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| Titel |
Structural and physiognomic associations between tropical savanna and forest examined at a pantropical scale. |
| VerfasserIn |
Mireia Torello Raventos, Elmar Veenendaal, Karlè Sýkora, Jon Lloyd |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048047
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| Zusammenfassung |
| Defining relationships between vegetation structural composition and ecosystem functionality
provides one means to improve the classification of complex savanna systems and we
here present a new analysis to classify savanna and forest vegetation forms and of
special relevance the transitional regions. As well as providing a new definition of
forest and savanna forms; we also present new data quantifying interactions of the
woody and the herbaceous layers, also providing a first analysis of the effects of
different soil types and environmental variables on tropical vegetation structural
characteristics.
We sampled 64 forest and savannas sites across West Africa, Cameroon, Bolivia, Brazil
and Australia used the same field methodology to determine the structural composition
of the vegetation for all the sites, almost all of which were 1 ha in area. Woody
cover was stratified into 3 layers, stems that have a diameter at beast height (DBH)
bigger than 1 dm, stems with DBH between 0.25 and 1 dm and stems with DBH
smaller than 0.25 dm. The herbaceous vegetation was defined as being consisting of
grasses, herbs, sedges and seedlings with differentiation being made between C3
and C4 plants with the woody species and their seedlings categorised as trees or
shrubs.
We also calculated crown area index (C) of the woody vegetation per layer and the foliar
projective cover of the herbaceous and seedling vegetation. For the clustering analysis we
also included the tree height and the 0.95 quartile height of all the trees with a diameter
at breast height (H)greater than 1 dm. Our aim was first, to create clusters that
define types of structural and physiognomic forms. And second, to determine the
relationship of the clusters with the different soil types and environments across the
continents.
Our analysis resulted in the definition 12 clusters in total with the main discerning factors
being the structural components of tree height and crown area index for the trees with D>
1 dm. Wood canopy crown cover and foliar projective monocotyledon cover were
highly correlated across the clusters with the proportion of the herbaceous layer
accounted for by C4 grasses declining with increasing C,even for relatively open
savannas.
A first analysis of the floristic variations in transitional zones showed very little overlap
between “forest” and “savanna” species for individual plots. Although in both South America
and West Africa we did find forest-like formations consisting almost entirely of species
usually associated with more open savannas. A mixture of structural and physiognomic
information is therefore needed in order to be able to accurately classify these vegetation
types.
Keywords: savanna, 13C, clustering, tropical biomes in transition, C3 and C4 plants,
crown area index, foliar projective cover |
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