| Popis: |
This study examined several aspects of canopy structure and their influence on growth of loblolly pine (Pinus taeda L.) plantations. Foliage distribution, crown hydraulic architecture, and the effect of chronological changes in canopy structure on stand development were explored as possible components of a future process-based model intended for management purposes. A model based on the Johnsons SB distribution was developed to predict leaf area distribution of loblolly pine trees. This is a preliminary step for building a submodel capable of simulating chronological changes in canopy structure and stand growth. The model accurately predicted the cumulative distribution of leaf area in the crown. It has the potential to be included in forest growth models where an accurate description of leaf area distribution is needed. A novel process-related, non-carbon-based growth model for predicting the growth of closed, unthinned, loblolly pine stands was developed. Its ability to represent the dynamics of the canopy and stand growth was evaluated. Overall, model predictions were in agreement with reported observations or proposed theories in relation to stand growth, size-density relations, and relationships between canopy dynamics and stand growth. Modeling the hydraulic architecture of the crown is important because it controls crown recession. Patterns in branch permeability with crown depth and permeability at the top of the main stem were analyzed for loblolly pine trees from families selected for differences in growth rate and crown size. The results showed that branch permeability decreased significantly from the top to the bottom of the crown and that genetic-based differences might exist in patterns of stem and branch permeability. The study showed the potential of using a process approach to develop a forest growth model and utilizing mechanistic and empirical elements in the construction of the simulator. In addition, the integration and synthesis of information coming from diverse sources in the model allow the possibility of detecting deficiencies in the understanding of key processes and provide a guide for formulating hypotheses and planning experiments to fill the gaps in knowledge of the processes regulating stand development. |
