words per minute
11
Neha_Tiwari
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Each year the tree forms new cells. These cells are arranged in concentric circles called annual rings or annual growth rings. These annual rings show the amount of wood produced during one growing season. In Canada and the North United States the growing season begins in the spring. At first the cambium produces numerous large cells with thin walls that form the springwood. If you look at a cross section of a tree this is the light-coloured ring. Towards the end of the summer the growth of the tree slows down. The cells manufactured at this time of year are small and have thick walls. They form the summerwood which appears as a darker ring on the tree cross section. One year of growth is therefore represented by a ring consisting of a light part and a dark part. Some people believe that the darker wood is not formed in winter. This is due to cambium being completely inactive in the winter. A new two-part ring is added the following year. The older rings are closest to the centre of the tree. The tree grows in diameter because it manufactures new cells around its circumference, not because the old cells get larger. The old annual rings form the heartwood of inactive cells. This is the dead part of the tree. The live portion includes only the most recent rings. The width of this portion depends on the age and species of the tree. This portion is generally one to seven centimetres in width. The dead wood is the largest part of the tree. It often takes on a darker colour. Annual rings generally exist in trees where the climate halts growth at some point during the year. Winter causes this shutdown in our country. For some countries it is caused by the dry season. Growth begins again in the spring or rainy season. All trees grow by adding successive rings. The beginning and end of the growth period may occur any time during the year. This depends on the local conditions. Some trees in tropical forests manage to create several dozen very thin rings in a year. The number of the rings are never the same from one year to the next. It is often difficult and sometimes even impossible to distinguish them with the naked eye. It is extremely hard to determine the age of the tree in such cases. Tree growth is not the same from spring until the end of the summer. Growth is faster in the spring. Stem elongation and diameter growth begin and end at different times. The diameter growth although continues longer. Oaks and all other long lived species grow slowly in our climate. Willows and aspen have a short life cycle but compensate with intense growth. Their annual rings are wider. Often we talk about reading between the lines. This means that someone can understand things that are not clearly stated. A cross section of a tree shows much more than its age. Diameter growth is particularly sensitive to fluctuations in the environment like the moisture in the soil and the air. It is also sensitive to temperature and sunlight. Very broad rings generally indicate a good growing year. The growth rate of a tree can be compared with that of a child.