The Tree That Feeds the Fish

Explanation: This week we find ourselves in another remote corner of the Congo River Basin in central tropical Africa. We have just traveled by motorized dugout canoe across the expansive Lake Tumba, down the wide Ituta Channel to the Congo River, and then a day's trip up the Ubange River.

We are staying at the riverside village of Mobenzino, and now trekking through what the locals call "forêt inondée," or seasonally flooded tropical forest. It is now the dry season (don't go by the daily and nightly deluges, though!) so we can walk where, a few weeks from now, the Ubange River will flood.

This is a wonderfully interesting forest, and a most important part of the jungle ecology ... and it holds a key lesson for treating people, cultures, and ecosystems as one. The trees that grow in this seasonally inundated are typically heavily buttressed at the base, or grow on a tangle of tall stilts, as this week's photos show.

Shown here is the tallow tree, and it has an amazing number of uses, including fence posts, building material, and fodder for livestock. It has many medicinal uses, as well, for treatment of oral ailments, killing pain, use as an astringent, treatment of gout and swelling, and can even serve as a laxative and to treat hypertension.

The tree can grow straight with a dense trunk which might have high value as timber ... but for a major reason, the tree is best left alone, to serve its purpose in these intermittently flooded forests. Why?

It is the fruits that interest us today. The nuts are used in the food and cosmetic industry, but they can have far greater value to the local people when they ripen on the tree and drop naturally.

And this is because ... the fruits feed the fish.

When the heaviest rains come, and the river swells and breaks its banks and floods this forest, so too come the fish, including some that provide key protein sources for the people, and that actually eat the fruits fallen from the tallow tree. In this region of the Congo Basin, such fish include the catfish Clarias (including C. lazera) of Family Clariidae, which we encountered in a previous EPOW.

Cutting the trees for timber might yield a one-time source of income, but that might ruin the fruit-to-fish food chain, destabilize the soil, and eliminate the all-important seasonal fishing supply (and not to mention eliminate an important medicinal plant). Indeed, during the wet season, the local people actually fish from boats in these forests where we now hike.

Moreover, the fish likely also serve to disperse the seeds of the tallow tree by ingesting and egesting the fruits as they swim. This may be a key ecological function worthy of some study.

So, do you think that fish that eat fruit from trees is unusual? It is, but it is not unique, as, amazingly, similar ecological links have evolved in the Amazon River Basin of South America. In the Amazon, it is the pacu (giant relatives of pirhana) and silvery Amazon brycons (Brycon spp.) that consume and disperse tree fruits.

And the fruits likely feed far more than just the fish; wild pigs, primates, rodents, and many other wildlife species enjoy fruits of the forest as well, and many of those animals are also important game species for local people whose life can be immensely harsh. Like fruits of other tropical trees, fruits of the tallow tree might be the center of quite a web of life.

What's the lesson here?

It is that we really should understand the entire system -- including how local people fit in and use their resources -- before we rashly decide to eliminate one resource, such as these trees for their timber. They may play a more far-reaching role than ever imagined for the people and ecosystems alike.

We are truly all linked in ecological functional webs.

The stilt root structure probably also serves as good hiding and resting
spots for wildlife of the region -- another important and key ecological function
of this most amazing tree ... !

EPOW - Ecology Picture of the Week