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Trees are simply amazing

Everything you need to know about woody perennials

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Many trees are sacred to Thais, and I can understand why. You may not give them a second thought, or you may admire their majesty with just a passing glance, but in reality, trees are extremely complex, diverse and very special living organisms. 

David Milarch, head of the Michigan-based Champion Tree Project International, looks at redwood trees that climbers will scale to take cuttings, in San Geronimo, California. The cuttings will be used to create clones to create new ‘old growth’ redwood forests in California and around the world. JIM ROBBINS

What makes a tree a tree?

Essentially, a tree is defined as a large, single-stemmed, woody plant. The single stem is a trunk that supports the plant, which has branches sprouting from the trunk on which leaves grow, providing the plant with glucose through the process of photosynthesis.

From this process, and using nutrients dissolved in water and taken up by the roots, the glucose can be converted to a variety of carbohydrates, fats and proteins, all of which are required for the growth, repair and cellular functions of the tree.

The trunk of a tree is mainly wood (made of a complex compound called lignin), consisting of xylem cells - tubes that run from the roots to the leaves of trees, and that transport water and dissolved nutrients in them.

Outside the xylem cells are the phloem cells, which transport sugars made via photosynthesis to all cells of the tree to foster growth and respiration. This process is known as translocation.

Outside of those is bark, which is primarily dead cells that form the outer layer of the wood.

Bark is used to make dyes, spices, perfumes and drugs. A great example is the bark of the cinnamon tree here in Thailand, which has a most pleasant aroma and is used as a spice for cooking and as incense in official ceremonies.

Thailand is also famous for producing rubber, the raw material of which comes from the sap (in the phloem), also known as natural rubber or latex. This is then treated to produce rubber sheets that are distributed throughout the world. Rubber is a major export industry for Thailand.

Aside from the uses mentioned above, the most important "use" of trees is in ecosystems, as they are producers (because they produce their own food) and are the basis of many food webs. They also provide homes for a multitude of animals, and take in carbon dioxide and produce oxygen, which is consumed by animals.

Symbiotic relationships

Surprisingly, many trees form complex relationships with plants, fungi and animals. Providing animals with "homes" is symbiotic, because the faeces and other waste produced by animals form nutrients, which get into the soil and are used by the trees.

Animals are also "employed" by trees as pollinators of their flowers or as seed dispersers, meaning that trees provide fruits for animals to eat and the animals take the seeds of the fruit to a location away from the trees, thereby expanding the tree population over a wide area.

Many trees have mosses and other plants growing on them that use nutrients from the tree, adding to the complexity of habitats in forests and jungles. Many others are parasitised by mistletoe plants and strangler figs that tap into their xylem or phloem and steal their water or sugars, often resulting in the death of the trees. A dead tree's skeleton may nevertheless provide habitats for animals and plants, making trees useful even after they are dead!

Fungi may also form a symbiotic relationship with trees, growing and living off the roots of trees. They, in turn, provide nutrients for the tree and also destroy potential competitive species' roots. Fungi and bacteria can also fix nitrogen from the air, converting it into nitrates to be used by the plants to make proteins.

Interestingly, only fungi can decompose bark and put the stored nutrients back into the soil. Basically, trees form complex relationships in all of their ecosystems, and quite simply, without them we and many other animals would not survive.

Dendrochronology

In my last article, I wrote about radiometric dating and its uses in science. In it, I also mentioned the degree of inaccuracy with the technique, but trees can also be used to date the distant past, and they are much more accurate than radioactive decay.

The science of tree-ring dating is called dendrochronology, and it is accurate to an exact year. This is because trees produce "rings" every year, with newer rings being produced at the outer edge towards the circumference of the tree trunk, allowing you to tell the age of a tree by taking a core sample and counting the rings in the trunk.

Every set of rings in a tree trunk is like a fingerprint, but a fingerprint for a region. When there is plenty of water in a season, the ring produced by a tree is wide and spaced apart from the previous year's ring. In seasons of drought, rings are narrow.

Trees in particular regions all have the same patterns of rings due to all of them suffering from the same climactic conditions. But the ring patterns will be at different sections in the wood, based on the tree's age.

So, analysing timber structures from ancient buildings and cross-matching (overlapping) the rings from more recent structures or trees, mapping them all the way to modern trees whose ages are known, will give you the precise year of the wood.

This dating method is useful for dating back just over 11,000 years, but theoretically, if we had tree fossils (petrified wood) that overlapped, we could go back literally millions of years!

As it is, dendrochronology is used for calibrating radiocarbon-dating ages, for dating old buildings that contain timber, such as viking ships or Tudor houses, and also for assessing climactic changes in the past.

Super trees!

Trees are the largest living things. General Sherman, a giant sequoia in the US, is currently the most-massive thing alive today, with a volume of 1,487 cubic meters!

The tallest living thing is also, of course, a tree, with the largest alive today being a 115m-tall redwood tree in North America. Records show that there was once an Australian Mountain Ash in Victoria that stood about 150m tall!

One of the oldest trees alive today is 9,550 years old! It is a Norway Spruce living in Sweden, and it has lived through Jesus' birth and death, and was alive long before the pyramids of Giza were even conceived. What a tree!

The oldest forest exists in Queensland, Australia. It is called the Daintree Rainforest and has been in existence for about 135 million years. Way back then, Australia was joined to Africa, Antarctica and South America as a single land mass called Gondwana.

Water to the top

Seeds themselves can remain dormant until conditions are suitable for germination, with the oldest known being 2,000 years old before germinating. Giant redwood trees can pump water from their roots to supply the needs of their leaves and branches 100m and more above without using energy.

Trees, like all plants, absorb water into their roots by osmosis. The water then makes its way into a tube called the xylem which runs the length of the plant up to the leaves.

Water evaporates through pores called stomata on the leaves in a process known as transpiration. This creates a low pressure area at the leaves which forces the water in the xylem to move upwards. This continuing process and pressure difference moves water from the roots to the leaves to as high a point as a tree requires without using energy.

Trees simply are amazing!

Dave Canavan has an MSc in Behavioural Ecology and is the Head of Secondary at Garden International School. Dave is fascinated by science and loves animals, especially the dangerous kind!

You may contact Dave at davidc@gardenbangkok.com .

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