Low net primary productivity of dominant tree species in a karst forest, southwestern China： first evidences from tree ring width and girth increment

Aboveground net primary productivity（ANPP）of two dominant species, one deciduous tree（Platycarya strobilacea） and one evergreen tree（Machilus cavaleriei）,was estimated based on the tree-ring width and the girth increment as well as allometric functions in a karst evergreen and deciduous broadleaved mixed forest in central Guizhou Province, southwestern China. Results showed that the ANPP increased from 1961 to 2015, especially during the last 20–30 years, but with strong variations. The deciduous tree had higher ANPP than the evergreen tree according to two kinds of estimates by the tree ring and girth increment. The averaged ANPP for these two mature trees was 2.27 kg/individual/year, ca. 8 t/ha/year considering the normal stand density. Such karst forest productivity was lower than the natural subtropical forests in China and in the world.