The evolution of trees

March 3, 2022
The evolution of trees
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To talk about trees, we have to talk about evolution and how plants have been transformed and diversified to result in the species we currently know. So let's start from its origin, which occurred more or less about 500 million years ago and, like all life, occurred in water.

The first plants were what we now know as green algae. These were very simple and were made up of a single cell. When they evolved, approximately 480 million years ago, they colonized the Earth and that's when the world discovered bryophytes (mosses), some of which remain today and others specialized their structures to give rise to ferns that came in a wide variety of shapes and sizes.

It was the latter, the ferns, that formed the first forests on Earth, but as time progressed and environmental conditions changed, they again diversified. A part of these, a group now extinct, gave rise to the first seeds and with this, gymnosperms appeared, which are those plants that produce seeds but lack flowers or fruits and have a vascular system, that is, a system for conducting water and nutrients inside.

The fact of having seeds opened up a world of possibilities for plants since they could survive more adverse conditions thanks to the protection of the embryo that is the seed, however, some plants evolved less than others and today we can observe some species that we could call living fossils since they preserve primitive characteristics. These include cycads (order Cycadales) and ginkgo (order Ginkgoales), which emerged together approximately 310 million years ago. They have had very few changes during their existence since they still have flagellated sperm that do not need an aqueous environment to move, since they have their pollen tube inside the female structures; so, although they do produce seeds, their way of doing so constitutes a primitive way of reproduction among plants.

These living fossils represent fascinating evolutionary and ecosystem exceptions because they tolerate poor soils, scarcity of light and water and, in the case of cycads, they have a very slow growth. Both species have resistance to harmful agents such as certain fungi, viruses and bacteria, which has made them remain while other animals and plants became extinct. As an interesting fact in the case of ginkgo, it has not been completely defined if it went extinct for a period of time or just its fossil record is not preserved, since it disappeared in the record for almost 100 million years. Despite this mystery, today there is only one species of ginkgo (Ginkgo biloba) on Earth and thanks to this it has been a source of multiple human uses, including medicinal, for thousands of years of cultivation in China.

Within gymnosperms, we also find the largest and longest-lived trees in the world, because this is where we have sequoias (Sequoiadendron giganteum), a type of conifer, which have reached more than 100 m in height, with diameters that exceed 10 m and also some of its individuals are more than 5,000 years old.

Starting with gymnosperms, evolution once again gave rise to another type of plant, angiosperms. There is a debate about their time of origin; studies carried out using molecular clocks place them approximately 140 to 190 million years ago, but the lack of a fossil record makes it difficult to date them. The characteristic of angiosperms is that they have flowers and fruits, as well as seed dispersion mechanisms. Thanks to the above, they were very successful, so much so that currently 90% of the plants belong to this group. Excluding conifers, cycads and ginkgos, all the trees we find today belong to angiosperms.

As we have seen, species have adapted, evolved or become extinct depending on the conditions in which they existed, however, around 10,000 years ago, man began with the domestication of different species. It is not clear if agriculture or forestry management occurred first, although it is believed that both were always hand in hand. There is evidence both in papyrus and in paintings that man was already gathering fruits and using wood, leaves, fibers and exudates from numerous trees and palms for his benefit.

In the Neolithic period (7,000 years ago), burning and stubble agriculture was born, which indirectly gave rise to forest management through agroforestry systems. However, unsustainable use also began and the preference to conserve only those species that have some value to humans, which has led to the extinction of some species and the proliferation of those considered useful. The magazine Nature, Ecology & Evolution In June 2019, he mentioned that plant extinction is happening 500 times faster since human intervention began in ecosystems, since they have transformed large percentages of forests, semi-deserts and jungles into cropland areas for the introduction of livestock, or for the establishment of human settlements. Some of the tree species recently extinct by human action are:

Nesiota elliptica, Santa Elena olive tree: After exploiting its habitat for more than 450 years on a tropical island in the South Atlantic, the last living specimen in the wild perished in 1994, while the only cultivated one came to an end in 2003. Unfortunately, there are no collections of any kind in international collections.

Encephalartos woodii, Forest Cyca: This cycada was declared extinct in the wild due to the extraction of its bark and wild plants. In 1916, a specimen was transferred to the Botanical Institute of Pretoria, where it died in 1964. Although genetic material is preserved, a female specimen would be needed to reproduce this undiscovered tree.

Sophora toromiro, Toromiro: Species endemic to Easter Island and extinct in the wild. The last wild specimen died in 1960 and is considered to be due to intensive exploitation by the original Polynesian inhabitants, followed by Europeans who arrived in the 18th century, who used the tree as food for domestic animals.

We can see that man began to benefit from tree species that were multipurpose, causing a modification of their distribution and even the natural way of their dispersion and, in turn, also greatly contributing to the extinction of a large number of species. This is why the need for the implementation of sustainable practices that guarantee the conservation and restoration of ecosystems, the recovery of species at risk, and the reduction of global warming becomes imperative.

Over the millions of years of tree evolution on the planet, how many species have we not been fortunate enough to know? Most likely, there were plants and trees that our imagination simply cannot conceive of. Looking to the future, how many species of trees should continue to evolve in their own way? The answer, hopefully, is all those that exist today, because again, our imagination is very limited in the face of the possibilities of evolution that can occur if we only allow it; if instead of triggering extinctions, we learn to live with our natural environment in a sustainable way.

References

Guillén, F.D. (2010, February). The process of domestication of plants. House of Time, 66-70.

Lobato-Cameselle, R. & Cidrás-Ferradás, J. 2012-2013. Plant evolution: the conquest of the mainland. Botany Course - Arquegoniadas. University of Vigo, Spain. PLANT EVOLUTION

Jorge Gabriel Sanchez-Ken & Brenda Yudith Bedolla-Garcia. (n.d.). Where do plants come from? Eco-Logical Journal of Scientific Dissemination. http://www.ecologia.edu.mx/inecol/index.php/es/17-ciencia-hoy/1087-de-donde-vienen-las-plantas

Eguiarte, Luis E. and Castillo, Amanda and Souza, Valeria (2003). Molecular and genomic evolution in angiosperms. Interscience, 28 (3), 141-147. [Date of Consultation December 10, 2021]. ISSN: 0378-1844. Available at: https://www.redalyc.org/articulo.oa?id=33907803

Carrión Garcia, J.S., & Cabezudo, B. (2003). RECENT PERSPECTIVES IN PLANT EVOLUTION. Annals of Biology, (25), 163-198. Retrieved from https://revistas.um.es/analesbio/article/view/31101

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