Replacing Scots pine with Norway spruce : implications for biodiversity in production forests

• The production forests of southern Sweden are mainly dominated by either Scots pine (Pinus sylvestris) or Norway spruce (Picea abies). Public concerns are now being raised regarding a decrease in the area on which Scots pine is being regenerated, and an increased reliance on Norway spruce production stands. The main reasons for a shift in regenerated tree species include concerns regarding higher ungulate browsing pressure on Scots pine regeneration, together with the expectation that Norway spruce provides more favourable management and profits. The aim of this thesis was to examine the potential consequences of a tree species shift from different perspectives, but with a primary focus on implications for biodiversity. To do so the diversity of vascular plants, bryophytes, lichens and birds were contrasted in three age classes (30, 55, 80 years of age) of Scots pine and Norway spruce production stands in southern Sweden. Although there was an overlap from many of the common species, the community composition of species groups varied between the stand categories contrasted. (I) The cover of understory vascular plants was higher in all stand age classes of the Scots pine stands, compared to Norway spruce. The semi-light conditions, created by Scots pine’s less dense canopy, seems favourable to at least some keystone species, including, for example, the ericaceous shrub Vaccinium myrtillus. The denser canopy of Norway spruce limited vascular plant cover and species richness. (II) The darker and more humid Norway spruce stands were instead more favourable to a higher diversity of bryophyte species than was found in Scots pine stands. Scots pine associated forest floor species included a higher species richness and cover of terricolous lichens and bryophytes associated with dryer and lighter environment. (III) Scots pine and Norway spruce production forests support overlapping but still distinct bird communities, of which 80- year spruce stands had the highest average bird species richness, and largest total number of species recorded. These stands were associated with more broadleaves and higher stand complexity, i.e. vertical zonation, tree size variation and availability of dead wood. Study (IV) reviewed the biodiversity and ecosystem services consequences of a shift in tree species. Few benefits can be expected (e.g. reduced stand-level browsing damage), and these benefits will likely come at the expense of a range of negative outcomes for biodiversity, production, aesthetic and recreational values, as well as increased stand vulnerability to storm, frost, and drought damage, and potentially higher risks of pest and pathogen outbreak. Overall the findings of this thesis should clarify for forest owners, forest managers, and policymakers the many potentially adverse biodiversity and ecosystem service implications that could be expected if sites traditionally regenerated with Scots pine production stands are instead converted to Norway spruce.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

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