sets acquired from temporary sample plots in nine stands. The models were used to simulate tree height, diameter, and branch diameter growth. Results indicate that Scots pine trees retained in Scots pine seedling stands had not brought about unstocked or very poorly stocked patches around their bases in the study stands. Each retained tree of 25–40 cm in diameter reduced the height growth potential of Scots pine seedlings about 9–17% within a circle of 10 m radius. Retained tree competition did not result in reduced tree diameter for a given height. Retained tree influence on the diameter of the thickest branch of a seedling was rather small for practical applications, but the sum branch cross-sectional area was reduced, especially on fertile sites. In stand level simulations, the retention of 48 ha−1 trees of 25 cm average diameter and 21 m height on a rather poor site resulted in 15 years in about 5–7% decrease in seedling height, 6–8% decrease in diameter, and 2–5% decrease in maximum branch diameter compared to no retention, varying with the seedling stand density. The effect of the spatial pattern of retention in random, regular, or clustered structures on seedling growth was marginal. [Copyright &y& Elsevier]

Pine-spruce forests are one of the commonest mixed forest types in Europe and both tree species are very important for wood supply. This study summarized nine European studies with Scots pine and Norway spruce where a mixed-species stand and both monocultures were located in an experimental set-up. Overyielding (where growth of a mixed stand was greater than the average of both monocultures) was relatively common and often ranged between 0% and 30%, but could also be negative at individual study sites. Each individual site demonstrated consistent patterns of the mixing effect over different measurement periods. Transgressive overyielding (where the mixed-species stand was more productive than either of the monocultures) was found at three study sites, while a monoculture was more productive on the other sites. Large variation between study sites indicated that the existing experiments do not fully represent the extensive region where this mixed pine-spruce forest can occur. Pooled increment data displayed a negative influence of latitude and stand age on the mixing effect of those tree species in forests younger than 70 years. [ABSTRACT FROM AUTHOR]