BIOTA Morocco - Results

Climate regulated vegetation dynamics of Tamarix amplexicaule stands on saline clay soil

Dr. Manfred Finckh & Markus Staudinger
Biocentre Klein Flottbek and Botanical Garden, University of Hamburg

Loose stands of Tamarix amplexicaule form the only woody stands in the central area of the saline clay pan of Lac Iriqui. After the construction of the Mansour Ed Dabbi dam this area has not any longer been flooded. To examine the long-term effects of the absence of floods on the stands of Tamarix amplexicaule we established a pair of permanent plots at testsite IRK.

On the exclosure site (Fig. 1) four of the initial ten Tamarix died since the investigation started in 2001. There has been no seedlings, neither of Tamarix nor of any other species. Plenty of individuals already dead in 2001 document an originally far higher density of individuals.

In contrast to the exclosure site, so far no Tamarix died on the open site (Fig. 2). Two intense rain events in winter 2003/2004 led to a short-term establishment of three further species, Mesembryanthemum nodiflorum, an annual species, and the two dwarf shrubs Zygophyllum gaetulum and Suaeda maritima. Only Suaeda maritma was able to outlast longer, however, by autumn 2005 all individuals were dead.

The difference between the two monitoring sites probably is caused by minimal differences in level regulating the water availability at the sites.

At this arid site with about 60 mm mean annual rain fall intense precipitation events play a major role as trigger for the mobilisation of the soil seed bank. However, even the torrential rain in winter 2003/2004, exceeding by far the average in this area, did not suffice to establish a new generation of Tamarix. Presumably Tamarix was not able to germinate after the dam was constructed in the early 1970ies. Therefore, in the long run the disappearance of this vegetation unit in central Lac Iriqui seems probable.


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