A forest is a complex ecosystem, where a variety of plants, animals, microbes, and soil interact to create a dynamic environment. At the heart of this ecosystem are trees, which play a crucial role in sustaining life on Earth, including human life.

Understanding trees, their history, and their functions can provide us with valuable insights into the natural world and the importance of conserving these vital organisms.

The earliest large trees known to science were branch ferns, which appeared during the late Middle Devonian period, around 390 million years ago. These ancient trees were remarkable for their time, capable of growing to heights of four to five meters. Such heights were impressive in the context of prehistoric plant life, which was just beginning to explore the vertical dimension.

The growth of trees, including their height and thickness, is primarily determined by their genetic makeup. However, environmental factors also play a significant role in shaping how tall and thick a tree can grow. One of the limiting factors is Earth's gravity, which prevents trees from growing infinitely tall. Additionally, the concentration of carbon dioxide in the atmosphere is a crucial factor for photosynthesis, the process by which trees convert light energy into chemical energy. Without sufficient carbon dioxide, a tree’s growth can be stunted.

Interestingly, the growth potential of trees is also influenced by the structure of the thin tubes, or capillaries, found in their trunks and leaves. These capillaries are essential for water absorption, and their diameter directly impacts how high water can travel within the tree. The finer the tubes, the higher the water can reach, and consequently, the more growth potential the tree has.

Leaves play a vital role in the life of a tree, primarily due to the presence of chlorophyll, the green pigment that enables photosynthesis. Chlorophyll captures light energy, which, in conjunction with other substances in the leaves, is converted into chemical energy that the tree can use for growth. However, leaves contain other pigments as well, such as yellow, orange, and red. Although these pigments do not participate directly in photosynthesis, some of them assist by transferring captured light energy to chlorophyll.

During the spring and summer months, chlorophyll is so abundant that it masks the other pigments, giving leaves their characteristic green colour. However, as autumn approaches, the days grow shorter and the nights longer, prompting trees to prepare for the winter months. One of the most noticeable changes is the reduction in chlorophyll production. As chlorophyll levels decrease, the other pigments become more visible, resulting in the brilliant yellows, oranges, and reds that we associate with autumn foliage.

Trees undergo a period of dormancy as a protective measure, especially in regions with harsh winters. During dormancy, many trees shed their leaves to minimize water and nutrient loss, conserving energy until conditions become favourable for new growth in the spring. However, some trees, like pines and cypresses, retain their leaves year-round. These trees have needle-like leaves that reduce water and nutrient loss, allowing them to remain evergreen.

Among the countless tree species in the world, a few stand out for their unique characteristics. The tallest tree in the world is the Australian almond eucalyptus, which can reach heights of over 100 meters, with some specimens growing as tall as 156 meters. To put this in perspective, standing beneath one of these giants is akin to looking up at a 50-story building.

In stark contrast, the tiniest tree in the world is the dwarf willow, which grows to a height of only three to five centimetres. The difference in height between the dwarf willow and the Australian almond eucalyptus is an astonishing 15,000 times, representing one of the most extreme size variations in the plant kingdom.

Finally, the ginkgo biloba tree holds the title of the world's most precious tree. Ginkgo trees have existed for hundreds of millions of years, earning them the nickname "living fossils." Some ginkgo trees are incredibly rare, making them highly valued not only for their age and history but also for their scarcity.