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Updating allometric functions outside a full inventory

29 November 2016

  

The Reforestation and Afforestation Methodology determination makes specific provision for the updating of stratum specific allometric functions as part of a full inventory, but is silent on the updating of stratum or regional allometric functions outside of a full inventory.

The Clean Energy Regulator advises that project proponents can update an allometric function during or outside a full inventory providing that the following requirements are adhered to:

The requirements for updating an allometric function outside a full inventory are set out in more detail below.

The update is conducted in accordance with section 5.31 (stratum specific) or 5.33 (regional) and is consistent with the process outlined in section 5.32 of the determination

Section 5.31 relates to developing stratum specific functions and Section 5.33 to developing regional functions. While Section 5.32 outlines the requirements for updating pre-existing stratum function as part of a full inventory, it is expected that the process specified in this section will be followed when updating a function outside a full inventory.

The following approaches to updating an allometric function are consistent with the process outlined in section 5.32 and would be acceptable:

  • The project proponent would sample a minimum of 10 trees that are of a size class that currently exceeds the allometric domain (only the larger trees will be sampled). The biomass dataset of these sampled trees would be combined with the original dataset, thereby expanding the allometric domain. The expanded allometric function must then meet the minimum regression fit requirements.
  • The project proponent would sample a minimum of 10 trees (including the smallest and largest) that span the full diameter range. The biomass dataset of these sampled trees would be combined with the original dataset, thereby expanding the allometric domain. The expanded allometric function must meet the minimum regression fit requirements.

The updated allometric function must be validated in a way that is consistent with section 5.42.(3) – 5.42 (21) of the determination

For stratum specific or regional allometric function updates that are occurring outside a full inventory, the Clean Energy Regulator requires the updated allometric function to undertake the validation test steps described in Section 5.42.(3) to Section 5.42 (21) of the methodology (inclusive). The validation testing will need to be documented in the first offsets report in which the updated allometric function is applied.

Project trees selected to expand the allometric domain must not be selected from permanent sample plots

Permanent sample plots, established during the full inventory, are regarded as reference plots, allowing sequestration increments to be calculated during the intervening years between full inventories. In order to provide valid estimates of sequestration for the broader planting, these reference plots should not be treated in any way that is different from the broader planting. The removal of trees to expand the allometric function may act like a 'thinning' event such that the remaining trees may have a favourable growth response due to reduced competition by removing individual trees.

Project trees selected to expand the allometric domain must be sampled from the same strata/region from which the project trees were sampled to develop the original allometric function at full inventory

Allometric domains are based on variability and distribution of growth that is characteristic of the full domain. Therefore, when updating an allometric it is important to not mix the allometric domain scales (e.g. use strata-specific data for updating a regional allometric domain) as this may bias the abatement either upward or downward if the allometric function is applied outside the strata/region on which the updates are based; therefore possibly impacting the integrity of the net abatement.

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