The role of environmental heterogeneity in determining arthropod diversity in boreal forests

Anne Oxbrougha, Sergio Garcia-Tejeroa, Stephane Bourassac, John O’Halloranb, John Spencec

a Department of Biology, Edge Hill University, United Kingdom; b School of Biological, Earth and Environmental Science, University College Cork, Ireland; c Department of Renewable Resources, University of Alberta, Canada anne.oxbrough@edgehill.ac.uk

Background and hypotheses• Habitat structure has a key role in the supply and variability of

resources, with more heterogeneous environments providing a greater array of niches, thus enhancing species diversity.

• Traditional approaches to forest management (e.g. clear-cutting) typically reduce habitat heterogeneity across large scales, though the effect at smaller scales, which are relevant to organisms such as arthropods, are not well known.

• The successional cycle of boreal forests typically takes place over several hundred years, and sustained clear-cutting reduces cover of the later coniferous stages.

We examined the relationship between habitat heterogeneity and arthropods and tested the following hypotheses:1. Habitat characteristics and arthropod composition are affected to

a higher degree by clear-cutting along the successional gradient.2. Habitat heterogeneity (variability of habitat characteristics) and

arthropod beta diversity increase along the successional sequence and are reduced by clear-cutting across spatial scales.

Hypothesis 2: Mean (± 95% CI) multivariate distance to group median at

several spatial scales as a measure of beta diversity and habitat heterogeneity*

ResultsHypothesis 1: Differences in composition and habitat structure across the

successional gradient tested with two-way Permanova

Methods• Spiders, carabid and staphylinid beetles were collected using

pitfall traps in boreal forests at the EMEND forestry experiment in Alberta, Canada during summer 2010.

• 18 stands were sampled with three replicates each of mature deciduous dominated (DD), conifer dominated (CD), mix (MX) and six of 12 year old regenerating stands.

• Habitat characteristics (vegetation, stem density, soil pH and litter depth) were measured.

• Data were analysed at small scales (within-plots, 20-40m), medium scales (between plots within a stand, 50-250m) and between stands (0.4-5km).

Key findings• Overall clear-cutting had a greater effect on composition and

habitat structure in the later successional stages.• Habitat heterogeneity was greater in mature stands and later

successional stages.• Beta diversity of spiders and staphylinids reflects this trend at small

and medium scales whereas carabids exhibited no difference in beta diversity between stands, possibly related to their more generalist nature.

• Beta diversity and heterogeneity did not differ at stand scale.• Management decreased habitat heterogeneity and beta diversity

at small scales. This effect was greater in later successional stages.

Acknowledgements Spence lab at the University of Alberta; Lindsey Dewart, Jason Edwards, Charlene Hahn for help in the field and laboratory; Fieldwork supported by the EMEND project and co-funders: Daishowa-Marubeni International Ltd.; Canadian

Forest Products Ltd.; Alberta Sustainable Resource Development; Foothills Research Institute; Photographs: Roy Anderson (http://www.habitas.org/), Ed Nieuwenhuys (http://ednieuw.home.xs4all.nl/l) , Stephen Creswell (www.americaninsects.net); This research was funded through an IRCSET-Marie Curie International Mobility Fellowship in Science, Engineering and Technology.

Ed Nieuwenhuys © 2010Stephen Creswell © 2010

Fig.2 EMEND experimental areahttp://www.emendproject.org/

Inset: Location in Alberta, Canada

Fig.3 Pitfall trap

Forest type Stage Interaction

Spiders ** *** *MXRegen ≠ MXMat

CDRegen ≠ CDMat

Staphylinids ** CD≠ DD, MX *** n.s

Carabids * CD≠DD ** n.s

Habitat structure ** *** *MXRegen ≠ MXMat

CDRegen ≠ CDMat

* P = <0.05; ** P = <0.01; ***P = <0.001

Mature deciduous

Fig.1 Key phases of boreal mixed wood succession

Mix of deciduous/conifer

Regenerating

Mature conifer

*only significant differences are shown in graphs