Sundry notes (on vegetation, termites, and rainfall) from a visit to Namaqualand, South Africa

@tonyrebelo @jeremygilmore @kevinatbrakputs @craigpeter @jrebman @pietermier @botaneek @mdevill @koosretief

On 21-22 May 2006, a colleague and I visited Kleinzee (https://en.wikipedia.org/wiki/Kleinzee) in Little Namaqualand (https://en.wikipedia.org/wiki/Namaqualand) in Northern Cape province of South Africa.

Today, I dusted off my field-notes from that visit.

Little Namaqualand falls within the succulent karoo biome (https://pza.sanbi.org/vegetation/succulent-karoo-biome).

Approaching Kleinzee from the northeast:

At the turnoff to Kleinzee from the Steinkopf-Port Nolloth road (https://en.wikipedia.org/wiki/R382_(South_Africa)), we found a vast vista of blanket-like vegetation consisting of low (0.5 m), succulent shrubs (https://www.inaturalist.org/observations/162520809), on flats, slopes, and drainage lines alike (https://upload.wikimedia.org/wikipedia/commons/a/a5/Houthoop%2C_Kleinzee%2C_Namaqualand%2C_Northern_Cape%2C_South_Africa_%2810465408374%29.jpg and https://www.flickr.com/photos/south-african-tourism/10993794574/in/photostream/ and https://www.flickr.com/photos/south-african-tourism/10993845063/in/photostream/ and similar to https://www.inaturalist.org/observations/11048822 and https://www.inaturalist.org/observations/120312638 and https://www.inaturalist.org/observations/58090550).

This landscape is completely exempt from wildfire, and the vegetation had not burned for at least half a century, for hundreds of thousands of hectares.

What struck me as noteworthy about this vegetation was that it was both shorter and denser than expected for a semi-desert.

Both heuweltjies (https://en.wikipedia.org/wiki/Heuweltjie) and the termitaria of Trinervitermes (https://en.wikipedia.org/wiki/Trinervitermes) were absent.

Houthoop Guest Farm (https://www.flickr.com/photos/south-african-tourism/10993785134/in/photostream/) got its name (English translation: wood pile) from an interesting circumstance in terms of the regional vegetation. Trees and even tall shrubs being absent as far as the eye can see, any incidence of wood much larger than gnarled twigs is exceptional in this region.

A major family in succulent karoo vegetation is Aizoaceae (https://en.wikipedia.org/wiki/Aizoaceae), the plants of which are usually small. However, the genus Stoeberia (https://www.inaturalist.org/observations?place_id=any&taxon_id=575290&view=species) - although not arborescent - is large and woody enough to be remarkably solid in the local context. Simply collecting the occasional dead plant of this genus, the landowner here eventually accumulated a pile (?several hundred kg) of wood, which became noteworthy enough to form the initial basis for a tourist-attraction.

Although I recall seeing this pile during our visit in 2006, I have found no photos of it on the Web, suggesting that it has not proven to be durable or renewable.

I know of nowhere else on Earth where the vegetation is

• perennial and technically woody (as opposed to herbaceous), and dense enough to appear to blanket the landscape, yet
• so low that dead wood is so hard to obtain that the collection of even of a few hundred kg is remarkable enough to become an anthropogenic landmark.

Herbivory/folivory in succulent karoo:

The main herbivores/folivores in this succulent karoo ecosystem northeast of Kleinzee at the time were Raphicerus campestris (https://www.inaturalist.org/observations/144416187) and, probably, Microhodotermes viator (https://www.inaturalist.org/taxa/568761-Microhodotermes-viator).

I observed the former (of which extremely dense populations have been reported near the coast hereabouts), but not the latter.

Two other indigenous species with similar diets, viz. Antidorcas marsupialis (https://www.inaturalist.org/observations/135399878) and Struthio camelus (https://www.inaturalist.org/observations/10816345 and https://www.inaturalist.org/observations?taxon_id=154483), were relatively scarce over much of the area owing to management by pastoralists.

(Driving south from Kleinzee subsequently, over a distance of about 50 km, I observed both A. marsupialis and S. camelus, but not R. campestris. This suggests competitive release, in which the bambi (body mass 10 kg) compensates for the scarcity of the gazelle (body mass 30 kg) and/or the large bird (body mass 80 kg).)

