Nils Fahlvik

Replacing monocultures with mixed-species stands: Ecosystem service implications of two production forest alternatives in Sweden

Whereas there is evidence that mixed-species approaches to production forestry in general can provide positive outcomes relative to monocultures, it is less clear to what extent multiple benefits can be derived from specific mixed-species alternatives. To provide such insights requires evaluations of an encompassing suite of ecosystem services, biodiversity, and forest management considerations provided by specific mixtures and monocultures within a region. Here, we conduct such an assessment in Sweden by contrasting even-aged Norway spruce (Piceaabies)-dominated stands, with mixed-species stands of spruce and birch (Betula pendula or B. pubescens), or spruce and Scots pine (Pinussylvestris). By synthesizing the available evidence, we identify positive outcomes from mixtures including increased biodiversity, water quality, esthetic and recreational values, as well as reduced stand vulnerability to pest and pathogen damage. However, some uncertainties and risks were projected to increase, highlighting the importance of conducting comprehensive interdisciplinary evaluations when assessing the pros and cons of mixtures.

Influence of precommercial thinning grade on branch diameter and crown ratio in Pinus sylvestris in southern Sweden

Precommercial thinning is regarded as one of the most important measures for influencing timber quality in stands of Scots pine (Pinus sylvestris L.). The present study considers the influence of both thinning intensity and tree height at the time of thinning on diameter of the thickest branch and crown ratio. A total of 115 plots (either naturally regenerated, planted or sown, and either thinned down to 528–8000 stems ha−1 or untreated) included in 20 sites in southern Sweden were analysed. The average tree height after thinning varied from 1.2 to 8.3 m. An increasing number of remaining stems resulted in a reduction in branch diameter, although the reduction appeared to be only minor if the number of stems after thinning was more than 3000 stems ha−1. It was found that late thinning reduced the diameter of the thickest branch. The crown ratio decreased with stand height, number of stems after thinning and average height at thinning. The results were consistent for all trees and for the 500 thickest trees per hectare.

Models for predicting individual tree height increment and tree diameter in young stands in southern Sweden

Abstract Individual tree height increment functions and general diameter–height relationships were developed for Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula pendula Roth and Betula pubescens Ehrh.) trees growing in young stands in southern Sweden. A random parameter approach was applied to account for the spatial correlation in the data. Variables for initial tree size and measures of both stand density and relative competitive status were common to all sets of functions. Data for constructing the models were collected from the HUGIN young stand survey, a large survey of young forest stands. The validation procedures indicate that the models give reliable estimates of tree height and diameter up to an average tree height of at least 15 m. However, height growth of birch in mixtures with conifers was slightly overestimated, probably because damage was not considered in the growth forecasts. The diameter of spruce was underestimated for regularly spaced experimental plots.

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.

Comparison of carbon balances between continuous-cover and clear-cut forestry in Sweden

Continuous-cover forestry (CCF) has been recognized for the production of multiple ecosystem services, and is seen as an alternative to clear-cut forestry (CF). Despite the increasing interest, it is still not well described how CCF would affect the carbon balance and the resulting climate benefit from the forest in relation to CF. This study compares carbon balances of CF and CCF, applied as two alternative land-use strategies for a heterogeneous Norway spruce (Picea abies) stand. We use a set of models to analyze the long-term effects of different forest management and wood use strategies in Sweden on carbon dioxide emissions and carbon stock changes. The results show that biomass growth and yield is more important than the choice of silvicultural system per se. When comparing CF and CCF assuming similar growth, extraction and product use, only minor differences in long-term climate benefit were found between the two principally different silvicultural systems.

Simulation of the long-term effects of different strategies for precommercial thinning in Pinus sylvestris

ABSTRACT The influence of the intensity and timing of precommercial thinning (PCT) on stand development and financial return was studied in Scots pine stands. Functions describing the early development of the stand structure after PCT were developed. The functions were based on 195 plots within 41 PCT experiments in Sweden. The dimension distribution of the established stand was estimated and used as input to the decision support system Heureka, to simulate the stand development until final felling. The studied treatments included PCT to 1000, 2000 and 3000 stems ha−1 at mean heights of 2, 4 and 6 m. Separate simulations were carried out for different site fertilities. Mean annual volume increment increased with increasing number of stems after PCT whereas the timing of PCT had only a small effect. The land expectation value (LEV) generally decreased with increasing mean height at PCT, primarily because of the increased cost of PCT. LEV decreased with increasing number of stems after PCT at low fertility sites whereas only minor differences were found for PCT to 1000 and 2000 stems ha−1 at medium and high fertility sites. The general pattern persisted when different scenarios of future timber quality were simulated.