The only vegetation on Earth naturally dominated by geophytes: a visit to Glenlyon farm, precursor to Hantam National Botanic Garden

@tonyrebelo @jeremygilmore @ludwig_muller @botaneek @adriaan_grobler @christiaan_viljoen @sedgesrock @prismatica @rupertclayton @jrebman @wdvanhem @kai_schablewski @graham_g @charles_stirton @matt_g @aguilita @lloyd_esler @ken_j_allison @frankgaude @sethmusker

Please see:
https://www.gardenvisit.com/gardens/hantam_national_botanic_garden
https://www.sanbi.org/gardens/hantam/history/
https://www.sciencedirect.com/science/article/pii/S0254629916313783
https://pdf.sciencedirectassets.com/273500/1-s2.0-S0254629987X56008/1-s2.0-S0254629916313783/main.pdf?X-Amz-Security-Token=IQoJb3JpZ2luX2VjEM3%2F%2F%2F%2F%2F%2F%2F%2F%2F%2FwEaCXVzLWVhc3QtMSJGMEQCIHpPxRSjdncMEzr49J%2BbcrAedG0wBZwDT2zQVfL%2BZSbxAiBxlkgCMi6n%2BvqNHz4mZO%2FMhqiYB%2FBY2aQEY8cuX7fORCqzBQg2EAUaDDA1OTAwMzU0Njg2NSIM0l4zgHXhKqCcLSKHKpAFuTQWQfvCIMjx56bOGg4rw5%2BLoXzS9muaC0Zl0IiKUk%2BoEbnXJcYvwCRe7BgNhvxbCj6uUIH%2FhAjReuO3qQ4YhpNtOcgLuHm5nMmUkfDoTQfiPazyNemgWCIoAE00Myn%2B3wZeFXTmSauQyqtGcn%2BOoidvOoBAu9qa35Wja6RIpzrH4i3G5djrgn4KduUEb%2BMzixjU6v7Ng6egVcFkVD5h3S9MYzTlVNl2PECxBEsnY4qSASKTSnizUdG0%2BzdjyAnrAvn0ScEdQc6BnM84QDVQjrjnJbHng3k6DistXqKeY5unMIgyx%2Br0IUVqpz%2FxphK4WmGs7nUCuzPMSl%2FnPr%2BWUwMZhI8YIJmUlzIY72Cv%2B4pvQc4u%2Fj8Q6N0sWxgtYWKVOoXxxzYtNDTGHdmLh%2B4%2FVPJE82fCOz%2Bi4cpjTyzXgznZifMFfKAIsQyND6NH6iOFjUKxF%2BnhH87Pfyqr04sGZwfiPkF5ZmTkJBrxyXdSFW3tSJ4rlE8Yn44726EPmGV1TF2dmv4Nk44s8HZBpckNguqsxox9T61XhMijalSF6EyAML2ve1g4Rqq44cjmralYB8ovw4f6zYUazot8pYuEdDAx%2BG%2F3v5iBhYYH%2BdpMdnE3Az8yMCFo%2FudLy5UjMta7a9TJnKSpUGaswLneVlG%2BlJMvS%2B21DmC%2BiASrjDzXrLOS36StMFLTayPqtYH4cvhwDDss6h2RPJEBn%2Fz3yzxE60sMAw11SfMtKnCqK%2FGZf8EO6pP9Qb1E2F7PhscoLjqmNzGTU49Gb5X4Ch9h9X1AXtIUKf%2FFrkXMMOk15eh09%2BXFMjM9kzXrJCLHcuYV7U9ZBn5AMWH6lGUBbLv86BLpoG9WPexLeE0NuIMMM2vl2mkw3MbipAY6sgGS0Juf30vWkGCmbOb4%2BSu5fOpiCiv54I%2BuLcLWwG6mEhjmDOHbEuCjlxFnl%2FoIKbCAiI6TrS%2FG4MGAQ8xmvHzzBt5HxPutjBo8hBPljf02f0OdWvIFWcwjBtnazxfjHjA1eETMLorxpOvz%2B2hkFmXXtBkutfOzj9AemVuDAJr1jDQV5m5KzW326cBEe%2BBUlLhXADwiWfUFuPDLx4T5sgpA51F2bDGd27aBWknEi3sJgQvk&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20230625T210616Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTY5PAEX4CE%2F20230625%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=8a991d3eae217c45ef8068d35f672c1c209a19c7c5503c243f74ae7af81f63af&hash=c2704bca50b9ffe894ef6c352c6e4ecbfbb729dcce599cbc190b39ac14c023d5&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=S0254629916313783&tid=spdf-709f2ab2-0cfe-4fc5-a57e-a2f63dd5c49b&sid=14f00a6527f6054b846829e289abe5d0c4aegxrqa&type=client&tsoh=d3d3LnNjaWVuY2VkaXJlY3QuY29t&ua=07175100015e5306575e&rr=7dd02c61cbec1f5c&cc=au

