Pruning Chinese trees : an experimental and modelling approach

Abstract

Pruning of trees, in which some branches are removed from the lower crown of a tree, has been extensively used in China in silvicultural management for many purposes. With an experimental and modelling approach, the effects of pruning on tree growth and on the harvest of plant material were studied. In Chapter 2 the aboveground biomass production and harvest of plant material of five subtropical Chinese tree species as affected by annual pruning were analysed. The biomass production of trees decreased following pruning, and the reduction in biomass production was correlated with pruning intensity. The results indicated that, for the investigated five subtropical tree species, the annual pruning regime could not provide enough time for a tree to fully recover its growth, which consequently prevented the sustainable gain of high harvests of plant materials. In Chapter 3, the aboveground biomass allocation and leaf dynamics of four tree species following pruning were investigated. Pruned trees allocated proportionally more of their aboveground biomass to leaves and less to wood, irrespective of species and pruning seasons. This allocation pattern was positively correlated with pruning intensity. The increased proportional allocation of aboveground biomass to leaves following pruning would benefit pruned trees to alleviate the negative pruning effects and recover from the pruning damage. Chapter 4 focuses on the leaf emergence and shoot production of trees after pruning. Pruning had no effect on the leaf density and shoot production. Pruning facilitated the shoot production on the bare stem parts beneath the remaining crown. In Chapter 5 the leaf efficiency of two Ficus tree species as affected by pruning is reported. The leaf efficiency of both species was increased after pruning. In Chapters 6, a tree growth model was constructed. In Chapter 7, this tree model was applied to simulate the effects of pruning on branch harvest, taking pruning intensity, pruning season, pruning frequency, and tree size at which pruning starts into consideration. To sum up, the effects of pruning on tree growth depended on many factors including pruning season, pruning intensity, pruning interval, tree species, and tree size. Heavy and repeated pruning with short intervals reduced tree growth always. This negative effect, however, can be mitigated to some extent by the increased biomass partitioning to leaves and the increased leaf productivity in the pruned tree.