Plant Adaptations to Sunlight

Trees have evolved adaptations that help them deal with various amounts of sunlight. Foresters are keenly aware of these adaptations and generally characterize trees as either shade tolerant, intolerant, or intermediate.

Shade tolerant trees are adapted to low light conditions. They generally grow more slowly than intolerant trees, but this habit makes it possible for them to grow in a forest understory. In the race between a rabbit and turtle, shade tolerant trees are most like turtles.

Shade intolerant trees are adapted to high light conditions and must have full sun in order to survive. They grow rapidly (high photosynthetic rate) which generally makes them more valuable economically. Shade-intolerant trees are well adapted to regions where disturbances such as fire, logging and hurricanes are frequent.

Trees with intermediate tolerance to sunlight can survive low light conditions as a seedling, but require full sun conditions for rapid growth. Many of these tree species survive for many years in a forest understory, then grow rapidly into the canopy when an overstory tree dies or is harvested.