The oldest forest fossils push the forest's "birthday" forward millions of years!

□ Feng Weimin

Recently, the international geological journal "Geological Society" reported that on the north coast of Devon and Somerset in the UK, researchers from the University of Cambridge discovered the oldest fossil forest remains on Earth. These trees are about 390 million years old, 4 to 5 million years older than the previously thought oldest forest - the remains of ancient trees in New York State, USA.

The Devonian period, about 419 million to 359 million years ago, is the era when forests began to appear on Earth. The emergence and continuous spread of forests is a major event in the Earth's biosphere, which is extremely important for shaping the atmospheric aerobic environment, reconstructing the terrestrial ecological environment, and promoting the development of biodiversity.

The latest forest fossil discovered in the UK is a strange tree called Araceae, with an incomplete trunk and a height of about 2-4 meters. It has a dense crown on top and looks like a foundation brush. Araceae is quite similar to today's palm trees, but it is not a palm tree and has no kinship with the tree species on Earth today. The trunk of Araceae is hollow, not solid, and has no leaves. The tops of the branches are covered with hundreds of branch-like structures instead of leaves.

Before this discovery, the oldest known forest fossils in the world were forest fossils discovered in New York State, USA about 385 million years ago, and ancient forest fossils in the Svalbard Islands, Norway, 380 million years ago.

In 2019, fossils of tree trunks and roots from the Devonian period about 365 million years ago were discovered near Xinhang Town, Anhui Province, my country, covering an area of ​​at least 25 hectares, which is about the size of 47 American football fields. In 2020, fossils of plant stems dating back about 371 million years ago were discovered in a desert grassland in Tacheng Prefecture and Bukesair Mongolian Autonomous County, Xinjiang, China. This fern plant has a diameter of 70 cm and covers an area of ​​about 80 square kilometers. It mainly grows lycophytes, ancient ferns and fern plants, as well as low shrubs and small herbs.

This oldest forest fossil discovered in the UK not only pushed the time of the appearance of forests on Earth forward by millions of years, but more importantly, the oldest forest discovered so far presents a completely different forest appearance from later ones. This ancient forest is very simple in species, and the construction of the forest system is still in its early stages. There is neither any understory vegetation nor herbaceous plants. The forests that appeared later in the Devonian period have changed greatly in appearance, and the forest ecosystem has improved, presenting a relatively complete multi-level forest appearance. The ancient forests discovered in Xinjiang, my country, have a very high degree of plant richness and diversity, with both centimeter-level low herbs and tree-like towering trees, a variety of ferns that reproduce by spores, and the oldest gymnosperms that reproduce by seeds.

The emergence of Devonian forests changed the interaction between water and land, because trees and other plants can help stabilize sediments through their root systems. And as they grow, these densely grown trees shed a lot of branches and leaves, which have a significant impact on shaping the landforms through which rivers flow and stabilizing riverbanks and coastlines. The Devonian period was an era when fish came onto land, and forests undoubtedly provided a very good covering environment for the newly arrived animals and played an important role in promoting the rapid evolution of amphibians.

Since the emergence of forests, plant photosynthesis has been enhanced, and the terrestrial ecological environment has undergone tremendous changes. Studies have shown that during the Devonian period, the oxygen content in the atmosphere rose sharply, and the carbon dioxide level dropped significantly, causing the earth to cool. The mass extinction that occurred in the middle and late Devonian period was closely related to this. The emergence and spread of forests undoubtedly activated the initial switch of this scene.

The discovery of Devonian ancient forests is still rare worldwide, but they evolved very quickly and have developed from primitive forests to relatively complete forest ecosystems, laying the foundation for the great development of forests in the Carboniferous period (359-299 million years ago). The construction of forest ecology has undergone several changes from ferns, gymnosperms to angiosperms, which not only made great contributions to the terrestrial ecological environment, but also played an important and critical role in the evolution of the earth and biological evolution, and this influence is still playing an important role today.

(The author is a researcher at the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, and the honorary curator of the Nanjing Paleontological Museum)