A contribution to the vegetation history of upper Teesdale

Abstract

The Post Glacial vegetational history of the Upper Teesdale National Nature Reserve has been examined by peat stratigraphical and pollen analytical techniques in order to show the persistence of the characteristic rare plants throughout the Post Glacial period. Although little direct evidence of the rare species (i.e. macro-remains or pollen) was found, the investigations show that conditions of instability, minimal competition and the presence of soils or water with a high base status were prevalent in certain localities throughout the Post Glacial period and probably enabled the Teesdale 'rarities' to survive through a period during which processes inimical to their survival were predominant. The late cessation of solifluxion which aided in the expansion of hazel, followed by the immigration of pine, elm and oak under conditions of fluctuating water levels in the late Boreal period (zone VI) indicate the persistence of instability from Late Glacial times. At the time of the maximum expansion of woodland in the Atlantic period, although a fairly dense woodland of oak, elm and alder existed in the Upper Tees valley, Cronkley and Mickle Fells carried a heterogeneous vegetation ranging from birch-hazel and oak- birch scrub to woodland, similar to that which existed in the valley, with some peat deposits (both soligenous and ombrogenous). The disposition of these communities was influenced by edaphic factors therefore no altitudinal limit of tree growth can bedemarcated although the closed woodland limit was approximately 1700 ft (517 m). Anthropogenic activity has affected the area since Atlantic times and human interference was a major factor in the degradation of the scrubland and woodland, especially on Cronkley and Mickle Fells, and the development and spread of blanket peat, especially in localities adjacent to the limestone outcrops. The present day environment of the Teesdale 'rarities' is the result of continued instability since the Late Glacial period, particularly after the appearance of man in the Atlantic period.