No. 35 The first maize in a Cameroon Inga alley, and A Controversial Topic
By Tiiu-Imbi Miller | Newsletter No. 35 July 2012


Gaston has just visited Mrs. Mendo Antoinette, and here are some more pictures of her plot with thriving young maize, the first to be grown in Cameroon in an Inga alley.

Young maize growing in Mrs. Mendo Antoinette’s Inga alley. Photo Gaston Bityo Delor, 2012

Cameroon farmers’ children in Mrs. Mendo’s Inga alley with maize, and the pepper she is also growing there. Photo Gaston Bityo Delor 2012.

If you read the last newsletter (available at’s-story-her-own-words-first-maize-inga-alley-cameroon-growing-well) you may recall that Mrs. Mendo was surprised by how everyone that went by asked her, what tree is this? Inga is not native to Cameroon. Introducing non-native plants and animals can cause problems. Some academics are strongly opposed to the introduction of non-native species anywhere. Have you wondered if we were right to use it in Cameroon?

We did not ourselves introduce Inga to Cameroon. We have been using seeds from the many Inga edulis trees already there.


Mature Inga tree in Yaoundé established a long time before we started alley cropping.  Photo Gaston Bityo Delor 2009.

Alien species can themselves become a problem, or they may bring pests or diseases with them. The latter should be avoidable with proper hygiene and quarantine, which we hope were observed by whoever introduced Inga to Cameroon.

It seems to be generally accepted that Inga edulis is a native of Amazonian Brazil, Bolivia, Peru, Ecuador and Colombia. It has been introduced to many countries of the tropical rainforest belt, notably Costa Rica and Honduras, where the original research on the alley cropping was done, and where it seems to be well established both on farms and in the wild, apparently without problems.

It has also been introduced to other Central American countries and many other places, at least to Tanzania, Cameroon, DR Congo and probably Nigeria and Uganda, as well as Australia. Some alien plants, (and even more animals) have indeed caused considerable problems. Japanese knotweed can damage concrete and so damage roads and buildings, and giant hogweed is not only invasive but also highly toxic. Eucalyptus plantations can suck the land dry, destroying other plants and finally itself when planted in places with insufficient water. There are no reports of any such serious damage from the many places where Inga edulis has been imported. Any vigorous plant, native or alien, can become a nuisance.  There has been some complaint about it becoming a weed tree in Queensland, Australia, though someone else wrote regarding it in Australia “Not an agricultural sleeper weed [a plant that is not yet a serious problem but could well become one]: not a threat to agriculture.”

The one potential problem that has been considered is that Inga burns well so could make a forest more susceptible to fire. But this possibility is surely more than balanced by the fact that many forest fires are started by slash and burn farming, and with the Inga this burning is no longer necessary.

The need for sustainable farming to replace slash and burn is immense and urgent, and Inga alley cropping is about the most effective, easy to understand and implement system.  One alternative would be however to seek for native trees that work like the Inga in the countries where it is not native.

The Inga has many special properties, all of which contribute to its success for alley cropping. It is a tall order to duplicate that. Here’s a list:

  • It grows well on the acid soils of the tropical rainforest and former   rainforest lands

  • It is a leguminous tree that fixes nitrogen (converts nitrogen from the air into a form usable by plants), and is not fussy as to which nitrogen fixing bacteria it takes into its roots for that purpose.

  • It grows with mycorrhizae  (special fungi that grow with its roots) that take up phosphorus allowing it to be recycled instead of being washed out from the soil. 

  • It is vigorous enough to be able to re-fertilize seriously degraded, unproductive land.

  • Withstands careful pruning year after year after year. The same plot has now been cultivated for at least 12 years.

  • Grows fast, allowing annual (sometimes even more frequent) pruning and therefore crops.

  • Has thick leaves which, when left on the ground after pruning, form a thick cover that protects both soil and roots from the sun and heavy rain, while the previous years’ leaves rot down to feed the crops.

  • It branches out to a thick canopy so as to cut off light from the weeds below. 

