Definitions of biodiversity generally cover all life forms, are vague, and only of limited utility value to the agricultural sector. For example, a classic definition describes biodiversity as, ‘the variety and variability among living organisms and the ecological complexes in which they occur’ (Office of Technology Assessment 1987). Here, biodiversity includes not only biotic but also abiotic ecological processes. A more recent, simpler definition, closely following that of Noss (1990), describes biodiversity as, “the variety of life, its composition, structure and function, at a range of scales” (Freudenberger and Harvey (2003)). This definition incorporates the important notion that biodiversity is related to scale, a major issue (as will be shown below) for the conservation of biodiversity in agricultural landscapes. This notion of ‘scale-dependency’ includes not only the understanding that individual organisms vary enormously in their requirements for space but, also, that conservation of the ‘variety of life’ implies a requirement for maintenance of species populations and their inherent variability across their natural ranges. Conservation of biodiversity must, thus, be considered at both the small (e.g. paddock or farm) and large (e.g. sub-catchment or catchment) scales.

Because the definitions of biodiversity are broad, different people will inevitably attach different interpretations to biodiversity. For example, naturalists may be more interested in describing an unambiguous name for a species, a scientist may be interested in the genetic diversity of a species and an environmentalist may be more motivated by protection or preservation of a species (Mayer (2006)). These definitions provide no clear application to real life and a definition of biodiversity (simple, comprehensive or operational) that is responsive to real-life management is unlikely to be found.

(Mayer (2006)) suggests a more useful definition would be to describe biodiversity as an intrinsic character, with each of the attributes of structure, function and composition operating at temporal and bio-geographical scales (Table 1.1). Ecosystems are generally considered as the largest units of biodiversity and comprise, ”an amalgam of habitats, the species within them and importantly the processes occurring within them” (Doherty et al. 2000). While an ecosystem function may be characterised by, for example, the ability of soils to break down plant matter and liberate carbon dioxide, nutrients and water, ecosystem processes that support this function may be nitrogen mineralisation and decomposition (Doherty et al. 2000).

Recognition that conservation of biodiversity involves ‘bio-geographic’ scales from genes to landscapes provides the major rationale for attempts to conserve biodiversity within agricultural production systems, since all of these ‘scales’ cannot be encompassed within discrete areas set aside for conservation. This is particularly true at the ‘genetic’ scale, since conservation of biodiversity at this level requires maintenance of viable species populations throughout their natural range. Indeed, the importance for biodiversity conservation of beneficial integration with agricultural production increases as we move down the hierarchy from landscape to genetic scale – representative conservation areas may well hope to preserve examples of landscapes, but can never expect to conserve the genetic variation within species.

While biodiversity in the sense discussed above, (biodiversity per se), is considered important in its own right (e.g. the potential for future benefits or simply the right to exist), it also underpins the functioning of ecosystem services (ES), the conditions and process through which ecosystems sustain human life (Daily (1997)). Agricultural landscapes are primarily managed to optimise provisioning ES of food and fibre, but depend on regulating services (e.g. pollination, drought and flood control) and, more importantly, supporting services (e.g. soil fertility and nutrient cycling) that underpin all other ecosystem services (Zhang et al. 2007) (Table 1.2).

Critical provisioning services to agriculture (which are often forgotten) are management practices that maintain, restore or regenerate ecological processes that depend in some way on biodiversity (Zhang et al. 2007). In agriculture, recognising the link between ecological functions and biodiversity is the first step towards understanding the utility value of biodiversity. However, acknowledging the potential for agriculture to adversely impact on biodiversity per se at a range of scales is also essential to recognising the dynamic relationship between them.

Broadly, agroecosystems comprise managed productive areas (intensive agriculture) and the semi-natural or natural areas surrounding these and areas of human settlement. Semi-natural areas may be seen as a threat to the productive areas (e.g. source of pests) and productive areas seen to have a negative impact on biodiversity per se, with little regard for their actual or potential interdependence.

Agricultural management practices should aim to maximise the positive benefits of biodiversity in the form of ecosystem services, while minimising the negative impacts on biodiversity per se. In the following section, major agricultural practises are examined in the context of their positive and negative impacts. However, these should be considered within the context of the condition of the landscape and its capacity to respond to changes in management (see Figure 1.1).