Can ground-based assessments of forest biodiversity be used as a proxy for changes

in the canopy assemblage?

Scott Pedley1, Anne Oxbrough2, Rebecca Martin3, Sandra Irwin3, Thomas Kelly3, John O’Halloran3

1 Durham University, UK

2 Edge Hill University, UK

3 University College Cork, Ireland.

Canopy research

Sampling the canopy

Can ground-based assessments of forest biodiversity be used as a proxy for changes in the

canopy assemblage?

Canopy and ground-dwelling fauna differ, but…

are there consistent similarities in diversity of ground and canopy fauna between forest types?

6 replicates• Ash semi natural woodland• Oak semi natural woodland• Sitka spruce plantation

• Canopy fogging• Pitfall trapping

Selected forest types known to differ in ground fauna and flora

Spiders in the canopy: generalist predators….

• Structural features: web builders and active hunters

• Prey availability:

size (aphids, diptera, beetles)

Canopy Fogging

• Once per site

• Petrol-driven fogging machine (SwingFog)

• A natural pyrethroid

• Non-persistent in the environment (24 hrs)

• No phytotoxiceffects

• Not harmful to mammals/birds at levels used

• Canopy fogged until fully covered in insecticide (6-9 mins).

• Dry, calm conditions (wind < 8kph) and after a dry night.

Arthropod collection

• 16 plastic sheets

• Combined area of 24m2

•1m above ground

• In place for 3 hours

Pitfall sampling 3 plots of 5 traps per standSampling for 12 weeks during summer

Results

• 3933 individuals of 109 species

• Pitfall trapping: 3205 spiders from 87 species

• Canopy fogging: 728 spiders from 36 species

• 14 species common to canopy and pitfalls

• 73 unique to pitfalls

• 22 unique to canopy

• Forest types ordered in a similar way

• in semi-natural forests than plantations for pitfall-trapped assemblages (GLM, F =5.1409

P=0.0200)

• No differences between forest types for canopy-fogged assemblages

• Both CF and Pit Sitka samples approaching asymptote

Sample based rarefaction curves

Assemblages among forest types• Forest types differ significantly (Deviance = 360.6, P=0.007 pitfall; Deviance=137.4, P=0.004 canopy)

• Significant concordances between pitfall and canopy (Procrustes: m2 = 0.77, correlation coefficient = 0.48, P=0.026)

• However, there is not strong surrogacy between sampling methods (m2 = <50, correlation coefficient >0.7)

Stress scores 0.14 and 0.15 respectively. Points are sampled sites with lines connecting to forest type centroids; polygons represent 95% CI of centroids

Habitat associations

• Contrasting patterns in woodland specialists

• Pitfalls: no difference

• Canopy: in spruce

Habitat associations: dominated by LinyphiidaeForest

type

Sampling

method Family Species

Habitat

association Hunting guild

Indicator

value P-value

Ash Pitfall trap Linyphiidae Ceratinella scabrosa Generalist Sheet web 0.831 0.013

Pitfall trap Linyphiidae Lepthyphantes tenebricola Woodland Sheet web 0.808 0.039

Canopy fog Tetragnathidae Tetragnatha montana Generalist Orb web 0.773 0.044

Oak Pitfall trap Linyphiidae Walckenaeria acuminata Generalist Sheet web 0.850 0.012

Pitfall trap Linyphiidae Microneta viaria Generalist Sheet web 0.793 0.039

Pitfall trap Linyphiidae Walckenaeria dysderoides Generalist Sheet web 0.772 0.033

Sitka Pitfall trap Linyphiidae Centromerus dilutus Generalist Sheet web 0.840 0.015

Pitfall trap Linyphiidae Diplocephalus latifrons Woodland Sheet web 0.809 0.042

Pitfall trap Linyphiidae Monocephalus fuscipes Woodland Sheet web 0.727 0.050

Canopy fog Linyphiidae Pelecopsis nemoralis Woodland Sheet web 0.921 0.006

Canopy fog Linyphiidae Lepthyphantes obscurus Woodland Sheet web 0.816 0.030

Hunting strategy

• Fewer active hunters caught in

canopy than expected

• In contrast with literature

• Irish fauna depauperate or

sampling effect?

• Greater ‘proportion’ of web

spinners that require structural

diversity are found in canopy

Conclusions: canopy assemblages changes broadly reflect those on the ground

• Community composition and species richness estimates

• Either method could be used to evaluate differences and test management regimes in well-replicated experiments of forest type.

• More than one fogging sample should be collected

Conclusions: separate surveys will be required when detailed inventories are the goal

• Web builders respond differently between canopy and ground

• Within-forest type differences in habitat structure may not be consistent between canopy and ground Both of these are

Sitka spruce forest floors!

Conclusions: separate surveys will be required when detailed inventories are the goal

• Fewer active hunters than expected due to depauperate Irish fauna with few specialists or not enough sampling?

• Irish forest cover <1% in the 1900s.

• Poor recolonisation ability of active hunters in the canopy?

• The majority of species were Linyphiidae, which readily balloon as juveniles and adults.

• More detail required on Irish spider forest fauna – are there any forest ‘specialists’?

Conclusions: more detailed knowledge required of Irish spider forest fauna

• Are there any true forest ‘specialists’?

• Sitka spruce had a greater number of forest-associated species than native forests?

• SS represent 60% of all forest in Ireland

• Since 1950s

• Predominately Linyphiidae in the canopy with good dispersal ability

• Native woodland in small patches, ~1% of land area, therefore depauperate?

Acknowledgements

• Colleagues on the PLANFORBIO research programme

• Coillte Teoranta, Irish Forest Service and various landowners