I encountered vigorous seasonal growth of Mesembryanthemum crystallinum (https://www.inaturalist.org/observations/163481201 and https://www.inaturalist.org/taxa/49319-Mesembryanthemum-crystallinum) on an old track.

I tried it as food, and found it remarkably palatable, raw. It was extremely succulent and tender, with a content of probably >95% water in the leaves and shoots. It lacked the taste I associate with oxalates in e.g. Tetragonia and domestic spinaches, and was only slightly salty and only slightly sour. I describe it, in my field notebook, as 'basically salad-flavoured green water, but very close indeed to a table-standard palatable wild plant'.

Farming of domestic sheep (Ovis aries):

The domestic sheep prefers grass as its staple diet, and cannot thrive in succulent karoo - in which the small shrubs virtually exclude grass - year-round.

Therefore, the pastoral practice in this region is for the livestock to be moved to Bushmanland (https://www.researchgate.net/figure/Northwestern-part-of-Northern-Cape-showing-the-area-that-we-consider-to-fall-within_fig1_336835392 and https://en.wikipedia.org/wiki/Bushmanland,_Northern_Cape), with its relatively grassy semi-desert vegetation (https://www.inaturalist.org/observations/150480278), for the summer, and then returned to Little Namaqualand for the winter.

It is noteworthy that the herbivorous termite in Bushmanland is not M. viator but instead Hodotermes mossambicus (https://www.inaturalist.org/taxa/558312-Hodotermes-mossambicus), which eats grass rather than shrubs.

Thus, the livestock spend winter in the habitat of M. viator, sharing a mainly dicotyledonous diet with one harvesting termite (https://www.inaturalist.org/observations/132288477 and https://www.inaturalist.org/observations/138127670), and spend summer in the habitat of H. mossambicus, sharing a mainly monocotyledonous diet with another harvesting termite (https://www.inaturalist.org/observations/150534825 and https://www.inaturalist.org/observations/139114838).

In Kleinzee:

At the time of our visit, Kleinzee was a mining town run by De Beers (https://en.wikipedia.org/wiki/De_Beers) - which subsequently abandoned the enterprise hereabouts.

Our official guide, Paul Kruger, told me that, at the stable on his property, M. viator had a noteworthy pattern of behaviour. This termite suddenly emerged from holes in the ground, just before rain, fervently cutting and burying the hay provided for Equus caballus.

I found it puzzling that M. viator was so eager to harvest grass, given that

• this species has a staple diet of small shrubs, and
• grasses are so uncommon in succulent karoo as to be hardly noticeable, even in good seasons.

Unusually wet season:

The normally dry Buffels River, which runs through Kleinzee, was in spate during our visit.

I was told that this river had flowed strongly three times in 2005, most recently in October; the current event brought that total to four times in one year.

Indeed, I was told that

• it had been drizzling about every 10 days in Kleinzee, since April 2006, and
• only a few days before we arrived, there had been a truly exceptional rain event in Little Namaqualand, with 130 mm recorded at Springbok (https://en.wikipedia.org/wiki/Springbok,_South_Africa), and 12 mm recorded at Kleinzee.

For comparison:
Mean annual precipitation is 16.7 cm at Springbok (part of the watershed for the Buffels River), and only 1.8 cm (plus frequent fog) at Kleinzee (https://tcktcktck.org/south-africa/northern-cape/kleinsee#:~:text=The%20district's%20yearly%20temperature%20is,%25%20of%20the%20time)%20annually.).

The situation at the time of our visit was exceptional, because drainage lines generally flow strongly only about once every 7-10 years in Little Namaqualand.

Based on a rule-of-thumb that depth of penetration is about tenfold the precipitation, 130 mm of rain can be expected to percolate >1 m deep in the substrate, but 12 mm cannot be expected to percolate much deeper than 10 cm.

The dominant small, succulent shrubs in succulent karoo have shallow roots, adapted to precipitation so light that the subsoil remains dry for years on end. It is by virtue of the fact that the precipitation, although minimal, occurs fairly frequently (on average, 36.5 days per year excluding the advection fog from the shore that occurs mainly in autumn and early winter), that perennial plants occur here, with enough density to seem to carpet an arid landscape.

Publicado el mayo 29, 2023 02:04 MAÑANA por milewski