Appendix 2 - Vegetation Communities and Regional Ecosystems

3.6 Scale of Survey
In vegetation survey, sampling scale is determined by sampling intensity, influenced by
vegetation complexity and the areal extent of remnant vegetation. The Agricultural Organisation
of the United Nations (FAO 1979) recommends 25 sites per km 2 for 1:10 000 scale soil survey,
although Neldner et al. (2005) recommend a minimum of half of this sampling density for
vegetation survey, dependant on the vegetation complexity and areal extent of remnant
vegetation. Reference to Table 5 indicates 1 372 survey locations recorded during the initial
phase of field survey, with an additional 34 sites recorded during previous mapping exercises
(EPA Corveg sites). Resultant sampling equates to roughly 1:25 000 scale, based on a total land
area of 892 km 2 and minimum site requirements as per Neldner et al. (2005). This data is suitable
for incorporation into detailed state wide regional ecosystem assessments at present sampling
intensity, although additional sites will be gathered during any subsequent survey phases.
The spatial scale and accuracy of a mapping product is determined in part by the scale of the
image base used for vegetation community delineation. Reference to Table 4 indicates
considerable disparity between aerial photographic scales used in the assessment, ranging from
1:4 000 scale on Iama Island to 1:85 000 on Moa. This disparity in spatial scales was addressed
to a degree during the photo rectification process, whereby photographic line work was registered
against satellite imagery at a standardised 1:25 000 scale, as required in the project brief. Whilst
this process will have rectified disparities in spatial scale between islands to a large degree,
variations in the scale of vegetation community delineation between islands as well as spatial
accuracy of vegetation linework can be expected.
3.7 Image Interpretation and Attribution Method
Aerial photography was purchased as contact prints and subject to detailed stereoscopic
assessment. The aim of stereoscopic analysis is to delineate consistently mappable units
(polygons) of homogenous vegetation characterised through similarity of aerial photographic
pattern or signature. During this process, geological and vegetation community boundaries were
marked directly onto the aerial photography with removable white china ink, and a 0.25mm
Rotring pen. The width of vegetation line work produced was between 0.25mm and 0.5mm with
finer line work resulting in a more accurate delineation of vegetation community boundaries.
Polygon attribution is based on a hierarchical system identifying landform/geological affiliation,
vegetation structure, and floristic composition. This stratification was consistent with basic rules
of vegetation classification detailed in Section 3.5.
Where suitable aerial photographic material was not available, satellite imagery was used as a
base for vegetation community delineation with vegetation line work established directly on the
digital image and incorporated into the broader spatial database. In the case of Saibai Island,
where suitable aerial photographic coverage was available for only half of the island, the line
work established during aerial photographic interpretation was extrapolated across the broader
study area, over the top of available satellite imagery.
3.8 Pre-clearing Vegetation Method
The oldest available photographic imagery was utilised to establish pre-clearing vegetation
communities within the study area. Vegetation line work was established on these photographs,
attributed accordingly, and overlain with the recent satellite imagery to determine the extent of
clearing. Vegetation polygons were clipped to cleared boundaries on recent imagery to produce a
‘Remnant Vegetation Layer’.
3d Environmental – Torres Strait Regional Ecosystem Mapping Project – August 2008
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