RECENT DEVELOPMENT OF HIGH-ALTITUDE PINUS-SYLVESTRIS SCRUB IN THE NORTHERN CAIRNGORM MOUNTAINS, SCOTLAND

Scots pine Pinus sylvestris has been colonizing the Northern Corries a rea of the Cairngorm mountains, following a reduction in grazing and b rowsing, and a natural subalpine scrub zone appears to be developing. The area was surveyed to assess the density and rates of tree coloniza tion, and identify the factors affecting the process. The pattern of c olonization was uneven. Although relationships between pine establishm ent and environmental variables were complex, it was possible to ident ify the main factors affecting pine colonization. They were: distance from the forest (the main seed source), altitude, vegetation (type and height), drainage and soil organic horizon depth. Combining the effec ts of all these factors, pine establishment was greatest close to the forest, at altitudes around 600-700 m, in Calluna vulgaris moor or lic hen-rich dwarf Calluna heath under 20 cm tall, on well-drained mineral soils with at most a shallow organic horizon. Establishment at low al titudes tended to be restricted by deep, wet peat and tall vegetation, and at high altitudes mainly by climate. The age structure of the pop ulation indicated a sudden increase in colonization around 1960, possi bly related to reduced deer browsing, but colonization decreased after about 1970. Some possible reasons for this pattern ave given. Compari sons with other tree-line populations suggest that, provided grazing/b rowsing pressure remains low, the area may develop a natural tree-line similar to the only other extensive natural tree-line presently known in Scotland, at Creag Fhiaclach, also in the Cairngorms. Some suggest ions are made of suitable management to accelerate this process. Copyr ight (C) 1996 Elsevier Science Limited