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(Kep/ 1I) anog 18Au Apguour aDeJoAg 
Figure 4. Monthly mean river flow, monthly total rainfall and 
average ETrF values for the Barmah Forest between 
1993 and 2008 
4. DISCUSSION 
This study explored the potential of remotely sensed data to 
contribute to understanding the response of riparian vegetation 
associated with changes in water availability. Measures of ET 
and NDVI were derived from satellite data over a 16-year 
period. ET indicates water availability to existing vegetation, 
and can be used to assess areas under water-stress. NDVI 
provides a measure of vegetation cover and can be used as a 
measure of vegetation primary production or vegetation health, 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
which are important indicators of general forest condition 
(Dexter and Poynter, 2005; Sims and Colloff, 2012). 
The ET data showed a decline in ET rates of up to 50% for most 
of the forest (Table 1, Figure 2), in line with declining surface 
water availability and river flow volumes (Figure 4). These data 
suggest the entire forest had shifted into a water stressed state. 
In November 1993 average forest-wide ET rates exceeded a 
value of one due to the presence of considerable surface water 
following the large river flow volumes and rainfall events in the 
preceding months. The spatial pattern of flooding depends on 
topology and water volume, and the spatial representation of ET 
values reflects areas where flood and surface waters have a 
greater influence and highlights areas that remain drier. A high 
mean ETrF value of 1.28 for WAV in 1993 is indicative of 
surface water present within areas mapped as this vegetation 
type. This is expected due to the strong association of this 
vegetation type with surface water bodies, and has been noted 
for other vegetation associated with surface water (e.g. flood 
irrigated rice prior to full crop cover (Whitfield et al., 2010b). 
The response in NDVI was less compared with ET rates, which 
may reflect the slower rates of change associated with tree 
canopy cover compared with vegetation water use. There was a 
decrease of approximately 15 % vegetation cover between 1993 
and 2008, compared with a 40-60 % decrease in ET rates (Table 
1, Figure 3). This difference highlights the power and 
uniqueness of using multiple assessment indicators. A decline 
in tree crown condition and regeneration of tree species has 
been observed within the forest in other studies (Kingsford, 
2000; Peake et al., 2011). 
There was an increase in NDVI between 1993 and 2003, which 
may be associated with the above average annual rainfall (516 
mm) experienced in 2003. There was also an increase WAV 
cover (Table 1, Figure 3) between 1993 and 2008, which may 
be associated with either a decrease in surface water associated 
with this vegetation type, increased vegetation growth within 
the extent of this vegetation type, or a combination of both. In 
particular, there is a noted incursion of rush species and River 
Red Gum saplings onto the Moira Grass Plains wetland 
vegetation, which is associated with changes to water 
availability (Kingsford, 2000; Chong and Ladson, 2003; 
Lawrence and Colloff, 2008). 
The information extracted from the remotely sensed data used in 
this study provided objective quantitative assessments of the 
status and water use of riparian vegetation at key points in time. 
This information can be used in addition to other contextual 
data to provide assessments of status and water use when the 
vegetation is considered to be in *poor' condition, for example, 
in 2008 after multiple years of drought or in ‘good’ condition, 
for example, in 1993 when water supply was not considered to 
impact vegetation condition. While the information extracted 
for vegetation in ‘poor’ condition can be considered to be 
reliable, information for vegetation in ‘good’ condition may be 
biased due to the contribution of surface water to NDVI and ET 
estimates, particularly for WAV (Table 1). 
A limitation of the analysis presented is the use of only three 
images within the 16-year time frame. An improvement to this 
work would incorporate additional images to provide a more 
detailed picture of changes in ET rates and NDVI within the 
forest. The use of additional images would improve the 
evaluation of vegetation in ‘poor’ and ‘good’ condition as the 
  
      
    
     
  
   
  
  
      
        
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