Healthy ecosystems provide the essential resources upon which human health and well-being depends. For example, forests help to regulate the composition of the atmosphere and produce oxygen, while oceans and river systems provide essential fishery resources. A great many ecosystems, including marine areas, forests, grasslands and wetlands, contribute to regulation of the world’s climate, and can influence local micro-climates. Many millions of people worldwide depend directly on ecosystems for the production of food, medicines, timber, fuel, and fibre. Ecosystems also play important roles in the water cycle, regulating the flow of water through the landscape, and the amount of sediments and contaminants which affect important water resources. They also provide important areas for recreation and amenity, supporting physical and mental well-being, tourism and other cultural pursuits.

These and other important benefits, called “ecosystem services”, are essential to our society, our livelihoods, and our health and well-being, and are worth billions of Euro to the world economy every year. Biodiversity underpins ecosystem services. Each species or ecological community within a system plays a role in its various biological or chemical cycles, such as the production, capture and cycling of organic matter, energy, or nutrients. For example, certain grassland plants, working in harmony with bacteria, help to take nitrogen from the air and fix it into the soil environment where it is available to a variety of plants, while fungi and other organisms assist with the breakdown of dead plant and animal material, returning essential nutrients to the soil.

Although the exact relationship between biodiversity and ecosystem health is not always clear (i.e. more diversity is not necessarily better in every ecosystem), it is widely acknowledged that biodiversity is an essential requirement for ecosystem stability, and helps to confer the properties of resistance and resilience that are essential to allow ecosystems, habitats and species to cope with environmental change and stresses.

The loss of biodiversity (i.e. when the variety of species, genetic resources or communities is reduced) through overexploitation, pollution, habitat disruption or the introduction of invasive species, threatens ecosystem health and the sustainability of the services on which we depend. Many of those benefits cannot be replicated by technology. Even where technology can provide some form of alternative, this often cannot be achieved at a sufficient scale to meet the demands of all users, or cannot be performed without entailing significant economic, environmental or social costs. It is important to note that the value of ecosystem services is often not just measured in benefits gained, but in losses averted. For example, ecosystems within a watershed that provides potable water might not appear to have any direct value in terms of marketable goods, however they may play a vital role in regulating the flow and quality of the water resource, thereby reducing the cost of managing and treating raw water to make it available or safe for human use. Similarly, habitats or species that play a role in the regulation of pests and disease organisms help us to avoid the costs and hardship associated with disease in livestock, crops or people.

Since the functioning of ecosystems and the sustainability of the essential services they provide are dependent on biodiversity, then biodiversity represents the foundation for human well-being. Stated more simply: without a global environment that is healthy and capable of supporting a diversity of life, no human population can exist.

In localities where the integrity of ecosystems has been compromised, e.g. in urban areas or areas of intensive agriculture, healthy populations can only exist if they are supported by healthy or productive ecosystems elsewhere. As an increasing proportion of the local environment is transformed and as the integrity of local ecosystems is compromised, a community may become increasingly dependent upon the biodiversity resources of other localities to provide the ecosystem services they require.

However, when a community draws on services and resources produced by ecosystems elsewhere, this may also place pressure on those ecosystems and increase health risks for local communities in those areas. In other words, for any human community, the risks and consequences of ecosystem disruption may extend far beyond their immediate locality. This, the ecological footprint of a population (the amount of global ecological resources consumed), can become unsustainable. Magnified on a global scale, this gives concern for global ecological stability, with very real consequences for the global economy and global health.

Some of what are arguably the most important health services provided by biodiversity - provision of fresh water and clean air, the regulation of the global climate, the provision of food resources, and the regulation of pests and diseases - are under particular threat on a global level. Thus it becomes increasingly important not only to protect the remaining ecosystems, but also to restore and enhance degraded ecosystems throughout the world.

In as much as the loss of biodiversity puts human well-being at risk, its conservation and sustainable use can help to combat poverty and hunger, prevent disease outbreaks, protect against natural disasters, and promote stability and security for millions of people worldwide. In this context, biodiversity and ecosystem services may be particularly important to reducing, or adapting to, the impacts of climate change.