ROOTS
The roots of trees or shrubs draw water from the soil around them. As a result, the ground shifts and affects the asphalt that is laid over it. Large tree roots will also grow and branch out toward the surface, shifting the pavement above them.
DRY WEATHER
When soil dries out, it contracts. When this happens, the ground beneath your asphalt shifts and strains the material above it. This causes fractures and cracks to appear as your pavement is forced to move with the dirt it's sitting on.
SEASONAL CYCLES
Severe weather puts a lot of strain on asphalt. As the asphalt freezes and thaws, it begins to rise and fall. This motion damages its structural integrity, resulting in cracks on its surface.