Plant Species Composition
The structure of the woody vegetation is not only reflected by the age
structure of each individual species, but by the number of different species
themselves (alpha diversity), and their individual characteristics.
Growth form
Different woody species have different growth forms. These range
from low shrubs like Baphia massaiensis and bushes like Bauhinia
petersiana and various Combretum species, through small trees
such as Terminalia sericea and Ochna pulchra to larger trees
such as Burkea africana, Gouibortia coleosperma, Pterocarpus angolensis
and others. The growth forms of the different species determine
the canopy cover of the woodlands, in height and in density. These
two parameters are of particular importance due to their effect on light
penetration to the woodland floor and their effective arangement of the
fuel load. but also on the interception and concentration of water around
tree roots.
Competition for water
The availability of water seems to be the factor that most limits the growth
and development of the vegetation. Plants therefore need to be able
to access as much water as possible. This is dependent on the rooting
strategy of the plant, soil conditions, and the water potential of the
soil and plant.
Competition for light
Although the light intensity in the savannah woodlands is much higher than
in tropical rain forest, the availability of light has a significant effect
on the establishment of the seedling of some species.
Fire tolerant species
Different plants have different ability to withstand the effects of fire.
While some plants are able to withstand fire quite well, and have adapted
strategies like copicing (Ochna pulchra and Grewia flava)
or survival as sufrutex (Pterocarpus angolensis), others are eventually
removed from the system by fire, as may be the case for Schinziophyton
rautanenii. The ability to withstand fire may be the reason that
some of the Burkea africana stands have developed (Rutherford
1981). He also reported, however, that most B. africana plants
that died the fires he studied were seedlings. The ability of plants
to withstand fires not only depends very much on the prevailing
fire regime,
but also on the size of the plants involved. Rutherford
(1975) found, for instance that even infrequent fires may kill Burkea
africana trees up to a height of 4m, while larger trees are not as
seriously affected.
Fuel Load Characteristics
Stem diameters of woody plants very significantly influence the behavior
/ condition of the fuel load. Many
small shrubs or bushes, with thin stems like Grewia flava or Bauhinia
petersiana will represent a higher fire danger than thicker stemmed
plants.
Appart from the size of fuel and its arrangement, von
Breitenbach (1968) mentions differences in flamability between different
woody plants.
| See also: |
| The characteristics and development of a fuel
load |