Trees as a group are more ancient than grasses. When the first plants evolved, around 450 million years ago, from aquatic algae, they resembled the mosses we see in damp places today. A little while later, ferns evolved, and became more widespread because they had something mosses did not – indoor plumbing to carry water from the soil up to the leaves. This allowed ferns to grow very large and woody, something you may have noticed in the art in children’s books about dinosaurs, or in the Jurassic Park movies where tree ferns abound. But ferns and mosses are somewhat limited to wet environments because both have flagellated sperm, rather than airborne pollen. The next group of plants to evolve were the gymnosperms which have male and female cones instead of flowers. Familiar gymnosperms are larches and pines. Lastly, and most recently, the flower-bearing plants, beloved of pollinators, evolved. These plants have male and female parts borne either together on the same flower (perfect flowers) or separately on male and female plants, and they use wind or pollinators to move pollen from male to female parts. Angiosperms were enormously successful and diversified into tree forms, shrub forms, and grass forms. Therefore, trees are more ancient than grasses, with trees horsetails and gymnosperms being more ancient by hundreds of millions of years than grasses. But trees have another superpower: size. They dominate the environment. This summer, I had a chance to see some of the greatest boles – another name for tree trunks –  that have ever lived: the redwoods, sequoias, Sitka spruces, and Douglas firs, all gymnosperms, and all on the west coast.

The forests on the eastern shores were also once breathtaking. The claim was that a squirrel could travel from treetop to treetop from the Atlantic coast to Mississippi without ever touching the ground. Those forests were dominated by chestnuts, but also boasted hemlock, hickories, walnuts, cherries, and beeches. Alas, chestnut trees fell victim to fungal blight in the early twentieth century, hemlocks to the wooly adelgid, and all of them were decimated by human population growth. From an estimated 60 million acres of forest before settlers came, today only 0.67% – 400,000 ancient forest acres – survives. Today, the tallest tree in the Eastern US forests is an angiosperm: a tulip tree in the Great Smoky Mountains at 192-feet tall. It is possible there were taller trees in the east once, but unregulated logging depleted unknown numbers of trees. Further, many of the tallest and straightest trees in the northeast were cut down for ships’ masts by the great seafaring nations of Britain and France during the battle for maritime supremacy with associated colonization benefits. Ancient forests which have been unlogged are patchy on the East Coast. Tree ring studies have shown that some trees are over a thousand years old. What saved them was either their remoteness, or their beautiful natural settings which drew fee-paying tourists.

Figure: Ancient forests in the United States.

Figure from the Public domain from Wikipedia (https://en.wikipedia.org/wiki/Forests_of_the_United_States)

But on the west coast of the US, cutting a patchy swath from the north of San Francisco to the tip of the Olympic peninsula are the coastal redwoods which are some of the grandest trees ever known in the grandest forests ever seen. They are down from 200 million acres once to a mere 0.5% of that acreage today. Jarid Boosters (https://youtu.be/Ik7q4TOX58U) collected photographic records of trees felled for lumber, and it makes for heartbreaking viewing. But thanks to the protections offered the establishment of national parks, a small percentage were saved from logging. In these forest stand trees of astonishing dimensions, so big and tall that my mind had trouble comprehending what my eyes were seeing. Trees whose tops were so distant they were invisible from the ground. Trees whose boles were so massive that their curvature, like the curvature of the Earth, was imperceptible from close to the tree. The width of tree trunks alongside roads dimensions matched my rented sedan car’s length. I drove my car through a hole carved into the trunk of a living tree and took a picture of a massive statue of Paul Bunyan and his blue ox, Babe, among the many roadside attractions in the area. One of the trees in the Humboldt National forest is reputed to be the largest living thing on the planet. But the grove it stood in, aptly called Atlas grove, is peppered with trees of similarly statuesque dimensions, so among those neighbors it was superficially unremarkable. In the Humboldt National forest also stands Hyperion, at 379.1 feet, the tallest tree in the world, stands taller than Westminster’s Big Ben in London. Its location is kept secret to stop tourists from stamping around and damaging its root structure.

Further up the coast, in the Olympic peninsula, is one of the largest temperate rainforests in the world. It stretches from Washington state, along the coast of British Columbia (Canada) into the Tongass National Forest in Alaska. (Note that national parks are protected from logging, but national forests are not.) The trees here are also staggeringly large, but are of a variety of species: Sitka spruces, Douglas firs, red and yellow cedars, and Western, silver firs, and mountain hemlocks. The Olympic national park is home to the world’s largest Douglas firs, Western red cedar, and Sitka spruce. But all the trees are majestic, and paths through the forest are carpeted with moss, and the trees are festooned footlong lichen, giving the forest a magical but brooding quality. Walking along the path, one falls silent in empathy. It’s an odd, disquieting feeling of being among lifeforms so ancient that one feels as inconsequential an ant among elephants.

Trees this large only grow along the west coast, and the reason is the mild temperature which allows water to remain liquid year-round. The cool temperatures and humidity along the coast reduce transpiration loss from leaves and allow enough water to reach the highest parts of the trees. They do not grow in hot or cold climates. Hot temperatures would cause the trees to transpire more, with a corresponding increase water demand. The inability to draw up water to make good transpiration loss would cause cavitation or the formation of air pockets in the tree’s water tubes. On the other hand, subzero temperatures would cause water to freeze in the tubes leading to cavitation and also cell damage. This is one of the reasons such large trees do not grow on the east coast – the climate is not temperate.

But the climate all over the world is changing. The west coast is becoming hotter and drier, and is now prone to both fires and landslides. Maybe they will see this out – maybe they won’t. Only time will tell.