Abstract
The establishment and expansion of alder [Alnus glutinosa (L.) Gaertner] in Britain between approx. 8000 and 5000 years ago is discussed in relation to changes of climate and sea-level, and to human influences. Detailed pollen analyses of Mesolithic layers at Newferry, Co. Antrim are presented. Evidence from this and other sites suggest widespread disturbance of forest cover which, by locally reducing competition, (cf. McVean, 1956) appears to have been one of the factors in the establishment of alder. Estuarine habitats are suggested as having importance in the spread of alder but the onset of climatic wetness was probably not a key factor (as bas often hitherto been supposed) other than in the sense of being permissive.