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Title Gradients of species diversity on the Saharan fringe in Southern Morocco

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Author(s) Finckh, M., Oldeland, J.; Augustin, A.

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Institution(s) University of Hamburg, Biozentrum Klein Flottbek, Ohnhorststr. 18. 22609 Hamburg

Keywords species diversity; altitudinal transect, arid environment; permanent monitoring,

Abstract The ecosystems of desert fringes and high mountains belong to those forecasted to be subject to drastic climatic changes over the next decades. A sound understanding of their diversity patterns is a necessary baseline information for scenarios of biodiversity changes.
Altitudinal gradients are more complex than latitudinal ones, because geological diversity as well as orographic, microclimatic and edaphic effects interact at relatively small scales. “Rapoport’s rule”, stating that species density decreases with increasing latitude, has already be stated to be wrong for subtropical regions by several authors.
Semi-arid mountains have not yet been studied extensively for gradients of phytodiversity. Based on a dataset of about 1000 vegetation relevés from Southern Morocco, we found a hump shaped distribution of species density on several environmental gradients with a mid-altitudinal peak. Species turnover increases with aridity, possibly due to stronger ecological specialisation in water limitated environments.
BIOTA-Maroc features 35 permanent plots along an altitudinal transect from the oromediterranean to Saharan ecosystems. Vegetation on these plots is annually surveyed. Accumulated species densities on these plots are significantly higher than the mean density along the gradient. Species density calculations in semiarid and arid environments based on single observations may thus have a strong bias. Especially the annual species guild is normally just present in part in a given moment.
These findings demonstrate the importance of permanent monitoring, particularly in arid environments.

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