Johan Sonesson

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.

Socio-ecological implications of modifying rotation lengths in forestry

The rotation length is a key component of even-aged forest management systems. Using Fennoscandian forestry as a case, we review the socio-ecological implications of modifying rotation lengths relative to current practice by evaluating effects on a range of ecosystem services and on biodiversity conservation. The effects of shortening rotations on provisioning services are expected to be mostly negative to neutral (e.g. production of wood, bilberries, reindeer forage), while those of extending rotations would be more varied. Shortening rotations may help limit damage by some of today’s major damaging agents (e.g. root rot, cambium-feeding insects), but may also increase other damage types (e.g. regeneration pests) and impede climate mitigation. Supporting (water, soil nutrients) and cultural (aesthetics, cultural heritage) ecosystem services would generally be affected negatively by shortened rotations and positively by extended rotations, as would most biodiversity indicators. Several effect modifiers, such as changes to thinning regimes, could alter these patterns.

Site index and productivity of artificially regenerated Betula pendula and Betula pubescens stands on former farmland in southern and central Sweden

Site index and productivity of artificially regenerated stands of silver birch (Betula pendula Roth) and downy birch (Betula pubescens Ehrh.) on former farmland in southern and central Sweden were examined. The material comprised sample plots in 27 stands, measured in both 1990 and 1993. Silver birch was the dominating species in most stands, and the average site index (SI) was nearly 28 m. Site quality ranged from 5.3 m3 ha−1 yr−1 (equivalent, from tables, to a SI of 22 m) to 11.4 m3 ha−1 yr−1 (equivalent to an extrapolated SI of 32 m). Soil moisture was the only site factor tested that significantly affected SI for silver birch. Moist sites were found to be inappropriate for this species especially on fine‐textured sediment soils. On moist sites, SI for downy birch was as high as SI for silver birch. Growth of artificially regenerated silver birch on former farmland differed significantly from growth of naturally regenerated birch on forest sites, according to two Swedish growth simulators.

Genetic variation in drought tolerance in Picea abies seedlings and its relationship to growth in controlled and field environments

Drought tolerance, phenology, height‐growth and biomass were studied in 36 open‐pollinated Picea abies families in a growth chamber over two growth periods. Three different irrigation treatments were applied: well‐watered, periodic drought and lethal drought (involving watering during the first growth period and withholding water during the second). The periodic drought treatment yielded significantly smaller seedlings than the well‐watered treatment. In the lethal drought treatment 5.6% of the seedlings were still alive after 3 months without irrigation. Heritabilities for drought damage score, days to wilting and days to necrosis in the lethal drought treatment were 0.41, 0.23 and 0.20, respectively. Additive genetic correlation estimates between drought tolerance traits and growth traits in the growth chamber treatments and in four field progeny trials were weak and mainly non‐significant. High drought tolerance was correlated with early budset and, to a lower extent, late budburst. In conclusion, selection for height growth and late budburst as practised in Swedish breeding and propagation populations is not likely to reduce seedling drought tolerance.

Retrospective Genetic Tests of Pinus sylvestris L. in Growth Chambers with Two Irrigation Regimes and Two Temperatures

The objective of this study was to estimate genetic correlations between stem volume in seven 19-30-yr-old field progeny trials and growth traits assessed in 1-yr-old Pinus sylvestris seedlings in growth-chamber treatments with optimal and limiting water availability at two temperatures. The seedlings in the growth-chamber experiment were open-pollinated families from two Swedish seed orchards. The field trials were established with full-sib families with the same parents. The genetic correlations between stem volume in the field progeny trials and height and biomass traits in the growth chamber were mainly low or zero. There was no clear pattern of juvenile-mature correlations with respect to combinations of growth-chamber treatments, field test site temperature and water availability. Periodic drought in the juvenile stage did not improve the juvenile-mature correlations, suggesting that at the juvenile stage, the mature stage, or both, the families used in this study do not appear to be specifically adapted to drought conditions.

Balancing seed yield and breeding value in clonal seed orchards

Seed orchards should produce seeds that are both abundant and of high genetic value. This study suggests methods to achieve such a compromise and study their efficiency. The methods were applied on data obtained from 41 seed orchard clones of Scots pine from mid-Sweden. The value of the seed orchard crop was set as a function of its breeding value, the amount of seeds produced and their gene diversity, measured as the effective number of clones. The proportion of ramets of different clones that maximized this value was regarded as the optimum for deployment of the clones in a seed orchard. The results were compared with truncation selection for breeding value, truncation selection for clone benefit (the product of seed production and breeding value) and linear deployment (where ramets are deployed linearly in relation to breeding value). The influence of two parameters was studied: the relative importance of breeding value for seed value and the size of the penalty for reducing the value of the seed crop with respect to lost gene diversity. The conventional wisdom is to select the clones with the highest breeding values, but that turned out to be the most inferior alternative studied. Clone benefit truncation provided a good approximation to optimal benefit for cases, where the effective number was low and dependence of breeding value limited.

