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Summary1. The effect of extreme climate events on ecosystems is an important driver of biotic responses to climate change. For forests, extreme drought has been linked to negative effects such as large-scale mortality and reduced primary production. However, the response of plant communities to extreme drought events remains poorly understood. 2. We used mortality data from a long-term monitoring programme in the core of the focal species' ranges, in combination with annual growth data from tree-rings, to study the effect of, and recovery from, an extreme drought event. We examined both the intraspecific and interspecific drought response and explored how differential responses affect competitive dominance between the dominant species Fagus sylvatica and Quercus petraea. 3. Mortality for the most drought-susceptible species, F. sylvatica, occurred alongside a temporary reduction in competition-induced mortality of Q. petraea, resulting in the long-term alteration of the relative abundance of the two species. 4. Significant intraspecific variation occurred in post-drought recovery in surviving F. sylvatica, with two distinct cohorts identified. A prolonged recovery period was coupled with the failure to regain pre-drought growth levels in this species, whereas for Q. petraea, no severe drought impacts were observed. This species instead experienced competitive release of growth. 5. Our results demonstrate that ecosystem responses to extreme drought can involve rapid, nonlinear threshold processes during the recovery phase as well as the initial drought impact. These sudden changes can lead to the reordering of dominance between species within communities, which may persist if extreme events become more frequent.

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Summary 0Changes in a population of Ulmus`labra in Lady Park Wood "UK#\ a mixed deciduous native woodland\ were studied by means of permanent transects[ All individuals reaching 0[2 m height were recorded at irregular intervals from 0834 to 0882[ 1 Dutch elm disease struck this population in about 0861[ Most of the canopy and subcanopy stems were killed\ but a few\ slow!growing\ subcanopy individuals survived unscathed[ 2 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 39)[ Disease has\ however\ continued to a/ict vigorous\ exposed individuals[ 3 The large!scale distribution of elm has been una}ected\ but the small!scale pattern has changed due to the concentration of seedling regeneration in gaps[ 4 The elm population appears to be di}erentiating 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[ Keywords] mortality\ regeneration\ temperate deciduous forest Journal of Ecology "0887# 75\ 194Ð107

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