Acacia seyal Del. is a typical tree in the African semi zones. It is a small to mediumsized
tree that reaches a height of 12-17 m (Hall and McAllan, 1993; McAllan, 1993;
von Maydell, 1990; National Academy of Sciences, NAS, 1980), has a stem diameter
of 30 cm (Mustafa, 1997), or 60 cm under favourable conditions, and develops a
characteristic umbrella-shaped crown (von Maydell, 1990). Acacia seyal usually
reaches 9-10 m in height at maturity (Nitrogen Fixing Tree Association, NFTA, 1994).
Several authors provide a valuable description of Acacia seyal (see for example;
Elamin, 1990; Hall and McAllan, 1993; McAllan, 1993; Mustafa, 1997; von Maydell,
1990; NAS, 1980).
Like other acacias, A. seyal is widely distributed in the African savannas (Booth and
Wickens, 1988; McAllan, 1993), often dominates the vegetation community and in
some areas forms pure stands (McAllan, 1993; Wickens et al., 1995). It is considered
one of the most common trees on clay plains that flood during the rainy season
(McAllan, 1993).
The species is an important source of fuel wood, building poles, forage, commercial
gums, and tannins (ELamin, 1990; Mustafa, 1997; von Maydell, 1990; NAS, 1979,
1980; Wickens et al., 1995) and is a source of nectar for honeybees (Booth and
Wickens, 1988). A. seyal produces gum which though of inferior quality in
comparison to that of Acacia senegal, is traded in Sudan under the name ´´gum
talha´´ and makes up to 10 percent of the annual exported gum Arabic (Barbier et al.,
1990; McAllan, 1993; NFTA, 1994). Unlike gum from A. senegal, gum talha is not
recognized as an acceptable food additive (Hall and McAllan, 1993).
Additionally, A. seyal serves valuable ecological functions such as reducing soil
erosion and acting as a defence line for desert encroachment in many parts of the
Sudan, as is the case for the selected location for the present study, the Umfakarin
forest reserve. Like other Leguminous, A. seyal is a nitrogen fixing tree which can be
integrated into an agro-forestry system to enhance the growth of agricultural crops. The species requires annual rainfalls of 250-1000 mm and it can withstand
inundation better than other acacias (von Maydell, 1990; NAS, 1980). The species
thrives in most soil types, even in heavy clay and stony soils found on the plains
(McAllan, 1993; NAS, 1980). It prefers temperatures between 15-35 ºC (Vogt, 1995).
It often grows with other tree species, such as Acacia sieberana, Anogeissus
leiocarpus, Balanites aegyptiaca, Faidherbia albida and Ziziphus mauritiana
(McAllan, 1993).
In general, there are two main varieties of A. seyal; variety seyal and variety fistula.
Variety seyal is found in both western and eastern Africa and also on the Arabian
Peninsula, while variety fistula is found in the eastern parts of Africa (McAllan, 1993).
NAS (1980) and NFTA (1994) indicate that variety seyal is native to northern-tropical
Africa and Egypt. The two varieties can be easily distinguished; variety seyal has a
greenish-yellow to reddish-brown bark, while variety fistula has white to greenishyellow
bark (McAllan, 1993). Figure 1.1 shows the distribution of A. seyal varieties,
with respect to rainfall.
In Sudan, the two varieties occur naturally in the low rainfall savannah zone and
extend from Gadarif, Blue Nile, and White Nile to clay plains around Nuba Mountains
and the Darfur Region (El Amin, 1990; Mustafa, 1997; Sahni, 1968). The species is
distributed throughout its natural range, and is usually associated with Balanites
aegyptiaca in the Acacia seyal-Balanites woodland area. In such formation, A. seyal
is the dominant species, forming pure dense stands in many areas. According to
Mustafa (1997), this formation begins to emerge with an increase in the annual
rainfall to accumulations of more than 500 mm.
In the savanna region of Sudan, A. seyal has been subjected to large-scale clearing
for mechanized agriculture (Mustafa, 1997; Vink, 1990; Wickens et al., 1995)
associated with firewood and charcoal production to meet energy requirements.
Besides clearance for mechanized farming and wood fuel, other factors such as
grazing, deliberate and undeliberate fires also have a significant negative impact, not
only on natural stands of A. seyal but also on natural forests in Sudan.