Distribution, longevity and survival of upland hawthorn (Crataegus monogyna) scrub in North Wales in relation to sheep grazing.
Hawthorn scrub in an upland area (>150 m alt.) of North Wales was surveyed, and at three typical study sites, hawthorn occurrence was studied in relation to vegetation type and sheep densities. Hawthorn generally occurred as scattered stands on steep slopes with Agrostis/Festuca grassland, with or without bracken (Pteridium aquilinum). Hawthorn bushes occurred as isolated individuals or in clumps. Some bushes in clumps were derived from root suckers, but most isolated bushes were from seeds. The mean age of single-stemmed bushes was 55 yr (range 10-115 yr), with few bushes <20 yr old. Because of variable growth rates, it was impossible to estimate age from girth with any degree of accuracy. Sheep appear to control hawthorn recruitment, which has decreased as sheep grazing has increased. Unless sheep numbers are halved for a period, probably at least 15 yr, most of the remaining hawthorns will probably disappear in 60-70 yr.