Do Tree-Climbing Goats Help Plant New Trees?

May 31, 2017

Do trees grow from seeds that goats eat and later expel?

That is a question that has long bedeviled ecologists.

Let's say it's a small seed. The goat will swallow it, poop it out and a tree could sprout.

But what if it's a sizable seed? It probably wouldn't make it through the goat's digestive tract intact. And so ... no tree.

Unless ... the goat spit out the seed instead of pooping it out.

A new study probes the question of excretion vs. expectorate. The answer has important consequences for the birth of baby trees — in particular, the gnarled argan tree of Morocco.

We were interested in this study for two reasons. First, our blog is, after all, called Goats and Soda. (Here's why.) And second, argan trees are an important part of the economy in this lower-middle income country. They bear fruit. And the seeds of the fruit are valuable — they can be pressed to yield argan oil, valued in beauty treatments and foodie circles. By some reports, argan oil exports bring in $6.5 million.

It's not easy to harvest seeds from atop a 30-foot-tall tree. In the arid parts of Morocco where argan trees grow, goats are encouraged to climb, dine and deliver the seeds to earth, where they are collected by humans and eventually turned into argan oil.

But argan trees don't always thrive because of overharvesting and climate change. It would sure be helpful if the goats did a little planting of their own.

The study is titled "Tree-climbing goats disperse seeds during rumination" and was just published in Frontiers in Ecology and the Environment.

We talked to one of the co-authors, biologist and ecologist Jose Fedriani, to learn more.

Okay, before I even get to the seeds, let's discuss the fact that goats climb trees!

Yes, they are climbers. You see them climbing rocks, they are able to climb on top of chairs, so they are good climbers.

But ... trees? How?

They go very slowly and they do it. Some goat keepers modify the trees to make them easier to climb, they cut some branches off the trees so the goats can start climbing the trees more easily.

Do the goats ever fall?

No, no, no, they don't fall. They are so good, they don't fall.

[Editor's note: Let's take a minute now to look at this video, which reveals that goats are indeed very, very good tree climbers, although some sources say they do take the occasional tumble.]

Your interest was not climbing but the dispersal of seeds. As I understand it, the conventional wisdom was that in Morocco goats climb argan trees, eat the fruit and then poop out the seeds. Your theory was that the goats spit out the seeds. Um, why should we care?

A small seed can go through the goat's stomach and intestine and get out without damage and grow into a tree. But large seeds cannot do the same thing. The large seed has to be split into small pieces or destroyed completely.

Let's get a sense of size. How big is the argan seed? The size of, say, a lemon?

Not like a lemon, much smaller, it would be like an acorn from an oak. It's the shape and size of the acorn.

In the study you fed lots of fruit with large seeds to goats. What happened?

They disperse the seeds by spitting them out during rumination.

I see from your study that sometimes they spit out the seeds within hours but sometimes take up to 6 days. In either case, the seeds are not damaged and can grow into new trees, correct? So are goats agricultural heroes?

The answer depends on the context. If we have a huge number of goats, they eat all the new baby trees, they kill them, so even though the goats are dispersing the seeds, they are eating the baby trees. So the effect is negative. But if there is a small or moderate number of goats, they will not kill all the baby trees produced by the dispersed seeds.

What happens in the areas where argan trees are grown in Morocco?

These people who take care of the argan trees get money from selling the argan fruit, so they buy more goats. So there is no rejuvenation of the argan forest because the goats are eating all the baby trees.

Sigh. So your study does not necessarily reflect well on goats.

This may not be the story you want.

What is the moral of the story?

We need to have a balance between the number of goats and number of trees and try to keep the equilibrium. That is the important point to me.

Are more studies needed?

More local studies should be done on trees and plants to find out the net effect of goats.

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