Tony Rinaudo (working with World Vision Australia) responded to the article about Faidherbia albida in EDN 107 with helpful comments. “In West Africa, crops growing under a canopy of the nitrogen fixing F. albida trees produce an extra 2.5 to 3 tons of stalks per hectare and two and a half times the grain (equating to an extra 1,200 to 1,500 tons of grain) with three times the protein content, compared to crops growing in the open. Twenty-five trees per hectare provide a full fodder ration for one to one-and-a-half sheep per year. This is three times the optimal stocking rate for the Sahel. The high protein seed pods are called sheep biscuits in Ghana. The trees also host cattle egret and many other predators of insects, helping to protect crops against pests. An adult egret for example eats 30 to 50 locusts per day.
“I think the role of trees like this will increase as the impact of climate change increases. Many crops in tropical / sub tropical areas are already growing at their threshold temperature range. Any increase in temperatures will translate to reduced yield (e.g. for each 1ºC increase in temperature, rice yields will decline 10%). For many countries, average temperatures are predicted to increase 4 to 5ºC, and this is only the mean—spikes in temperatures will also occur. The future for agriculture as we know it looks bleak. What will the impact of a 40% decline in food production mean for a country already unable to feed its population?
“However, an email conversation I had with Roland Bunch leads me to think there are practical strategies which we can implement to reduce the impacts.”
[Roland’s e-mail indicated that after a decade or so of research in Honduras, the FAO concluded that light shade will actually increase crop yields in the lowland tropics by about 50 to 70%. All the crops they studied tended to stop growing in the lowland tropics’ mid-day heat. FAO calculated that 15% shade would lower the temperature approximately 10ºC.
The ideal would be to maintain about 15% shade, which is tricky but not impossible. Roland wrote, “[FAO] experiments showed that, with shade, farmers got about 50% higher yields in the good years than did their neighbors. But even more important for smallholder farmers, in the bad years, when their neighbors harvested virtually nothing, those with the shade got about the same yields as their neighbors did in good years. Their risk [of crop failure] was tremendously reduced. This happened both when there was not enough rain (when we had El Nino) and when there was too much (Hurricane Mitch).”]
Tony Rinaudo continued, “Trees like F. albida could be critical for agricultural production in the future. Even so, I have not promoted it outside of Africa as I am concerned about its potential for weediness. In Africa, a weevil destroys much of the seed and so there are some limits to its rapid spread. It is always good to find what the local best match is for a particular purpose.
“I would also like to add that it is important to not focus on single species no matter how outstanding they are. Faidherbia does not produce good firewood and its timber is not durable, being very susceptible to borers. Therefore it is important to promote other species as well, especially appropriate indigenous species.
“I once visited an 18-year-old F. albida project in Niger. The trees were planted on farmland at 10 x 10 meter spacing and they had a very good impact on crop yields. However, for a number of years the trees had failed to produce seed pods. I do not know the cause, but suspect that insects that destroyed the flowers had increased in numbers, or perhaps an insect eating bird normally present in a more balanced environment may have been missing due to lack of suitable habitat.”