Tree growth

The tree growth habit is an evolutionary adaptation found in different groups of plants: by growing taller, trees are able to compete better for sunlight Trees tend to be long-lived, some reaching several thousand years old, as well as tall.Trees have modified structures such as thicker stems composed of specialized cells that add structural strength and durability, and that allow them to grow taller than non-woody plants and to spread out their foliage. They differ from shrubs, which are also woody plants, by usually growing larger and having a single main stem but the distinction between a small tree and a large shrub is not always clear, made more confusing by the fact that trees may be reduced in size under harsher environmental conditions such as on mountains and subarctic areas. The tree form has evolved separately in unrelated classes of plants in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimated 100,000 species, the number of trees worldwide might total twenty-five percent of all living plant species.The greatest number of these grow in tropical regions and many of these areas have not yet been fully surveyed by botanists, making tree diversity and ranges poorly known.