Validation of allometric biomass models: How to have confidence in the application of existing models

Our results indicate that although an allometric model for a given species or plant functional type may be applied across multiple sites, validation will be important when an existing generic multi-site and multi-species model is applied to a new species. Results obtained demonstrated that an independent sample size of N ≤ 15 frequently (37-46% of the time) provides insufficient power to avoid incorrectly accepting “validation” (type II errors). Hence, to ensure a useful outcome from resources spent in sampling biomass, it is recommended that at least 50 trees be sampled for each species. An equivalence test may then be applied to determine if the minimum detectable negligible difference between the existing model and the new independent data is <25% (or whichever threshold is deemed acceptable). If so, the new data set may then be combined with existing data to refine a generalised model, which may then be applied with confidence. If not, then the resources expended need not be wasted as the sample size is sufficient to develop a new model suitable for application to the specific species sampled.