Tzeng Yih Lam

Critical Height Sampling

Critical Height Sampling (CHS) was developed more than four decades ago independently by Kitamura (1964) and Iles (1979). CHS is the only variable probability sampling design that samples with probability proportional to volume. It unbiasedly estimate stand volume (m³ ha^-1) without any models. CHS was largely dismissed over the decades due to perceived field impracticality. However, this assumption was never fully tested. To our knowledge, we are the first to establish a large field trial of CHS. The field trial consists of 65 plots distributed across Cryptomeria japonica and Taiwania cryptomerioides silvicultural experiments in central Taiwan. The silvicultural experiments cover a variety of planting density, thinning treatment, and establishment year; hence, resulting in diverse stand structures. We also conduct time study on CHS by recording the amount of time required to complete measurements in a CHS plot. The major goal is to demystify field practicality of CHS. This large field dataset allows us to explore a variety of topics concerning CHS such as model estimation bias, precision, relative efficiency, and multiphase sampling strategies. This research was funded by the National Science and Technology Council Taiwan.