Example V the movement of alpine treeline. A variety of evidence indicates that trees grew high on mountain slopes prior to the Little Ice Age and then retreated. Trees may now be advancing into tundra as the climate warms. Another aspect of change is local change over shorter time scales. Directional change in the composition of a plant community is called succession.
Primary succession occurs if there is no remnant of a prior biological community.
If a volcano erupts lava that cools to rock, then life can take hold. Disturbances such as fire, flood, windstorms that destroy plants but leave a remnant of the biological community V in soil, seeds, resprouts V lead to secondary succession. We can think of a shifting mosaic of patches in the environment. Disturbance resets a patch to age zero and it then proceeds to change through succession. Each patch is a different age since disturbance and has a different disturbance history.