Fine root production and nitrogen content in roots of Pinus sylvestris L. after clear-felling.

Effects of clear-felling on fine root production and N content in roots were studied in a Scots pine (Pinus sylvestris L.) stand. A plot was clear-felled and root samples were compared with a control plot. Even if reduced by 50%, a significant fine root (diameter<2 mm) growth was noticed up to 1 yr after the clear-felling. For live roots (diameters 2-4 and 4-6 mm) nitrogen content in root-wood and root-bark samples from the clear-felling, compared with the reference plot, were 30-50% already higher 2 months after the clear-felling. The difference did not increase in later comparisons. Nitrogen content in buttresses did not differ during the period studied, except for a higher percentage in bark at the clear-felling after two summers. A second study confirmed the results. It is suggested that there exists a continued nitrogen uptake in live roots after a clear-felling.

Simulated long-term effects of varying tree retention on wood production, dead wood and carbon stock changes

Boreal forests are an important source of timber and pulp wood, but provide also other products and services. Utilizing a simulation program and field data from a tree retention experiment in a Scots pine forest in central Sweden, we simulated the consequences during the following 100 years of various levels of retention on production of merchantable wood, dead wood input (as a proxy for biodiversity), and carbon stock changes. At the stand level, wood production decreased with increased retention levels, while dead wood input and carbon stock increased. We also compared 12 scenarios representing a land sharing/land sparing gradient. In each scenario, a constant volume of wood was harvested with a specific level of retention in a 100-ha landscape. The area not needed to reach the defined volume was set-aside during a 100-year rotation period, leading to decreasing area of set-asides with increasing level of retention across the 12 scenarios. Dead wood input was positively affected by the level of tree retention whereas the average carbon stock decreased slightly with increasing level of tree retention. The scenarios will probably vary in how they favor species preferring different substrates. Therefore, we conclude that a larger variation of landscape-level conservation strategies, also including active creation of dead wood, may be an attractive complement to the existing management.

Varying rotation lengths in northern production forests: Implications for habitats provided by retention and production trees

Because of the limited spatial extent and comprehensiveness of protected areas, an increasing emphasis is being placed on conserving habitats which promote biodiversity within production forest. For this reason, alternative silvicultural programs need to be evaluated with respect to their implications for forest biodiversity, especially if these programs are likely to be adopted. Here we simulated the effect of varied rotation length and associated thinning regimes on habitat availability in Scots pine and Norway spruce production forests, with high and low productivity. Shorter rotation lengths reduced the contribution made by production trees (trees grown for industrial use) to the availability of key habitat features, while concurrently increasing the contribution from retention trees. The contribution of production trees to habitat features was larger for high productivity sites, than for low productivity sites. We conclude that shortened rotation lengths result in losses of the availability of habitat features that are key for biodiversity conservation and that increased retention practices may only partially compensate for this. Ensuring that conservation efforts better reflect the inherent variation in stand rotation lengths would help improve the maintenance of key forest habitats in production forests.

Genetic variation in responses of Pinus sylvestris trees to natural infection by Gremmeniella abietina

Abstract In 2001 large areas of Pinus sylvestris L. stands in Sweden were attacked by Gremmeniella abietina (Lagerb.) Morelet. The resultant damage was assessed in five genetic field trials and one clonal seed orchard, with the aims of quantifying the genetic variation in tree responses to G. abietina, studying the genetic relationship between G. abietina susceptibility and growth traits, and examining the implications of the results for P. sylvestris breeding. A comparison of G. abietina damage between plus-tree progenies and seed stand check-lots in each of four tree classes (dominant, co-dominant, subordinated and suppressed) found no significant differences except in the suppressed tree class, where plus-tree progenies were damaged less severely than trees from the seed stands. Narrow- and broad-sense heritability for G. abietina damage traits were in the range 0.22–0.42. Genetic correlations between G. abietina damage and growth traits were weak and not significantly different from zero. The results imply that selection for growth capacity in P. sylvestris breeding programmes using plus-tree selection or field progeny tests does not increase susceptibility to G. abietina. In addition, there is scope for selecting genotypes with increased resistance if this is required in the future.