Ecosystems on land, whether in a comparatively natural state or artificially constructed and managed, are a fundamental part of the environment in which most humans live. They also provide or help to control a variety of resources and intangible values vital to the health and economic conditions of human society (e.g. Costanza et al. 1997). These so-called ecosystem services, which are particularly important in a relatively populous region such as that of the Baltic Sea Basin, include the provision of food, fibre and wood products. Ecosystems also contribute to controlling water supplies, air and water quality, and conditions for the maintenance of biodiversity. Through their part in the Earth’s carbon, water and energy cycles they may ameliorate — or exacerbate — climate change.