In the context of urban trees, infrastructure can severely limit the growing space available to the roots. Bottom, crowded roots are girdling this linden tree. Top, exposed roots of this tree growing on a hill side show their horizontal structure. These roots are opportunistic РІР‚вЂњ they will grow wherever the conditions are suitable, and will die back if resources are not available. Small, ephemeral absorbing rootsgrow out of lateral roots, soaking up water and oxygen and other nutrients. In the first 3-6 feet, woody lateral roots spread out and taper down to 2-4 inches in diameter. Buttress roots right near the trunk help stabilize the tree. Roots become smaller as they grow outward from the root collar (base of the trunk). This wine glass sitting on a plate represents the basic shape of a tree and its roots. Tree roots actually grow outward horizontally from the base of the tree (picture a wine glass sitting on a dinner plate). Many people imagine tree roots as a mirror image of the branches, but this is a common misconception.

What does this mean for the structure of a root system? For this reason, roots tend to grow right under the surface. The depth that oxygen can reach depends on the type of soil and amount of compaction, and the most oxygen will be found near the surface of the soil. Tree roots grow best when they have sufficient growing space and well-drained soil with enough oxygen and water (but not too much water). Too much water in the soil will also limit the amount of oxygen the roots can take in. If the soil is dense and compacted (with no soil pores), there will not be enough oxygen available for respiration. In the ground, air and water are held in little pockets called soil pores. However, while the crown of a tree is usually surrounded by open air, roots need a source of oxygen in the soil in order to grow. Most tree growth occurs at the tips of branches and the tips of roots. Just as a person who is exercising needs to breathe deeply, a tree that is actively growing needs an immediate source of oxygen. While trees take in oxygen from their surroundings, humans breathe it in with their lungs. Humans do the same thing when they process stored sugars. The energy that is released can then be used to make new tissues. During respiration, sugar and oxygen are combined to produce energy, with water and carbon dioxide created as byproducts. In order to use stored starch for growth, trees must convert the sugars back into energy through a process called respiration. While trees use carbon dioxide to make their own food, they actually need oxygen (much like humans do) to process that food into energy. It is well known that trees act as carbon sinks, taking in carbon dioxide from the air during photosynthesis and releasing the oxygen that humans breathe. Topping a tree can limit its growth in the short-term, but is very bad for the tree. Likewise, cutting roots or restricting the rootsРІР‚в„ў growing space will limit the amount of water that can be transported to the leaves for photosynthesis. Topping a tree will stunt its growth by limiting the amount of photosynthesis that can occur in the leaves (by the way, NEVER top trees- it is very dangerous and bad for the tree). In this way, the tree must balance its above ground and below ground growth. A small root system can only support the photosynthesis of a small canopy, and roots can only grow larger if they have enough energy (sugar) provided by the leaves. The amount of photosynthesis that can occur in the leaves is directly related to the amount of water that the roots can absorb. Sugar is converted into starch, and can be stored in the trunk or the roots, or used for immediate growth.

Sugar is transported back to the rest of the tree through phloemР’В cells (see diagram below). Water is carried from the roots to the leaves through xylemР’В cells. Trees make their own food through photosynthesis, using energy from sunlight, water (from the roots), and carbon dioxide (from the air) to create sugar that is used to fuel the rest of the tree.

Trees - like all other living things - need food, water, and nutrients to survive.

Htere is no tree it is said