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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.

Summary Studies evaluating plant–soil biota interactions in both native and introduced plant ranges are rare, and thus far have lacked robust experimental designs to account for several potential confounding factors. Here, we investigated the effects of soil biota on growth of Pinus contorta, which has been introduced from Canada to Sweden. Using Swedish and Canadian soils, we conducted two glasshouse experiments. The first experiment utilized unsterilized soil from each country, with a full‐factorial cross of soil origin, tree provenance, and fertilizer addition. The second experiment utilized gamma‐irradiated sterile soil from each country, with a full‐factorial cross of soil origin, soil biota inoculation treatments, tree provenance, and fertilizer addition. The first experiment showed higher seedling growth on Swedish soil relative to Canadian soil. The second experiment showed this effect was due to differences in soil biotic communities between the two countries, and occurred independently of all other experimental factors. Our results provide strong evidence that plant interactions with soil biota can shift from negative to positive following introduction to a new region, and are relevant for understanding the success of some exotic forest plantations, and invasive and range‐expanding native species.

This paper reviews regeneration research during the past 20 years. The focus is mainly on planting of Norway spruce and Scots pine. Research on root morphology and nursery practices has played an important role in the introduction of containerized seedlings in northern Europe. In recent years, mini-seedlings have been tested. Conventionally, seedlings are planted in spring and early autumn but recent research indicates that Norway spruce seedlings can be planted from spring until the end of September. Soil temperature strongly influences seedling establishment in the harsh northern Scandinavian climate and a good way to increase soil temperature is to plant in elevated planting spots, which can be achieved by mounding. Soil scarification also reduces competition from field vegetation and damage by pine weevils. In southern Finland, Sweden and Norway, pine weevils are by far the most serious causes of damage to both Norway spruce and Scots pine. Therefore, designing regeneration treatments for decreasing pine weevil damage without using insecticides is one of the more important current research challenges. Examples of possible future trends in forest regeneration research are an emphasis on more basic research, use of fast growing tree species, multidisciplinary approaches and site-specific regeneration regimes.

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