The special ecological features of Britain are related primarily to geographical and climatic position in the world. The British Isles as a whole lie in the temperate zone, but they differ from much of continental Europe in experiencing a strongly oceanic climate. A climatic regime of this kind is reflected in certain general ecological trends. The temperature range favours forest, composed largely of broad-leaved, relatively thermophilous trees, as the climax life-form over much of the country. The moisture balance, with a general excess of precipitation over evaporation, promotes leaching of nutrients from the soil, so that podsolisation is a widespread phenomenon, and there is a prevailing tendency towards development of acidic surface humus horizons. Where topography also contributes to waterlogging of the soil, peat mire inhibits tree growth and becomes the climax formation.

The high atmospheric humidity associated with an oceanic climate satisfies the needs of many hygrophilous plants; the fern, bryophyte and lichen floras are especially rich and the British Isles are the European headquarters of many Atlantic species, including some which have an interesting world disjunction. The equable temperatures of an oceanic climate also allow the survival locally of southern thermophilous plants, which reached their maximum extent at the Postglacial Climatic Optimum, and also of a northern, montane element which cannot tolerate hot summers, and is a relict flora from the cold Late-glacial Period. Thus, although the insular position of the British Isles has resulted in a numerically poorer flora than many European countries, there is a unique blend of different phytogeographical elements which has given our flora an international distinction. Species of oceanic distribution which reach their greatest European abundance in Britain include a number of distinctive community dominants such as ash Fraxinus excelsior, heather Calluna vulgaris, bluebell Endymion non- scriptus, gorse Ulex europaeus, U. gallii, U. minor and heath rush Juncus squarrosus. Plant formations of strongly oceanic character, such as blanket mire and moss heath, are also more extensively developed in Britain and Ireland than in the rest of Europe, and some plant communities appear to be unique to this country, albeit usually recognisable as relatives of various continental types.

The Nature Conservancy's responsibilities did not extend to Ireland, but many of the important ecological features of Ireland are represented in the west of Britain, which has a strongly oceanic climate. There is a lesser representation in Britain of southern Atlantic and Lusitanian species, and no limestone karst country here is quite as fine and unspoiled as the Burren of County Clare, but on the whole the flora and fauna of Ireland are less rich than those of Britain.

Faunistically, the British Isles are internationally important for a number of insular races and subspecies which have diverged in isolation from the main European populations ; as the breeding station for large populations of several globally rare and local birds, especially seabirds; and as the wintering haunts of a significant proportion of the total world or European population of certain wildfowl (Anatidae) and waders (shore-birds). The fauna also contains an interesting and diverse combination of different zoo- geographical elements. The mammal fauna of Britain is poor in species, partly as a result of extinctions caused by man, and the invertebrate fauna is much less rich than that of continental Europe.

Although relict elements of both flora and fauna are well represented, Britain has very few endemic species of either plant or animal. The British flora and fauna is, however, interesting for its ecological diversity, as the response to an unusual blend of climatic conditions within a small area. The particular combination of plant species in communities is, however, the most distinctive feature of this country, compared with the rest of Europe.