Holding on for dear life
In order to grow without toppling over under its own weight or at the first gust of wind, the tree must be firmly rooted in the soil. And the structural roots don't stop at anything in order to handle this very important job. They often weave together with the roots of trees of the same species, or even different ones.
This means that two American elms standing less than two metres apart are almost sure to be grafted. By forming underground webs like these, which also trap all kinds of underground rocks, the trees build themselves an especially solid structural base. Structural roots are different in this respect from branches, which are independent. As an African proverb says: "While the branches of trees in the forest are fighting, their roots are kissing".
Studying roots is a complicated business. After all, most of the time they're buried underground. Here, the researchers had to use powerful streams of water to see how the root systems of these trembling aspens are interconnected.
