Most city inhabitants know of solitary trees growing in their neighborhoods. Trees is yards, on playgrounds, or in flowerpots places on the sidewalk. I know of many such lonely trees. Separated from other trees by street pavement, skyscrapers, and playgrounds. In many places in Manhattan, trees grow on top of large residential buildings, as a decoration I presume. Many times I have witnessed trees plated in pots way too small for their extensive root system, only to die few years leaving behind wooded carcasses. It saddens me, because tress are so much more than meets the eye. When I see solitary tree in a planter, I feel like we have robbed it from it’s own society. This isn’t anthropomorphism, trees in fact form extensive ecological communities.
Many trees have complicated ecological relationship. One of the most famous symbiotic relationships is with mycorrhiza, a symbiotic relationship between roots and fungi to exchange sugars made by the trees for water and minerals. Mycorrhiza is thought to also aid in tree-to-tree communication. Yet, we don’t get to see those interactions.
Protection of offspring isn’t only an animal trait. Many species of trees protect their young, communicate with neighbors when being attacked by insects or when infected. Mother trees can send nutrients and water to their offspring as well. Trees send warning signals through their root system as well, and the extent of such communication is still poorly defined. Many of such signals we are only beginning to understand. Many of such interactions are described by Peter Wohlleben in his book “The Hidden Life of Trees.”
Over millions of years of evolution, trees made an important trade off, they adapted to stay in place. This seems like a huge risk, but trees evolved to take in the Sun’s photons, water and atmospheric carbon dioxide to make their own food and oxygen we breathe through a process called photosynthesis. With a few exceptions of carnivorous plants, mainly trapping insects or protozoans, or requiring bacteria for nutrients, most plants are quite self-sufficient. Photosynthesis is a remarkable adaptation. Plants learned how to split water over 3 billions of years ago, all at low temperatures.
While the tree trunk may stay out in place, it’s progeny travels the world. Significantly, trees generate millions of seeds that are spread by wind and other animals. Seeds are special, as they all have special features required for their survival, making them some of the toughest embryos inhabiting the planet. Those features can include, thorns to attach to passing animals, heather-like fluff to be easily carried by the wind, or protective coating when ingested by animals and spread away from the mother tree. A more poetic description of such movements can be found in a book by Stefano Mancuso, “The Incredible Journal of Plants,” a true inspiration for this blog entry.
However, the tree trunks may be relatively static, it’s leaves and branches do no such thing. Trees move their leaves for sunlight exposure, and they grow new branches towards the Sun. Their movements are slow and subtle, but always have a purpose. When trees grow back their leaves, look up and you will see trees’ space tiling in action. It’s remarkable that every leaf matters and can be oriented with such precision. And that’s the part we see, imagine what the roots are doing.
Tree roots are an ecosystem in itself. We don’t have a full understanding of its mysteries. As many trees live in very harsh environments, they figured out some tricks. One interesting example are halophytes, plants that can tolerate high salt concentrations. Halophyte trees are rare, fewer than 2% of trees have those abilities. Although true mainly for other plants than trees, halophytes are often used to clear the earth from salt, to make it more hospitable for other plants. This is called phytoremediation, and is extensively uses is many agricultural settings.
Trees are also long-lived. Under the right circumstances, many trees can live hundreds of years. One astounding example are trees in Japan, which survived the destruction of the atomic bombs. Hibakujumoku, also called survivor trees. Hibakujumoku represent a gamete of species, and a nature’s perseverance to survive. What made this possible is that trees as we see them are not only made out of a trunk, leaves and branches. Trees have extensive root systems, allowing them to regenerate from many insults.