Programme des sessions > Recherche par auteur > Ejarque Ana

The low-steppe regions of Tunisia are highly sensitive to both climatic changes (e.g. increasing aridity) and anthropogenic pressures (e.g. agriculture, over-grazing, urban sprawl). A retrospective approach is essential to unravel the complex environmental, climatic and landscape shaping processes to understand how climate and social-ecological interactions have impacted this ecosystem throughout the Holocene. To this end, a 16.54 m long sequence was recovered from the Sebkha El Bhira (Kairouan Governorate, Tunisia) and provides a thorough pollen record spanning the Holocene.

Preliminary palynological analyses highlight three main pollen zones. The first zone, from 16.54 m to 5.56 m depth, is characterized by high values of Artemisia, Amaranthaceae and Poaceae, alongside smaller contributions of Asteroideae and Helianthemum. Mediterranean ligneous taxa like Juniperus, Quercus ilex-type and Olea all show a steady decline. The second zone, between 5.56 m and 2.60 m depth, is marked by a heavy contribution of Poaceae and Amaranthaceae, whilst Artemisia rates decline. Higher values of Brassicaceae, Asteroideae, Cichorieae, and Mediterranean plants are observed, along with minor inputs from the riparian vegetation (e.g. Salix, Alnus, Fraxinus) and the first appearance of Anthropogenic Pollen Indicator taxa (e.g. Cerealia-t., Plantago lanceolata-t.). The final zone, from 2.60 m depth until the surface, displays a resurgence of Amaranthaceae values and a decline in Poaceae. Artemisia rates gradually increases, reaching their acme in the uppermost samples, accompanied by notable peaks of Olea and Brassicaceae frequencies.

Overall, the pollen data reveal an early phase dominated by an Artemisia low-steppe surrounding an Amaranthaceae-dominated chott around the sebkha, with a Mediterranean matorral vegetation covering the neighboring djbels slowly declining. The second phase suggests episodic rises of the sebkha water levels, inferred from the replacement of halophytic Amaranthaceae values by Poaceae. The final phase indicates a shift in land-use practices, marked by clear evidence of olive cultivation and grazing-induced degradation of the steppe.

Ultimately, this preliminary palynological study outlines significant changes in vegetation composition over the Holocene and highlights a tipping point in the landscape shaping process driven by the onset of intensive agricultural land-use within the past two centuries.