Why Do Trees Grow Straight Up?

Why Do Trees Grow Straight Up?

D E Bradley

Trees are impressive living beings with their wide canopies of color-changing leaves, thick tall trunks, and the potential to house many species – including humans. A common feature shared by different species is their ability to grow straight vertical trunks. Why do trees grow straight up and how is it possible?

Why Do Trees Grow Straight Up?

The answer is more complicated than you might imagine. The simple version is that trees grow towards the sun and the more competition there is for sunlight, the taller and straighter they will grow. However, even lone trees without competition will grow straight up due to microscopic systems that rely on biology and physics. There are exceptions to the rule, depending on the conditions, but most trees will have straight upright trunks of some kind.

Trees Rely On Sunlight For Photosynthesis Like All Plants.

Trees may be massive living things vastly different from grass and bedding plants, but they are still plants that need to obtain sunlight to generate energy. The further they are from the ground and all the competing plants down there, the better the chance of making the most of the sun’s rays throughout the day. So, it makes sense for these trees to grow straight up towards the light and not stop until they are at a suitable height.

Some Trees Grow Taller And Straighter Than Others.

This need to reach the sunlight and enjoy the best possible conditions for photosynthesis will determine the growth, shape, and overall height of a tree. In some areas, trees will remain relatively short and stocky with branches shooting out in all directions from fairly low to the ground. This happens when there isn’t much in the way of competition and there is room to spread out. These trees in gardens and parks can create a wider canopy to sustain life and produce plenty of seeds and fruit.

It is a different story in the forest where the density of plants in the area is much greater, leading to greater competition for sunlight and resources. Here, it pays for trees to stretch as high as possible to out-compete rivals. This is why there is often a rich canopy of greenery and fruit high above the forest floor and then meters of bare trunk below. A great example of this is the tallest redwood in Sequoia National Park, California, which is 84 meters tall.

All Trees Use Biology And Physics To Grow Straight Up.

There is an extraordinary combination of physics and biology at play here to create these vertical trunks wherever trees take root. Even if a squirrel buries a nut on a steep slope and it germinates into a viable tree, it will readjust and grow vertically in line with the plane of the earth rather than the angle of the slope.

It does this thanks to a process called gravitropism and a series of cells called statoliths. The statoliths with the roots and shoots detect gravity and use this to determine the direction of growth. They will always settle to the bottom of the structure due to this gravitropism, meaning that roots always go straight down and shoots and trunks straight up.

Some Trees Become Bent Due To Other Conditions During Their Growth.

While it is within the biology of the tree to grow straight up, wherever it is, it doesn’t always achieve this. There are plenty of trees manipulated by man that form a different shape. Some are pruned and trained with supports to increase their width to form denser hedgerows or more practical shapes for fruit-picking.

Then there are the trees that are so continuously battered by high winds in exposed areas that they develop a natural lean as they grow. The trunk wants to go straight up but the winds push it to the side. This creates some impressive features on a harsh landscape, like the 45-degree angles of rowan trees in the Scottish uplands.

The Desire To Grow Straight Is Hard To Tame.

Even though humans do manipulate the shape of trees, it takes a lot of work. The cellular structure and strong gravitropism in trees provide that instinct to head vertically towards the sun. The stronger the need and greater the competition, the taller it will grow.