Eric Agestam

The effects of shelterwood density and site preparation on natural regeneration of Fagus sylvatica in southern Sweden

Abstract The natural regeneration of beech (Fagus sylvatica) was studied under various shelterwood densities and soil preparations in a 130-year-old beech stand in southern Sweden. Between 1990 and 1996, seedling emergence, survival, growth and damage were followed in a clear-cut and in two shelterwoods with different densities, in plots with undisturbed ground, bare mineral soil or ridges with mineral soil on top of humus. Irradiation, soil and air temperatures, soil moisture and precipitation were continuously recorded during the first three growing seasons. The seedling emergence was higher in the shelterwoods than in the clear-cut. The mortality was the highest during the first year. The seedling number was the highest on bare mineral soil and the lowest on undisturbed ground, for all cutting regimes. The increase in seedling height and dry mass was greater in the clear-cut and in the sparse shelterwood than in the dense shelterwood. Damage due to frost was more frequent in the clear-cut than in the shelterwoods. Effects of most kind of damage had only minor influence on the seedling height, whereas in seedlings experiencing frequent damage height was reduced.

Scarification and seedfall affects natural regeneration of Scots pine under two shelterwood densities and a clear-cut in southern Sweden.

A study was undertaken to evaluate the effect of Scots pine (Pinus sylvestris) shelterwood density and timing of removal on the regeneration of forests with improved wood quality. This paper focuses on the effect of scarification and seedfall on the success of natural regeneration of Scots pine under two shelterwood densities and in a clear-cut. Wood quality aspects will be addressed later in the study. After 4 yrs, natural regeneration of Scots pine under a 200 stems ha-1 shelterwood reached 90000 seedlings ha-1, 53000 under a 160 stems ha-1 shelterwood and 3700 in a clear-cut. The high natural regeneration under the densest shelterwood resulted from a high seedfall, slower invasion by competing vegetation, consequent prolonged recruitment and low mortality. Since mortality largely decreased for both shelterwood densities and recruitment seems to continue, the success of regeneration should be maintained in the future if proper release operations are conducted. The latter could begin when seedlings reach a height of about 0.5 m and the cover should be maintained until they reach a height of about 6 m. Therefore, it may be possible to use 200 stems ha-1 Scots pine shelterwoods in southern Sweden to obtain dense stands and thus improve wood quality (stem taper, wood density, etc.).

Modelling incidence of root rot in picea abies plantations in Southern Sweden

An empirical model is presented to forecast the incidence of root rot at stand level. In addition, the impact of different thinning programmes on the incidence of root rot is evaluated. The model is based on data from 152 permanent forest research plots of pure Picea abies in southern Sweden, within which the incidence of root rot at stump height in thinned trees has been recorded after each thinning since 1950. In total, about 20 000 stumps have been studied. According to simulations with the model, areas previously used as fields or for grazing are particularly susceptible to root rot, while old hardwood sites are less susceptible. Furthermore, simulations with the model imply that the earlier, the harder or more often a stand is thinned, the faster will be the development of root rot.

Increment and Yield in Mixed and Monoculture Stands of Pinus sylvestris and Picea abies Based on an Experiment in Southern Sweden

Experimental growth data collected over 20 yrs were used to assess volume increment and yield in mixed and monoculture stands with Scots pine and Norway spruce. Differences in volume increment were generally small between the different types of stand, indicating that there is little to be gained in total volume increment from using mixed stands with Norway spruce and Scots pine instead of monocultures on sites with medium fertility. However, since the volume increment of pine per unit area was higher in the mixture than in the monoculture, the results indicate that retaining some Norway spruce in Scots pine stands would result in an increase in the total volume increment. The diameter of the Scots pine was 1.2 cm greater in the mixture than in the monoculture at the end of the observation period. There was no layering on the plots, but the Scots pine trees were slightly taller and thicker than the spruce. The Scots pine stems tapered more in the mixture than in the monoculture. Stem defects were not consistently different between the stand types. The diameter distribution of the total tree population in the mixture was less tightly clustered round the mean than in the monocultures. Research designed to identify ways to increase total volume increments using mixed stands should probably focus on mixtures of species that differ more in growth patterns than Scots pine and Norway spruce apparently do.

