How do trees grow on vertical cliffs?

Trees can grow on vertical rock faces because of common vertical cracks called joints (see arrow above). These cracks formed when the rocks were forced to bend or flex due to intense pressure from colliding continents (in the distant past) and from the immense weight of glacier ice (in the much more recent past). Soil and seeds sometimes fall into exposed joints. Then weeds, trees and bushes begin to grow. These plants hold on to the cliffs by the roots, which grip the edges of the joints.

Larger trees and bushes also play an important part in breaking the rocks down. As trees grow their roots get longer and wider. Growth of roots pushes the rocks apart with enormous force, and the rocks eventually they loosen and fall into the gorge.