Spatial and microgeographical genetic differentiation of black alder (Alnus glutinosa Gaertn.) populations Dus ˇan Go ¨mo ¨ry * , Ladislav Paule Faculty of Forestry, Technical University in Zvolen, T.G. Masaryka 24, SK-960 53 Zvolen, Slovak Republic Received 22 June 2000; received in revised form 16 November 2000; accepted 16 November 2000 Abstract Three Alnus glutinosa populations from central Slovakia were investigated by means of isozyme analysis. The average expected heterozygosity ranged from 0.151 to 0.173. Despite significant differences in allele frequencies among populations, genetic differentiation was low (F ST ¼ 0:022). Intrapopulation fixation indices indicate no or very slight deviation from panmictic expectations towards the heterozygote deficiency. No indications were found that the investigated populations have experienced recent bottlenecks in population size. A spatial autocorrelation analysis based on Moran’s I indicates the existence of a spatial genetic structuring in the population Kra ´l’ova ´. Patch size was estimated to be 70–100 m, which is more than observed in other broadleaved tree species. This difference is explained by the linear shape of alder populations and a higher mobility of seeds. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Alnus glutinosa; Isozymes; Genetic differentiation; Spatial autocorrelation 1. Introduction Black alder (Alnus glutinosa [L.] Gaertn.) is a tree species with a pan-European range. In the north, it reaches the Polar circle, whereas the southernmost occurrences are located in North Africa. In the east, it grows behind the Ural mountains under the con- tinental climate of the western Siberia. Within this vast range, it mounts from lowlands up to 1800 m a.s.l. in the Alps and 1300 m a.s.l. in the Carpathians. It means that it is a species able to adapt to very variable climatic conditions. At the same time, it requires specific soil conditions, mainly concerning moisture. It occupies primarily sites with flowing ground water along streams, but also sites with stagnating ground water like peat bogs. However, in contrast to most hygrophilous tree species, it survives also on drier sites, where it behaves as a pioneer species (Pancer- Kotejowa and Zarzycki, 1980). Site requirements lead to a considerable fragmentation of the distribution range. Black alder regenerates generatively as well as vegetatively, mainly by sprouts, rarely by root suckers. Sprouts are mostly very vigorous and lead to the formation of polykormic individuals. Rooting of lateral branches of fallen trees was also observed, after the maternal stem decayed, the sprouts form clonal groups. In central Europe, large alder stands, which were occurring on the river terraces, in dead arms of rivers and lakes, swamps, etc. have mostly been destroyed by Forest Ecology and Management 160 (2002) 3–9 * Corresponding author. Tel.: þ421-855-5206-226; fax: þ421-855-5332-654. E-mail address: gomory@vsld.tuzvo.sk (D. Go ¨mo ¨ry). 0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0378-1127(01)00465-0