Ecosystems of Mountain Zebra National Park and Bergplaas
(writing in progress)
In 2015 I visited Mountain Zebra National Park (https://en.wikipedia.org/wiki/Mountain_Zebra_National_Park) and Bergplaas (https://www.bergplaas.com/)(also see my Post on Searsia pallens).
I have before me van der Walt P T (1980) A phytosociological reconnaissance of the Mountain Zebra National Park. Koedoe 23, pp. 1-32.
I have gone through this paper carefully and I can make the following notes and comments.
At the time of van der Walt’s (1980) study, the national park was far smaller than it is today, a large area of relatively low-lying land having been added since then on the northern side between the Bankberg and the Cradock-Nieu Bethesda road.
As at Bergplaas, the geology of MZNP is mainly dolerite but does include some sandstone, because there are sandstone layers in the shale beds. So one cannot categorically rule out nutrient-poor rocks just because one is in a mainly dolerite-over-shale landscape. It is from this ambiguity that people has slipped into confusion, thinking that polgrasveld is somehow naturally sour.
On relatively high-lying sandstone in MZNP, the following vegetation is described by van der Walt (1980). Merxmuellera disticha and Euryops annuus dominate, with Elytropappus rhinocerotis giving the vegetation some affinity with renosterveld. I infer that, as at Bergplaas, this vegetation is anthropogenic, after a history of abuse by sheep farmers. As at 1980, the National Parks policy was to protect the pograsveld from fire. I wonder how that has played out?
Also indicating past overgrazing, at higher altitudes in MZNP, are the grass Elionurus muticus (KOPERDRAAD, called E. argenteus by van der Walt) and the karoid dwarf shrubs Selago corymbosa and Felicia filifolia. Are these shrubs flammable like M. disticha and Euryops?
When it comes to Searsia pallens, van der Walt (1980) is a disappointment because he neither describes this plant’s extraordinary growth-form nor even identifies it correctly. He merely calls is ‘Rhus lucida’, which is misleading, and mentions it only superficially. Van der Walt (1980) is a completely damp squib when it comes to Searsia, which to my mind was such an obviously fetching and remarkably bizarre plant during my visit of July 2015. Either van der Walt was simply blind to its growth-form or it did not occur commonly in MZNP at that time?
Searsia erosa, a flammable-looking shrub which we saw at Bergplaas, was common also in MZNP, where it seemed to be associated more with Heteropogon contortus and Hyparrhenia hirta.
The lawn grass Cynodon incompletus was locally common in MZNP, forming a community van der Walt (1980) calls ‘Ridge Top Trampled Grassland’. He does not use the term ‘lawn’ but instead refers to this grass as a ‘creeper’. Associated plants include Cyperus usitatus, Lasiospermum bipinnatum, Selago albida (toxic and avoided by wild ungulates) and Melica decumbens (ditto).
Pentzia incana, a characteristic karoid dwarf shrub, is a plant that manages to be both palatable and weedy (in the sense that it proliferates after sheet-erosion). It dominates certain karoid parts of MZNP. I see now that in a way Pentzia incana is ‘opposite’ to Merxmuellera and Euryops, in responding to veld abuse by maintaining palatability and excluding fire. Food for thought? Pentzias in MZNP tend to be associated with Eragrostis lehmanniana, which is a biennial grass according to van der Walt (1980). In places P. incana is replaced by Pentzia globosa or (on alluvia) Pentzia sphaerocephala.
Another dwarf shrub proliferating locally after overgrazing is Ocimum burchellianum, which I infer also to be non-flammable. Ocimum is the genus of cultivated basil, as in Italian pesto sauce. I suppose one can view the Ocimum vegetation, which forms small patches in MZNP, as the local equivalent of ‘sagebrush’ in the American sense, because Ocimum is confamilial with Salvia and likewise defends itself from herbivory by means of ‘secondary chemicals’.
