Erosion control, Grevillea and the hills around Aksum, northern Ethiopia — videoblog

Hillside erosion following deforestation for firewood and overgrazing -  Aksum, Ethiopia

Hillside erosion fol­low­ing defor­est­a­tion for fire­wood and over­graz­ing — Aksum, Ethiopia

Erosion is one of the most envir­on­ment­ally destruct­ive pro­cesses, lead­ing to loss of biod­iversity in plants and anim­als, as top­soil with all its nutri­ents washes and blows away, end­ing with stony ground that can­not sus­tain plants or store water. When water is not stored, plants need con­tinu­ous rain, mak­ing them drought-prone, and rain­fall runs off fast, caus­ing flood­ing down­stream, col­lapse of hill­sides, and silt­ing up of dams (although sea­sonal inund­a­tions with top­soil and its nutri­ents have been part of tra­di­tional crop­ping in many areas).

I some­times ask classes to think about the ques­tion of ‘how far is the human race from extinc­tion?’; answers come back in terms of the months of food we have stored now, the ran­dom time until the next huge vol­cano erupts or aster­oid hits us, the years until there is not enough food with cur­rent unsus­tain­able pro­duc­tion meth­ods, or a few dec­ades before wars over water or hun­ger lead to our extinc­tion. My answer to the ques­tion: we are about 15 cm or 6 inches from extinc­tion, the depth of the top­soil that sus­tains most plant and micro­bial life.

Erosion has been with us from the start of agri­cul­ture: tra­di­tional slash-and-burn agri­cul­ture was able to grow crops for only a few years before plots lost top­soil and nutri­ents, so they were aban­doned without pro­duc­tion for sev­eral dec­ades before restart­ing the cycle. Landscape-wide erosion caused huge areas of lime­stone to be exposed in the Burren area of Ireland, now inter­est­ingly con­served as a very spe­cial eco­sys­tem but with min­imal bio­lo­gical pro­ductiv­ity com­pared to the tem­per­ate rain forests that pre­ceded the lime­stone pave­ments. In the US, the dust­bowls of the 1930s, with many plowed (ploughed) and fal­low fields dis­pla­cing deep-rooting per­en­nial grasses.
(Please view in HighDefinition/HD; for non-embedded video­play­ers, http://​tiny​url​.com/​a​k​s​u​m​e​r​o​s​ion)

In the video, we start with the hill­sides behind the city of Aksum (Axum) in Tigrai, north­ern Ethiopia, about 45km / 30 miles south of the Eritrean bor­der. Eucalyptus is grow­ing at the top of the hill­side, but between the set­tle­ment and the top, it is obvi­ous that in recent years, all the sticks and wood have been col­lec­ted to burn in open fires, while smal­ler plants have been eaten by groups of goats driven by a goat-herd. While the top of the hill, still with Eucalyptus, only has a few vis­ible rocks and stones, much of the sandy soil the lower part of the hill­side has washed and blown away leav­ing boulders exposed. Among the few plants doing well, as seen in the walk up to the base of the hill­side, is the cent­ral American invas­ive poppy spe­cies, Argemone mex­ic­ana. This is one of the few plants that is ‘goat proof’ with both vicious spines and toxic seeds (resem­bling closely Brassica seeds): it has no value.

I didn’t see any sig­nage about the erosion con­trol pro­ject, but it was clear that goats and fire­wood col­lec­tion had been con­trolled within the area being planted. Rudimentary ter­ra­cing had been con­struc­ted, import­ant to slow the run­off of sur­face water, as farm­ers have known for 8000 years. In pits, some Eucalyptus has been planted, but mostly another Australian spe­cies is being intro­duced, Grevillea robusta. This is phys­ic­ally the largest spe­cies in the plant fam­ily Proteaceae, grow­ing upto 35m tall, and does well in dry forests with more than 1000mm rain per year, and it seems to be increas­ingly used for erosion con­trol by plant­ing along con­tours or in gul­leys. As well as the men involved in plant­ing, irrig­a­tion is crit­ical and a chain of women is seen car­ry­ing 25 litre yel­low con­tain­ers of water about 1km from the water tanks, involving a steep climb of 100m or more up the slopes start­ing at 2100 m in the high­lands. In flat­ter areas, don­keys are car­ry­ing four of the con­tain­ers. Presumably, the employ­ment from this

Grevillea robusta plantings for erosion control on terraces above Axum

Grevillea robusta plant­ings for erosion con­trol on ter­races above Axum

back-breaking work is more valu­able than an expens­ive pump­ing and pip­ing sys­tem. The con­tain­ers them­selves are reused 25 l drums from palm oil, not­ably impor­ted from Indonesia, rather than across from the tra­di­tional pro­du­cing areas of West Africa.

Women carrying 25litre drums of irrigation water up an eroded hillside

Women car­ry­ing 25 litre drums of irrig­a­tion water up an eroded hillside

From 400BC, Axum was a power­ful centre and the cap­ital of the Aksumite king­dom until the 10th cen­tury. Among the reas­ons quoted for the fall of the empire was envir­on­mental degrad­a­tion and over-farming, along with cli­mate change. Hopefully the erosion con­trol and refor­est­a­tion seen in this video will enable the cur­rent Axum to increase its prosper­ity in the next few years.

Part of www​.AoBBlog​.com
This mater­ial is used in University of Leicester course BS2072 — Biodiversity and Sustainability.

Related video: Grain and Chilli Mills in Axum

Editor Pat Heslop-Harrison. ORCID 0000-0002-3105-2167

Pat Heslop-Harrison is Professor of Molecular Cytogenetics and Cell Biology at the University of Leicester. He is also Chief Editor of Annals of Botany.

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