ACTA UNIVERSITATIS UPSALIENSIS ACTA PHYTOGEOGRAPHICA SUECICA 76 Plant cover on the limestone Alvar of Oland Ecology - Sociology - Taxonomy Editor Erik Sjogren UPPSALA 1988 ACTA UNIVERSITATIS UPSALIENSIS ACTA PHYTOGEOGRAPHICA SUECICA 76 Plant cover on the limestone Alvar of Oland Ecology - Sociology - Taxonomy Editor Erik Sjogren Almqvist & Wiksell International, Stockholm UPPSALA 1988 The publication of this volume has been economically supported by the "Axel och Margaret Ax:son Johnsons stiftelse". ISBN 91-7210-076-1 (paperback) ISBN 91-7210-476-7 (cloth) ISSN 0084-5914 Respective author 1988 © Drawing of Hel ianthemum oelandicum on cover by Marie Widen. Edidit: Svenska Vaxtgeografiska Sallskapet Box 559, 751 22 Uppsala Editor: Erik Sjogren Technical editor: Gunnel Sjors Phototypesetting: Textgruppen i U ppsala AB Printed in Sweden 1988 by Centraltryckeriet AB, Bon\s Acta phytogeographica suecica 76 Contents Studies of vegetation on Oland-changes and development during a century. By Erik Sj ogren . 5 Limiting factors on seed production in Crepis tectorum ssp. pumila. By Stejan Andersson. 9 The dry alvar grasslands of Oland: ecological amplitudes of plant spe­ cies in relation to vegetation composition. By Karin Bengtsson, Honor C. Prentice, Ej vind Rosen, Roland Moberg & Erik Sj ogren . 21 Calcicolous lichens and their ecological preferences on the Great Alvar of Oland. By Lars Froberg. 47 Floristic diversity and guild structure in the grasslands of Oland's Stora Alvar. By Eddy van der Maarel. 53 The effects of colonizing shrubs (Juniperus communis and Potentilla fructicosa) on species richness in the grasslands of Stora Alvaret, Oland. By Marcel Rejmdnek & Ejvind Rosen. 67 Das Naturschutzgebiet in Gosslunda. By Lars Rodenborg. 73 Shrub expansion in alvar grasslands on Oland. By Ej vind Rosen. 87 Plant cover in alvar junipers on Oland. Distribution features correlated to shrub size and shape. By Ej vind Rosen & Erik Sj ogren . 101 Reproductive regeneration in grazed and ungrazed limestone grassland communities on Oland. Preliminary results. By Graciela Rusch. 113 Biomass structure of limestone grasslands on Oland in relation to graz­ ing intensity. By Argenta Titlyanova, Gracie/a Rusch & Eddy van der Maarel. 125 Partitioning of variation in pubescens of a dwarf shrub, Helianthemum oelandicum. By Bj orn Widen . 135 Acta phytogeographica suecica 76 Abstract Plant cover on the limestone alvar of Oland. Ecology, sociology, taxonomy. - Acta phytogeogr. suec. 76, Uppsala, 160 pp., ed. by Erik Sj<>gren. ISBN 91-7210-076-1. A thematic volume on plants and vegetation on the limestone alvars of the Island of Oland, Sweden, is presented. Papers present recent results of botanical research (after 1982) in vari­ ous fields such as ecology, sociology and taxonomy. The continuous variation in pubescence of Helianthemum oelandicum is studied (Widen, B.). The most important bottlenecks in seed production of Crepis tectorum var. pumila are traced (Andersson, S.). Consequences of grazing of the alvar are discussed considering biomass structure (Titlyanova, A., Rusch, G. & van der Maarel, E.), shrub expansion (Rosen, E.) and reproductive regeneration (Rusch, G.). The pronounced decrease in species richness following an invasion of junipers and Potentilla fruticosa is described (Rejmanek, M. & Rosen, E.). The alvar vegetation of Oland is famous for a large number of species being either at the limits of their geographic ranges or characterized by highly disjunct distributions. Ecological amplitudes of such species within alvar plant communities of dry grasslands are studied (Bengtsson, K., Prentice, H. C., Rosen, E., Moberg, R. & Sj<>gren, E.). Studies on calcicolous lichens and bryophytes in the alvar vegetation are limited to the lichen flora on limestone rocks (Fr<>berg,L.) and bryophytes within juniper shrubs (Rosen, E. & Sj<>gren, E.) and in dry grasslands (Bengtsson, K. et al.). A comprehensive enumeration of vascular plant taxa (388) of dry habitats on Gland's Stora Alvar is given (van der Maarel, E.), these taxa being subjected to spectrum analyses regarding syntaxonomy, chorology, life-form, growth form and strategy type. The vegetation of juniper shrubs and juniper scrub is studied (Rosen, E. & Sj<>gren, E.) and correlated to variables such as shrub height, area, cover and plot positions. The survival of alvar plants within the shrubs is discussed, also from the nature conservation point Qf view. The management and actual status of grazed vegetation units in a protected area on Stora Alvaret have been comprehensively treated (Rodenborg, L.). Keywords: alvar, A venetum, calcicolous lichens, calcicolous bryophytes, chorological spec­ trum, diversity, disjunct species, grazing, growth form, guild, Helianthemum oelandicum, juniper