Something I did not previously realise is that the genus Hibiscus stretches to the dwarf shrub growth-form in South Africa. In MZNP a species with this growth-form is Hibiscus pusillus. Karoid dwarf shrubs are a mish-mash of all sorts of families bent to the growth-form of a ‘shrubby lawn’, not so?
A grass for which I’ve previously had a blind spot (i.e. I’ve been oblivious to this grass) is the tussock grass Setaria sphacelata (called neglecta by van der Walt). This species is one of the most palatable of grasses in MZNP (despite its robust size) and occurs in association with Vachellia karroo on low-altitude doleritic soils, where the mountain zebra preferred to graze during the early years of the (then much smaller than today) MZNP. Setaria is yet another example of generic meaninglessness among grasses, because in tropical savannas at least some setarias are shunned by ungulates owing to their cyanogenic nature. Setaria sphacelata has been ‘domesticated’ (some cultivars being too rich in oxalates to be palatable to equids) and is also an invasive weed in Australia. As I’ve mentioned previously, it’s a fool’s errand for an ecologist to try to get one’s eye in for grass genera in the way one does for other plants and indeed for most animals. Genus means little in grasses, and I’ve yet to get to the bottom of why this is so. However, I digress.
Biogeography of grass genus elionurus, seen at Bergplaas in form of wiry small tussock koperdraad
At Bergplaas last month, you and I encountered koperdraad grass, a low, wiry grass obviously unpalatable to ungulates. Because this grass is so obviously sclerophyllous, I wondered whether the genus occurs also in Australia, to which it would seem suited.
Like many genera of Poaceae, the genus Elionurus does occur on several continents. And indeed, there is one species in Australia, viz E. citreus.
Although I have not found a photo of Elionurus citreus on the internet, its name suggests that it is known mainly as a lemon-scented grass rather than a wiry grass. So I looked up the features of koperdraad grass in South Africa and I see that it is likewise known to be lemon-scented. So it seems that Elionurus is mainly a lemon-scented grass (i.e. defending itself from grazers chemically) and only secondarily a sclerophyllous grass (defending itself from grazers by means of lignification). All of this is based on sparse information, because there’s really not much on Elionurus on the web.
As so often happens when one investigates grasses at a generic level, there is a tantalising prospect of a biogeographical/ecological pattern, which evaporates on inspection. Like so many grass genera, Elionurus is widespread to a point suggesting ‘cosmopolitan’. And like so many grass genera, this one does not seem to have any particular growth-form or ecological strategy. Elionurus muticus (please see map below) is widespread in the eastern half of South Africa down to Humansdorp, reaching its western limits at Bergplaas because it is a Highveld grass and not a Karoo grass. (It does not seem even to reach the more westerly occurrences of Merxmuellera disticha, e.g. in the Karoo National Park near Beaufort West.) And sure enough Elionurus in Australia is mesic too. But in Australia, the local species (E. citreus) hardly reaches the temperate zone, being instead more typical of the tropics (please see map below). I would hesitate even to assume that all species in the genus Elionurus are lemon-scented, even though E. muticus and E. citreus seem to be.
So, I find that, although Elionurus muticus is a good grass to know about at Bergplaas, for its seemingly extreme anti-herbivore defences combining wiry, unpalatable leaves and an unpalatable lemon-like scent (lemon smells pleasant to humans but is essentially toxic to ruminants), it turns out to be yet another ‘damp squib’ at the genus level, when one investigates its global biogeography. Grasses just don’t work like other plants biogeographically, do they?
Poaceae: Elionurus citreus
http://ausgrass2.myspecies.info/sites/ausgrass2.myspecies.info/files/1elcit.gif
Poaceae: Elionurus muticus
http://redlist.sanbi.org/imgs/distribmaps/9/Plants-90059.png
Poaceae: Elionurus muticus
http://www.ispotnature.org/sites/default/files/imagecache/mid/images/41019/0d6d7ee353db93703e5d4bdb21522ca6.jpg
Bergplaas Nature Reserve near Graaff-Reinet lies on the ‘roof of the Karoo’. It is a poorly-appreciated outlier of the Highveld, situated in the eastern Karoo on the Great Escarpment where the dolerite mountains are so large and bring so much rain that a mesic rather than semi-arid vegetation prevails. It is impossible to reconstruct the original ecological regime of the Bergplaas area without two bold invocations of the imagination: envisaging a Serengeti-type migration and envisaging a radical perversion of the vegetation once this regime changed to sedentary farming with sheep from about 1800.
