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Tree types and rooting

Themes: Introduction | Tree types and rooting | Water and nutrients | Quiz

The trunk of the English Oak tree There are two main kinds of trees, called deciduous and coniferous. Broad-leaved deciduous trees, shed all their leaves every year during the period when temperatures are cold and sunshine limited. They then grow new leaves when temperatures become warmer again and there are more hours of sunshine. Thus for part of the year they will be green and leafy and at other times bare-branched. A very common such tree in Britain is the Oak (Quercus). Evergreen trees, unlike deciduous trees, keep their leaves for several years and lose their leaves only gradually. New leaves develop in among the older established leaves - so they are never bare. Conifers are the best known type of evergreen. They tend to form needle-like, semi-circular or elliptical leaves so as to limit transpiration as much as possible, and in this way are adapted to cold and/or droughty climates.

Soil allows tree roots and the rooting system to develop and anchor the parts of the tree above ground. For successful establishment of woodland and commercial forests it is important there is nothing preventing roots growing through the soil and that there is ample depth of soil. Soil depth requirements vary from tree to tree. Oak, ash, sweet chestnut and lime require at least 75 cm of soil, whereas spruce, beech and larch will grow well in shallower soils. Ideally a tree needs sufficient depth to anchor the tree at its likely maximum height - consistent with the nature of its rooting system. However, many soils are less than perfect in this respect.

Beech tree roots in chalky soil Seeds of potential trees cannot choose where to settle to germinate, there is an element of chance. Trees may begin growing in soils less than ideal for the species. This lack of ideal soil conditions either leads to poor growth or for instance in shallow soil by the tree falling over at some stage. If soils are waterlogged, tree roots can become deprived of oxygen. While some trees may thrive on this situation, for example the mangrove forests of India, in most situations and climates trees will not be able to tolerate waterlogging for long periods and this may lead to shallow root development and reduced anchorage for the growing tree. Some soils can also become compacted in the root zone. It is interesting that the soil type that develops most typically in the coniferous forests of northern Europe and America, the podzol, has a thin iron pan which as it develops will prevent roots of trees passing easily through it. As this is usually developed in the top 50 cm of the soil it can form a barrier to roots and thus make the trees prone to windblow.

Coniferous pine needles. These leaves stay green - even in winter

Themes: Introduction | Tree types and rooting | Water and nutrients | Quiz