Potential for restoration of temperate deciduous forest by thinning of mixed forests on abandoned agricultural land

Abstract

The highest pressure biomes globally include the temperate deciduous forests (TDFs) of Europe (1). This biome has declined mainly due to agricultural land-use (2), and only small and isolated remnants exist today. Conservation and restoration are thus urgent priorities, and following the Nagoya protocol ratifying countries have committed to restore 15 % of degraded ecosystems within 2020.

The temperate deciduous forest biome is of outstanding importance for biodiversity, but presently covers only a small fraction of its former distribution area in Europe. Most land within the former distribution of TDF is under continuing high pressure from agriculture. However, recent and ongoing abandonment of marginal agricultural land in S Scandinavia (3) may represent a window of opportunity for restoration of TDF.

In Scandinavia, the recent, often mixed, forests often have closed canopy due to spruce succession, which may decrease biodiversity and ecosystem services associated with (semi-) open habitats, such as pollination. I will present data on the area of convertible recent forest with temperate deciduous trees in Norway and Sweden based on the National forest inventories. I will also report results from a field experiment on the economy of conservation-oriented thinning in this kind of forest. and 2) to evaluate the economic revenue and costs of partial cutting based on 26 field trials, 13 in Norway and 13 in Sweden.

The area of forest suitable for restoration according to our method implies a potential increase of TDF by about 100000 ha totally in Norway and Sweden should the whole area be restored. However, the geographical distance among sites and the possibility to combine the harvesting with other forms of forestry may be limiting factors and should be studied. Further, there are differences among the sites in terms of forest composition and structure and operating conditions, which means there is a significant variation in the cost of the thinning and the value of the wood. Our data indicate that sales of wood from the initial cutting may compensate the costs, but revenues may be limited. Subsidies to the land-owners may therefore be needed to stimulate activity.

In addition I will briefly mention potential effects on biodiversity. Based on published studies of similar forestry actions, I suggest that our restoration measures may have positive effects on biodiversity of several organism groups.

References

1. Venter O et al. (2016): Nature Communications 7: 12558, DOI: 10.1038/ncomms12558.

2. Spiecker H et al. (2004): Norway Spruce Conversion - Options and Consequences. European Forest Institute Research Report 18. Brill, Leiden. 269 p.

3. Bryn A et al. (2013): A high-resolution GIS null model of potential forest expansion following land use changes in Norway Scandinavian Journal of Forest Research 28: 81-98.