-John Muir-
Forest bathing
Personally I really like the sight of a gorgeous pristine raised bog, but there is nothing more relaxing than a walk in the woods, especially in times as stressful and uncertain as the actual pandemic. The need for a connection to nature to feel grounded is very common and its benefits have been known for a very long time. In fact, more than 2’500 years ago Cyrus the Great, founder of the first Persian empire, already knew it. He had a lush public garden built in the middle of the capital city, to help people to stay healthy and calm, in the mid of city life chaos1. Much more recently, in particular in Japan in the 1980s, there has been a scientific interest in explaining how being out in nature restores the mood, eases stress and brings a general feeling of peace2.
Since then, nature therapy, or ecotherapy, has been encouraged to help manage mental health, and in particular the practice of shinrin-yoku, which translates as forest bathing. Forest bathing consists in finding a spot in the woods and let the senses go. Explore the senses and let them guide you. The sight of a ray of sunshine through the bare trunks in winter, the smell of the soil and leaves in fall, all the noises of the animals, the leaves and the wind. Beautiful.
When did forest appear on Earth?
Forests have been around for hundreds of millions of years. Traces of what is believed to be the oldest forest have been discovered in 2009 in an old quarry in Cairo, New York, USA. In there, palaeontologists found 385 million years old fossils of a plant genus called Archaeopteris3. Before this extraordinary discovery, the forest believed to be the oldest on Earth was in Gilboa, NY, a few km away from the Cario site. The difference between Archaeopteris, which is not present in the site of Gilboa, and the plant fossils that are found there, is that Archaeopteris present a more evolved structure.
Archaeopteris had wooden large roots, a trunk, webbed leaves and a vascular system. Strong deep roots allowed Archaeopteris to colonise land further from watersheds and still be able to get water from the soil, the trunk allowed it to grow bigger and taller, the vascular system allowed for circulation between leaves and roots of gasses (oxygen and carbon dioxide), water and nutrients.
What are trees made of?
Compared to other ecosystems, forests contain an impressive amount of biomass. Biomass is the amount of living matter in an ecosystem, the volume of bodies of all creatures. While animals make their own bodies from what they take from the food they eat, plants build themselves from the carbon of the carbon dioxide they take from the atmosphere, through the process of photosynthesis. The growth of forests in the mid-Devonian era, approximately 393 to 383 million years ago, was so important that the amount of carbon dioxide in the atmosphere dropped drastically (relative to geological times) in consequence. The drop in Carbon dioxide in the atmosphere is believed to have strongly contributed to a significant increase in the concentration of oxygen in the atmosphere4.
Global changes
The global expansion of forests completely changed the aspect and conditions of the planet. Before forests started covering land, the more archaic forms of plants had root-like structures that gave them some stability, but were too weak to infiltrate in the rock. Bigger and wooden roots meant that plants started to modify the geology of the land, allowing water infiltration and movement of nutrients.
The weathering of some of these nutrients eventually modified the chemical composition of the ocean5. In addition, the deposition of leaves from deciduous plants increased the amount of organic material at the surface. The mix of organic and rock material contributed to the formation of thick soils. The dense root system stabilised soil, decreasing erosion and influencing the flow of water. The cover by trees fronds decreased the temperature of the soil. Together with the decreased greenhouse effect following the decrease of carbon dioxide in the atmosphere, they caused the atmospheric temperature to drop to the point of starting a small ice-age.
Everything is related
It was a period of big instability with atmospheric carbon dioxide and oxygen concentrations, temperature, soil structure and ocean levels changing drastically which caused what is known as the second massive extinction during which three quarters of all species to go extinct. at the time most species were aquatic from shallow and warm waters. But the development of forests and changes in the ecosystems also created the conditions for life on land to develop. The first vertebrate evolved in the form of arthropods, the most common fossil found are some sort of giant scorpions. Land plants were not impacted by the great extinction and went on evolving into the beautiful trees and more that we see in our forests today.
What happened to the Devonian era forests? In geological terms, after the Devonian period comes the Carboniferous (from 358.9 to 298.9 Mya). The term carboniferous come from Latin and it means coal-bearing. Indeed some of those early forest accumulated organic matter in swamps and peat bogs, eventually fossilising into what is called coal. The formation of the first forests decreased the atmospheric carbon dioxide causing massive extinction but also the expansion of life on land, and now the extraction and combustion of the coal originating from those same forests is dramatically increasing atmospheric carbon dioxide causing the beginning of what some believe is going to be the sixth massive extinction. Ironic.
Plant a tree. Protect the forests. We need them to relax, and so much more.
1 Hansen, Margaret M.; Jones, Reo; and Kirsten, Tocchini. 2017. Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review. International Journal of Environmental Research and Public Health 14, no. 8: 851.
2 Song, Chorong; Ikei, HHarumi and Yoshifumi Miyazaki (2016). Physiological Effects of Nature Therapy: A Review of the Research in Japan. International Journal of Environmental Research and Public Health 13, 781. DOI 10.3390/ijerph13080781.
3 Stein, William E.; Berry, Christopher M.; Morris, Jennifer L.; VanAller Hernick, Linda; Mannolini, Frank; Ver Straeten, Charles; Landing, Ed; Marshall, John E.A.; Wellman, Charles H.; Beerling, David J.; and Jonathan R. Leake (2020). Mid-Devonian Archaeopteris Roots Signal Revolutionary Change in Earliest Fossil Forests. Current Biology 30( 3), ISSN 0960-9822, DOI 10.1016/j.cub.2019.11.067.
4 Lenton, T. M., Dahl, T. W., Daines, S. J., Mills, B. J., Ozaki, K., Saltzman, M. R., & Porada, P. (2016). Earliest land plants created modern levels of atmospheric oxygen. Proceedings of the National Academy of Sciences of the United States of America, 113(35), 9704–9709. DOI 10.1073/pnas.1604787113.
5 Qie, W.; Algeo, T.J.; Luo, G. and A. Herrmann (2019). Global events of the Late Paleozoic (Early Devonian to Middle Permian): A review. Palaeogeography Palaeoclimatology Palaeoecology 531 (Part A), DOI 10.1016/j.palaeo.2019.109259.