In early August 2001, I visited Glenlyon farm near Nieuwoudtville, before this property was converted to a central part of the newly-established Hantam National Botanic Garden (https://en.wikipedia.org/wiki/Hantam_National_Botanical_Garden). My gracious host was the late Neil MacGregor (https://journals.co.za/doi/abs/10.10520/EJC113534).

In this Post, I transcribe and discuss the notes I took at the time.

CLIMATE

The climate at Glenlyon was one of sparse rainfall in winter, and negligible rain in summer. Exceptional rain (550 mm) fell in 1996.

However, the eastern part of the property occasionally received heavy, local showers in summer, producing spectacular shows of Gorteria diffusa (https://www.inaturalist.org/taxa/119916-Gorteria-diffusa).

TWO GEOLOGICAL SUBSTRATES

The substrates at Glenlyon were

• dolerite, an igneous rock producing cracking clay ('red vertisol'), and
• Dwyka, a sedimentary rock (https://en.wikipedia.org/wiki/Dwyka_Group) producing loam, here at its western limit in South Africa (https://upload.wikimedia.org/wikipedia/commons/e/e2/Geology_of_Karoo_Supergroup.png).

Both are nutrient-rich, relative to the sandstone occurring west and south of Nieuwoudtville (e.g. at Oorlogskloof, https://www.inaturalist.org/posts/72728-ecology-of-fleshy-fruits-in-oorlogskloof-nature-reserve-southwestern-cape-south-africa#).

At Glenlyon, the boundary between the two substrates was marked by the occurrence of dwarf shrubs on Dwyka, but not on dolerite - where above-ground perennials were few, and virtually all the plants were herbaceous (mainly geophytes and annuals, with few grasses). On the dolerite ridge, I observed that the vegetation was dominated by geophytes, with scattered shrubs, but no indigenous annuals.

I was told that

• the ground was virtually bare in the dry season, on dolerite-derived soils at Glenlyon; this was because the vegetation consisted mainly of diverse geophytes (https://en.wikipedia.org/wiki/Storage_organ); and
• in summer, the height of the perennial vegetation went from zero to 0.5 m, as one crossed from dolerite to Dwyka, on the same plain.

Put differently:

• the vegetation on dolerite here seemed to be a form of Karoo, in which the characteristic dwarf shrubs had been excluded by herbaceous plants, virtually all of them deciduous (particularly geophytes), whereas
• the vegetation on Dwyka here seemed to be a form of renosterveld (https://en.wikipedia.org/wiki/Renosterveld), in which woody perennials had been largely replaced by geophytes and indigenous annuals.

Furthermore, a distinction between the two substrates was that the vegetation on dolerite tended to be dominated by monocotyledonous plants, whereas that on Dwyka tended to be dominated by daisies (Asteraceae).

ANNUALS

The most conspicuous annuals at Glenlyon seemed to be daisies (Asteraceae, https://www.inaturalist.org/observations?nelat=-31.35780888329466&nelng=19.1605890877534&place_id=any&swlat=-31.41192095775881&swlng=19.06667907167892&taxon_id=47604&view=species).

I observed a site on Dwyka where annuals covered virtually the entire surface. Neil MacGregor told me that the species-diversity was great here, in both annuals and geophytes. I have already mentioned Gorteria diffusa on Dwyka-derived soils.

I observed the following spp.:

Helichrysum indicum (https://www.inaturalist.org/taxa/533085-Helichrysum-indicum) dolerite

Nemesia leipoldtii (https://www.inaturalist.org/taxa/590477-Nemesia-leipoldtii) Dwyka

Heliophila collina (https://www.inaturalist.org/taxa/587086-Heliophila-collina) dolerite

FORBS

The leaves of the perennial Arctotis acaulis (https://www.inaturalist.org/taxa/569425-Arctotis-acaulis) were said to be excellent food for Ovis aries (https://www.inaturalist.org/observations?place_id=6986&taxon_id=121578).

