The Hidden Life of Trees_ What They Feel, How They Commnicate

join the butterfly larvae in the pines. Sawflies “saw” open plant tissue so that they can lay their eggs
there. It’s not the appetites of the adults but the larvae that the trees have to worry about: up to twelve
needles a day disappear into each tiny mouth, which quickly gets dangerous for the tree.
I’ve already explained, in chapter 2, “The Language of Trees,” how trees use scent to summon
parasitic wasps and other predators to rid themselves of pests. However, there is yet another strategy
they can employ, as demonstrated by the bird cherry. Their leaves contain nectar glands, which
secrete the same sweet juice as the flowers. In this case, the nectar is for ants, which spend most of
the summer in the trees. And just like people, from time to time these insects crave something heartier
than a sugary snack. They get this in the form of caterpillars, and thus they rid the bird cherry of its
uninvited guests. But it doesn’t always turn out the way the tree intended. The caterpillars get eaten,
but apparently, sometimes the amount of sweet nectar the tree provides doesn’t satisfy the ants and
they begin to farm aphids. As I’ve explained, these creatures tap into the leaves and when the ants
stroke the aphids with their antennae, they exude droplets of sugary liquid for them.
The feared bark beetle basically goes for broke, seeking out weakened trees and trying to move in.
Bark beetles live by the principle “all or nothing.” Either a single beetle mounts a successful attack
and then sends out a scented invitation for hundreds of its kin to come on over and they kill the tree.
Or the tree kills the first beetle that bores into it and the buffet is canceled for everyone. The coveted
prize is the cambium, the actively growing layer between the bark and the wood. This is where the
trunk grows as wood cells form on the inside and bark cells form on the outside. The cambium is
succulent and stuffed full of sugar and minerals. In case of emergency, people can also eat it. You can
try this out for yourself in the spring. If you come across a spruce recently downed by the wind, cut
off the bark with a pocketknife. Then run the blade flat along the exposed trunk and peel off long
strips about a third of an inch wide. Cambium tastes like slightly resinous carrots, and it’s very
nutritious. Bark beetles also find it nutritious—that’s why they drill tunnels into the bark so that they
can lay their eggs close to this energy source. Well protected from enemies, the larvae can eat here
until they are nice and fat.
Healthy spruce defend themselves with terpenes and phenols, which can kill the beetles. If that
doesn’t work, they dribble out sticky resin to trap them. But researchers in Sweden have discovered
that the beetles have been arming themselves. Yet again, the weapons are fungi. These fungi are found
on the beetles’ bodies. As the beetles make their tunnels, the fungi come along for the ride and end up
under the bark. Here, they disarm the spruce’s chemical defenses by breaking them down into
harmless substances. Because the fungi grow faster than the beetles drill, once they make it under the
bark, they are always one step ahead. This means all the terrain the bark beetles encounter has been
decontaminated and they can feed safely.46 Now there is nothing to stop a population explosion, and
the thousands of larvae that hatch eventually weaken even healthy trees. Not many spruce can survive
such massive attacks.
Large herbivores show less finesse. They need to eat many pounds of food daily, but deep in the
forest, food is hard to find. Because there’s hardly any light, there isn’t much greenery on the forest
floor, and the juicy leaves high up in the crown are out of reach. So, in the natural course of things,
there aren’t many deer in this ecosystem. They get their chance when an old tree falls over. After the
fall, light reaches the forest floor for a few years, and not only young trees grow but also, for a short
period of time at least, wild flowers and grasses. Animals rush to this oasis of green, which means
that any new growth is heavily browsed.
Light means sugar, which makes the young trees attractive to browsers. In the dim light beneath the
mother trees, their tiny meager buds usually get hardly any food. What little food they need to survive