There are a number of environmental conditioins that must be met for seedlings to be able to establish successfully.  The most important of these is the availability of water not only for successfull germination but also the initial growth phase during which a root system must be developed that is able to support a plant. Vermeulen (1990) reports for instance that seedling establishment is closely related to the amount of rain.

Due to environmental requirements for seedling establishment, some plant species do not follow what could be classed as a healthy population structure in any one area.  However, when population structure is also considered spatially, a mosaique of even-aged patches of different age classes may be observed.  This is probably the case for Pterocarpus angolensis, Schinziophyton rautanenii and Burkea africana in northern Namibia, although this has not been investigated formally.

P. angolensis and B. africana both go through a suffrutex stage that protects the plant against fire, but also alows the plant to develop a sufficiently large root system that may support a permanent shoot.
 

See also:

Water availabiltiy in the woodland areas.