Keywords:aerial photograph / Alnus glutinosa (L.) Gaertn. / dendrochronology / land abandonment / secondary succession / wetland Abstract • The secondary succession of wet grasslands to communities of alder carr dominated by Alnus glutinosa was recorded in different parts of Europe during the 20th century. However, knowledge of such development of alder carr remains insufficient.• The development of alder carr was reconstructed at five sites in the Czech Republic, using historical aerial photographs and methods of dendrochronology. The aims were to investigate the succession from wet grasslands to alder carr at sites previously intensively managed for agriculture and to find out the role of fluctuations in the groundwater table, caused by artificial drainage channels, in the observed stand dynamics and tree growth.• The spread of forest (i.e., an increase in forest cover) predominated until the 1970s at all sites. This trend was disrupted by a large-scale dieback of forest stands in four of the five sites after the 1970s, followed by an increase in patch heterogeneity, as indicated by landscape metrics. The radial growth increment in Alnus glutinosa has been affected predominately by local environmental factors, probably including the changing degree of waterlogging. Forest dieback was presumably connected with a lesser extent of drainage channels.• Our results indicate that observed successional pathways at sites of alder carr were probably caused by local changes in the groundwater table.Mots-clés : photographie aérienne / Alnus glutinosa (L.) Gaertn. / dendrochronologie / abandon des terres / succession secondaire / zones humides Résumé -Développement de taillis d'aunes après l'abandon des prairies humides au cours des 70 dernières années.• La succession secondaire des prairies humides en communautés de taillis d'aunes dominées par Alnus glutinosa a été enregistrée dans différentes parties de l'Europe au cours du 20 e siècle. Toutefois, la connaissance du développement de taillis d'aunes reste insuffisante.• Le développement de taillis d'aunes a été reconstruit dans cinq sites en République Tchèque, à l'aide de photographies aériennes historiques et des méthodologies de la dendrochronologie. Les objectifs étaient d'étudier la succession de prairies humides en taillis d'aunes sur des sites précédem-ment exploités intensivement par l'agriculture et de découvrir le rôle des fluctuations de la nappe phréatique, causées par le drainage artificiel des canaux, et d'observer la dynamique des peuplements et la croissance des arbres.• La progression de la forêt (c'est-à-dire, l'augmentation du couvert forestier) a prédominé jusque dans les années 1970 dans tous les sites. Cette tendance a été perturbée par un vaste dépérissement des peuplements forestiers dans quatre des cinq sites après les années 1970, suivie par une augmentation de l'hétérogénéité des bouquets d'arbres, comme indiqué par les paramètres du paysage. L'augmentation de la croissance radiale de Alnus glutinosa a été affectée principalement par les facteu...

Extreme radial growth reactions were analyzed over a 79-year period (1922-2000) to compare response of Norway spruce (Picea abies [L.] Karst.) along an altitudinal gradient (376-1221 m a.s.l.) in the Šumava Mountains, the Czech Republic. Extreme growth events were defined as pointer years, when an average percentage of the site pointer years reached at least 50% strength observed at the relevant altitudinal zone (low < ca. 700 m; middle ca. 700-950 m, high > ca. 950 m). The comparison of the pointer years showed a specific pattern for altitudinal zones (Low: negative pointer years 2000, 1992, 1984, 1976, 1971 and positive 1997, 1975, 1960, 1949, 1932, 1926; middle: negative 2000, 1992, 1976 and positive 1997, 1989, 1978; high: negative 1996, 1980, 1974, 1965 and positive 1989, 1963, 1927). Negative pointer years were usually induced by summer drought at low elevations and by wet-cold summer at high altitudinal zone. These two main limiting factors were probably combined at the middle altitudinal zone. Detailed understanding of the extreme tree ring pattern along the altitudinal and geographical scale may be used as one of the additional indicators of dendrochronological dating and provenance identification of spruce sample among altitudinal zones in the Šumava Mountains.

Abstract:Complex of Nature reservation Zbytka is the rest of various fen vegetation in the northeast part of the Czech Republic. It represents an important spring area which provides high quality potable water for more than 150 000 inhabitants. Waterworks utilization was started in the 1960s and the change of land-use practices has had a strong effect on the ecosystem. Oak chronology has been showing different tree growth trends since the start of the waterworks utilization. Also the occurrences of negative pointer years differ markedly before and after initiation of pumping underground water. Dendroclimatological analyses primarily revealed a close relationship between the temperature and tree growth -positive influence of spring and summer temperature. The period 1983-1992 of maximum artesian water pumping is expressed as higher tree-ring increments, but linear model analyses showed that the growth reaction of oak is not due to simple causality between temperature and underground water level. The radial increments reacted positively to the combination of high temperature during the vegetation season and low or, the contrary, high depth of underground water level. No direct relationship was detected between tree growth and fluctuation of underground water level; despite of the results dendrochronological data may be useful in historical ground water modelling studies. Results are also crucial for conflict of interests between nature preservation and potable water supply.

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