Biodiversity is the heritage of millions of years of evolution. Human society has had a dramatic impact on this ecological heritage. In the last 200 years more species have become extinct than at any time in the last 65 million years. This threatens ecosystems’ ability to provide the air, water and soil on which we depend. Recognition of the need to protect biodiversity is enshrined in the UK Biodiversity Action Plan.

A basic understanding of ecology is important in order to understand the factors that influence biodiversity. Ecology is the study of ecosystems: communities of species and the physical environments and habitats that they have adapted
to survive in.

Each type of habitat, such as woodland, wetland or grassland, supports a community of distinct, and well-adapted native vegetation. Exotics, non-natives and hybrid species, are to be found in natural habitats and may be well-adapted to polluted urban environments. However, in general native vegetation will sustain the greatest biodiversity. Emulating the composition and structure of natural ecosystems will therefore tend to create the best opportunities for biodiversity.
When nature colonises a new habitat it follows a process called succession: the natural order of events as successive species colonise. Hardy ‘pioneer’ communities change their environment, improving it and creating more stable conditions for self-sustaining and structurally diverse ecosystems, such as oak-ash woodland.

Functioning natural systems are required to sustain biodiversity, and successional processes. Habitats and their characteristic communities of flora and fauna rely on specific physical conditions and ecological processes for their survival. Changes in water flows, water chemistry, air quality, shading, or disturbance may result in a loss of species and a change in the nature of a habitat.

Processes such as succession, water uptake, nutrient recycling, pollination, predator-prey (‘food chain’) relationships are features of functioning ecological systems which if disrupted can also lead to rapid changes. An understanding of ecological function should therefore inform decisions when planning and designing for biodiversity.

The size and spatial relationships between habitat patches also influences biodiversity. The fragmentation of habitats by agriculture and urbanisation has highlighted the need for habitat networks: continuous, linked areas of habitat. Whilst planning can create opportunities for habitats, urban form will influence their size and extent. Masterplanning of a community’s ‘green infrastructure’ can therefore play an important role in creating ecologically functional habitat networks.