Warming unsynchronised tree radial growth and regional vegetation canopy growth in semi-arid areas of north-eastern China--a case of Pinus sylvestris var. mongolica in plantation.

Abstract

Exploring the synchronisation between radial growth from a specific tree species and the regional vegetation canopy growth covering a certain area (obtained from remote sensing data) and their climate responses contributes towards clarifying the influence of climate change on aboveground forest biomass. We assessed the variation and correlation between the radial growth of Pinus sylvestris var. mongolica (PM) and regional vegetation canopy growth along with their climate responses in the semi-arid area of northeastern China, investigating the synchronisation and temperature limitation of the two growths. We also clarified the variation in the synchronisation of radial and canopy growth in a warming climate. The radial growth of PM and canopy growth of regional vegetation increased significantly. Positive correlations between tree-ring width index (RWI) and leaf area index (LAI) during May and June were higher than those during the rest of the months and month-combinations of a year. The synchronisation of the radial growth and the canopy growth significantly increased along increasing gradients of latitude, and significantly decreased along increasing gradients of temperature. Radial and canopy growth were limited in July by minimum temperatures in the northern high-latitude sample sites (cold and arid) of the study area. Warming induced the unsynchronised radial and canopy growth in the semi-arid area. The synchronous change of the two growth types will weak in the study area in the future; the decoupling of tree growth is expected to occur earlier in the cold, dry areas than in the warm, wet areas. Weakened or broken statistical linkages, such as the synchronisation between the radial growth of a tree species and the canopy growth of the regional vegetation, indicate that the decreased effectiveness of a specific tree radial growth as an indicator of regional vegetation growth complicates the up- or down-scale assessment of forest biomass dynamics and its carbon sequestration potential.