Notes on a visit to Gamkaberg Nature Reserve, Western Cape province, South Africa, in 2001

@tonyrebelo @ludwig_muller @henrydelange @christiaan_viljoen @sandraf @botaneek @mr_fab @matthewinabinett @charles_stirton

On 1 August 2001, I visited Gamkaberg Nature Reserve (https://en.wikipedia.org/wiki/Gamkaberg_Nature_Reserve and https://www.capenature.co.za/reserves/gamkaberg-nature-reserve), in the company of a former warden of this reserve, Kenneth Coetzee (https://www.conservationmanagementservices.co.za/profile.php).

This reserve occupies 10,000 hectares, mainly on a sandstone plateau surrounded by the shale of the Little Karoo (https://en.wikipedia.org/wiki/Karoo).

The history of the environment concerned is of frequent, mild fires and grazing by the European bost (Bos taurus), followed by removal of the livestock but prolonged understocking with wild ungulates.

All of the vegetation on the plateau had been subject to an exceptionally intense fire 3-4 years before my visit, viz. presumably in the summer of 1997-1998.

The stands of fynbos burnt on this occasion had been 8-40 years old. In the case of the grazing lawns (with Themeda triandra) scattered through the fynbos, the intense fire produced a flush of Hermannia. Apparently, these lawn-like patches had been studied before the fire by Richard Dean and Suzanne Milton, who reputedly found them to be utilised intensively by Equus zebra (https://www.inaturalist.org/observations?taxon_id=43330) and Lepus saxatilis, but not utilised by Sylvicapra grimmia grimmia or Hystrix africaeaustralis.

The source of drinking water in this reserve is natural springs.

The same sandstone substrate supports fynbos on the plateau and spekboomveld (https://www.dailymaverick.co.za/article/2021-02-23-the-spekboom-miracle-plant-or-just-another-succulent/ and https://www.researchgate.net/figure/Spekboomveld-dominated-by-Portulacaria-afra-Didiereaceae-in-the-Ecca-Pass-north-of_fig1_268443219) on the slopes, where the climate is semi-arid. This is remarkable, because the textures of the photosynthetic organs are extremely different in restioids (sclerophyllous, i.e. dry and lignified) and Portulacaria (succulent). However, Portulacaria afra also occurred, within the boundary of the reserve, on lower slopes of shale, where Themeda triandra was abundant among the shrubs after rain.

On the plateau, I observed large populations of Aspalathus pedunculata. These alternated with small patches of low plants, particularly

• Themeda triandra (https://www.inaturalist.org/taxa/208571-Themeda-triandra), kept low by grazing,
• a species of Hermannia (possibly Hermannia odorata, https://www.inaturalist.org/observations/67294697 or https://www.inaturalist.org/observations/99449328) that seemed to be untouched by herbivores, and
• a 'mesemb' species of Aizoaceae.

Dicerothamnus rhinocerotis (https://www.inaturalist.org/taxa/1200667-Dicerothamnus-rhinocerotis) was absent from the plateau. Furthermore, the flora of the lawn-like patches differed from both that typical of renosterveld (https://en.wikipedia.org/wiki/Renosterveld), and that typical of restioid fynbos.

Ken Coetzee had encountered the kills of Panthera pardus (https://www.inaturalist.org/taxa/41963-Panthera-pardus) regularly in Gamkaberg Nature Reserve.

FAUNA OF LARGE HERBIVORES, fide Kenneth Coetzee, as at 2001

Equus zebra:
fully indigenous; population failed to increase for years, only increasing now that much of the reserve had been burnt, producing a grassy successional stage; the founder population seemed to be demographically limited by uniform age, because there had been die-offs of even-aged cohorts or family groups; three individuals died in the fire of 1999; despite these losses, the population increased from 18 to 28 after this fire, within 4 years; the postfire flush had proved to be crucial for the reproductive rate of E. zebra; in an adjacent reserve, this species descended in winter - probably the normal pattern for E. zebra - to the now-farmed lowlands

Diceros bicornis
not mentioned

Loxodonta africana:
not mentioned

Hippopotamus amphibius:
fully indigenous to rivers in the nearby Little Karoo, which were formerly fringed by reedbeds; however, its occurrence on the plateaunseems out of the question

Phacochoerus aethiopicus aethiopicus:
unknown, but probably did not occur in fynbos

Potamochoerus larvatus koiropotamus:
I did not ask: presumably has never occurred

Bos taurus:
had previously been farmed on the plateau for years, at least on a seasonal basis, by means of frequent burning of the fynbos

