Long-term change in an unmanaged population of wych elm subjected to Dutch elm disease

Abstract

1 Changes in a population of Ulmus glabra in Lady Park Wood (UK), a mixed deciduous native woodland, were studied by means of permanent transects. All individuals reaching 1.3 m height were recorded at irregular intervals from 1945 to 1993. 2 Dutch elm disease struck this population in about 1972. Most of the canopy and subcanopy stems were killed, but a few, slow-growing, subcanopy individuals survived unscathed. 3 Subsequent seedling regeneration and growth of sprouts from rootstocks of infected trees was substantial and vigorous. Twenty-three years after the outbreak of disease the number of elm individuals had increased by about 40%. Disease has, however, continued to afflict vigorous, exposed individuals. 4 The large-scale distribution of elm has been unaffected, but the small-scale pattern has changed due to the concentration of seedling regeneration in gaps. 5 The elm population appears to be differentiating into (i) a large high-turnover subpopulation of fast-growing, but repeatedly diseased maiden individuals and sprouts, and (ii) a small, low-turnover subpopulation of slow-growing individuals rooted in suboptimally dry, secluded sites.