Bergplaas is ostensibly a reconstitution of the original ecosystem of the mountainous Karoo, in which livestock have been removed and the indigenous wild ungulates reintroduced. The truth is different and much more interesting.
Firstly, it is wrong to think of Bergplaas as Karoo. The upland of which Bergplaas forms a part is surrounded by Karoo but in fact represents the westernmost outlier of the Highveld. Its natural vegetation was not only grassland, but lawn, a strictly seasonal paradise for migratory ungulates. Read more
[I envisage something about which little seems to have been written. This is a Serengeti-like migration of black wildebeest, springbok, eland and the extinct quagga that is now a world away because of the fencing of this area and its century-long abuse by sheep farmers. And, perhaps even more boldly, we envisage a natural vegetation of lawn grasses rather than anything one would associate with the Karoo or its mountains today. A seasonally deserted paradise for grazers, something that Bergplaas – although now a nature reserve once again devoid of domestic livestock – has yet to revert to, and probably never will without being managed with deep ecological understanding.
In the Serengeti, the four main migratory ungulates (white-bearded wildebeest Connochaetes mearnsi, grant’s zebra Equus quagga boehmi, Thomson’s gazelle Eudorcas thomsonii and the northern ssp. of the common eland Taurotragus oryx livingstonii) gravitate towards the nutrient-richest part of the ecosystem, which happens to be its driest area, to capitalise on nutritious grass in the rainy season. The Serengeti migrations are based on the Serengeti Plain, a flat area of volcanic ash which is largely deserted by ungulates during the dry season when the wildebeest, zebra, gazelle and eland find what food they can farther afield in savannas which are more luxuriant but poorer in the quality of grazing.
Although the topography is different along the Sneeuberg escarpment – the highest-lying part of South Africa apart from the Drakensberg – the nutritional theme would be similar. Because these mountains consist of dolerite, a particularly nutrient-rich rock, and because they attract extra rain owing to their altitude, they form the centre of attraction in our conceptual reconstruction of the ungulate migrations several centuries ago. The main species participating in this migration are all close counterparts of those in the Serengeti Ecosystem and in two cases belong to the same species: black wildebeest (Connochaetes gnou), extinct quagga (Equus quagga quagga), springbok (Antidorcas marsupialis) and eland (Taurotragus oryx oryx). As in the case of the Serengeti, we visualise Bergplaas, and the similar areas of escarpment mountains near it, virtually deserted of large ungulates for most of each year in the dry season.
Secondly, the original vegetation depended to some extent on the migrations, and is difficult to maintain with year-round grazing. The original ecosystem can probably not be retrieved, but if anything like that ecosystem is to be emulated then it will take artful management of what is now inevitably a resident presence of the wild ungulates. Read more.
[I suggest that the original vegetation at Bergplaas was a lawn, green in summer when the migratory ungulates were present and brown and deserted in winter – but a far cry from the present vegetation of wiry tussock grass and asteraceous low shrubs that is accepted by today’s farmers and nature reserve managers as natural in the area.
The Serengeti migration is indeed based on a lawn, consisting mainly of Sporobolus and Kyllinga. In the case of Bergplaas and the adjacent highlands, the two main grasses suggestive of a former lawn are Tetrachne dregei and Cynodon incompletus. Both grass species have restricted ranges in and near the eastern Karoo, and have largely been replaced by less palatable grasses as well as low shrubs, which tend to burn instead of being consumed by ungulates.]
