PhD Scholar

Crown and canopy dynamics in subtropical eucalypt plantations

E-mail: Philip.alcorn@anu.edu.au

Growth and wood quality of forest stands are intimately linked to the development of the forest's canopy. The size and distribution of leaf area within crowns set limits to biomass production by defining light interception. While it may be desirable to grow trees with large crowns to facilitate rapid stem biomass accumulation, the enlarged branches to support high leaf areas are usually undesirable in the early growth phase until a sufficiently long branch-free section of the stem has formed. It is therefore standard practice in plantations grown for solid wood products to control branch development through stand density and/or pruning. Understanding the effect of these silvicultural treatments on the morphology and physiology of tree crowns can aid the development of models to explain and predict the growth of forest stands.

The aim of this project is to provide a mechanistic understanding of crown and canopy dynamics in a number of subtropical eucalypt species, to build the scientific foundations for stand manipulations to enhance wood quality and productivity. Field experiments will be employed to test the hypotheses that:

1. The plasticity of green crowns (length, shape, number and size of branches) in response to stand density is greater in the more shade-tolerant eucalypts than in the intolerant eucalypts,
2. The effect of green crown pruning on biomass production in eucalypts is related to the amount of foliage removed, the nutrient status of pruned foliage, the water status of pruned trees and the shade tolerance of the species.

Specifically, the study will examine crown dynamics in the early growth phase of three plantation eucalypts (Eucalyptus pilularis and E. cloeziana) with differing branch shedding habits. In addition, a detailed investigation of the physiological and morphological responses to differing green pruning severities will be conducted on two of these species exhibiting differing crown dynamics. Allometric relationships between stem, branch and crown components will be developed to aid the investigation. The outcomes from this project will aid the development of a stand management simulation model for the species in question.