Update from The Mlesa Spring: Taller Trees = More Water
As previously reported here, the Irente planting site in the Usambara Mountains region of northern Tanzania spreads across 2,200 hectares. There are one million trees here, but there is need to get another two million trees planted in this area as soon as possible.
As part of this initiative, our partners planted 69,000 trees in 2021 near the Mlesa Spring water intake. The Mlesa Spring provides drinking and irrigation water to thousands of people residing downhill in the Irente Villages area. As discussed below, the agenda of these trees was to sink straight and deep roots as quickly as possible, with the goal of helping the soils retain as much water as possible during the rainy seasons. Much has happened since then and we wanted to provide an update.
First the good news: It’s working! We started with strong healthy seedlings from an amazing nursery, and combined with careful pruning and mulching over the years the results are encouraging: 95%+ survival rates!
An albizia schimperiana tree at two meters tall. Besides having straight roots that channel water deep into the soil, this species is used to treat various inflammatory diseases.
How exactly do certain trees support the water cycle? Ecologists and hydrologists have studied this question extensively, and while trees “use up” water to grow they also play a crucial role in regulating, storing, and redistributing moisture. Here’s how:
- Trees intercept rain and fog, slowing runoff and allowing much of it to infiltrate into the soil.
- This water slowly seeps down into aquifers that feed streams, springs, and wells.
- Up to 30–50% more rainwater infiltrates the ground in forests compared to bare or deforested land.
Also, via “transpiration” trees release water vapor that rises into the atmosphere, cools, and condenses — helping to form clouds and increase local rainfall. Studies in East Africa show that moisture recycled by forests accounts for 20–40% of regional rainfall. That means tree cover actually generates rain that later falls downwind.
The bottom line is that Trees don’t “steal” water — they manage it. They act as living infrastructure that captures, filters, stores, and gradually releases the water we depend on.
And speaking of management, maintenance is as non-exciting as it is important. Even for trees. In the Irente2 planting site, maintenance has meant regular pruning and mulching around the new trees. Tall fern plants had taken over after too many trees had burned or been cleared from the slopes years before. While the ferns are native and deliver many benefits in their own right, they tipped the balance of nature by crowding out our small native trees, stealing their nutrients and light.
This photo of a Markhamia lutea tree shows what happens when the ferns crowd out too much sunlight been stunting growth. This trees one is only about a third the size it should be for its age. Now that the surrounding ferns have been cut back, it’s busy drinking in sunlight trying to catch up.
Herbalists use the Markhamia lutea plant for management of anemia, liver disease, inappetence, stomachache, headache, skin rash, cataracts, throat diseases, conjunctivitis, and snakebites.
Our local partner staff has to manually clear tons of these ferns two or three times a year. The job is no small effort and the whole village is employed for about two weeks. Just to give a sense of scale, in the photo below their work shows as striped lines where the groundcover has been cut back. Fortunately, the ferns will remain as the trees get taller, they just won’t be as dense.
Young seedlings get more sunlight and grow faster as a result of major pruning efforts.
Patience is required, but… luckily we’re patient. Check back soon for more good news updates!
With your support, ForestPlanet can methodically address problems like this, one planting site at a time. There are many more potential planting sites like Mlesa Spring in Tanzania alone, and thousands more worldwide. Our goal is to help revitalize them all. At 15 cents per tree, even a $15 donation can go a long way, and we welcome your support here!
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