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.