Just beneath the surface of the Kalahari Sands, underground forests are among the most remarkable features of the African flora in this region.
Hidden beneath the surface of the Kalahari Sands concentrated in south-western Zambia are unseen forests closely related to the forests above ground.
All that is usually seen of these subterranean 'trees' are clumps of leaves emerging from the sand, like a canopy at ground level. The woody stems grow horizontally through the soil, often extending for metres in all directions, so one plant can create an almost circular patch of erect leaves.
This form of underground tree is called ‘geoxylic suffrutex.’ More than a hundred species have been identified, across a wide range of plant families. A distinctive feature of the habit is that each suffrutex species can be paired with very similar tree or climber species from which it may have evolved. For example, the tasty mobola, Parinari curatellifolia, has a suffrutex relative known as Parinari capensis (kabolabola). Their leaves, flowers and fruits are almost identical, but P. capensis hugs the ground.
Some suffrutex species have edible fruits, which are a valuable source of nutrition for people who rely on gathering food in the Kalahari. Examples include Diospyros chamaethamnus, a mini-version of D. batocana; Pygmaeothamnus zeyheri, the ‘sand-apple’; and Annona stenophylla in the custard-apple family. There is even a suffrutex waterberry, Syzygium huillense.
A good time to look for these plants is between September and November, as flowers and fruits appear at the very end of the dry season. Flowering is squeezed into a short period after annual burning and before the arrival of rain, thus pollination can happen while there is no restricting grass and herb layer.
A vivid example is Combretum platypetalum, with its scarlet blossom bursting into life on bleak, parched soils, among the remains of charred plants.
The suffrutex habit may be an evolutionary adaptation in response to annual fires, giving underground protection to perennial woody growth and new buds and shoots. However, it seems that the seasonally waterlogged and low-nutrient soils found in depressions in Kalahari Sands and at the edges of dambos influence its distribution.
Lovely examples can be found under those soil conditions even on the outskirts of Livingstone, so now you can add ‘Suffrutex’ to your sightseeing list for Zambia!
Read more articles from this issue:
Zambezi Traveller (Issue 10, Sept 2012)
Read more about the region in our destination guide:
More articles in this series:
Rainforest Riches (ZT, Issue 13, June 2013)
Berry banquet (ZT, Issue 12, March 2013)
Marvellous Mangoes (ZT, Issue 11, December 2012)
Underground Forests (ZT, Issue 10, September 2012)
The healing powers of Aloes (ZT, Issue 09, June 2012)
Dogbane Drugs (ZT, Issue 08, March 2012)
Devil’s Claw (ZT, Issue 07, December 2011)
Elephant Toothpicks (ZT, Issue 06, Sept 2011)