Ground-dwelling spider diversity
in rare oak and yew woodlands
and the impact of grazing
Lauren Fuller
Overview
•
•
•
•
•
•
Introduction
Research questions
Methods
Results
Conclusions
Future research
% Total land area
12
10
8
6
4
2
0
1650
1700
1750
1800
1850
1900
1950
2000
Year
2% of total land area
is semi-natural
woodland
Forest
Forest Service
Service and
and National
National Parks
Parks and
and
Wildlife
Wildlife Service
Service
Killarney National Park
• UNESCO biosphere reserve since 1982
• Most extensive areas of semi-natural woodland in Ireland
• Internationally important woodland
– yew (Taxus baccata) on karst limestone pavement
– acidophilus sessile oak (Quercus petraea)
• Annex I of the EU Habitats Directive
Yew
Sessile oak
Deer in KNP
• Red deer (Cervus elaphus) present in County Kerry
since the Neolithic period
• More recently introduced Asian sika deer (Cervus
nippon)
• Estimated deer density in the Killarney area is 5–28
animals per km2
• Grazing pressure reduces the cover and diversity of
field layer vegetation, decreases the survival of tree
saplings and inhibits woodland regeneration
What’s spiders got to do with it?
Research questions
1.
Does KNP support rare or specialist species?
2.
Does deer grazing have an effect on spider diversity?
3.
What management recommendations can be made for deer
grazing to enhance biodiversity?
Methods
•
Derrycunihy wood – sessile oak
– 3 x exclosures and adjacent control area
•
Reenadinna wood - yew
– 1 x exclosure and adjacent control area
•
3 x plots in each exclosure and control
•
5 x pitfall traps set 2m apart in a linear
arrangement
•
Contents collected every 3 weeks from May to
August 2011 = 84 trapping days
Key results
Rare species
• Most species common in many types of broad-leaved and
coniferous woodland in Ireland
• Coelotes terrestris - range-restricted in Britain, threatened by the
lack of coarse woody debris and loss of semi-natural woodland
• Philodromus albidus - only recently discovered in Ireland and
range-restricted in Britain, favours open woodland
• Tapinocyba insecta - vulnerable in Britain, long-term decline due
to loss of ancient semi-natural broadleaved woodland
• Saaristoa firma, Agyneta subtilis, and Walckenaeria dysderoides vulnerable in Britain, but able to utilise a variety of habitats
Key results
P = <0.001
P = <0.001
60
P = <0.001
40
20
P = <0.01
P = <0.001
0
Total species
Forest specialists
Ground runners
Space web-builders
Exclosure
Spider species richness
Spider abundance
80
Grazing in oak woodland
20
P = <0.05
15
10
5
0
Total species
Oak exclosure
Tangle weaver
Oak control
Sheet/ tangle
weavers
Control
Key results
Spider abundance
50
Grazing in yew woodland
Exclosure
P = <0.001
40
30
20
10
0
Total species
Forest
specialists
Yew exclosure
Sheet/ tangle
weavers
Yew control
Control
Conclusions
• Lack of ancient semi-natural woodland in Ireland
• Killarney National Park may provide an important and nationally
scarce habitat for vulnerable and range-restricted spider species
• Deer grazing has an indirect negative effect on spider diversity by
reducing structural diversity of the habitat
– Although not in yew, possibly due to
culling in the area
Exclosure
Control
Conclusions
• Deer exclusion = initial
increase in vegetation
cover
• Ground flora diversity can
decline as understory
vegetation cover increases
- competitive plant species,
e.g. Luzula sylvatica,
bramble and ivy,
outcompete woodland
specialists
• Long-term deer exclosures
may lead to a decline in
vegetation diversity and a
decline in spider diversity
Conclusions
•
Temporary exclosures to allow woodland regeneration
•
Low level of deer grazing is a better solution
– Benefits woodland specialist ground vegetation
– Prevents woodland closure (P. albidus)
•
Forestry Commission Woodland Grazing Toolbox
– light grazing = sward generally >10 cm tall
•
Spider diversity was higher in ungrazed oak plots with greater cover of
lower field vegetation (10–50 cm high)
– light grazing to prevent woodland closure whilst maintaining a sward
height of >10 cm
•
Absence of deer predators
– Culling
Future research
• Long-term monitoring of exclosures to assess
effect of woodland closure vs. deer grazing
• Sample more yew woodland
• Other bioindicator taxa – carabids or
lepidoptera
Acknowledgements
Miles Newman – Trinity College Dublin
Killarney National Park rangers
Sandra Irwin, Tom Kelly and John O’Halloran – University College Cork
Funded by COFORD - Department for Agriculture, Food and the Marine
Thanks for listening
Key results
Spider species composition
NMDS ordination
Oak exclosure ()
Yew exclosure ()
Oak control ()
Yew control ()