Effect of spacing on 23-year-old lodgepole pine (Pinus contorta Dougl. var. latifolia) in southern Sweden

Abstract The objective of this study was to compare volume growth and external timber quality properties of lodgepole pine (Pinus contorta Dougl. var. latifolia) stands planted in different spacings (1.41×1.41, 2.00×2.00, 2.83×2.83, 4.00×4.00) in southern Sweden. In northern Sweden lodgepole pine has been grown for a long time and shows superior volume production compared to Scots pine (Pinus Sylvestris L.). The Swedish Forestry Act restricts establishment of lodgepole pine plantations in southern Sweden. However, it is important to increase the knowledge about lodgepole pine and its potential use also in this part of the country. Two experiments in southern Sweden were studied. Each trial was designed as a random block experiment with two blocks. Both investigated stands had an age of 23 years at the time of assessment. The mean diameter and the volume production differed significantly between the spacings. The highest volume production was found in the narrowest spacing, 313% compared to the widest spacing. Significant differences between spacings were also found concerning external quality traits. The frequency of dominant and co-dominant trees without defects was 24% in the most open spacing compared to 46% in the narrowest one. Under current circumstances approximately 2500 seedlings/ha in the initial stand seems to be a reasonable compromise between growth, diameter development and timber quality.

Development of single-storied mixtures of Norway spruce and birch in Southern Sweden

Abstract In a stand with planted Norway spruce (Picea abies (L.) Karst.) and naturally regenerated birch (Betula pendula Roth and B. pubescens Ehrh.) in southern Sweden, the proportion of birch was reduced in 0.1-ha plots at pre-commercial thinning to 0%, 20% or 50% of the total stem number (2000–2500 stems ha−1 after the thinning). The growth of both species was surveyed 4 and 10 years later. No significant between-treatment differences were observed on either occasion in total yield or in spruce diameter (apart from a more negative skewness of the diameter distribution of Norway spruce in the mixture with 50% birch compared to pure spruce). Birch retained its initial advantage in dominant height (of about 2 m) throughout the 10-year measurement period; hence, height growth rates of Norway spruce and birch were very similar. After three, four and 10 growing seasons, whipping damage to Norway spruce caused by birch was registered in the 20% and 50% birch mixtures, in which the proportions of damaged spruces were found to be similar, with 17% and 15% of damaged trees at the last inventory, respectively. In addition, simulations of the stands’ development from the time of the last measurement until final felling at a total age of 66 years indicated that growth, yield and net present value decrease with increasing birch proportion, but if the proportion of birch removed in subsequent thinnings is increased, the between-treatment differences are reduced.

Mixed Forests as a Part of Sustainable Forestry in Southern Sweden

Abstract We review and discuss the applicability of mixed stands in the context of sustainable forestry in southern Sweden. This is done from a silvicultural perspective regarding aspects such as regeneration, pre-commer-cial thinnings, production, economy, damage and policy implications. The paper is based on literature reviews and on studies performed in southern Sweden or under comparable conditions. After considering the underlying mechanisms, we find that it is possible to establish a mixed stand in the regeneration phase and sometimes even to a lower cost compared to monocultures. To keep the mixture, or to create it, with pre-commercial thinnings is, however, often more expensive. The reviewed studies, together with a new simulation, show that the effect on productivity of mixed stands compared to monocultures is minor. Some positive effects on damage (i.e., decreased levels) in mixed stands have been found. The economy and the policy implications of mixed stand management were found to be dependent on the specific stand and situations. A general finding was that research and knowledge of managing mixed stands, as compared to monocultures, are limited, which in turn could limit the applicability of mixed stand management.

A site index model for lodgepole pine (Pinus contorta Dougl. var. latifolia) in northern Sweden

ABSTRACT A model was developed for predicting site index (SI) values and top height growth of lodgepole pine in northern Sweden. Data on 169 experimental plots from 61 experiments were used for model construction. Six dynamic site equations derived using the generalized algebraic difference approach (GADA) were tested. All of the equations estimate height and SI values on the basis of a known height and total age, and are base-age invariant. Unbiased parameter estimates were obtained by non-linear modelling without accounting for autocorrelation of residuals. The special formulation of the Hossfeld model and the GADA-transformed logistic function produced the most reliable SI curves. The Hossfeld model is recommended as it did not produce extreme outlying estimates for young stands. The developed model is polymorphic with variable asymptotes and can predict SI and dominant height growth for lodgepole pine between 20 and 50 years old.