Can Equitably Mixed Plantation Forests Support an Arthropod Fauna
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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? Selected forest types known to differ in ground fauna and flora 6 replicates • Ash semi natural woodland • Oak semi natural woodland • Sitka spruce plantation • Canopy fogging • Pitfall trapping 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 phytotoxic effects • 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 3 plots of 5 traps per stand Pitfall sampling Sampling 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 Sample based rarefaction curves • 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 • Forest types differ Assemblages among forest types 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 Linyphiidae Forest Sampling Habitat Indicator type method Family Species association Hunting guild 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.