Thirdly, Bergplaas Nature Reserve has inherited the damage of a century of farming with sheep. This makes it even harder to revert to anything resembling the original ecosystem.
Fourthly, what is currently assumed by farmers and nature conservationists alike to be the natural vegetation is actually not just anthropogenic, but a veritable perversion of the natural vegetation. Instead of the original lawn, Bergplaas Nature Reserve, like surrounding areas in these dolerite-and-shale uplands along the Great Escarpment near the centre of South Africa, is covered by a benign-looking nightmare: a tweedy-looking heathland in which the most important plant is the wiry tussock Merxmuellera disticha.
Bergplaas near Graaff-Reinet lies on the ‘roof of the Karoo’. It is a poorly-appreciated outlier of the Highveld, situated in the eastern Karoo on the Great Escarpment where the dolerite mountains are so large and bring so much rain that a mesic rather than semi-arid vegetation prevails.
It is impossible to reconstruct the original ecological regime of the Bergplaas area without two bold invocations of the imagination: envisaging a Serengeti-type migration and envisaging a radical perversion of the vegetation once this regime changed to sedentary farming with sheep from about 1800.
I envisage something about which little seems to have been written (we should look at Eve Palmer’s ‘The Plains of Camdeboo’ to see if she hinted at it). This is a Serengeti-like migration of black wildebeest, springbok, eland and the extinct quagga that is now a world away because of the fencing of this area and its century-long abuse by sheep farmers. And, perhaps even more boldly, we envisage a natural vegetation of lawn grasses rather than anything one would associate with the Karoo or its mountains today. A seasonally deserted paradise for grazers, something that Bergplaas – although now a nature reserve once again devoid of domestic livestock – has yet to revert to, and probably never will without being managed with deep ecological understanding.
Let us explore our first bold invocation: that of a Serengeti-type migration.
In the Serengeti, the four main migratory ungulates (white-bearded wildebeest Connochaetes mearnsi, grant’s zebra Equus quagga boehmi, thomson’s gazelle Eudorcas thomsonii and paterson’s eland Taurotragus oryx patersonianus) gravitate towards the nutrient-richest part of the ecosystem, which happens to be its driest area, to capitalise on nutritious grass in the rainy season. The Serengeti migrations are based on the Serengeti Plain, a flat area of volcanic ash which is largely deserted by ungulates during the dry season when the wildebeest, zebra, gazelle and eland find what food they can farther afield in savannas which are more luxuriant but poorer in the quality of grazing.
Although the topography is different along the Sneeuberg escarpment – the highest-lying part of South Africa apart from the Drakensberg – the nutritional theme would be similar. Because these mountains consist of dolerite, a particularly nutrient-rich rock, and because they attract extra rain owing to their altitude, they form the centre of attraction in our conceptual reconstruction of the ungulate migrations several centuries ago. The main species participating in this migration are all close counterparts of those in the Serengeti Ecosystem and in two cases belong to the same species: black wildebeest (Connochaetes gnou), extinct quagga (Equus quagga quagga), springbok (Antidorcas marsupialis) and eland (Taurotragus oryx oryx). As in the case of the Serengeti, we visualise Bergplaas, and the similar areas of escarpment mountains near it, virtually deserted of large ungulates for most of each year in the dry season.
Now let us explore our second invocation: that the original vegetation was a lawn, green in summer when the migratory ungulates were present and brown and deserted in winter – but a far cry from the present vegetation of wiry tussock grass and asteraceous low shrubs that is accepted by today’s farmers and nature reserve managers as natural in the area.
The Serengeti migration is indeed based on a lawn, consisting mainly of Sporobolus and Kyllinga. In the case of Bergplaas and the adjacent highlands, the two main grasses suggestive of a former lawn are Tetrachne dregei and Cynodon incompletus. Both grass species have restricted ranges in and near the eastern Karoo, and have largely been replaced by less palatable grasses as well as low shrubs, which tend to burn instead of being consumed by ungulates.
(writing in progress)
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