Damien Enright: Miracle tree tagasaste can turn desert into arable land

This is common knowledge; however inconvenient, emblematic of the Canary Islands, they must not be cut. My friends have found two on the land, wild sown, of course, one tiny and one only 50cm high. They certainly will not cut them.

It was a 4m tagasaste that the cut-it-down enthusiast had pointed to. It was a tree my pals knew nothing about, nor did I. It seemed the man had something against it, but why we didn’t know. Perhaps long ago, tagasastes, 4m tall, evergreen trees indigenous to the dry, rocky slopes of this and the other Canary Islands, were so prolific that they had to be cleared to make arable land by the first colonist-farmers — Normans, strangely enough, in the 15th century, led by a Norman noble and adventurer, Jean de Béthencourt. However, even when they were cut, they kept coming back.

Cytisus proliferus is the binomial name, and prolific it certainly is, and it makes prolific every plant that grows around it. In fact, it is likely that, in its native environment, such plants wouldn’t grow at all but for the nitrogen enrichment of the soil by the tagasaste.

It is known as tree lucerne in Africa, where it is the life saver for possibly millions of dirt-poor farming families in Ethiopia, Rwanda, Burundi, Tanzania, Kenya, Uganda, and Nigeria. In Australia, it has made deserts arable and, as in New Zealand, has made cattle and sheepfarming viable where it is grown.

Tree lucerne delivers 587kg of nitrogen per hectare per year, 50% below ground by nitrogen fixation, and 50% above when branches are regularly trimmed or grazed by goats, sheep or cattle and thus kept in a permanent juvenile state. Forty kg of nitrogen per hectare per year yields a tonne of maize, 400kg yields eight tonnes.

Not alone does the tree bring fertility to the soil, however poor it may be, its presence provides fertile land for other plants and also, for peasant farmers, shelter, firewood, and cash-crop charcoal.

The tap roots of my friend’s tagasaste tree may well penetrate 10m into the soil beneath it. In summer, these roots, in a process known as hydraulic lift, will carry moisture from deep in the earth to the shallow surface soil, thereby enabling the tree to continue to extract nutrients from that soil which would, otherwise, be too dry.

The feeder roots in the surface 1.5m of land spread to more than 15m from the trunk on all sides, harvesting mineral nutrients all year, and water in a dry winter.

In Western Australia deserts, the tagasaste has increased fertility tenfold, and doubled the number of sheep that can be fed on a hectare.

As forage for ruminants, the leaves are palatable and protein rich. Grazed, or cut and fed fresh or dried, the weight gain in cattle is 1.3kg a day.

In east Africa, tagasaste is one of the fastest growing trees and small-scale subsistence farmers plant it in groups or rows on their land.

Its fodder supports their grazing animals which, on a typical one hectare would include 1 to 3 goats for milk and meat, half a dozen chickens, for their eggs, a couple of calves and up to two dairy cows. For these and the farmers family, the trees provide windbreaks, shade, and shelter. Cut branches are used for green manure or can be burned for charcoal to make a cash crop.

The potential of tagasaste was first identified by a Dr Perez, a medical practitioner on La Gomera’s neighbouring island La Palma, in the 1870s. Dr Perez sent seeds to Kew Gardens where, its potential apparent, its seeds were ‘dispersed’ to British colonies around the world.

What a blessing did the Canaries give to the poor of the earth and the poor lands of the earth! Meanwhile, on my friends’ terraces of volcanic earth, they find grape vines, sorrels, tabaibas and cactuses carrying cochineal beetles. All may be in debt to the humble tagasaste, green journeyman traveller of renown.