FACTORS AFFECTING THE DISTRIBUTION AND SPREAD OF RHODODENDRON IN NORTH WALES

The invasive alien shrub Rhododendron ponticum causes considerable land management problems where it becomes well established in woodland, grassland and heath. The distribution of rhododendron and its pattern of spread has been assessed near Beddgelert, Snowdonia, north Wales, using coloured aerial photographs taken in 1968 and 1986. By 1968, it had already spread extensively from obvious sources (old gardens and estates). Between 1968 and 1986, its spread continued slowly and steadily (apart from a rapid expansion into newly-planted woodland). A multiple regression analysis of a previous (1982) ground survey indicated which factors were significant in affecting the local distribution of rhododendron. Important factors favouring the shrub were a northerly aspect, steep slopes and a 'mixed woodland' habitat where soil had been disturbed in the presence of a seed source of rhododendron. Inhibiting factors were improved pasture, wet rough grazing and sheep grazing in general. Such results, using modelling and GIS techniques, could be used to identify vulnerable sites before rhododendron became well established and difficult to eradicate. © 1993 Academic Press Ltd.