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| Titel |
On the functional role of tree species in two forest ecosystems |
| VerfasserIn |
Werner Leo Kutsch, Mathias Herbst, Chunjiang Liu |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034350
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| Zusammenfassung |
| Ecosystems can be characterized in different ways depending on the point of view or the
scientific background. Summarizing these views, one can describe ecosystems by their
structure and metabolism. The species composition is part of the ecosystem structure.
Moreover, ecosystem structures are detailed by biomass or soil and canopy architecture.
Ecosystem metabolism represents the functional side. It can be described by primary
production, nutrient retention, or control and use of water resources.
Structure and function are connected. The biomass that is produced by the ecosystem
metabolism is used to construct the ecosystem structure, which vice versa the structure
controls the efficiency of the ecosystem metabolism. One hypothesis is that ecosystems with
many species provide a more efficient metabolism than ecosystems with fewer species. We
tested this hypothesis by using two ecosystems functional parameters in several deciduous
forest ecosystems.
The first example are possible relations between canopy carbon uptake capacity (FP,max)
as measured with the eddy covariance technique (ecosystem metabolism) and LAI as well as
spatial and temporal variability of leaf traits (ecosystem structure). We investigated
leaf traits of four tree species in a mixed deciduous forest in northern Germany in
search for an explanation for the differences in canopy photosynthetic capacity
between different forest sectors consisting of different species and species numbers
(Quercus robur + Fagus sylvatica, Fraxinus excelsior + Alnus glutinosa, pure Fagus
sylvatica).
We identified leaf traits that were adjusted to the canopy light profile in species-specific
ways, and for these traits the plasticity indices were calculated. Canopy photosynthetic
capacity did neither correlate with leaf area index (LAI) alone nor with canopy plasticity
indices which were almost similar between the three sectors although it differed at the species
level. It is suggested that the spatial variability of FP,max in deciduous forests can be
explained by a combined effect of LAI and some species-specific reference leaf traits, rather
than by the plasticity index or by pure LAI.
In a second study we compared a mixed canopy of Fagus sylvatica and Fraxinus excelsior
to a pure Fagus sylvatica stand during a drought period in summer 2006. Leaf gas exchange
measurements suggested that beech trees responded faster and stronger to soil drought and
changed stomatal sensitivity to leaf to air water vapour pressure deficit, while ash
trees remained more progressive. Scaling these results in a modelling approach
resulted in an lower impact of drought in a two-species canopy than in a beech
monoculture and an increase of the Fraxinus contribution to total ecosystem carbon
uptake.
Both results support the hypothesis that multi-species canopies may buffer unfavourable
environmental constraints and increase efficiency in the use of resources. |
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