Assessment of leaf mass and leaf area of tree crowns in young Eucalyptus grandis and E. globulus plantations from measurements made on the stems

Leaf area is a key driver of growth models and leaf weight is important for studying carbon and nutrient cycling in forestry. Both can change over relatively short intervals in young plantations in response to silvicultural treatments and climatic conditions. Relationships to estimate leaf dry weight and leaf area of young Eucalyptus grandis W. Hill ex Maiden and Eucalyptus globulus (Labill.) were developed from harvested trees ranging from 0.28 to 15.85 m and 0.12 to 34.4 m in height respectively. Trees were harvested from existing experiments in south-eastern Queensland and south-west Western Australia in order to assess the effects of spacing and application of nitrogen and phosphorus fertilizer on early plantation growth. A range of tree measurements were taken to determine the most efficient way to monitor the performance of young plantation eucalyptus. Leaf weight (W_leaf, kg) and leaf area (m²) were related to stem cross sectional area at the height of the base of the green crown (SA_CB), but the slope and intercept of the relationship differed for trees with predominantly juvenile foliage and those with predominantly intermediate or adult foliage. Specific leaf area (m² kg⁻²) changed as the trees aged and leaf area was more closely related to the size of the support structure, represented by the stem volume within the green crown, approximated by the volume of a cone above the base of the green crown (V_C,gc). Significantly, the relationships also applied to individual branches, that is, leaf weight was related to sectional area near the base of the branch (SA_b) and leaf area to the volume of the main (first order) branch (V_C,br). Most of the published work has been directed at trees of commercial size or to small trees in pot experiments, much less to small trees in the establishment phase of growth of interest to experimenters and managers looking at early intervention. This study provides a mechanism to directly assess canopies of intermediate size trees which are of interest for assessing treatment effects or early intervention for managers.