Hewitt - Natural Capital Vegetation Assessment - Narwietooma.

Hewitt.

Vegetation Environmental Asset Account.

Environmental Account ID: AU00062
Account Holder: Hewitt
Purpose: Measure the condition of native vegetation to communicate and inform sustainable land management decisions
Current land use:
Agriculture - Pastoral properties
Environmental Asset: Vegetation - Native
Asset Account ID: AU00062V1
Registration date: 10 October 2023
Baseline Certification date: 10 February 2025
Certification pathway: AfN-Verified
Accredited Expert/s: Anu Singh, Mitchel Rudge
Asset Account area: 1,150,867 ha (100% of property area)
Method:
AfN-METHOD-V-10

Environmental Asset Account snapshot.

Environmental Asset Account Econd® summary.

Environmental Asset Account statement.

Significant outcomes.

The overall Econd® was found to be 83.5, which demonstrates that the properties have been well maintained. The predominant vegetation types are shrublands dominated by Mulga tall shrublands, spinifex, Acacia on hard spinifex and Alluvial woodlands. The properties contain vast productive areas that are grazed by beef cattle. The sub-asset scores were fairly consistent, demonstrating the consistent management and condition state across the Environmental Account. While still a strong score, the Mulga tall shrublands sub-asset exhibited the lowest sub-asset Econd® (75.8), while the Sandy Red Earth (SRE) spinifex/mulga plains recorded the highest sub-asset Econd® (92.9).

Eragrostis subtilis was observed near the western side of Lake Lewis (SE of Tilmouth Well), and at sites north of the Stuart Bluff Range. Significant vegetation communities include small pockets of cracking clay soils around the Mt Chapple area on Narwietooma, and around Qualpa Dam on Glen Helen. The ecologists identified potential presence for night parrots in Triodia longiceps patches in the northern part of Napperby. Spinifex/mallee communities identified in the southern half of Glen Helen may reach long-unburnt stage in the absence of burning and large wildfire events; these can be important areas for birds (e.g., rufous crowned emu wrens, not recorded on surveys but present in similar habitat on adjacent Tjoritja/West MacDonnell National Park) and reptiles (e.g., jewelled gecko) that rely on large spinifex hummocks for shelter.

Limitations & disclosures.

Uncertainty in ground layer indicators - arises from combining field observations with drone-derived estimates, leading to inaccuracies in cover classification and spatial variation. This issue was amplified at Ambalindum, where litter data were estimated from photographs, causing discrepancies between drone imagery and benchmark values. Future work may benefit from direct observation of drone imagery.

Cryptogam cover - was excluded from the account due to the difficulty of developing benchmarks without large regional datasets. While field observations of cryptogams were collected, they were not included in the final condition score calculations. These observations have been preserved and could be used if benchmarks become available in the future.

Native tree size structure - was excluded from the account due to significant uncertainty. The method involved converting DBH-based benchmarks to tree crown characteristics using drone data. However, errors in tree segmentation and uncertainties in the benchmarks led to unsatisfactory results. As more accurate benchmarks and segmentation methods become available, this indicator may be revisited in future accounts.

Classification accuracy - at certain sites reduced the model's overall reliability, due to high-resolution data noise, blurred indicators, and canopy height model inaccuracies. For sites with less than 50% accuracy, a manual approach was used to calculate cover proportions. These sites were excluded from validation, preserving original data for future re-processing with improved classification methods.

Coarse woody debris - the computer vision model for segmenting and classifying coarse woody debris lacked sufficient accuracy. Instead, coarse woody debris was manually digitised using a line draw tool in Drone-Deploy within 0.1-hectare sub-plots at each site. The total line lengths were summed and multiplied by 10 to estimate debris length per hectare.

Last update: 02 September 2026

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