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Population structure of Artemisia genipi in a glacier foreland of the Central Alps Erich Schwienbacher & Brigitta Erschbamer Institute of Botany University of Innsbruck Contact: [email protected] e. V. Club Allegra München Introduction Primary succession in an ecosystem Plant community level • Change of species composition Population level • Change of population structure – Number of individuals – Life stage spectrum Levels of successional changes Population size Population Plant community Rabotnov (1945), White (1985), Urbanska (1992) Species 1 Species 2 Species 3 Invasion Type A Optimum Regression Time Type B Type C Time Succession Stage X Stage Y Stage Z Time Hypotheses Population structure changes according to the chronosequence of the successional stages For early successional species: Successional stage Population density Dominating life stage (I) Young Young (II) Middle aged Balanced (III) Old Old (IV) Population density and life stage spectrum correlate with coverage of vegetation and coverage of bare soil, respectively Species Artemisia genipi Weber Family: Asteraceae • Endemic of the Alps • In the alpine & subnival belt In the glacier foreland early successional species ROTMOOSFERNER Tyrol, Austria 2001 1956 1921 Extension of the glacier in the Little Ice Age 2300 - 2500 m a.s.l. 1858 46°49‘N 11°02‘E Study site Design of the experiment Plots: n = 30 á 1 m² 2 sections of the study site: • Younger section • Older section 15 plots each 3 groups of plot surface types: Coverage of bare soil • Low < 40 % • Medium 40 - 55 % • High > 55 % 5 plots each Design of the experiment Single census of plots in 2001 • Number of individuals per plot For each individuum: Number of inflorescences Diameter of cushion Life stages Number of rosettes Characterisation of life stages Life stages State of reproduction Plant size Number of rosettes Seedlings/Juveniles Small Vegetative Vegetative 1 <= 0.5 cm 1-3 > 0.5 cm 4-6 ___ >6 ___ Generative Medium Vegetative Diameter of cushion Generative Large Vegetative Generative Results Comparison of Younger and Older section No. of indv. * life stage-1 * plot-1 (mean + stddev) 60 Seedlings/Juveniles p < 0.05 Small p > 0.05 Indiv/m² 40 Medium p > 0.05 20 Large p > 0.05 0 n = 30 Younger Older Section of study site Sum of all life stages p < 0.05 Comparison of Younger and Older section Number of individuals Life stage: Small-Vegetative 120 Small-Generative Indiv./m² p < 0.05 Medium-Vegetative Medium-Generative 80 Large-Vegetative Large-Generative 40 0 Younger Older Not significant! Comparison of surface types Number of individuals Life stage: Seedlings/Juveniles Indiv./m² 100 p > 0.05 75 For all life stages 50 25 0 < 40 40 - 55 > 55 [%] Coverage of bare soil Not significant! Cluster analysis of population census data Seedlings Small Medium Large & Juveniles ‚Highly dense‘ ++ + +++ + Dendrogram 0 5 10 15 20 25 +---------+---------+---------+---------+---------+ - ++ + - + - -- - -- -- ‚Dense‘ ‚Sparse‘ -- ‚Transient‘ Median-Method with Squared Euclidean Distance Plots n = 30 - Distribution of population types in the field Seedlings Small Medium Large & Juvenile Study site Older section ‚Transient‘ -- Plot - -- -- + - -- ++ + - +++ + - ‚Sparse‘ ‚Dense‘ + ‚Highly dense‘ ++ Younger section Coverage of bare soil due to population types Coverage of bare soil [%] Invasive population types 75 p > 0.05 50 25 0 ‚Transient‘ ‚Sparse‘ ‚Dense‘ ‚Highly dense‘ Summary • Population types – A change in the life stage spectrum following Invasion Optimum Regression could not be proved – Small individuals are dominant in all population types • With proceeding primary succession – Decreasing population density – Decreasing number of Seedlings/Juveniles – Decreasing number of Small-Vegetative life stages • No correlation found between coverage of bare soil and population density or population structure, respectively Conclusion In a rapidly changing ecosystem such as a glacier foreland early successional species may not establish balanced population structures Long term studies are necessary to know more about the dynamics of such populations Best thanks to the colleagues of the Univ. of Innsbruck Thank you for your attention! Contact: [email protected] Contact: [email protected]