Growth dominance and growth efficiency in response to thinning treatments in Chinese fir plantations with long-term spacing trials

Abstract

Growth dominance is a relatively new, simple, quantitative metric of within stand resource partitioning, while growth efficiency can be used to quantify the efficiency of resource use at both stand and tree level. We examined long-term silvicultural experiments in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) to characterize how growth dominance and stand growth efficiency in stands thinned from below develop with age, cumulative thinning intensities, residual density, and planting density. Results showed that growth dominance in unthinned plots increased with increasing age, while stand growth efficiency displayed the reverse pattern. Both of them were not significantly different between planting densities, which indicates that the efficiency of resource use and relative growth of Chinese fir was always proportional to its size, even in dense stands. Thinning improved the relative growth of larger trees and decreased stand growth efficiency. When the dense plots were thinned to the next lower initial planting density, the growth dominance of the thinned plots were higher than that of the unthinned plots, and stand growth efficiency of the thinned plots were lower than the respective unthinned plots. When plots with different planting densities were thinned to the same stand density, growth dominance increased with cumulative thinning intensities, while stand growth efficiency showed the reverse pattern. Growth dominance was positively correlated with the growth efficiency difference between smaller and larger trees in both unthinned and thinned plots, while negatively correlated with stand growth efficiency.