VTM data helps us understand changes to California forests

Some press on our PNAS paper: Twentieth-century shifts in forest structure in California: Denser forests, smaller trees, and increased dominance of oaks.

In the paper we document changes in forest structure between historical (1930s) and contemporary (2000s) surveys of California vegetation. The shorthand is:

  1. Statewide, tree density in forested regions increased by 30% between the two time periods, and forest biomass declined by 19%.
  2. Larger trees (>60 cm diameter at breast height) declined, whereas smaller trees (<30 cm) have increased.
  3. Large tree declines were more severe in areas experiencing greater increases in climatic water deficit since the 1930s.
  4. Forest composition in California in the last century has also shifted toward increased dominance by oaks relative to pines, a pattern consistent with warming and increased water stress, and also with paleohistoric shifts in vegetation in California over the last 150,000 years.