1.The genus Castor comprises two species: the Eurasian beaver Castor fibre , and the North American beaver Castor canadensis . Both species suffered from overexploitation, but have seen a revival since the 1920s due to increased protection and reintroduction programmes. Increases in the populations and distributions of species that are able to modify ecosystems have generated much scientific interest. Here we review the available literature concerning the possible ecological impact of beaver species in the Old and New World. 2. Beavers, being ecosystem engineers, are among the few species besides humans that can significantly change the geomorphology, and consequently the hydrological characteristics and biotic properties of the landscape. In so doing, beavers increase heterogeneity, and habitat and species diversity at the landscape scale. Beaver foraging also has a considerable impact on the course of ecological succession, species composition and structure of plant communities, making them a good example of ecologically dominant species (e.g. keystone species). 3. Nevertheless, the strength of beavers' impact varies from site to site, depending on the geographical location, relief and the impounded habitat type. Consequently, they may not be significant controlling agents of the ecosystem in all parts of their distribution, but have strong interactions only under certain circumstances. We suggest that beavers can create important management opportunities in the Holarctic, and this review will help land managers determine the likely outcome of beaver activity.

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This article discusses the development of the normalization thesis in respect of monitoring sustained increases in young Britons' consumption of illicit drugs and alcohol over the past decade. It describes five dimensions of normalization which have been applied in a cluster of studies undertaken by the author, highlighting results from the N.W. England Longitudinal Study showing easy accessibility, high rates of drug trying (76% at 22 years) and long-term recreational drugs careers involving both alcohol and illicit drugs. The social accommodation of 'sensible' substance use was apparent amongst most drug abstainers in the cohort who routinely had close friends who used drugs 'recreationally'. Further cultural acceptance of recreational drug use is described. A sixth dimension -state or government responses to widespread recreational drug use -is introduced and illustrated. The article concludes by emphasizing the negative outcomes associated with recreational poly substance use in terms of personal and public health highlighting the 'slippage' from recreational to problem drug use as a growing phenomenon. It calls for a more integrative national strategy to address negative aspects of normalization.

An anonymous self-report survey of drug use among a cohort of 776 14-15 year olds in North-West England was conducted at the end of 1991, aiming to estimate prevalence and profile users. Six in 10 reported being offered drugs, and 36 per cent to using drugs (20 per cent in the past month). Over half of those offered drugs had tried them. Lifetime prevalence was highest for cannabis (32 per cent), with five other drugs each being used by 10-14 per cent. Three groups identified were cannabis smokers, solvents sniffers, and stimulant/psychedelic (or dance drug) users. The population parameters of drug use were estimated at 33-40 per cent, suggesting up to 200,000 local young adults have used drugs. Most significantly, the proportion of young women being offered and using drugs and the prevalence of drug trying amongst young people in 'middle-class' schools, suggests a substantial social transformation is underway in respect of recreational drug use. The results of this survey confirm a general trend apparent in other British studies. As this cohort is tracked into the mid 1990s, the sociological implications will be significant.

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