Soil biodiversity and ecology

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This report presents a review of some aspects of soil biodiversity and ecology, with emphasis on macro-invertebrates, as part of the Australian Terrestrial Biodiversity Assessment 2008 for the National Land and Water Resources Audit (NLWRA).

Soils are not just inert means to support plants; rather they teem with a unique biodiversity that fundamentally influences above and below ground plant and animal communities, and provide important ecosystem services. Soil biodiversity is nonetheless relatively poorly understood in comparison to above-ground biota. In Australia, sampling records are patchy and we possess a limited ecological understanding for most species. Despite this, soil biodiversity is critical in regulating major ecosystem processes (e.g. decomposition of organic matter and nutrient cycling) and Australia is home to many iconic as well as Gondwanan relictual species. While a reduction in the abundance and diversity of soil biodiversity will compromise overall ecosystem function, we lack understanding of how much redundancy is present in our soil communities and thus how resilient our systems are to change.

This report focuses on earthworms, termites and ants as three key “ecosystem engineer” groups that are relatively well known and comprise a large proportion of soil invertebrate biomass. The functional roles of some earthworm species have been well documented in agricultural land in southern Australia, where exotic species typically predominate. Little is known regarding native earthworms in Australia, and knowledge of earthworm biology generally is more limited in northern regions. While the ability for earthworms to influence soil properties has been repeatedly demonstrated in southern regions, addressing both exotic and native species in terms of functional biodiversity and how we manage this biodiversity in multi-functional landscapes represents a future challenge.

The termites of Australia are poorly understood both taxonomically and ecologically, despite the clear economic importance of some pest species. Several species of termite are iconic and construct massive mounds in northern Australia that attract considerable ecotourism interest. Work has also shown termites may improve soil porosity (and thus water infiltration) and increase nutrient levels in localised soil patches long after the colony becomes inactive. In Australia, ants have the greatest potential as bioindicator species based on studies of mining site rehabilitation. Australian ants are comparatively well described and researched among soil invertebrates and exert considerable influence on soil properties as well as participating in often highly specialised plant seed dispersal mutualisms. Overall, soil biodiversity and ecology requires further research to more fully describe and understand Australia’s soil biota as well as how local-scale ecological processes impact on ecosystem services and the links between soil communities and above-ground systems.

This report reviews current scientific knowledge for these key soil macro-invertebrates, in particular their capacity to act as bioindicators, the species and communities which are regarded as most significant amongst them, threatening processes which influence their abundance, and the roles of these taxa in ecosystem function. We conclude with a discussion of management principles which might guide conservation and sustainability.