An Introduction to Tree Biology: Roots II

As tree biology seems to be a favourite I have decided to pick things up there with another post about tree roots, such a very vital part of a tree. To view the first post regarding tree roots click here.

We have recently purchased two new trees for our garden. The trees were pot planted however have been in the nursery for some time and as a result the root system had persisted through the drainage holes in the pot and into the surrounding soil and gravel.

We asked an assistant to help us with freeing the trees and she kindly provided secateurs and a strong hand to support the trees while we freed the roots. Her initial response had been to simply pull the trees free however this would have been disastrous and snapped most of the roots off. With a small amount of effort we were able to unearth the existing roots and prune any larger roots that could not be freed.

As previously discussed the finer string like fibrous roots provide water and nutrient uptake, without them the tree struggles to feed itself until new feeder roots can be established. The larger roots in addition to providing anchorage are storage facilities for sugars termed photosynthates produced by means of photosynthesis. These photosynthates are the energy providing material for the tree and are utilised to achieve growth and defense amongst other functions.

Planting should ideally be undertaken within the dormant season i.e. autumn and winter thus allowing trees to recover from transplant shock and begin establishment of their root system within the new area of soil usually moist due to the environmental conditions at this time of year.

Trees can be planted during the spring and summer however will almost undoubtedly require watering to prevent drought stress.

Upon planting, the tree root system should be spread evenly around the planting pit having loosened up the sides of the planting pit walls to allow easier root penetration into the soil. Trees grown in containers often develop what is termed girdled root which occurs when tree roots develop to the extents of their container and as they continue growing begin to circle the container. Any such barrier that a tree encounters in early root development may result in girdled root.

Trees planted with girdled roots can in some cases suffer stem failure later in life as a result of the girdled root exerting pressure against the main stem and vice verse as they put on their annual growth and increase in girth.

The reason that so much care is required when dealing with trees, and such a delicate and complex component as roots, is that trees have a finite amount of energy available to them. If this energy is utilised inappropriately due to unnecessary wounding or other actions the energy already ring fenced for normal annual operations is not available and trees begin to decline.

For example a tree planted carelessly during winter that is required to utilise stored energy for root repair or re-development will have less energy available to produce it's leaves in the spring. As a result the leaves may be undersized and therefore have a smaller surface area to photosynthesise during the summer months. This results is a lesser yield of photosynthates during the summer and the cycle continues.

Similarly if fertiliser or other organic matter is applied to a tree when it is not required the tree will still utilise the available food to it's own detriment. The increased food levels will stimulate growth in excess of normal levels. As every function of a tree uses energy this forced growth takes energy away which is required for another process.

Depleted energy reserves make a tree more at risk from pests and diseases as it is less able to instigate it's defense systems.

If sever drought stress occurs the parts of a tree responsible for photosynthesis can be damaged permanently resulting in a photosynthetic disability for the remainder of that trees life.

Trees can recover from small levels of stress over a period of time however an accumulation of stress can lead to decline and premature death. An excess of stress is termed strain.

It should be noted that trees are very good at looking after themselves without any of our assistance however when we start to place trees in demanding situations such as urban planting there are precautionary measures that can be taken to ensure the best environment for the tree is achieved. Appropriate ground preparation and consideration of a developing root system and it's specific needs is vital.

If you have any questions about this or any other post please feel free to leave me a comment and I will do my best to answer your query.