E. van der Maarel - Böcker

biological attributes of the three species according to the sequence in which they invade successively as a conse­ Studies on sample plots in Halimione portulacoides com­ munities show that environmental disturbances, either quence of environmental disturbance. It can therefore be concluded that for understanding this mechanism in the natural or induced by man, start a sequence of partly salt-marsh ecosystem a thorough study on the functioning overlapping density maxima in Suaeda maritima, Aster of these and other relevant biological attributes in the local tripolium and Puccinellia maritima successively, before the populations is essential. original Halimione community totally recovers. When Returning to the basic questions put in the introduction succession time before recovering is long enough, there are it is concluded that: tendencies in redundancy of this sequence stressing the unilinear character of the succession. Minor environmental a) There exist orderly and predictable succession patterns in the investigated salt-marsh vegetation. impacts induce a longer time-lag period of the Suaeda b) Following occasional disturbances, whatever these may density maximum, suggesting threshold values of these impacts for the species to maintain minimal population be, the vegetation recovers via a sequence of overlapping interim species populations showing a unilinear or obliga­ densities or to become locally extinct. This sequence of tory (Hom 1976) succession pattern.

July 8 -13, 1985, an international group of scientists met in Uppsala for a symposium on the subject 'Theory and models in Vegetation science' . A volume of over 70 extended abstracts had already been published in time for the symposium (Leemans et at., 1985). That volume included contributions from nearly all of those who gave talks or presented posters at the symposium. The present volume represents the fully-refereed proceedings of the symposium and features articles by a majority of speakers, plus a handful by poster authors, and two that were sent independently to Vegetatio and seemed timely and relevant to the symposi­ um's theme. As organizers, we tried to bring together for the symposium people whose interests covered several key aspects of modern vegetation science: vegetation dynamics, on shorter or longer time scales; the analysis of community data, and of vegetation-environment relationships in both time and space; and the functional basis of vegetation in terms of the individual plants and plant populations that it comprises. We encouraged contributors to focus on theory and models - not necessarily mathematical models, but also conceptual models that might contribute to the development of theory and mathematical models.

This volume contains most of the contributions presented at the Symposium on Vegetation dynamics in grasslands, heathlands, and mediterranean ligneous formations, which took place at the Centre d'Etudes Phytosociologiques et Ecologiques 'Louis Emberger' (locally organized by the Department of General Ecology and the Directory Staff of this institute) at Montpellier. It was organized by the Working Group for Succession research on permanent plots, and the Working Group for Data-processing in phytosociology, both of the International Society for Vegetation Science. The editors of this volume represent both working groups and the organizing institute. They acknowledge the considerable material assistance provided by the Centre National de la Recherche Scientifique, Direction des relations exterieures de l'information, and Programme lnterdisciplinaire de Recherche sur I'Environnement (PIREN); the Conseil general de I'Herault; and the Ministere de I'Environnement et du Cadre de Vie. The Symposium was opened by Prof. M. Godron. The many lectures and poster contributions were organized around five themes. A complete list is added to this volume (Appendix).Abstracts of these contributions were sent in prior to the Symposium and collected by the CEPE in a volume 'Actes du Symposium sur Dynamique de la Vegetation dans les formations herbacees, les landes et les formations mediterraneennes ligneuses'. The 27 ela borated papers accepted for this volume are presented in roughly the same sequence.

(RANKIN) of equivocation information (1-:) and interaction information (M). The method is described in the present paper for I: and in a previous paper (Orloci, 1976) for M. The results presented in this paper suggest that for Species Rank order Information Percentage of total* species to be weighted according to their suitability to I· M I M r M characterize isolated groups of releves in a phytosociolo­ 5 7 54.15 2.31 17.97 0.82 gical table, the equivocation information may serve as a 9 5 49.86 23.19 16.55 8.22 3 3 9 47.79 0.56 15.86 0.20 suitable weight. The appropriate formulations are derived 6 4 8 36.18 1.18 12.01 0.42 4 5 3 24.36 59.34 8.09 21.03 and computed for some data from a salt marsh community. 8 6 4 24.25 39.04 8.05 13.84 10 7 I 21.96 71.17 7.29 25.23 7 8 2 18.67 69.01 6.20 24.46 9 10 18.40 6.11 10 6 5.64 16.31 1.87 5.78 References Total 301.00* 282.11 * 100.00 100.00 Feoli, E. 1973. An index for weighing characters in monothetic classifications. (Italian with English summary). Giorn. Bot. Ita!' 107: 263-268. Gower, J.e. 1967. A comparison of some methods of cluster is a monotone, increasing function of sample size if .. ).

Eddy V AN DER MAAREL This volume is the first of two volumes covering the Sym­ computer programmes for the rapid clustering and ordina­ posium 'Advances in vegetation science', which was held at tion of very large sets of reI eves and for (subsequent) table Nijmegen, The Netherlands, from 15-19 May 1979. This rearrangement (this volume as well as the book Data­ symposium was organized on behalf of the Working Group Processing in Phytosociology contain various new pro­ for Data-Processing of the International Society for Vege­ grams). What we do not have is a manual in which the tation Science. After this group held its final meeting two apparently successful methods are compared and applied years earlier it decided to continue its activities, but within a to some data-sets. H. Lieth, editor-in-chief of a new Junk wider scope. Most members of the Group felt that the series 'Tasks for vegetation science' already suggested to original aim, i. e. the introduction of data-processing and produce such a manual in this series. multivariate methods for use in the systematic description The present volume contains the texts of the lectures and of plant communities, was more or less fulfilled. The book most of the poster demonstrations of the first three sessions Data -Processing in Phytosociology, largely based on papers of the Symposium, dealing with classification and ordina­ in Vegetatio, edited by E. van der Maarel, L. Orloci & S.

Eddy VAN DER MAAREL All in all 16 contributions could be collected. The This volume is the second of two volumes covering the symposium 'Advances in vegetation science', which was arrangerr. ent is as follows: held at Nijmegen, The Netherlands, from 15-19 May The contribution by Sjors may serve as a general intro- duction to the types of changes and their names. The 1979. This symposium was organized on behalf of the added paper by Noble and Slatyer provides appropriate Working Group for Data-Processing of the International Society for Vegetation Science. After this group held its facts and views on the mechanisms of vegetation dynamics. final meeting two years earlier it decided to continue its Then a group of contributions follows in which data on species behaviour, plant demography and diversity during activities, but in a wider scope. Most members of the succession are discussed. This includes Faliriski's study on Group felt that the original aim, i. e. the introduction of data-processing and multivariate methods for use in the sex structure and dynamics of pioneer woody species, a systematic description of plant communities, was more or fynbos diversity study by Campbell & van der Meulen and less fulfilled.The book Data-Processing in Phytosociology, studies on Mediterranean shrubs and trees in post-fire and postcultural developments by Trabaud and Lepart, Hous- largely based on papers in Vegetatio, edited by E. van der Maarel, L. Orl6ci & S. Pignatti, and to be published by sard, Escarre and Romane, and Debussche and Romane.