Distribution of Hair among Acacia tortilis Forssk (Hayne) Complex Growing in the Red Sea Hills, South Eastern Egypt and North Eastern Sudan

Howaida Faisal AbdElRahman

University of Bergen, Biology Department, Bergen, Norway
e-mail: Howaida.abdelrahman@bio.uib.no

Abstract

Arid lands are characterized by scarcity in rainfall that supports only sparse vegetation. Therefore arid lands vegetation developed some modifications to adapt to water scarcity. Among arid vegetation is the Acacia tortilis which represents the only arboreal species growing in the Northern Africa and Arabian Peninsula arid regions. The A. tortilis sub-taxa are mainly separated by the presence or absence of pubescence on the pods and pods width, and the differences in the pubescence of branchlets. The presence of hair, one of the evapotranspiration regulators, in different parts of the plants reflects their adaptation to arid environment. In connection to this, the main aim of the present work is to study the correlation of the hair density in A. tortilis branchlets and water availability in khors/ wadis in the Red Sea Hills of Egypt and Sudan. The landscape of the study area is characterised by the presence of the khor/wadi, i.e. seasonal water courses. Thornthwaite (1948) and Goldman et al (1968), the two regions experience difference in their aridity index. Therefore the hypothesis of this study is “the higher the amount of the hair in the branchlets the more probable that the plant is growing in the part of the catchment where soil moisture is low”. During February to April 2003, the density of the hair was recorded on field as (i) no hair was seen by the naked eye in the branchlets, (ii) hair was only seen in the petiole or (iii) hair was distributed in the whole branchlet. Principal Component Analysis, PCA, was the technique used to study the concerned correlation. XLSTAT is the software used to perform PCA. Results showed that plants samples that were collected from Sudan have denser hair distributed on the whole branchlets. A. tortilis growing in the upper part of the catchment is correlated to plants possessing hair covering the whole branchlets. On the other hand, those possessing no hair where found to be growing on the lower part of the catchments. These results concurs the assumption that the higher the amount of the hair, the more arid the area in which the plant is growing; and hence accepting the hypothesis of this study. Since Sudan is lesser in its aridity than Egypt, therefore species growing in Sudan are expected to possess more hair. Within the catchment itself, soil moisture is expected to be higher at the lower parts of the catchment. This also agrees with the obtained results. These results can be an indication that A. tortilis sub-taxa are ecotype. The various growth forms of the sub-taxa can be formed due to change in climate that the area experienced.

Keywords: Soil moisture, Red Sea Hills, Acacia tortilis, Arid lands, Hair density, khoe/wadi