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| Quantifying Competition between Beech (Fagus sylvatica) and Norway Spruce (Picea abies) |
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Grams, T.E.E.(1), Kozovits, A.R.(1), Reiter, I.(1), Blaschke, H.(1), Winkler, J.B.(2), Häberle, K.-H.(1), Matyssek, R.(1)
(1) Forest Botany, Department of Ecology, Technische Universität München,
Im Hochanger 13, D-85354 Freising, e-mail: thorsten.grams@gmx.de
(2) Institute of Soil Ecology, Phytotron Unit, GSF-National Research Center for Environment and Health, Ingolstädter Landstr. 1, D-85764 Oberschleißheim
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We compared the competition between mature beech and Norway spruce trees in a mixed forest stand with the competitive behavior of young saplings of a phytotron study. The phenological, allometric and physiological (photosynthetic) performance of the trees was analyzed. Experimental exposure to twice-ambient ozone levels was used to limit the primary production of the trees in the field (through "free-air" canopy fumigation) and in the phytotrons. Plants under ambient O3 regimes served as a control in both experiments. In addition elevated CO2 concentrations in the phytotron were used to stimulate the primary productivity of the saplings. We tested the hypothesis that the competitiveness of beech rather than spruce is affected by both the elevated O3 and CO2 regimes.
To analyze and quantify the competitive performance of the trees we defined efficiency parameters of competitiveness which are related to below- and aboveground space occupation (crown volume and fine root length per biomass investment), resource gain (C assimilated per crown biomass or volume) and maintenance costs (transpiration per crown biomass or resource gain). One tool in this approach is the calculation of annual carbon balances and water consumptions as based on modeling which is being parameterized through CO2- and light-response curves of the leaf gas exchange.
The phytotron study displayed a higher competitiveness of young spruce trees which resulted in an increased root and shoot biomass as well as in a higher crown volume as compared to beech. This competitive advantage does not seem to be related to an improved efficiency in the below-ground space occupation. Likewise, calculated C gain efficiencies (C assimilated per crown biomass) are very similar in beech and spruce saplings. The better competitive performance of spruce results from a higher efficiency of aboveground space occupation. This conclusion was confirmed in the field with mature spruce and beech trees. Similar to the saplings competitiveness is determined by space occupation and branching patterns rather than C gain efficiencies (i.e. C gain per invested biomass).
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