You're standing at a 600mm DBH yellow box on a rocky slope at the edge of the proposed clearing boundary. There are two confirmed hollows visible — one at approximately 8m height with an entrance diameter of around 180mm, one higher at 14m that you can't fully assess from ground level. The target species list for this site includes superb parrot and squirrel glider, both of which have minimum hollow entrance requirements. Whether this tree is retained, flagged for further assessment, or cleared depends on what's in the record.
The Biometric Baseline
Tree height, Diameter, and Crown Width are the three physical parameters that establish the tree's structural profile. In hollow-bearing tree assessments for development impact and offset calculations, height and DBH (diameter at breast height) are the primary predictors of hollow-forming potential. Trees above a threshold diameter and age class are disproportionately valuable as hollow habitat because large internal chambers take decades to form after the initial hollow entry point opens. A 400mm DBH eucalypt that's been assessed and removed from a development site represents a habitat loss that a planted replacement will not compensate for within the lifetime of the development.
Crown Width captures the crown spread that determines the tree's light capture and structural resilience. A hollow-bearing tree with a significantly reduced crown relative to its trunk diameter has often suffered crown dieback that indicates internal decay — and internal decay is what produces the hollows. A full-crown tree of the same diameter may be decades away from producing suitable hollows.
Species is the field that determines which hollow size and depth criteria apply. The hollow entrance diameter requirements for a glossy black cockatoo breeding hollow are substantially larger than those for a pardalote nesting chamber. Species alongside HBT form — the hollow structure classification — and Hollow size creates the record that allows the target species assessment to be performed objectively.
Hollow Inventory
Definite Hollows and Potential Hollows create the confirmed versus unconfirmed count. Definite hollows are those with visible, accessible entry points confirmed as functional chambers. Potential hollows are formation cracks, spout holes, or elevated cavities that couldn't be visually confirmed as functional from ground level but meet the morphological criteria for hollow formation. Both counts matter for offset calculations — the potential hollows are the habitat uncertainty that may require targeted inspection by climbing arborist or remote camera deployment.
Hollow size associated with each tree record provides the dimensional classification. Hollows are typically classified into size categories — small, medium, large — that correspond to the functional requirements of specific wildlife guilds. A tree with only small hollows is relevant for micro-bat and small parrot species but not for large owls or duck species that require large internal chambers.
Target species lists the fauna species of conservation significance for which the tree provides or potentially provides habitat. This field drives the regulatory significance determination — a tree with confirmed large hollows and a target species list that includes a vulnerable species will trigger a specific assessment pathway regardless of its position on the development plan.
Status is the assessment outcome: retained, to be further assessed, impacted, offset required. GPS location with Site, Plot, and Tree ID create the spatial record that links the assessment database entry to the survey map — the connection that allows the ecologist to relocate the specific tree during a follow-up assessment or before site works commence.