Answer:
There are two kinds of respiratory chemoreceptors: arterial chemoreceptors, which monitor and respond to changes in the partial pressure of oxygen and carbon dioxide in the arterial blood, and central chemoreceptors in the brain, which respond to changes in the partial pressure of carbon dioxide in their immediate ...
The best possible explanation is phototropism.
Since the trees are very dense, some plants don't get enough sunlight. A reaction to this is to seek out sunlight. This would result to trees growing taller than the rest in order to obtain sunlight.<span />