A significant species was Berkheya glabrata (https://www.inaturalist.org/taxa/581082-Berkheya-glabrata and https://www.inaturalist.org/observations/59033253), which is foliar-spinescent (thistle-like) and restricted to this area.

GEOPHYTES

Even more than in the case of annuals, geophytes were bewilderingly species-rich at Glenlyon.

I observed the following spp.:

Ferraria variabilis (https://www.inaturalist.org/taxa/524577-Ferraria-variabilis)
(Ferraria ferrariola, https://www.inaturalist.org/taxa/585873-Ferraria-ferrariola, also occurs here)

Romulea luteoflora (https://www.inaturalist.org/taxa/593300-Romulea-luteoflora) Dwyka

Massonia angustifolia https://www.earth.com/plant-encyclopedia/angiosperms/asparagaceae/massonia-angustifolia/ja/

Haemanthus coccineus (https://www.inaturalist.org/taxa/410993-Haemanthus-coccineus)

Colchicum burchellii pulchrum (https://www.inaturalist.org/taxa/752640-Colchicum-burchellii)

Pauridia serrata (https://www.inaturalist.org/taxa/559920-Pauridia-serrata) Dwyka

Lapeirousia oreogena (https://www.inaturalist.org/taxa/120061-Lapeirousia-oreogena) Dwyka

Brunsvigia bosmaniae (https://www.inaturalist.org/taxa/429914-Brunsvigia-bosmaniae and https://www.inaturalist.org/observations/152388398) abundant on dolerite ridge (https://www.sanbi.org/gardens/hantam/garden-information/geology/), where Pentzia incana, Searsia undulata, Asparagus capensis, and Asparagus retrofractus also occurred

Neil MacGregor told me that any ploughing exceeding shallow tine-tilling was disastrous for geophytes in this area. Lands previously ploughed remained uncolonised by geophytes, long after being abandoned.

NITROGEN-FIXING LEGUMINOUS PLANTS

There was a surprisingly important leguminous component to the vegetation, some species of which were themselves geophytic.

Dolichos decumbens (https://www.inaturalist.org/taxa/584097-Dolichos-decumbens) common on Dwyka

Medicago polymorpha (https://www.inaturalist.org/taxa/53151-Medicago-polymorpha) indigenous, present on Dwyka. (Neil MacGregor reminded me that archaeological research on Medicago had found that this genus, instead of simply having been introduced by Europeans, has been present in the southwestern Cape since Khoekhoe pastoralists arrived, more than two thousand years ago, https://www.jstor.org/stable/124639 and https://www.jstor.org/stable/25130648.)

Lotononis maximiliani (https://www.inaturalist.org/taxa/589433-Lotononis-maximiliani) geophytic (with fist-size tuber), present on dolerite

Leobordea hirsuta (https://www.inaturalist.org/observations?taxon_id=588910) geophytic

Indigofera meyeriana (https://www.inaturalist.org/taxa/587840-Indigofera-meyeriana) dolerite

Indigofera humifusoides (https://www.inaturalist.org/taxa/1421501-Indigofera-humifusoides)

I was shown a paddock that had last been ploughed in 1991. After a decade, it was still dominated by nitrogen-fixing plants, but devoid of geophytes - although exceptionally rich in annuals.

SHRUBS

Examples of dwarf shrubs at Genlyon are as follows:
Pentzia incana (https://www.inaturalist.org/taxa/166469-Pentzia-incana)
Eriocephalus purpureus (https://www.inaturalist.org/taxa/585332-Eriocephalus-purpureus)
Eriocephalus microphyllus (https://www.inaturalist.org/taxa/585326-Eriocephalus-microphyllus)
Eriocephalus africanus (https://www.inaturalist.org/taxa/430981-Eriocephalus-africanus)

During my visit, I observed the following species:

Asparagus capensis (https://www.inaturalist.org/taxa/580633-Asparagus-capensis) particularly common on the dolerite ridge; although a monocotyledonous plant, it was shrubby and spinescent. Neil MacGregor told me that O. aries sometimes ate small amounts.

