Forest dynamics

Forest dynamics describes the underlying physical and biological forces that shape and change a forest. That is, the continuous state of change that alters the composition and structure of a forest. Two basic elements of forest dynamics are: forest succession (or ecological succession) and forest disturbance.

Disturbance

Forest disturbance is an event that causes change in structure and composition of the forest such as fire, flood, wind, or earthquake or mortality caused by insect, disease outbreaks, Forest disturbance can also be human caused such as timber harvest.

tand replacing disturbance

A major disturbance that removes most or all of the existing trees in a forest is called a "stand-replacing" disturbance. This begins the first stage of forest succession called "stand initiation". Trees that arrive by seed begin to grow. When the canopy becomes closed the second stage "stem exclusion" begins. Trees begin to compete for light and mortality rate becomes high. At this point the canopy will be relatively smooth and consist one dominant cohort (age group).

As the trees which make up the canopy begin to age, mortality rate may be high as the trees are the same age. "Understory reinitiation" begins. The crowns of the largest trees are now big enough and the growth rate of the mature trees slow that canopy gaps are filled with a younger cohort. The forest will now consist of two age classes. At some point there will be few or no remaining trees of the original cohort. The forest will consist of many age classes. Mortality is continuous. When large individual trees die large gaps are created in the canopy. This is a late-succession forest.