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Ancient forests – modern threats:
challenges for biodiversity
management in forest reserves
Jörg Brunet – Swedish Univ. Agricultural Sciences, Alnarp
Contents
• Temperate forest reserves in southern Sweden
• Conservation goals in forest reserves
• Emerging threats to forest biodiversity The Dalby Söderskog case
• Some lessons learnt
Forest reserves in Sweden
• Increasing areas (currently ca 175 000 ha in
the temperate part of the country)
• Focus on conservation of temperate
broadleaved forests in southern Sweden
• Many protected temperate forests
regenerated under semi-open conditions and
low or absent ungulate browsing during the
1800s
• High share of light-demanding long-lived tree
species: oak, ash, pine
Conservation goals for forest reserves
• Maintain desired successional
cycle (or stage) and its
biodiversity
• Full life cycles of native tree
species can be completed
• Natural regeneration of these
tree species
• Emerging threats may put
these goals at risk in many
reserves
Dalby Söderskog as a case for
emerging threats (and opportunities)
• “Skånes Suserup
skov”
• 36 ha forest reserve
since 1918
• Mixed oak-beechelm-ash forest
• 5 tree taxations
1909-2012
• 6 herb layer surveys
1935-2013
Old and emerging threats for
biodiversity in Dalby Söderskog
Earlier: Less disturbance after protection --> canopy
closure --> decreased plant diversity and lack of oak
regeneration
Now: Multiple emerging threats
• 1980s Dutch elm disease
• 1990s Invaded by the slug Arion vulgaris (lusitanicus)
• 2000s Ash dieback
• 2010s Invaded by wild boar Sus scrofa
Earlier: Crown encroachment and
increased mortality of “pasture” oaks
Result: Old-growth forest until 1980s
Ulmus - Fraxinus - Mercurialis perennis type
Now: Canopy opening by new diseases
Hymenoscyphus
pseudoalbidus:
Ash dieback
Ophiostoma
novo-ulmi:
Dutch elm
disease
Phytophthora plurivora
& P. cambivora affect
old beech trees
Ash dieback
Dutch elm
disease
The future: A new oak generation ?
Dalby Söderskog with live oaks (green dots),
dead oaks (crosses), and oak saplings 1.3-5m
m height (red dots) in 2012
A successor for the
fallen veteran oak?
Taking the opportunity…
Oak & hazel
Maple (& lime)
Open glades and flowering shrubs increase
Euonymus europaeus
Viburnum opulus
Crataegus spp.
Rosa spp.
Alternative successional pathways in
response to tree dieback?
• Source populations needed
• Most broadleaves sensitive to ungulate browsing
• No diverse natural regeneration in much of southern
Sweden due to heavy browsing pressure
Emerging threats affect all vegetation layers:
Slug herbivory causing decline of the dominant
forest herb: Mercurialis perennis
Wild boar invasion causing decline of
the vernal wildflower vegetation
2009
2012
Gradual decline of springflowers by yearly rooting
Plot 18 in spring 2010
Plot 18 in spring 2013
But: Wild boar may eat the slugs!
Exclosures needed to study effects on
tree regeneration
Conclusions
• Globalization of plant diseases and pests leads to
novel forest successions in many reserves
• Loss of old-growth structures and associated
biodiversity (e.g. epiphytes)
• Gain of open-habitat structures and regeneration
opportunities for valuable light demanding trees
• Herbivore control needed to enable natural
regeneration of remaining broadleaf species and pine
• Many reserves with minimum intervention or
traditional management may need active restoration
measures
Thank you
Acknowledgements:
Yulia Bukina, Per-Ola Hedwall, Emma Holmström,
Goddert von Oheimb, Emmelie Wahlgren