Abstract
PHENOLOGY OF ACACIA TORTILIS SUBSP. RADDIANA IN TUNISIA'S BOU HEDMA NATIONAL PARK: SITE EFFECTS ON PHENOPHASES
Acacia tortilis subsp. raddiana, a slow-regenerating species with high ecological value, was previously common across thousands of hectares in Central and South Tunisia, but is now only found as a true population in the Bled Talah zone (Bou Hedma national park). In order to characterise the variability of phenophases in this taxon, phenological observations of the species were conducted in all three national park zones over three successive years. Blossoming and fruiting occur during the dry season, indicating that the species cycle is of a tropical nature. Observations of the trees at different phenological stages (leafing, blossoming and fruiting) show high inter-site and intra-site variation. The earlier appearance of these phases in the zone II population (Belkhir) compared to zone I (Bou Hedma) and zone III (Haddej) may be due to different edaphic characteristics: the Belkhir site is a south-east facing limestone glacis, the Haddej site is in a hollow of sandy loam, while Bou Hedma is in a foothill zone with detritic-colluvial deposits spread by wadis and is therefore cooler than the other sites. The differences observed within the same site may be accounted for by individual variability within the population, closely linked to the genetic characteristics of the trees. However, it must be pointed out that one of the fundamental characteristics of the Acacia tortilis life cycle in Tunisia is that it is not dependent on precipitation or, therefore, on soil moisture reserves. This phenological study covering the different zones of the national park has shown inter- and intra-site variations in rhythm, intensity and diversity; however, the phenological status of the tree would be better assessed with a greater emphasis on quantitative aspects of blossoming and fruiting.