Human beings have no trouble accepting that animals can communicate with each other.
But plants? That's something else entirely.
Still, as scientists study what goes on underneath the surface of the ground, they have discovered a living substance called mycelium — a mass of interwoven fungal filaments — that associates with, and exchanges substances with, the roots of trees.
Scientists describe this exchange of substances, such as water and nitrogen, as communicating.
This communication idea received a big boost in 2015 when German forester Peter Wohlleben laid out his research in a book titled, "The Hidden Life of Trees: How they feel, how they communicate. Discoveries from a secret world."
Originally, only 2,600 copies were printed, but much to his amazement, the book kept selling and, in translation, became a New York Times bestseller. Apparently readers found the idea of tree communication intriguing.
And what Wohlleben reported profoundly changed how many people think of trees and forests.
Some readers have difficulty with Wohlleben's book because in an attempt to bring to life what otherwise would be dry, scientific terms familiar only to scientists, Wohlleben personalizes trees and the reactions among them.
In trying to make concepts understandable to lay people, he uses anthropomorphisms — that is, he ascribes human characteristics to plants, writing about how a tree "feels" and its "emotional life."
This can turn people off, and that's too bad, says Rafael Medina, an Augustana College professor of biology.
"You don't have to make it fantastic; it's fantastic enough already," Medina said of the mycorrhizal communication underground.
Both Medina and colleague Jason Koontz very much defend Wohlleben's basic premise. There is a lot going on underground between trees, between plants, that humans are still learning about, they said.
So how do trees share information? In a TED Talk, Canadian scientist Suzanne Simard explains that it occurs through chemical messages, electrical impulses and the language of carbon, nitrogen, water and hormones.
And, depending on the information, other roots respond. Two-way communication.
As an example, Wohlleben says in his book that "if a root encounters toxic substances, impenetrable stones, or saturated soil, it analyzes the situation and transmits the necessary adjustments to the growing tip.
"The root tip changes direction as a result of this communication and steers the growing root around the critical areas."
Similarly, if a tree is attacked by an insect, it feels pain and will pump poison to kill the insect. But because trees are so very, very slow they cannot always keep up with infestations of new, invasive insects.
Mother trees send food to young trees. Trees in the forest are not competitors, they are cooperators.
"Trees are very social," Wohlleben says in one of the many interviews he gave about his book, interviews now available on YouTube. "They care for each other. They try to support each other."
As for emotions: "As human beings we need social structure to feel well." Trees, he maintains, need the same. "When you discover trees, it's like looking in a mirror."
"Trees count, remember, learn. I don't 'claim' this, this is actual research. Scientists use language that people can understand. Trees are social, trees have feelings. They suckle their children (new trees) with a sugar solution. They talk to each other."
Augustana's Koontz said the study of communication among plants began around the 1990s.
Now there is an entire field of study dedicated to the rhizosphere, defined as the region of soil in which the chemistry and microbiology is influenced by the growth, respiration, and nutrient exchange of plant roots.
Medina said research has shown that plants "retain some sort of information and use it for their advantage in the future." Then added, "We need to stretch our concept of memory."