Modern non-organic agriculture is characterised by monoculture, which means widespread production of crops formed from a single species, variety or gene combination. The advantages seem clear: the crop can be treated as a single commodity from seed production, through planting, pesticide application, harvesting, processing and marketing. However, such systems are entirely dependent on continuous and large-scale inputs of synthetic chemicals, at each stage, which leads to large direct and indirect costs.
As a consequence, biodiversity is minimised not only in terms of cropping but also in relation to non-crop organisms small and large, above and below ground.
At the other extreme, natural plant communities usually comprise a range of species, varieties or gene combinations. The community and its components are never constant: they vary in composition and frequency both within and between seasons. The diversity and dynamism of the community is driven by environmental variation, both physical (climate and weather) and biological (pests, parasites, competition). The nature of the diversity buffers the community against environmental variation and restricts development of pests and pathogens (there are exceptions – but these often prove the rule. For example, Dutch Elm disease became rampant partly because of human intervention and partly because elm populations lack variation in resistance to the pathogen and its carrier. However, elm is still common as a hedgerow bush). Such communities are characterised by a wide range of biodiversity all of which has some function in the dynamics of the community.