Searsia undulata (https://www.inaturalist.org/taxa/575088-Searsia-undulata) dolerite

Lycium cinereum (https://www.inaturalist.org/taxa/532043-Lycium-cinereum) dolerite ridge, with heavily-browsed appearance

Dicerothamnus rhinocerotis (https://www.inaturalist.org/taxa/1200667-Dicerothamnus-rhinocerotis) present on Dwyka

(The following shows how dense D. rhinocerotis has become, more than a decade after O. aries was removed: https://www.inaturalist.org/observations/59113309 and https://www.inaturalist.org/observations/11238979)

GRASSES

The following perennial grasses occurred at Glenlyon:

• Tenaxia stricta (https://www.inaturalist.org/taxa/595154-Tenaxia-stricta), which forms coarse, flammable tussocks, and dies if burnt; occurs in patches on Dwyka-derived soil; can burn intensely, but does not regenerate vegetatively after fire,
• Tribolium echinatum (https://www.inaturalist.org/taxa/595629-Tribolium-echinatum and http://redlist.sanbi.org/species.php?species=1206-6),
• Ehrharta calycina (https://www.inaturalist.org/taxa/76766-Ehrharta-calycina), and
• Chaetobromus involucratus dregeanus (https://www.inaturalist.org/taxa/582037-Chaetobromus-involucratus).

HERBIVORY

The regime of herbivory of livestock was that Ovis aries - in lieu of the original community of indigenous ungulates - lightly grazed the whole farm.

Neil MacGregor told me that O. aries fared extremely well on the plants growing on dolerite-derived soils, despite this calcium-rich substrate being technically somewhat deficient in phosphorus, according to agronomic trials. The ratio of calcium to phosphorus is regarded as crucial for sheep and other ruminants, and that on dolerite at Glenlyon exceeded the optimum value. Nonetheless, O. aries seemed to enjoy optimum nutrition here.

The nutrient-richness of the soils at Glenlyon was reflected by the edibility of e.g. Trachyandra falcata (https://www.inaturalist.org/taxa/528459-Trachyandra-falcata) to humans.

A noteworthy pattern of herbivory here was that O. aries ignored the green foliage of geophytes, but readily ate the same foliage when it dried and turned brown, seasonally.

The latter generalisation applied to almost all spp. of geophytes.

However, it was particularly noticeable in the case of Brunsvigia bosmaniae, a phenologicaly odd, particularly large geophyte, the leaves of which were avidly eaten by O. aries once they turn brown in spring. (A congener also occurring here is Brunsvigia striata, https://www.inaturalist.org/taxa/581443-Brunsvigia-striata.)

The generalisation seemed also to apply to folivorous insects. John Donaldson (https://stapgef.org/sites/default/files/2021-02/John%20Donaldson%20CV%20Aug%202020%203265570.pdf) had found that geometrid looper caterpillars (https://www.inaturalist.org/observations?nelat=-31.35780888329466&nelng=19.1605890877534&place_id=any&swlat=-31.41192095775881&swlng=19.06667907167892&taxon_id=49530&view=species) ate only the old, not fresh, leaves of Brunsvigia.

Neil MacGregor told me that O. aries, when coming off Medicago polymorpha (which is rich in protein), will accept small quantities of Dicerothamnus rhinocerotis.

Ovis aries fared well on dolerite, because it was able to utilise virtually all of the vegetation: 99.9% of the plant spp. (a possible exception being Moraea spp.) were palatable to the domestic sheep at one or other phenological stage.

There was an implication that the green foliage of geophytes generally tended to be toxic to ruminants. However, that of Moraea was so toxic that even small quantities tended to be lethal to O. aries.

I observed Searsia undulata, on the dolerite ridge near Camel Rock, to have been eaten ragged by insects.

Asparagus capensis was toxic to O. aries, according to local farmers. Neil MacGregor told me that its rapidly elongating shoots were eaten to a small extent by the domestic sheep.

Neil MacGregor viewed vegetation characterised by Bulbinella as an example of natural dominance by geophytes. An example of this vegetation had recently collapsed, possibly owing to well-meaning but misguided exclusion of Ovis aries.

He was sure that ungulates were essential for the maintenance of this geophytic vegetation.

(Species of Bulbinella occurring at Glenlyon were https://www.inaturalist.org/taxa/120055-Bulbinella-nutans and https://www.inaturalist.org/taxa/120095-Bulbinella-latifolia and https://www.inaturalist.org/taxa/120063-Bulbinella-eburniflora and https://www.inaturalist.org/taxa/581565-Bulbinella-elegans and https://www.inaturalist.org/taxa/528769-Bulbinella-cauda-felis.)

