Why are the southern and western boundaries of the Ituri Forest difficult to define?

The southern and western boundaries of the Ituri Forest are difficult to define because the forest is contiguous with the broader lowland rainforest of the Congo River basin in those directions. Unlike the northern and northeastern borders, which are clearly demarcated by savanna, or the eastern border, which is defined by the Western Rift Valley, the southern and western edges transition seamlessly into the surrounding tropical forest ecosystem.1