Syncerus caffer:
unknown whether this species was present historically; not introduced

Strepsiceros strepsiceros strepsiceros:
only recently arrived in the reserve, and of its own volition, jumping the fence to enter; extremely common in the surrounding karoo (drainage lines and spekboomveld)

Taurotragus oryx oryx:
the population remained about 6 for years, failing to increase owing to the incorrect demography of the founders, and a failure to burn the fynbos; in fynbos ecosystems, this species seems to depend on dicotyledonous plants, apparently not eating grasses

Antidorcas marsupialis marsupialis:
presumably only in karoo vegetation

Ovis aries:
was not present on the plateau during the period of farming, prior to the declaration of the nature reserve

Capra hircus:
was not present on the plateau during the period of farming, prior to the declaration of the nature reserve

Alcelaphus caama:
as at 2001, only recently introduced, but in fair numbers as a nucleus; the delay in reintroduction had been owing to benign neglect, not any doubt as to its suitability; the species is particularly mobile for a grazer, and does not make or maintain lawns

Damaliscus pygargus pygargus:
not indigenous to this area, and not introduced

Redunca fulvorufula fulvorufula:
I did not ask

Raphicerus campestris campestris:
shows a clear pattern habitat-wise, occurring in the reserve only in karoo vegetation, and being absent from the plateau; in this it parallels the aardvark

Raphicerus melanotis:
common in fynbos, where it coexists with Sylvicapra grimmia grimmia; I did not ask whether it occurs in vegetation dominated by the succulent shrub, Portulacaria afra (https://upload.wikimedia.org/wikipedia/commons/a/ac/Gamkaberg_Nature_Reserve%2C_South_Africa_%281020302%29.jpg)

Oreotagus oreotragus:
common wherever there are rocky slopes, and often spotted at the access road where this zigzags up the steep slope

Sylvicapra grimmia grimmia:
common throughout the reserve, including the fynbos on the plateau

Pelea capreolus:
present in fynbos

Struthio camelus australis:
absent

TERMITES and MYRMECOPHAGES

I observed that termitaria of Trinervitermes trinervoides were common on the plateau.

Equus zebra had been observed biting large chunks from the termitaria, ostensibly a case of geophagy similar to https://www.researchgate.net/publication/47296223_Soil-eattng_by_Cape_Mountain_Zebras_Equus_Zebra_Zebra_in_the_Mountain_Zebra_National_Park and https://www.academia.edu/25359445/Soil_eattng_by_Cape_Mountain_Zebras_i_Equus_Zebra_Zebra_i_in_the_Mountain_Zebra_National_Park. This was recorded also in the Kammanassie Mountains (https://en.wikipedia.org/wiki/Kammanassie_Mountains), according to Ken Coetzee. In Gamkaberg Nature Reserve, Alcelaphus caama was also recorded eating material from the termitaria.

Proteles cristatus (https://www.inaturalist.org/taxa/1306005-Proteles-cristatus) was common on the plateau, whereas Orycteropus afer (https://www.inaturalist.org/taxa/47062-Orycteropus-afer) occurred only on the karoo flats to the north and south, outside Gamkaberg Nature Reserve.

PLANTS EATEN BY HERBIVORES in Gamkaberg Nature Reserve

Anthospermum (possibly Anthospermum spathulatum, https://www.inaturalist.org/observations/99402446):
this genus is palatable to herbivores; I myself observed individuals obviously shaped by browsing

Aspalathus hystrix (https://www.inaturalist.org/taxa/580493-Aspalathus-hystrix):
I myself observed the effects of browsing on the shrubs, 1.5 m high

Aspalathus pedunculata:
apparently untouched by herbivores (as are most other spp. of this genus)

Carpobrotus mellei (https://www.inaturalist.org/observations/11170047 and https://www.inaturalist.org/observations/10886034):
associated with the faecal middens of Oreotragus oreotragus (https://www.inaturalist.org/observations/11146672 and https://www.inaturalist.org/observations/137864220 and https://www.inaturalist.org/observations/10826466), where it starts as a circular patch and grows into a ring with a wide dead centre

Cliffortia:
apparently virtually exempt from herbivory

Dodonaea viscosa (https://www.inaturalist.org/taxa/122711-Dodonaea-viscosa):
avidly eaten in Gamkaberg Nature Reserve by Taurotragus oryx and Strepsiceros strepsiceros, the latter sometimes eating the shrubs down to stumps

Ficinia:
all spp. in this genus are likely to be heavily grazed in fynbos and related vegetation

