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Journal Article

Extreme sites and diversity - an example from Amazonian floodplain forests


Parolin,  Pia
Working Group Tropical Ecology, Max Planck Institute for Limnology, Max Planck Institute for Evolutionary Biology, Max Planck Society;

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Parolin, P. (2003). Extreme sites and diversity - an example from Amazonian floodplain forests. The Botanica, 53, 23-34.

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How diverse are extreme sites? How diverse can the species, and their adaptations and life history stratgies be on extreme sites? How specialized do species need to be, which ecological amplitude can / must the species possess on extreme sites? The term ,extreme site' is frequently used in current publications, but its delimitation and definition are not clear. In this paper, the above mentioned question shall be analysed with examples which are focussed on the ecology of trees. A definition of the term ,extreme site' is found basing on the biological stress concept: resulting from cumbering climatic conditions, reduced nutrient availability, biological competition and damage, plants are subjected to a variety of strains for which the term stress is used. Extreme sites are therefore environments in which one or more factors are over- or underrepresented in a manner that the organisms can live there only if they possess special adaptations. These environments normally are represented by polar deserts, arid deserts, alpine environments or inselbergs which are not colonized by angiosperm trees. Ecosystems with extreme conditions where non-coniferous trees dominate, for example gallery forests in deserts and savannas, or mangrove forests along tropical coasts, normally represent forests with low diversity of species and a low variety of growth patterns. Amazonian floodplain forests show all the characteristics typical for a stressful extreme site: uninterrupted flood duration with high amplitudes, rapid changes of water levels, anoxic conditions in the rhizosphere, high sedimentation in várzea, nutrient scarcity in sediment-poor igapó, high mechanical stress, sometimes even drought contribute to make growth and establishment difficult for most organisms. Despite these strongly restricting environmental conditions, Amazonian floodplain forests are characterized by an extremely high diversity of species and life history stategies, even within phanerophytes. This diversity results from the fact that the stressors in this extreme site possess only a low level of restriction for tree life, and disturbances may even represent an enhancing factor for resistance and adaptive evolution. The high complexity of the system and the short but regular presence of factors favourable for tree growth allowed the evolution of highly diverse survival strategies. The species living there partly are highly specialized, but most have rather high ecological amplitudes. One may say, the ecological specialization of the trees is low enough to be able to react flexibly to changing environmental conditions and guarantee survival. On the other hand specialization is high enough to allow a high diversity and establish different species along hydric and edaphic gradients.