Twiglet: Trees and roots

  • First thing to emerge from a seed is the embryonic root – the radicle.
  • In most plants, this primary root will develop secondary or lateral roots that grow out away from the main root as the plant grows.
  • The growth of any root is dependent on a small ball of dividing cells just behind the root tip. This collection of cells is called a meristem; it generates new cells to extend the root and form new root tissue (such as the xylem and phloem – the conducting tissues).
  • A long tap root may develop in suitable soils, whilst, in sandy ot peaty soils, the lateral roots may dominate.
  • Studies indicate the dominance of the young tap root is often lost quite early in development in many tree species.
  • The deepest root systems are probably found on desert plants.
  • Tree roots do not generally occur too deep in the soil, with the majority of roots found in the top one to two metres.
  • Trees tend to have shallow but extensive root systems.
  • The spread of the lateral roots can be as great as the spread of the canopy or crown, even further in some cases.
  • One study showed that the root spread of poplars was three times the crown radius. This type of root system is sometimes referred to as an extensive system.
  • An intensive root system is one that is confined to a smaller volume of soil, relying on shorter lateral that have numerous fine endings. This system is seen in beech (Fagus sylvatica), which was one of the species that suffered more than most in the drought of 1976.
  • The survey of trees blown over in the October 1987 Great Storm showed that only 2-3% had distinct tap roots.
  • Oak, pine and silver fir are among the species with persistent tap roots.
  • Other species have what are known as “heart root systems”, where larger and smaller roots penetrate the soil diagonally from the main trunk. Trees such as larch, lime and birch can fall into this category.
  • A surface root system is one where the roots tend to run horizontally just below the soil surface, with a few roots going deeper and vertically. Ash, aspen and Norway spruce are examples of trees with these kinds of roots.
  • The root system depends upon the local geology, soil type, climate, drainage… so, if a local area is water logged, this will limit the gas exchange which in turn will affect the amount of oxygen the roots can get for respiration (which generates the energy needed for growth and the absorption of minerals).
  • When oxygen levels in the soil falls, root growth is reduced or stops completely — the availability of oxygen can also be reduced by the compaction of the soil.

Source: Woodland Trust

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