Using crown characterisation variables as indicators of the vigour, competition and growth of Brazilian pine

Abstract

Crown variables are used in growth and production models to increase the accuracy of estimates. These variables are costly and difficult to measure, mainly in dense native forests such as mixed ombrophilous forests (MOF), where Araucaria angustifolia is the predominant species. Thus, this study aimed to evaluate the effect of qualitative and quantitative variables to describe the vigour of the crown, competition and growth of A. angustifolia in Southern Brazil MOF. We selected trees in the MOF area and measured circumference at breast height (CBH) and total height (h). For the crowns, a ranking of values was established in the variables: Crown Shape (CS), Vertical crown Shape (VS), Distance between Branches (DB), Sociological Position (SP), percentage of Green Leaves (GL) and Crown Size (CZ). Periodic Annual Increment in basal area (PAIg) and a Competition Index (CI) were calculated. We used principal component analysis (PCA) and Hierarchical Cluster Analysis (HCA) to describe and classify the sampled trees. Two groups were generated: i) dominant and codominant trees, with higher growth, better vigour and better crown quality; and ii) suppressed trees with low vigour, consequently low increment and worse crown quality. The CI, when based only on diameter information, was inadequate to describe the competitive status of the trees, so information about crowns was necessary. Qualitative crowns variables are important to classify the vigour, current level of competition and to understand the different trends in A. angustifolia growth.