Why does little sunlight reach the floor of much of the Ituri Forest?

In the Ituri Forest, little sunlight reaches the forest floor primarily because of the high, nearly continuous canopy formed by giant hardwood trees that can reach heights of 170 feet (52 metres). This dense overhead layer acts as a barrier to sunlight, allowing only small, elusive patches of light to penetrate to the lower levels.1

The lack of light at the ground level is further accentuated by the foliage of the few shrubs and small trees that are adapted to grow in these shaded, dark conditions. Sunlight only reaches the forest floor in significant amounts where gaps occur in the upper canopy, such as in areas disturbed by natural treefalls or human activity, which allow the strong equatorial sun to break through.1