Productivity as related to diversity and age in planted versus natural forests

Abstract

Aim Little is known about the performance of plantations relative to natural forests of the same climate zone and age. China has more plantations than any other country as a consequence of massive afforestation efforts. We use data from China to comparatively examine tree biomass and productivity of planted and natural stands in relation to climate zone, latitude, elevation, age and species diversity (richness). Location Six forest climate/vegetation zones in China. Methods We used a database completed in 2007 and then updated in 2013 that contained extensive records of forest stands (10 m × 10 m plots) across China. The database records included a total of 6153 forest stands (1716 planted forests aged 0-80 years and 4437 natural forests of aged 0-400 years), located from 18.1 to 53.2° N and 75.53 to 131.8° E, and between elevations of 7 and 4240 m above sea level. These forests were grouped into six climate zones for comparisons. Results Under generally similar physical conditions (climate zones) to those in natural forests and despite having low diversity (i.e. often a single tree species), plantations aged 0-80 years already had similar biomass but much higher productivity, and thus much higher carbon sequestration rates, than natural forests. Tree biomass, productivity and their above/below ground ratios showed stronger latitudinal and elevational trends in natural forests than in planted forests. No difference in productivity was observed between the planted forests with one or two species; in natural forests, however, high diversity usually led to high productivity. Main conclusions The differences in performance between planted and natural forests were mainly explained by: (1) age (the plantations were in early succession), (2) elevation (plantations were located at lower elevations), and (3) species selection (only highly productive species were planted). As the plantations were all still young, closer monitoring of their performance is needed.