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| Titel |
Structural, physiognomic and above-ground biomass variation in savanna–forest transition zones on three continents – how different are co-occurring savanna and forest formations? |
| VerfasserIn |
E. M. Veenendaal, M. Torello-Raventos, T. R. Feldpausch, T. F. Domingues, F. Gerard, F. Schrodt, G. Saiz, C. A. Quesada, G. Djagbletey, A. Ford, J. Kemp, B. S. Marimon, B. H. Marimon-Junior, E. Lenza, J. A. Ratter, L. Maracahipes, D. Sasaki, B. Sonké, L. Zapfack, D. Villarroel, M. Schwarz, F. Yoko Ishida, M. Gilpin, G. B. Nardoto, K. Affum-Baffoe, L. Arroyo, K. Bloomfield, G. Ceca, H. Compaore, K. Davies, A. Diallo, N. M. Fyllas, J. Gignoux, F. Hien, M. Johnson, E. Mougin, P. Hiernaux, T. Killeen, D. Metcalfe, H. S. Miranda, M. Steininger, K. Sykora, M. I. Bird, J. Grace, S. Lewis, O. L. Phillips, J. Lloyd |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 10 ; Nr. 12, no. 10 (2015-05-21), S.2927-2951 |
| Datensatznummer |
250117940
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| Publikation (Nr.) |
 copernicus.org/bg-12-2927-2015.pdf |
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| Zusammenfassung |
| Through interpretations of remote-sensing data and/or theoretical propositions, the idea that
forest and savanna represent "alternative stable states" is gaining increasing
acceptance. Filling an observational gap, we present detailed stratified floristic and structural
analyses for forest and savanna stands located mostly within zones of transition (where both
vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant
leaf area index variation was related to tree canopy cover in a similar way for both savanna and
forest with substantial overlap between the two vegetation types. As total woody plant canopy
cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey
grasses and herbs progressively replaced by shrubs as the canopy closes over was found for
both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are
taken into account, a less marked transition in woody plant cover across the savanna–forest-species
discontinuum is observed compared to that inferred when trees of
a basal diameter > 0.1 m are considered in isolation. This is especially the
case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total
subordinate cover is also observed as savanna stand canopy closure
occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and
Australia attained greater heights and stored a greater amount of above-ground biomass than
in South America. Up to three times as much above-ground biomass is stored in forests compared to
savannas under equivalent climatic conditions. Savanna–forest transition zones were also found to
typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three continents
coexistence was found to be confined to a well-defined edaphic–climate envelope with soil and climate the key determinants of the
relative location of forest and savanna stands. Moreover, when considered in conjunction with the appropriate
water availability metrics, it emerges that soil exchangeable cations exert considerable control
on woody canopy-cover extent as measured in our pan-continental (forest + savanna) data set.
Taken together these observations do not lend support to the notion of alternate stable states mediated
through fire feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical
lands. |
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