Hermannia:
this genus spans fynbos and karoo, in various spp.; the spp. of karoo vegetation are, according to Ken Coetzee, palatable to herbivores, whereas those of fynbos - which are associated with regeneration after fire - are less so

Lobostemon:
eaten by ungulates; spp. known to be common in Gamkaberg Nature Reserve include https://www.inaturalist.org/taxa/589356-Lobostemon-marlothii and https://www.inaturalist.org/taxa/524438-Lobostemon-fruticosus and https://www.inaturalist.org/taxa/589350-Lobostemon-decorus

Lycium (https://www.inaturalist.org/observations?place_id=48634&taxon_id=58333&view=species):
heavily browsed and inconspicuous on the lawn-like patches

'Merxmuellera':
eaten to some degree by Equus zebra; this probably refers to Tenaxia stricta (https://www.inaturalist.org/observations/24789147)

Metalasia:
I myself observed the results of heavy browsing; species known to be common in Gamkaberg Nature Reserve include https://www.inaturalist.org/taxa/589932-Metalasia-massonii and https://www.inaturalist.org/taxa/589938-Metalasia-pallida and https://www.inaturalist.org/taxa/589904-Metalasia-acuta

Mistletoes (genera and spp. unspecified):
eagerly sought by Taurotragus oryx and Strepsiceros strepsiceros; Ken had observed males of the latter breaking down the plants with its horns

Osteospermum incanum:
particularly palatable

Osteospermum moniliferum:
particularly palatable

Pelargonium:
eaten by Equus zebra; species unspecified, but those known to be common here include https://www.inaturalist.org/taxa/554305-Pelargonium-tricolor and https://www.inaturalist.org/taxa/574121-Pelargonium-exstipulatum and https://www.inaturalist.org/taxa/591596-Pelargonium-glutinosum and https://www.inaturalist.org/taxa/591673-Pelargonium-ribifolium

Phylica:
not exempt from herbivory

Proteaceae:
apparently exempt from herbivory

Restionaceae:
routinely eaten by Equus zebra (as elsewhere in the Fynbos biome); this equid clips the restioid swards at about 20 cm high, and grazes 30 cm-high tussocks of Restionaceae wholesale; this family of graminoids is uncommon on the lawn-like patches

Roepera (https://www.inaturalist.org/taxa/593247-Roepera-fulva and https://www.inaturalist.org/taxa/560274-Roepera-flexuosa):
palatable to herbivores

Searsia:
generally palatable to herbivores, in the order Searsia longispina (https://www.inaturalist.org/taxa/593892-Searsia-longispina) > Searsia glauca (https://www.inaturalist.org/taxa/564119-Searsia-glauca) = Searsia undulata (https://www.inaturalist.org/taxa/575088-Searsia-undulata) > Searsia lucida (https://www.inaturalist.org/taxa/593894-Searsia-lucida)

Thesium (https://www.inaturalist.org/observations?place_id=48634&taxon_id=146804&view=species):
tall and short spp. alike were heavily browsed in Gamkaberg Nature Reserve

THE ODDITY OF ASPALATHUS PEDUNCULATA

A conspicuous shrub in Gamkaberg Nature Reserve was Aspalathus pedunculata (https://www.inaturalist.org/observations/11030758 and https://www.inaturalist.org/observations/143372653 and https://www.inaturalist.org/observations/11204532).

The shrubs were up to 1.5 m high, over a lower stratum typical of fynbos, consisting of ericoids (https://en.wikipedia.org/wiki/Ericoid#:~:text=Applied%20to%20a%20plant%2C%20ericoid,cover%20the%20usually%20slender%20branchlets.) and graminoids (https://en.wikipedia.org/wiki/Graminoid). Aspalathus pedunculata is said to regenerate germinatively, and to be promoted by fire; I assume that it is a rhizobial nitrogen-fixer.

It is unusual for fynbos to have an indigenous leguminous plant as its upper stratum; this role is typically taken by Proteaceae, which have cluster roots and do not fix nitrogen. Various spp. of Aspalathus are common as small shrubs (about 0.5 m high) in the first few years after fire in fynbos, but these typically yield successionally - at least on well-drained ground - to taller, non-leguminous shrubs that do not fix nitrogen.

Observations in iNaturalist suggest that today, decades later, A. pedunculata remains prominent on the plateau.

Therefore, what I find puzzling is that

• the leguminous nitrogen-fixing plant, in this case, has persisted into what look like mature stands, and
• it seemed untouched by herbivores at the time of my visit, despite the nutritional benefits of ash and nitrogen-fixation.

Publicado el junio 13, 2023 11:32 TARDE por milewski