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FOREST'S SECRETS

Learn how trees communicate with each other. What they use to do that and how effective this communication is?

We have only to wait and see if someday we will find what else is stopping trees from growing in height forever.

How tall can trees get?

There are forests here on Earth which are homes to some incredibly big and spectacular trees. Some reach a hight of more than 100 meters like the mighty sequoias growing in the mountain of Sierra Nevada but even they seem to have their limits.

Some of the tallest trees on our planet have been here for thousands of years but even if they spend the whole eternity growing in perfect conditions they seem that will never grow any further than that.

But what exactly is stopping trees from growing and what is the ultimate limit they can reach?

It turns out that trees cannot grow forever because of a juicy substance called sap. This substance functions like the blood in humans transporting important compounds for the tree to continue growing.

There are two types of sap and they circulate in the tree non-stop to keep the tree alive. They carry sugars and water which are produced during photosynthesis or absorbed by the root system. The two types of sap are carried as follows from where the nutrients are produced to the roots and then to where they are needed to support the growth of the tree.

The first type of sap is phloem - this sap is contained mostly from sugars and transports them from the leaves where they are produced to the roots. 

The second type is Xylem (‘Zailləm) sap which starts its journey in the roots of the tree. It contains a lot of minerals, and ions like Calcium (Ca) and Potassium (K) which the tree has absorbed from the roots.

Because of the concentration of nutrients in the one tissue the water is absorbed by the Xylem to compensate for the difference.

This process is called osmotic movement. This movement creates rich in nutrients Xylem sap which then begins its journey from the base of the tree and finally reaches even the highest parts of it transporting vital for life elements and sugars to every place where they are needed.

But in its way to the top Xylem faces nearly irresistible obstacle - gravity. To reach its final destination the sap relies on three forces - transpiration, capillary action, and root pressure.

During the process, photosynthesis leaves open and close little pores with the name stomata. By doing this they allow Oxygen (O2) and Carbon dioxide (CO2) get in and out of them but also allow water to evaporate This way a negative pressure is created in the Xylem which pushes it up in the tree. 

Capillary action also helps Xylem in its journey. This property of water allows it to beat gravity by penetrating in narrow tubes getting higher in them than where its source is.

This property of water is stronger than you can imagine in the thin xylem filaments where the sap is transported.

When these two forces take place the pressure in the roots starts pumping fresh Xylem sap to incredible heights up the trunk.

Even though these forces appear as an unbeatable ally for the Xylem every centimeter is a stuff battle. Eventually, trees reach heights where they cannot afford any further loss of water and nutrients and they have no other choice but to focus on their already existing limbs and branches.

This model is known as the “Hydraulic Limitation Hypothesis”. Currently, this is the best explanation of the answer - Why threes cannot grow indefinitely in height?

This model has been used to predict the maximum possible height of different tree species. But in most cases, the predicted cap is of up to 15 meters more than the current maximum.