  • Has other benefits besides fertilizing the soil. The pulp round the seeds is edible, and the pruned branches make good quality firewood for cooking. That makes farmers more willing to take it up, and  growing their own firewood helps to further save the rainforest.

  • It can withstand periods of drought.

  • It has good resistance to pests and diseases.

  • It can grow fairly high up in the mountains.

  • It is good at preventing erosion on slopes.

  • It did well after a hurricane in Honduras.

  • It is not poisonous.



Young Inga edulis growing well at the start of a new alley system in Cameroon. Photo Tiiu Miller 2011Years of research went into proving its worth (see How long would it take to find native alternatives? And are we even guaranteed success? Many trees, including at least 13 species of Inga were tested and Inga edulis, Inga oerstediana and possibly I. vera were found to be suitable. All are closely related. Imagine that in the first batch of native trees tested one was actually suitable. It would take say 2 years to first pruning, then another year to the second pruning, another year to the third. How many times should this cycle be repeated before we can have confidence that it isviable long term? Would 3 years of crops give us confidence? That would make a total of 5 years, as the very soonest that we might have a suitable native tree. Three repeated pruning and cropping cycles actually sound like rather too little, whereas a five year wait is long when you consider the need.

Nor would a few repeated cycles in a research facility be all that is needed. What about different soil and local climate conditions? You would need to plant it on a slope and take measurements to check for erosion resistance, then wait for a good storm or hurricane to see how well it fared. Resistance to drought, diseases and pests would also become apparent only over time. Of course prior botanical knowledge about any species to be tried would help, but is not a substitute for actually trying it out as an alley cropping tree in field conditions.  Maybe someone with more botanical knowledge would like to comment, but my own guess would be that, if the researchers were lucky and hit on the right tree/trees early on, it would be 7 to 10 years before we could be confident enough to distribute it to some of the poorest people on the planet. They cannot afford to make mistakes, and if they are given false hope that could destroy their trust in future efforts to help them. But of course there is no guarantee that we would be successful that quickly, or indeed at all. Or even that funds for this research would be available, or available long enough if there were no promising results early on. 

It cannot be right to let the forests burn and children go hungry when we already have a solution, with perhaps minor problems that may not be any greater than those from propagation of native, vigorous plants. Those ash trees that keep springing up in our own garden are very hard to eradicate, and I do believe they are native to Scotland where I live.



Atanga Wilson Nebafor hopes to recover this degraded deforested land, now no longer good for farming, with Inga for reforestation and farming to benefit local people. Photo Atanga Wilson Nebafor, 2011.


       Farmer family that may benefit when the above grassy area is made     productive again. Photo Atanga Wilson Nebafor, 2011.

Nonetheless the search for native trees is definitely to be encouraged. Native or not, using the same species all the time, or at most a couple of related species, is a worry. A worry made all the greater because there is likely to be a lack of genetic diversity within the species when it is cultivated, particularly when it is cultivated from a few trees that have been brought to a different country. In time, when more research has been done, we hope to diversify our farmers’ plantations.

Alley cropping trials by Dr. Guillermo Valle with Gliricidia sepium and moluca (Acacia mangium) at CURLA, Honduras. Photo Tiiu Miller 2009.

Throughout the ages man has imported plants and animals from one region to another. For the most part surely it has been beneficial. Maybe we can be grateful that our ancestors were not so worried about it, or here in the UK we would not have potatoes or chickens, just to give a couple of obvious examples.  In fact it seems we would not have anything much.Which of our food plants are native? What about wheat, carrots, turnips, cabbages, apples? Surely these are native? Well, that depends on how far back you go. I did a little 'googling', and found they were all brought here, though someone did think there might have been a wild form of native turnip, but all the rest came originally from other parts of the world.

Perhaps, now that we know that sometimes there are serious problems, we should think twice before importing plants simply because they are pretty in our gardens. But the Inga is urgently needed to save the forests we all depend on, and to feed the hungry. If there is a small risk involved it is surely well worth taking for the definite benefits to be obtained, rather than waiting an unknown time in the hope, but with no guarantee, that better alternatives will be found.