me XXXIX-B3, 2012
the mapped occurrence of
/andoo occurrence were
nd knowledge (figure 1).
ies (jarrah and marri) and
» powderbark wandoo (E.
s not capture all wandoo
nds that are not wandoo.
this region enables broad
s to be made.
ING
spectral index images that
stigated and vary linearly
cated using a combination
magery shown in equation
(I)
nd in other studies in the
strongly related to changes
1 Behn 2009, Garkalis and
2d for all available images
) image was later removed
understorey growth not
y. In the winter of 1999
rainfall was higher than
the analysis meant that it
nage sequence and caused
alculations.
for several time periods
(Draper and Smith 1980)
thematics, Informatics and
contains the slope value
f 0-255. Firstly the trend
02-2010 were calculated.
xamination of long term
; individual image date
assified into five classes;
in and gain cover classes.
ind the classes compared
boundaries were modified
the Land Monitor Project
vere calculated using four
rend images were created
e one date at a time. This
occur over several years
or drought which have a
al. The decline does not
but is diverse in its effect
trend epoch length and
late the opportunity for
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B3, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
identifying the effect of WCD across a large geographic area is
increased.
4. INVESTIGATION
41 General descriptive statistics
These give an overview of the dynamics across the whole of the
wandoo occurrence. From the sequence of index images the
year of highest and lowest cover can be determined for a pixel
and the areas summarised. ^ The majority of areas with the
highest cover were in the period 1990 to 1998 with 1990
covering 40% of the wandoo occurrence (figure 2). The largest
areas of lowest cover occur in the period 2002 to 2010 with
2008 covering 2846 of the area.
[J Year Highest Vegetation Cover
BEN Year Lowest Vegetation Cover 80
— Mean Annual Rainfall (BOM)
>
wv
40 - r70z
3
35 1i 60 =
30 4 3
| $02
25 m
| 40 1
m
30
ei i | ] :
à co co c^ c cO cQ cv cv co cà co co ce co A
e co. Lo S
PFS SAINI AS OASIS OSES
Year
=
bs]
e
(wo) jjeju
% Area of Wandoo Occurrence
ua
ce
9 c9 ov a.
bcd 9
FESS
Figure 2. Bar graph showing percentage of wandoo occurrence
area for each year in the image sequence with the highest and
lowest cover. Line graph shows mean annual rainfall across
wandoo occurrence from interpolated rainfall data (Bureau of
Meterology Australia).
The longer trend epochs provide a general view of what is
happening in the wandoo woodlands without being as affected
by seasonality as the index image sequence and four date trends
are. The long term trends show that the largest declines
occurred during the period 1990-2002, this correlates with the
observations of WCD in the late 1990's (Wills 2005, Manning
2009). Any decline in this period would be exacerbated by the
1990 high cover image. In the 2002-2010 period declines are
still occurring, but not over the same extent, this change in
decline area has been observed in Mercer (2008). In the 1990-
2002 epoch the percentage area of the small decline class is
4696 compared to 3646 in the 2002-2010 epoch. The stable area
has increased from 31% to 40%. Gain areas have increased in
the more recent epoch with the small gain class changing from
2% to 4% and the gain class from 0.8% to 1.7%. Recovery of
previously impacted areas has been observed in recent years
(Whitford et al 2010).
42 Where does wandoo crown decline (WCD) occur?
Red and blue displays of the long term linear trends enable
geographic identification of areas of loss and gain in cover.
These are constructed by assigning the slope component
indicating decline to red and the gain component to blue. This
approach was used with success in the Garkaklis and Behn
(2009) study. Fire and other disturbances have not been
removed from the trend calculation and need to be understood
when examining the image. This type of display is very
effective in communicating where there have been impacts on
the vegetation cover.
The effect of fires on the trend imagery can be mitigated by
using the four date trends in the same display process. The
image date with a fire impact will influence these trend images,
but will not have the enduring impact on the sequence it does in
the long term trends.
43 In what time period does WCD occur?
In the four date trend epochs decline is apparent in all images.
Comparison of the magnitude of declining trends above stable
(i.e. slope) for all four date epochs yields interesting results. On
a per pixel basis the maximum declining and gaining values
above stable were determined and the epoch identified. Area
calculations show that the greatest area of declines are observed
in the 1996-2003 epoch (figure 3), with 4696 of the wandoo
occurrence. Other large areas of decline occur in the epochs
1994-2002 (10%) and 2004-2007 (12%). This method assists to
increase the certainty of determining when declines occurred
and is more specific than the longer term trends.
[1 Epoch Largest Gain
E Foch Largest Decline
50 ean Epoch Rainfall(BOM) ^ . 60
8 45- |
£ |
9 40- z
5 D
9 35. >
Ô =
o 3 9
| o
$25. =
: ?
= 20 - | 5
5 15 4 [20 B
$ $
ul n A.
CD VD STD ES SH S LS AS
P dV qM qe qu V gU quo go q^
ua NN LN quU NUN
Epoch
Figure 3. Bar graph showing percentage of wandoo occurrence
area for each four date epoch with the largest declining and
gaining trend in cover. Line graph shows mean epoch rainfall
across wandoo occurrence from interpolated rainfall data
(Bureau of Meterology Australia).
4.4 Is there recovery from the decline?
From previous studies of WCD and the four date trends the
greatest observations of crown decline were in the period 1998
to 2003. Therefore the trend classification of the period 2002-
2010 should show some of the recovery. In this epoch the gain
and stable class areas have increased and the decline class areas
decreased compared to the previous 1990-1998 epoch
When querying the sequence of four date epoch trends the areas
with a gaining trend above stable only covered 62% of the
wandoo occurrence, whereas the decline trend area covered
96%. Of the areas with a gaining trend the largest trends are
observed in the epochs 2003-2006 (20%) and 2007-2010
(10%). In five years of surveys from 2006 to 2010, by the
