The Cederberg

The range and its rivers

Where rooibos grows, by each source's line

The sources do not draw the same boundary. Each describes a slightly different thing: the whole species, its wild populations, or the farmed core.

SANBI's wider line covers the natural distribution of Aspalathus linearis as a species.

Why the Cederberg counts as the centre

Kraaij and Pretorius surveyed 45 wild rooibos populations. The vegetation types they grew in most often were Cederberg Sandstone Fynbos and Bokkeveld Sandstone Fynbos.

Brooks and colleagues' data suggest genetic diversity in wild rooibos falls along a line from Melkkraal in the Suid Bokkeveld to Jamaka in the Cederberg. They write that this may support the view that the Cederberg is rooibos's centre of endemism, with the Suid Bokkeveld populations spreading out from it over time.

The mountains also split the Cederberg's own populations. Heuningvlei, in a valley at 868 m (about 2,850 feet), and Jamaka, at 405 m (about 1,330 feet), lie only 18 km (about 11 miles) apart. The study measured its largest genetic difference between them. Rooibos seed is dispersed by ants, which range only a few metres, and the authors say this may limit gene flow.

Acid sand

Kraaij and Pretorius describe rooibos soil as nutrient-poor, sandy and acidic, derived from sandstone, quartzite or shales. At every one of their survey sites the ground was sand or loamy sand with gravel or rock. SANBI's growing advice says seed must be scarified and planted in acid, sandy soils.

The authors conclude that soil depth is a critical factor for rain-fed rooibos, particularly in drought. Martin Bergh, chairman of the Rooibos Council, told ProAgri that roots reach about a metre (3 feet) deep. Where soil turns clayey at 60 to 80 cm (about 2 to 2.5 feet), he said, it drains poorly and plants can die. Shallower ground gives only two harvests before it is exhausted.

In the same Vaalkrans trial, young plants given moderate fertiliser grew about a third as much above ground on deep soil as unfertilised plants. The authors say this was probably due to a high phosphorus concentration in the soil, which can inhibit cluster-root growth. The plant is a legume that fixes nitrogen with root bacteria, mostly Mesorhizobium, as told in how the red bush works its soil.

Winter rain and summer heat

Around Clanwilliam, van Schalkwyk and colleagues report, 90% of the year's rain arrives from June to August. The Rooibos Council describes summer temperatures above 40 °C (104 °F) and freezing winter nights.

The sources give different rainfall figures.

The 2016/17 season at Vaalkrans brought 98.9 mm (about 4 inches), roughly a third of that optimum. The hottest day reached 47.49 °C (about 117 °F).

ProAgri reports that seedlings raised in nurseries from February and March go into the fields from June to August. They must be in the ground by the end of August to use the rest of the winter's rain. The fields are not irrigated. A 2023 study puts production over the previous 18 years or so at 10,000 to 18,000 tons a year, all of it rain-fed.

Fire

Fynbos is a treeless, hard-leaved shrubland marked by summer heat and drought, gale-force winds, cold wet winters and recurrent fires that burn through the plant tops. The Cederberg's namesake cedar dies when burned and does not resprout.

Wild rooibos survives fire in one of two ways. Reseeders are killed and come back from soil-stored seed, which fire stimulates to germinate in early winter. Resprouters regrow from an underground lignotuber. Brooks and colleagues report that a wild population uses one strategy or the other, never both.

Cederberg populations are typically reseeders and Suid Bokkeveld populations typically resprouters, though resprouters do occur in the Cederberg. Kraaij and Pretorius distinguish four wild types, set out in the wild ecotypes of rooibos.

The median interval between fires recorded for the Cedarberg Nature Reserve is 13 years. The 45 wild populations Kraaij and Pretorius surveyed had gone about 26 years on average between fires, long by fynbos standards of 10 to 20 years. Rooibos persisted well in that old vegetation.

Wild bush and farmed field

Until the 20th century all rooibos was gathered wild. Kraaij and Pretorius, citing a 2003 study, put the wild share at 0.001% of production. Wild bushes are generally cut by hand sickle once every second year, a practice described in the wild harvest.

The cultivated area reached 95,000 hectares (about 235,000 acres) in 2016, according to van Schalkwyk and colleagues.

A wild stand holds anywhere from 25 to almost 30,000 plants a hectare, with a median of 839. By co-author G. Pretorius's observation, a farmed field is planted with 8,000 to 16,000 seedlings a hectare, and usually fewer than half survive. SANBI reports that a field is first cut after 12 to 18 months, then once a year for up to five years before replanting.

SANBI reports the species is not under threat, but its natural populations are shrinking. Land is converted to plantations, and overgrazing, invasive alien plants, climate change and uncontrolled wild harvesting also reduce them. Brooks and colleagues note that drought and soil depletion have lowered commercial yields, and that subsistence farmers rely more on wild plants when cultivated yields are low.

The name tied to the place

The climate ahead

Global climate models estimate that winter rainfall in the rooibos production region will fall below 165 mm (about 6.5 inches) a year, van Schalkwyk and colleagues report. Martin Bergh told ProAgri that under one model, MIROC, conditions on the higher-lying parts of the traditional growing area stay the same from 2041 to 2070. On the West Coast nearer the sea, and on lower ground with shallower soil, they become less favourable.