Woody Vegetation History
Remnant vegetation plays a crucial role in the maintenance of land condition and water
quality. It is also important for conservation and aesthetic reasons.
Calibrated sequences of satellite images can be used to provide broadscale information
on the present condition of remnant vegetation, and how it has changed through time. The
same techniques can also be applied to assess disturbance and recovery in forest areas.
Image maps can be produced which summarise the changes within an area of interest. The
impacts of short-term disturbances can be separated from long-term decline or recovery.
The vegetation history image above was formed by combining image
data from three dates (1990, 1994 and 1996). Vegetation condition index values
from 1990 are displayed in blue, from 1994 in green and from 1996 in red. The
different colours in the image show different changes in vegetation condition
through time, where:
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shades of grey indicate unchanged woody vegetation;
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shades of red indicate areas where the woody vegetation
cover decreased after 1994;
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shades of green indicate areas where the woody vegetation
cover decreased after 1990 and increased again before 1996; and
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shades of blue indicate areas where the vegetation cover
increased between 1990 and 1996.
In this region typical causes of vegetation decline include
logging, fire and clearing for agriculture. Typical causes of increase in
vegetation cover are recovery from logging and fire and new plantations. The
following images show parts of the above image in greater detail.
The area shown above includes areas of state forest that are
dominated by karri forest and cleared agricultural land. Logging patterns can be
clearly seen in red and green within the karri forest. Red areas were logged
after 1994, while green areas were logged between 1990 and 1994 and are
regenerating. There are also numerous new plantations of bluegums shown in
shades of blue. Dark blue indicates areas that were planted between 1990 and
1994 and light blue (cyan) indicates areas planted after 1994.
The area shown above is dominated by jarrah-marri forest and the
colour variations relate to managed burning of the forest to control fuel
loads and prevent uncontrolled fire.
This image shows the transition from jarrah forest in the west
to karri-dominated forest in the east. The spatial pattern of the coloured
regions reflect different forest management strategies particular to the
vegetation type. The large disturbances on the left are typically caused by
controlled burning rather than logging since the jarrah forest is logged
selectively. The disturbances on the right are caused by clearfelling of the
karri forests.
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