Tom Gittings1, George Smith2, Mark Wilson1, Laura French2, Anne Oxbrough1, Saoirse O

1
Biodiversity across the forest cycle in ash and
Sitka spruce plantations Comparison of trends
between taxonomic groups and management
recommendations
Tom Gittings1, George Smith2, Mark Wilson1, Laura
French2, Anne Oxbrough1, Saoirse ODonoghue2,
Josephine Pithon1, Vicki ODonnell3, Anne-Marie
McKee2, Sue Iremonger2, John OHalloran1, Daniel
Kelly2, Fraser Mitchell2, Paul Giller1 1
BIOFOREST Project, Department of Zoology, Ecology
and Plant Science, University College Cork 2
BIOFOREST Project, Department of Botany, Trinity
College Dublin 3 Coastal and Marine Resources
Centre, University College Cork
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BIOFOREST Project Objectives

• Assess the range of biodiversity in
  representative Irish plantation forests at key
  stages of the forest cycle
• Develop indicators of Irish plantation forest
  biodiversity
• Assess the effectiveness of the Forest
  Biodiversity Guidelines

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Methods

• 3 forest types Sitka spruce (Picea sitchensis),
  ash (Fraxinus excelsior) and Sitka spruce-ash
  mixes
• 5 structural groups reflecting degree of
  structural development
• Sites matched for geographical location, soil
  type, altitude and drainage, as far as possible
• Surveyed plants, spiders, hoverfly and birds and
  collected GIS data for surrounding landscape

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Objectives of this presentation

• Identify similarities and differences between
  taxonomic groups in how their biodiversity
• - Changes over the forest cycle
• - Varies between forest types
• Discuss management recommendations

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Biodiversity in ash and Sitka spruce plantation
forests

• Over the forest cycle, ash and Sitka spruce
  plantations can support diverse vegetation,
  spider, hoverfly and bird assemblages.
• Assemblages contain a large proportion of
  generalist species and we recorded few species of
  conservation importance.
• Mature stands develop a characteristic woodland
  flora and support forest specialist spiders and
  hoverflies.

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Assemblage structure

• Pre-thicket sites (red) clearly separated from
  the more structurally developed sites (all
  groups).
• Greater variation among sites in pre-thicket
  (red) compared to most other structural groups
  (spiders, hoverflies and birds).
• Semi-mature and mature ash sites (green circles)
  clearly separated from the other structural
  groups (vegetation, spiders and hoverflies).

Vegetation
Birds
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Mantel test analyses of similarity between
patterns of variation in species composition

• Using an appropriately specified single
  structural classification as a framework for
  biodiversity conservation planning in ash and
  Sitka spruce plantation forests will represent
  the broad variation in assemblages of these
  taxonomic groups

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Mantel test analyses of similarity between
patterns of variation in species composition

• Selecting complementary sites for conservation on
  the basis of their vegetation assemblages will
  tend to capture the range of assemblage variation
  in spiders. But this pattern may reflect major
  environmental differences between sites, so may
  not apply when looking at sites from a narrow
  environmental range.

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Comparison between taxonomic groups of trends in
species richness across the age-cycle

• Total species richness
• Most groups that show differences, except
  bryophytes, have high species richness in the
  pre-thicket stage and low species richness in the
  intermediate stages.
• In Sitka spruce, the mature stage generally has
  high species richness.

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Comparison between taxonomic groups of trends in
species richness across the age-cycle

• Forest species richness
• Generally increases with increasing structural
  development in all the taxonomic groups.
• Open species richness
• Generally decreases after the initial stages of
  structural development.
• May increase again at the mature stage (vascular
  plants in Sitka spruce, spiders in all sites).

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Pairwise correlations of species richness between
taxonomic groups I

• Total species richness
• Few significant correlations.
• But significant correlation between spiders and
  hoverflies consistent across most structural
  groups.

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Pairwise correlations of species richness between
taxonomic groups II

• Forest species richness
• All pairwise correlations significant, or nearly
  significant reflecting low species richness in
  pre-thicket sites.
• Most relationships (except between spiders and
  hoverflies) do not hold when pre-thicket sites
  removed.

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Pairwise correlations of species richness between
taxonomic groups III

• Plot scale (vegetation vs. spiders)
• Few significant correlations.
• Differences in responses of species assemblages
  to structural development complicates
  interpretation.

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Comparison between ash and Sitka spruce

• Few overall differences in species richness
• Total species richness of spiders and bryophytes
  significantly higher in Sitka spruce.
• Greater species richness of forest spiders in
  Sitka spruce.
• Greater species richness of vascular plants and
  saproxylic hoverflies in ash.
• Crop species (ash or Sitka spruce) does not have
  a
• major effect on stand-scale biodiversity in
• plantation forests

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Effect of adding ash to a Sitka spruce plantation

• Few differences in species richness within
  plantations between ash and Sitka spruce
  components.
• Did not detect many differences in species
  richness between pure and mixed plantations (but
  due to problems of matching sites?).
• Differences within plantations in assemblage
  composition between ash and Sitka spruce
  components.
• Retention of mature ash component of mixed
  plantations into the next rotation will enhance
  plantation biodiversity.
• Adding ash to a Sitka spruce plantation increases
• vegetation, spider and hoverfly biodiversity at
  the
• plantation scale

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Forestry Management
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Recommendations Forest planning

• Modifications to Forest Biodiversity Guidelines
• Choose improved grassland sites over semi-natural
  habitats for afforestation
• Establish plantations in close proximity to
  semi-natural woodland (vegetation).
• Leave small unplanted areas to maintain gaps
  through the forest cycle (vegetation, spiders,
  hoverflies).
• Leave small areas of wet habitat unplanted and
  avoid drainage where possible (hoverflies).
• Design complex edges and leave boundaries
  unplanted to increase proportion and diversity of
  edge habitat (birds).
• Leave areas of scrub unplanted (birds).

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Recommendations Forest management

• Modifications to Forest Biodiversity Guidelines
• Guidelines to help foresters to identify
  potentially important habitats for ground flora,
  spider and hoverfly biodiversity (vegetation,
  spiders, hoverflies).
• Rigorous thinning to prevent canopy closure
  (vegetation, spiders, hoverflies).
• Retain mature Sitka spruce forests, where there
  is no risk of damage to adjoining semi-natural
  habitats (vegetation, spiders).
• Retention of standing and fallen trees
  (hoverflies).

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Project Funding
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• Project Website
• http//bioforest.ucc.ie