Determination of optimal tree height models and calibration designs

In our new article in ANFS, we present a workflow for determining the optimal tree height model and calibration design for forests affected to varying degrees by anthropogenic disturbance. We used data from Araucaria-Nothofagus forests in Chile, which are affected by anthropogenic disturbances such as intentional forest fires, grazing, and seed harvesting, causing forest structure to become more heterogeneous.

How does the structure of these forests vary by different levels of anthropogenic disturbance? And, more specifically, which models for estimating tree height of Araucaria araucana and Nothofagus pumilio are most reliable and generally usable? Considering their application in stands they have not been fitted to, which calibration design is optimal for these models?

Twelve mixed Araucaria-Nothofagus forest stands in soith-central Chile were studied. Comparing different quantitative stand-level properties, also involving a cluster analysis, we found that forest structure greatly varied among stands affected by different levels of anthropogenic disturbance. To identify the optimal height-diameter (H–D) model, simple models including diameter only as well as generalized models including stand variables were tested, each additionally extended by a nonlinear mixed-effects (NLME) modeling framework accounting for nested and random effects. Of all the simple H–D models considered, the Gompertz model was the best for A. araucana and the Näslund model for N. pumilio. The models progressively improved by adding stand variables and using NLME techniques. However, our final model comparisons indicate that a calibrated simple NLME model without stand variables should be preferred. The optimal model calibration design was identified involving the empirical best unbiased predictor technique. According to this, tree height predictions in newly surveyed stands are most accurate and effective when the height of up to five random trees is measured to recalibrate predefined nonlinear mixed-effects models. A detailed workflow for height-diameter model development and the identification of most cost-effective measurements for recalibration is provided to guide further applications.

Full open access article:
Zhou, X., Kutchartt, E., Hernández, J. et al. Determination of optimal tree height models and calibration designs for Araucaria araucana and Nothofagus pumilio in mixed stands affected to different levels by anthropogenic disturbance in South-Central Chile. Annals of Forest Science 80, 18 (2023).

GitHub Repository:
Zhou, X., Zwanzig, M. (2022) Steps for tree height model development and calibration with R. Zenodo.