Musangu – TOTM, January 2012

I’m going to try to start featuring a different tree each month. Hopefully this will indeed be a monthly post where I can share some information about the local trees as well as the introduced species I’m promoting here in Zambia. My aim is to make you aware of some of these trees, not to make you experts on their identification, uses or propagation. When possible I will include pictures of these trees I have taken here in Zambia.

For this first edition of Tree of the Month I will feature the mighty musangu.

A large lone musangu tree amongst a field of Maize (Photo by Rob)

Local name: musangu

English name: apple-ring acacia, winter thorn

Botanical name: Faidherbia albida

Family: Fabaceae – Mimosaceae

As a matter of principle I don’t have a favorite tree. It depends on the intended use, site and plant associations. However, here in Zambia, if I had to name a favorite it would be the musangu.

FAAL (Faidherbia albida) is a large deciduous tree reaching heights up to 30 meters with a large, wide crown. While the tree is listed as indigenous to Zambia,  large trees are not to be found up here in Central Province. However, this is a very common tree down south. Even within the town of Livingstone mature musangu can be found adjacent a large supermarket. The bark is gray-brown, cracked when mature. Young twigs are shiny gray and hold pairs of straight sharp spines about 2 cm long. Once cataloged as an Acacia, this tree looks similar to the many spiny acacias found here in Zambia and can be easily confused.

Looking up at a musangu canopy in March

FAAL has many uses, including firewood, charcoal, lumber, posts, medicine and windbreaks, but the reason I like it so much is it’s benefit to crop production. Unlike Oregon, the growing season here in Zambia coincides with the rains. The start of the rainy season is similar to the end of the Oregon rainy season (spring). The grass begins to magically turn green and grow, trees put out new leaves and gardens begin producing abundant crops without watering. Ironically, this is the time of year FAAL loses its leaves! This peculiar behavior is what makes musangu an excellent agroforestry tree. The falling leaves and seed pods fall to the ground, adding organic matter, nitrogen and other nutrients to the soil. The loss of leaves also enables nearly full sunlight to reach the plants and ground below. In terms of tree species that improve the soil and benifit crop production, Faidherbia albida is one of the best.

Musangu is so effective at adding nutrients back to the soil that crops grown under its canopy need no added fertilizer. Note, when I use the term fertilizer I am referring to synthetically manufactured chemicals, often containing nitrogen, phosphorous and potassium.  One of my surprises here in Zambia is how much fertilizer is used. Much of my work revolves around reducing the farmers dependence on fertilizer for many reasons. First, the small scale farmers do not sample the soil. The Conservation Farming Unit (CFU) has guidelines for fertilizer and lime application, but of course soils vary from region to region, site to site and field to field. Second, fertilizer is expensive. Currently it’s subsidized by the government which creates another challenge in promoting organic farming. Third, when not accompanied by lime to raise the pH of the soil it may have little to no beneficial effect. Forth, repeated use of fertilizer spoils the soil to the point that acceptable crops can not be grown without some type of input. Fifth, fields with consistent fertilizer use are more prone to erosion. Sixth, small-scale farmers often to not account for all their costs when calculating profit, and crops are often sold at a perceived profit when in reality it was a loss. Seventh, what are the farmers to do if the subsidy is taken away? Now, this might sound like a contradiction, but I’m not against the use of fertilizer if used appropriately. However, as you can see above, there are a few reason why it might not be the best or most appropriate option for the small-scale village farmer.

Musangu Research Plot in December

As an agroforestry tree it is recommended to plant musangu on a 10 by 10 meter grid. After about 5 to 7 years crops planted between the trees will begin to benefit from the added nutrients and organic matter. Once established there will be no need to add any fertilizer, though other farming techniques like crop rotation should still be practiced. The tree will provide shade during the hot season when cultivation (typically done by hand with a hoe on the small-scale farms) is taking place and the leaf fall will add nutrients and organic matter to the soil each year. Organic matter (also called decayed plant material or humus) is important in soil as it improves the structure of the soil – increasing the air space and water (and nutrient) holding capacity, reducing the susceptibility to erosion, thereby creating a easier and better medium for roots to penetrate deep into the soil to extract nutrients. For the farmers working their fields by hand, buying and applying fertilizer this seems like a dream tree to me. Why not plant this incredible helper?

Musangu Seedling planted in a Maize field

The first hurdle in planting this tree is acquiring the seeds. There aren’t local nurseries here like back home in Oregon. The forestry department has some nurseries and there are a few scattered private nurseries where seedlings can be bought, but usually they grow pine or eucalyptus and not much else. Therefore, the general planting method generally involves buying or gathering the seeds then planting at home in a nursery. This is an area where I’ve been trying to help – encouraging planting and helping to make seeds available (just see your local Forestry Extension Agent!) To aid germination the seeds should be treated, generally with scarification to break the hard seed coat, though other methods including a hot water soak can also be used. Once seeds are planted the second hurdle to overcome is this tree’s relatively slow growth. Farmers want a solution that has immediate effects. Five years is a long time to wait for work to pay off. This slow growth also can jeopardize the survival of the seedling once planted in the field. The tree can easily be trampled, cut or uprooted while working the field, weeding or harvesting, not to mention what the goats and other livestock might do. Because of this slow growth this is one time I might recommend the application of fertilizer. It may seem ironic to fertilize a fertilizing tree, but if fertilizing 100 trees on a hectare can reduce the time until the benefits of the tree are realized then an overall reduction in fertilizer can occur.

Leaves Open and Leaves Folded together

FAAL is reported to have a phenomenal rooting depth of up to 40 (forty) meters deep! I’m sure this helps enable the musangu retain it’s leaves even during long periods of drought when water near the surface is scarce. Water competition during the dry season when the crops are maturing can also be fierce, so the ability of musangu to get water deep down from other sources and not compete directly with the food crop is important for the final yield. Another interesting thing I found out about the musangu is its ability to fold its leaves together. I’ve noticed that the seedlings I planted begin to fold their leaves up just before sunset. Then, just after sunrise they begin to unfold again. Perhaps this is another technique this tree uses to reduce transpiration and conserve water.

I hope you’ve enjoyed the first edition of Tree of the Month. I hope to make time and continue this during the the rest of my service. At one tree a month I certainly won’t run out of species to choose from!

A Musangu About 5 Years Old