MYRMECOPHAGY

(Also please see https://www.inaturalist.org/journal/milewski/59182-comparisons-of-termites-and-termite-eating-animals-in-africa-and-australia-part-1#.)

This area seemed like a paradise for not only geophytes and annuals, but also myrmecophages (https://en.wikipedia.org/wiki/Myrmecophagy).

Glenlyon was, after all, the habitat of the largest myrmecophage on Earth (Orycteropus afer, https://www.inaturalist.org/taxa/47062-Orycteropus-afer), the largest specialised termite-eater on Earth (Proteles cristatus, https://www.inaturalist.org/taxa/1306005-Proteles-cristatus), and the only bird on Earth specialised to any significant degree for a diet of termites (Smutsornis africanus, https://www.inaturalist.org/taxa/144498-Smutsornis-africanus).

Other relevant species were

• Otocyon megalotis (https://www.inaturalist.org/taxa/42095-Otocyon-megalotis) and Cynictis penicillata (https://www.inaturalist.org/observations/105707551), both of which take hodotermitid termites as a major part of their diet, and
• Myrmecocichla formicivora (https://www.inaturalist.org/taxa/12873-Myrmecocichla-formicivora).

Heuweltjies and termitaria were completely absent at Glenlyon, and there was neither much evidence of ants and termites, nor the fibrous detritus usually associated with termites. However, I assume that Microhodotermes viator (https://www.inaturalist.org/taxa/568761-Microhodotermes-viator) and Messor capensis (https://www.inaturalist.org/taxa/426213-Messor-capensis and https://www.inaturalist.org/observations/143272259 and https://www.inaturalist.org/observations/141544573 and https://www.inaturalist.org/observations/143272300) were common at Glenlyon, forming an exceptional resource for consumers despite the bareness of the ground for much of the year.

Glenlyon lies just beyond the limit of the distribution of M. viator, as portrayed by observations in iNaturalist. However, it is noteworthy that Hodotermes mossambicus (https://www.inaturalist.org/taxa/558312-Hodotermes-mossambicus) - which is even more productive than M. viator - may be the main termite at Glenlyon (https://www.inaturalist.org/observations/60190530 and https://www.inaturalist.org/observations/33416738), despite its general avoidance of the winter-rainfall climate in South Africa.

Another noteworthy point is that both large termites (despite the minimal amount of plant detritus) and large earthworms (despite the semi-arid climate) occur in this ecosystem, Together, they constitute a powerful system of non-combustive recycling of nutrients.

DISCUSSION

The regime at Glenlyon, at the time of my visit, may seem paradoxical to visitors to this property today: the land was intensively farmed with a species of ungulate livestock, yet the natural geophytes and annuals thrived to the degree that Glenlyon had become an international attraction for botanical tourists, long before there was any thought of a botanic garden in the conventional sense.

It is possible that the local vegetation on dolerite was the only vegetation on Earth naturally dominated by geophytes. I refer to its 'mature' state, in the context of what I assume to have been an intense natural regime of herbivory.

The original ungulates were presumably Antidorcas marsupialis marsupialis (https://www.inaturalist.org/taxa/42283-Antidorcas-marsupialis), Alcelaphus caama (https://www.inaturalist.org/observations?taxon_id=132658), and Taurotragus oryx oryx (https://www.inaturalist.org/taxa/75192-Tragelaphus-oryx). These were partly replaced by O. aries when Khoekhoe pastoralists arrived, and then completely replaced by the same species when European settlers arrived.

I have not revisited this area for many years, and I have not kept up with the shifts in ecological management with the conversion of farm to botanic garden.

However, my impression is that the influence of ungulates may have been reduced to an unnatural level, in a well-meaning but misguided 'botanocentric' policy. To the degree that this policy has been adopted, the full expression of the flora at Glenlyon may have been eclipsed, and the true botanical 'health' of the ecosystem may have suffered.

Another way of putting this:
The paradise for geophytes and annuals that was Glenlyon, in its heyday, may have been not despite the fact that this was a 'sheep farm', but because of this fact.

I realise that it is easy to overstate an 'animocentric' rationale, because there is a difference between continual grazing by resident livestock and the transience of wild ungulates that grazed the area intermittently, according to their long-range movements. However, the implication remains worth considering: that if Hantam National Botanic Garden is fully to conserve the local flora, it needs to involve ungulates - whether wild or domestic - to a degree exceeding that usually associated with botanic gardens.

Posted on June 22, 2023 10:48 PM by milewski