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MILJØFORSK-Miljøforskning for en grønn samfunnsomstilling

Transformation of recent forest on abandoned agricultural land for the benefit of biodiversity, ecosystem services and green solutions

Alternative title: Omforming av ny skog på nedlagt jordbruksmark for biologisk mangfold, økosystemtjenester og det grønne skiftet

Awarded: NOK 7.6 mill.

Expansion of agriculture and other land-use has during the last millennium led to a steep decline of temperate deciduous forest (TDF), a biome of outstanding importance for biodiversity. However, the total area and standing volume of temperate deciduous trees are now increasing due to re-colonization on abandoned (marginal) agricultural land. Most of the recent forests within the boreonemoral zone in Scandinavia is a mix of deciduous trees and Norway spruce, and management approaches may be needed to restore biodiversity and ecosystem services. Based on national forest inventories there is > 100.000 hectares of 40-80 year old mixed forest with temperate deciduous trees to in Norway and Sweden. At 26 field sites we studied the effects on biodiversity of restoration cutting by removal of spruce. We hypothesized that creating a semi-open canopy may favour flowering plants, pollination, regeneration of oak, and recreation value. We also studied cost efficiency, social acceptability and policy restrictions and opportunities of the restoration. The recent forests, prior to restoration cutting, had limited value for biodiversity of forest plants, but were relatively rich in insects and wood-decaying fungi. Relatively few red-listed species were found compared to old-growth forests. We related biodiversity of plants and fungi to land-use history at the sites as interpreted from aerial photos. The results showed that recent forests in the boreonemoral zone are richer in biodiversity in landscapes with low forest cover (both in 1960 and at present), which should be taken into account in restoration planning. Each site had one managed plot and one reference plot, each 1 ha. About 25% of the wood volume, mainly spruce, was removed from the managed plots in the winter 2016/2017. Vascular plants, fungi on dead wood, insects, were recorded in both plots in 2016. Surveys were repeated in 2019 to evaluate effects of restoration cutting on biodiversity. The number of vascular plants and their flowering frequency increased significantly in restoration cut plots compared to reference plots, as did the number of insect individuals and species. It also favoured the survival of oak seedlings, one of the most important trees for biodiversity. In addition, we measured tree growth and production of dead wood at 14 sites that are part of a related project in Sweden, 16 years after similar restoration cutting. Canopies had largely closed and tree growth had compensated for half of the extracted volume, but optimal cutting interval needs to be studied further. The volume of dead wood had increased by 78% in managed plots leading to a more natural forest structure and probably more favourable conditions for saproxylic organisms. To study where restoration of TDF is most favourable, we used the systematic planning tool PrioritzR to identify areas in SW Norway where restoration may optimize several relevant goals: to cover hotspots for threatened species, possibilities for outdoor recreation, and opportunities for spruce timber extraction. We found synergistic landscape effects: sites with high biodiversity value often overlapped with high recreation value and possibilities for extraction and sale of spruce timber, implying possibilities for cost-efficient restoration. In interviews, the land-owners expressed commitment to conserve and restore biodiversity in their forests, and were positive to the improved aesthetics and accessibility as a result of restoration cutting. However, variation in forest composition and structure, and operating conditions, lead to significant variation in the cost of restoration cutting and the value of the wood. Sale of wood compensated for the cost of restoration cutting only at a volume above ca 50 m3/ha, and there is a need to provide subsidies to promote interest. TDF and its biodiversity seems to a large extent to have been left out in the Biodiversity White Papers, the hearings and parliamentary debate and among stakeholders in Norway in general, despite all informants having a positive image of deciduous woodlands. The sectorial responsibility needs to be defined since these areas have been managed by partly agricultural, partly forestry, practices. There are a number of incentives for landscape and biodiversity management that may be applicable, but the TDF will compete with other landscape types and more established types of restoration, management etc. If these forests are defined as 'nature' the Ministry of Environment and Climate would be the responsible actor. Payments to transform these areas into 'nature' are possible, but if the defined aim is to re-establish 'nature', they may not qualify for continued (long term) management payments. We conclude that recent mixed forests should be seen as an opportunity to restore TDF in the boreonemoral zone by removal of spruce, but that increased activity will be dependent on targeted subsidies.

Land use has historically led to a steep decline of temperate deciduous forest, a habitat of outstanding importance for biodiversity that presently covers only a fraction of its former distribution area in Europe. However, the total area and volume of temperate deciduous trees are now increasing, mainly due to encroachment of agricultural and pastoral land. The recent, often mixed, forests pose both problems and possibilities for biodiversity conservation, opening for novel solutions with the potential to counteract multiple pressures. Canopy closure by spruce succession, introduced forest pathogens and excessive browsing by deer may interact to decrease biodiversity and ecosystem services associated with (semi-) open habitats, such as pollination. By field experiments, we aim to test if negative effects can be countered by a novel forestry practice that may enhance the level of ecosystem services, while improving the conditions for threatened biodiversity, and to test its technical and economic feasibility. To identify sustainable management we will analyze the social, economic and environmental impacts for different actors. Further, we will analyze the policy opportunities and potential to govern the development of abandoned agricultural land towards semi-open temperate deciduous forest while balancing conservation objectives, climate mitigation targets, energy production from renewable sources, and impacts for local communities. This approach can offer a valuable supplement/alternative to the Climate Forest program, a Norwegian policy implying cultivation of dense well-stocked spruce forest within the range of temperate deciduous forest. We will compare effectiveness of our restored forest to alternative land uses in terms of achievement of multiple goals, with particular focus on biodiversity, carbon sequestration and storage, and recreation. Our studies will be performed in south Norway and Sweden, with cooperation of a team of leading international scientists.

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MILJØFORSK-Miljøforskning for en grønn samfunnsomstilling