Slash, Burn, and Plant the Staple

Explanation: After several days' travel in 4-wheel-drive vehicles on rutted dirt roads, switching to a pirogue across vast Lac Tumba and up a side channel, and trekking six miles through the central African jungle, we have arrived at the isolated Bantu village of Botuali in western Democratic Republic of the Congo. Here, we will experience local hospitality and will help evaluate their community timber and agricultural resources, to assist in community-level natural resource planning.

Lesson one: food. What is there to eat when the river runs low, the swamps recede, and fish are difficult to find?

Throughout the tropical world, the one staple that continues to feed millions is a modest plant that serves many functions and that goes by many names: manioc, cassava, yucca, and many other local names. The plant is native to Paraguay and Brazil in South America, but was introduced by Europeans to Africa in the 16th century.

The root is prepared by grilling, frying, mashing, baking, broiling, and steaming. It is dried and pounded into flour and made into cassava bread or turned into tapioca. Although mostly starch, here in central tropical Africa manioc is a vital source of food.

Manioc is cultivated in slash-and-burn agricultural plots throughout the Congo Basin. Crop fields must be rotated on short-duration cycles because the tropical soils are so thin and quickly become depleted of nutrients. In fact, that is the point of the dual photographs in this week's main presentation, above; the left photo shows a healthy manioc planted in a field slash-and-burned just a year ago, and the right photo shows a degraded manioc struggling to survive in a farm plot just 5 years old when the depleted soils have begun to laterize and harden.

So let's take a trek around some manioc fields in the Congo Basin:

Hiking through the Congo Basin jungles, we commonly skirted
many farm plots of manioc.

Farm plots must be rotated over time so as to replenish soil nutrients.

Here is step one in the slash-and-burn process, also called shifting cultivation.
Trees and other woody plants are initially felled, usually with a hand axe, a
tedious and exhausting process.

The surrounding forest is often retained as a source of
seed for when the farm plot is eventually abandoned
and left to return to forest growth.

Step two in the process is to burn the fallen woody material on site.
The fire releases nutrients held in the woody debris and feeds the
soil, but only for a few years.

In some plots, a few older trees are left standing, sometimes because they are too large to fell.
But they can serve an important ecological function of providing roost sites for some wildlife. For example, I observed Congo Serpent Eagles (Dryotriorchis spectabilis) flying tree to tree at dusk, eventually selecting one as a night roost.



This young man has used a machete to fell, gather, and burn
small woody plants in this newly-cleared section.


Once cleared, small hummocks are made in the soil so as to
help drain the incessant rain and prevent the plant's roots from rotting
in standing water. Then small "starts" are planted.


And here is why the farm plots must be rotated: soil in the tropics
is typically incredibly thin and "wears out" quickly.
The technical term is that tropical soils have a "tight nutrient cycle,"
meaning that most of the nutrients are bound up in the
vegetation and not available in the thin duff or humus layers.

And most of the vegetation in the tropics occurs in the above-ground,
growing plants, which continually shed their leaves.
It is a tough life to provide a continual food source
in these lush but harsh lands.

EPOW - Ecology Picture of the Week