Editorial

There are many, often relatively anecdotal, observations suggesting that agricultural activities affect lichens. However, the nature of the ' agricultural effect' involved is much less clear. Agriculture practices can involve anything from the use of pesticides, to inorganic fertilisers, to ammonia volatilised from animal waste, or pollution from farm vehicles. The nature, scale and extent of the effect will depend on the differential sensitivity of lichens to the cocktail of chemicals involved and the extent of their dispersal under the particular conditions. The result is a fascinating field of research to separate the different factors involved. Surprisingly little has been written on this subject. Currently, much of the published work has sought to demonstrate the impact of farms or farming without identifying the agents responsible. This is a necessary prelude to further investigation. Valuable advances have been made by categorising lichen species as ' acidophilous ' or ' nitrophilous ', even though the nature of the chemicals responsible are still unknown. Moreover, there is little comparative work reported. In northern Europe, the assemblage of epiphytic species observed around an active farm may, superficially, resemble that of a dust-impregnated mediterranean tree. But how close is the resemblance, and is it related to nitrogen enrichment? In order to try to develop this field of study further, Dennis Brown and Han van Dobben organised a small international workshop that met in Wageningen, the Netherlands, between 16th and 18th April 1993. The meeting was supported by the European Environmental Research Organisation and attended by researchers from ten countries. Although judged a successful exchange of ideas, for various reasons, no proceedings were produced. Some speakers' work was already in press, while others appeared, for example, in publications linked to the IAL symposium ' Progress and Problems in Lichenology in the Nineties ', held in Sweden. More recently, it was proposed that, to further develop this field of study, the original participants at the Wageningen workshop should be invited to submit manuscripts to form the nucleus of an issue of The Lichenologist devoted to ' agricultural effects '. This issue is the result and shows part of the range of studies and approaches reported at the earlier meeting. Some articles have been developed further than the original reports, whereas others remain relatively preliminary studies but ones that were judged to have the potential to stimulate further research. If this issue stimulates more discussion, debate and even disagreement, which finally helps clarify how farming may influence lichens, then the original workshop will be judged to have had a wider influence than just an enjoyable meeting, skilfully organised by Han van Dobben.