scrub, life-form, limestone grasslands , seed production, shrub expansion, strategy type, syntaxonomical spectrum. Acta phytogeographica suecica 76 Studies of vegetation on bland­ changes and development during a century Erik Sjogren The botanical exploration of the calcareous island the most unusual edaphic and climatic conditions of Gland in the Baltic started in 1741 when Carl of the alvar and their consequences for the com­ Linnaeus carried out his famous 'Glandska resa' position of its vegetation. Grevillius treated not (Linnaeus, C. 1745). During his stay on Gland, only the morphology and anatomy of typical alvar Linnaeus recorded 311 species of vascular plants plants but also the peculiar forms of mainland (cf. Sjostrand 1850), at that time a remarkably species participating in the calcicolous vegetation large number considering the taxonomical knowl­ of the island. This was a new approach. edge available. In 1821, Goran Wahlenberg iden­ A doctoral thesis on the vegetation of Gland was tified one of the most peculiar members of the published by Hemmendorff (1897). He described flora of Gland, the southeast European Plantago especially the alvar vegetation, which was arranged tenuiflora. More important, he became the first in different formations, using what then was a botanist to describe the Alvar of Gland, giving young terminology of the developing plant sociol­ comparisons to both African and Alpine condi­ ogy. He also described the relation between vegeta­ tions and vegetation. tion types of the alvar such as between shallow Further botanical investigations on Gland until lakes ('vatar') and mires, from a dynamic point of the beginning of this century were mainly concen­ view, which was a fairly modern approach at that trated on the hunting of species new to the island. time. Lots of valuable information was given by This floristic work was carried out by many skilled Hemmendorff, for example, in his description of botanists. Some of them spent decades of their grazing pressure on the alvar and cultivation of the lives with these floristic studies. In the 1930s at alvar margins ('horvor'). Furthermore, it is inter­ least 1100 species of vascular plants were esting to note that the most common tree forma­ documented from the island. One of the encourag­ tion on bland at that time was the wooded ing conditions inspiring so many botanists to go meadow. Hemmendorff was a pioneer in pointing plant-hunting on Gland was the fairly good chance out the vegetational and floristic differences be­ of finding species new to the country or at least tween the Stora Alvaret of southern bland, the new localities of species with widely disjunct Scan­ Borgholm alvar with locally high and dense juniper dinavian or even European distribution. The scrub, and the more species-poor alvar areas on results and the principal participants of the northernmost Gland. floristic research on Gland have been given a During the first twenty years of this century, detailed description by Ake Lundqvist in the studies on the bland vegetation became rapidly in­ largely revised and extended 2nd edition of tensified and also increasingly varied. The ecology Sterner's "Flora der Insel Gland" (1986). of the Swedish alvar plants was treated in a com­ prehensive way in a doctoral thesis by Witte Here I shall deal quite briefly with the start and de­ (1906). His publication greatly widened our knowl­ velopment of research on structure and ecology of edge of the alvar vegetation of Oland, which be­ vegetation on the island of Gland. came for the first time also compared to similar In 1896 Grevillius published his work on vegetation types in other parts of the country. He xerophilous vegetation on Gland. This work be­ gave comprehensive information on the known came a starting point for further investigations on European distribution of the most peculiar alvar Acta phytogeographica suecica 76 6 Erik Sj ogren plants. Edaphic and climatic conditions in relation one of this country's most prominent plant to alvar vegetation became more efficiently treated sociologists, working with widely different types of than before. Witte summarized his description of vegetation in Scandinavia. He also described (Du the alvar vegetation, including important ideas on Rietz 1923) the famous Helianthemum oelandicum its steppe or heath character. In his opinion the · associations of Gland, showing their different alvar vegetation has a steppe-like character and has composition on the southern and northern alvars nothing in common with typical heath vegetation, of the island. an approach maintained since then. His descrip­ During a time period of almost 30 years, until tion represents a modernized view and is worth the early 1950s, the most prosperous and intense