Zimbabwe's forest genetic resources at ecosystem level are still reasonably intact, particularly the flora Zambesiaca. The situation is slightly different for the Afromontane vegetation system and some species that are now severely threatened by over-exploitation and infrastructural development. The Afromontane vegetation particularly at high elevations, (above 1 500 meters a.s.l.) may require some attention to arrest the invasion of natural forest by the exotic industrial species.
Four indigenous species can be considered to be under threat (see appendices 4 and 5). These are Bivinia jalbertii, Warbugia salutaris, Milicia excelsa and Strychnos mitis. Urgent work is required to assemble their germplasm and to establish ex situ field gene banks and, at the same time, improve their conservation in situ through better protection of their natural habitats.
The second group of species requiring attention includes Afzelia quanzensis, Andostyachis johnsonii, Baikiaea plurijuga, Entandophragma caudatum, Pterocarpus angolensis and Ricinodendron rautenanii. The species are under threat from furniture manufacturers and wood carvers. Although their numbers are not likely to fall to threatening levels, it is the possibility of genetic impoverishment from selective harvesting of all phenotypically superior trees (usually large trees are harvested) that is worrying. Studies should be initiated to investigate genetic variation of these species and recommend management practices that will ensure sustainable management and utilization of these species.
The third group of species is the indigenous fruit tree species which include Uapaca kirkiana, Ziziphus mauritiana, Strychnos cocculoides, Sclerocarya birrea and Vangueria infausta. Again, the number of trees of these species are not likely to fall to sub-optimal levels but, like the timber species, it is the large scale marketing of fruits harvested from the wild that could be worrying. The selective harvesting and mass movement of the better quality fruits could have a bearing on the natural regeneration of the preferred trees. In Zimbabwe, harvesting of Uapaca kirkiana fruits has already been shown to be highly damaging to the trees. Research into these species will involve assembly of germplasm, evaluation in provenance/progeny and clonal trails, biology of the species, management in situ and establishment of ex situ production areas. Some of these, like Uapaca kirkiana, Strychnos cocculoides and Sclerocarya birrea, are already being evaluated in field trials in Zimbabwe.
The fourth group of species is the acacias for livestock fodder production from pods and also for gum arabic production. The species considered are Acacia albida and A. erioloba for pod production, as well as A. senegal var senegal for Arabic gum production. These three species are already evaluated in provenance/progeny trials in Zimbabwe.
The threat of exotic species that have become invasive is also an important area of management or research. Although sometimes considered to be far-fetched, consideration should be made to investigate the possibility of introducing male sterility genes in the planted species to curb their invasiveness. For now, however, encouraging development of other small-scale industries to utilize these trees is another option.
