This week I had my first encounter with the largest living thing by volume – the magnificent Sequoiadendron Giganteum, or more simply the Giant Sequoia. Fabulously large trees that reside in small groves.
Just a short hike from the main trail in Yosemite National Park, California, Merced Grove is the home to approximately 20 of these beautiful trees. Trying to stare to the top is a difficult task, as the Giant Sequoias grow to a height of 50–85m, with an average diameter of 7m. What is really clever is how the trees are able to fulfil their water needs.
Osmotic pressure is the term used to describe the movement of water through a semi-permeable membrane. The tree roots use this to take water from the surrounding soil, but the method can only push water up a few meters. To get the water higher the trees use a branching capillary network made up of xylem, or water tubes. When water enters these tubes, the liquid near the sides is attracted and rises higher than the water level in the middle. This allows water to move upwards; similar to when a paint brush sucks up paint. However, at some point the mass of this liquid will be sufficient for gravity to once again want to pull the water back down… but the tree has another trick in its leaves! By evaporating water from the leaf surfaces, the tree can create depressurisation, helping to keep the water moving to the top.
Finally, to reach the tallest, lofty heights, the Giant Sequoia use one last method in their tool kit – aerial roots. Whilst often warm and sunny, the Californian region is also prone to fog. Aerial roots allow the tree to utilise the water content from within the fog, supplementing the water requirements right at the top of the tree.
So through osmotic pressure, a network of tubes, leaf evaporation and regional fog, the wonderful Giant Sequoias can continue to grow a branch above the rest! Well worth a visit if you ever get the chance.