Ecosystems are generally complex and difficult to define and, more often than not, comprise a wide range of habitats; typically combining semi-natural, agricultural and non-natural components. This part of the website describes the main habitat groups in Wales, and the more recognisable seral phases of those habitats, some of which are now confined to small fragments and located in areas unsuitable for human land-use. The more common reference states, i.e. states that arise through natural processes, and modified states, i.e. states that arise as a consequence of anthropogenic impacts, of the habitats are also described. These illustrate how different pressures on the landscape have impacted on the habitats over varying time frames and led to the habitats that we see today. The text provides identifies the main management pressures on each habitat and promotes the need for strategic restoration programmes that take into account the likely impact on the biodiversity associated with each habitat.