Platbos - arguably the most unique forest patch
in the Southwestern Cape
By Professor Eugene Moll and Dr. Bruce McKenzie
Back in 1990 we published(1) our study of the forests of the Swartkransberg. Platbos was one of the five forest patches we sampled. We knew from Taylor´s work in 1961(2) that Platbos was significant - for a number of reasons:
There are extremely few forest patches remaining on flat ground in the Southwestern Cape Province, and even in South Africa - with those at Alexandria, just NE of Port Elizabeth, being perhaps the best known; together with those in northern KwaZulu-Natal that have been studied in more recent times.
The tree species composition is unique, with the Afromontane species of Celtis africana and each contributing more than 12m2/ha of basal area, followed by Sideroxylon inerme at >8m2 (this being a lowland species, and in the Cape Region mostly on coastal sands). These three species make up>32m2/ha of a total of 56.49m2/ha and are, therefore, the dominant canopy trees.
The structure of the forest is also unique. The almost totally closed upper canopy is not high, being between 4-6m to a maximum of ~10m. Yet it has all the characteristic structural features of true forest. Interestingly most of the canopy species have almost no trunks, they branch low down. Thus walking through the forest one has the impression of walking through the lower canopy.
Platbos, meaning "flat forest/bush" is aptly named because from a distance one cannot readily distinguish the forest from the surrounding shrublands. Platbos is surrounded by proteoid fynbos mixed with elements of South Coast Strandveld that is heavily infested by the Australian aggressive alien, Acacia cyclops. The forest area is a mere 40 ha, of which some 27 ha is owned and now managed by the Krige´s.
Historically many of the bigger trees were harvested for their timber, but with protection over the last few decades the forest is slowly returning to its former glory; and this is a long and slow process. The Krige´s have killed and/or removed the aliens in the forest, and are slowly rebuilding the integrity of the margin. This is, however, a major operation because of all the historical and contemporary disturbance and the alien thickets. This restoration of the margins is essential as the current threats to Platbos are fire and wind - the latter penetrating under the canopy and drying the forest understorey (this also increases the fire risk).
The intention of the present owners is to replant the forest with Platbos tree species in the areas where it originally occurred; both on their property and on two neighbouring properties. This is a viable project and will provide growth that will out-compete the encroaching alien thickets.
Platbos is situated on the slopes of the Baviaanspoort Hills and is the largest remaining fragment of the Swartkransberg Forests. Whether these were all once contiguous in historical times is doubtful, and unfortunately not all the fragments are being as well conserved as Platbos.
The forest itself is on gently undulating alkaline sands that are covered with a thick leaf litter and humus layer. The rainfall of the region is quite low, being between 600-800 mm, which is generally not considered sufficient for forest. However, during the dry summer months coastal fog is a feature at Platbos, and this not only helps to sustain the forest but also helps to support large quantities of epiphytes. The epiphytes are not rich in species numbers, with Usnea sp. festooning the upper branches of many canopy trees. Peperomia sp. is common along with a few fern, bryophyte and lichen species - particularly on larger branches in sheltered places. Because trees like Sideroxylon have thick, corky bark that provides an ideal substrate for these epiphytes.
Although there are no known rare and/or endangered vascular plant species in Platbos, it is the unique forest structure, position in the landscape, and unusual assemblage of Afromontane Forest species, Coastal Forest species, and Strandveld elements that make Platbos valuable. Not a great deal is known of the fauna, but we have no doubt that in time as this forest is better studied Platbos will rewrite the record books as far as animal distributions are concerned. We know from Skead´s work that the Swartkransberg Forests are the southern and western limit of Bushbuck and possibly Blue Duiker. The former still occur at Platbos, but the latter are unknown.
In conclusion Platbos is uniquely special and should at all costs be conserved and protected for future generations. The owners are currently developing a long-term conservation management plan of action.
(1) McKenzie, B., Moll, E. and Denman, S. 1990. The forests of the Swartkransberg, South Africa.
Proceedings of the Twelfth Plenary Meeting of AETFAT. Mitt. Inst. Allg. Bot. Hamburg: 119-128.
(2) Taylor, H.C. 1961. Ecological account of a remnant coastal forest near Stanford, Cape Province. J.S. Afr. Bot. 27:153-165.