The role of climate in a pine forest regeneration pulse in the southwestern United States

:The role of historical influences in patterning forest landscapes was explored in a case study of forest structure change in the American Southwest. A group of ponderosa pine trees was destructively sampled and year of germination identified in order to assess the strength and nature of the climate signal in influencing ponderosa pine germination in this century. A novel methodology for estimating year of germination in woody species by identifying the root-shoot boundary appears to be promising. Both rare seasonal and interannual climatic factors and a unique set of circumstances associated with anthropogenic disturbances played a role in shaping a germination pulse early in the 20th century. A cohort originating in 1919 captured available space and, barring major disturbance, will dominate forest structure at the site for centuries. Such rare germination events support the view that forest communities are essentially dynamic and non-equilibrial over the long-term.