A definition of the «edge effect», considered as a case of synergism at the ecosystem level, is given. A quantitative method to study edge effects is proposed, with fitted sam¬ple designs. This «triple census technique» was tested during the pilot-study of a woodland-open field mosaic in Burgundy, whose results are summarized. A better knowledge of edge effect values on bird abundance and species richness is important when studying patchy habitats.

Abandoned old quarries have a completely artificial origin but a near-natural ecosystem functioning, because human pressure is often very low in such habitats. Communities of plants and animais generally have low productivity, but rare and colonising species are present, particularly in early successional stages. These communities develop as ecological successions (near primary succession type), the speed of transformations depending mainly on hydrological conditions (high in permanent water sites, low in dry sites, intermediate in temporary waters).Biodiversity value for conservation in such habitats must be measured with many meth odological precautions and with objectivity. Particular attention must be paid to: the scales of space (the site itself and the site in its landscape) and time (at !east severa! years, better sorne ten years); the ecosystems (or states) of reference, to compare the studied site; it may be use fui also to refer to sorne natural disturbances; the criteria used for evaluation (richness and diversity, abundance of individuals, area of site, rarity of species and/or communities ... ); the taxons studied (in place of the total list of species), and considered as representative or indi cators.We practised such evaluations in numerous sites of quarries of different types. One con clusion is the necessity to compare sites with strongly standardized methodologies. Moreover, the numbers of species (and other diversity indicators) must be measured with a constant sam pling effort.

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