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Forestry |
An
evaluation of LANDSAT MSS and TM data for
mapping vegetation change since European
settlement for conservation management
Waqar Ahmad
Department of
Geographical Sciences &
Planning
University of Queensland, Brisbane,
Australia
Abstract
In order
to formulate appropriate management and
conservation strategies, the Department of
National Parks and Wildlife Service (NPWLS) in
the state of Queensland, Australia, require a
knowledge of the past and present distribution
and status of different land cover types of the
state.
Presently, Queensland NPWLS
department rely on vegetation change map based
on historical and recently acquired aerial
photographs. These change maps are characterized
by four categories. Category 1 (Minimal or no
discernible changes from original condition i.e.
pre European settlement), Category 2 (Moderate
change from original condition), Category 4
(Complete change from original condition).
In this paper an attempt have been made
to evaluate the applicability of Landsat MSS and
Thematic Mapper data for replicating the above
vegetation change for a shire. Image processing
technique followed, results obtained and
accuracy assessment procedure followed is
discussed.
Introduction
Various agencies
responsible for managing and conserving their
natural resources are increasingly under
pressure because many of these resources are no
longer plentiful. In addition, many natural
resources are obviously being degraded as a
result of inappropriate human actions. Maps of
natural resources are an important basis for
nature conservation. These maps allow natural
features to be identified, located and described
and their relative extent and conservation
status to be assessed (Pressey and Bedward,
1991). The conservation of some National Parks
and Wildlife Service (NPWLS) in the state of
Queensland, Australia, is involved is dependent
upon a knowledge of the past and present
distribution and status of those components.
Such knowledge with respect to the flora of the
State is required for selecting reserves that
represent the diversity of the flora of the
State; planning rural nature conservation
programmes and actions; responding to
environment investigation agencies, town plans
and monitoring the change in the status of
vegetation communities and hence the
effectiveness of the services as a conservation
agency.
Stanton and Morgan (1977) have
mapped the state of Queensland into biogeography
regions and sub-regions. However, this study is
not detailed enough to properly plan for nature
conservation. In order to assess the present
distribution, air photo mapping at 1:25,000 and
1:100 000 scales has been used to test the
feasibility of depicting present vegetation
ground cover both on a land system and
vegetation community basis. This has been found
quite satisfactory. Ideally, such type of
mapping and assessment should be done at a
regular interval. However,
Presented at
the Twelth Asian Conference on Remote Sensing,
at Regional English Centre, Singapore, Oct. 30 –
Nov. 5, 1991. the time required for
interpretation and later processing and storing
the information is considered impractical for
general application.
For the shire of
Gatton, Queensland, the Department of NPWLS has
mapped four classes of change by comparing these
with the original pre-European settlement data.
Class 1 showing minimal or no discernible
changes from original condition i.e. majority of
the original cover types still present. Class 2,
showing moderate change from original condition.
This class represents changes as a result of
either selective logging or grazing improvement.
Class 3 showing considerable change from the
original condition i.e. considerable alterations
mainly because of clearing for agriculture and
grazing. Class 4 representing complete change
from original condition i.e. complete removal of
original vegetation.
Main purpose of
this study was firstly to evaluate the
applicability of Landsat MSS and Thematic Mapper
data for depicting these four classes
representing different degrees of vegetation
change. Secondly, to investigate the methodology
for periodic monitoring of vegetation change
enabling quick and accurate evaluation of the
nature conservation management policies.
Study Area and Changed Classes
Assessment
The research was undertaken in
the Gatton Shire of Queensland. The northwest
and southeast coordinates of the study area are
27° 44’ 05” N, 152° 25’ 15” W and 28° 02’ 15” S,
151° 54’ 03” E. The major reason for its
selection was the existence of map showing
distribution of four categories of changes.
Moreover, the recent aerial photographs,
vegetation type maps and other ancillary
information were available.
A field
survey of the study area was conducted prior to
image classification. This was done so as to
gain some familiarity with the study area and to
determine the number of land cover classes which
could later be identified using remotely sensed
data. A rectified colour composite image of the
Landsat raw data covering the study area was
produced at a scale of 1:100 000 on an Applicon
inkjet plotter and taken to the field. During
this visit, major land cover types of the study
area which could be easily identified were
marked on the laminated Landsat image. This step
was accomplished with the help of field staff of
the department of NPWLS who had extensive
knowledge of the study area.
In some
case a difference in the colour or texture of
the image was related to information gained from
photo-interpretation maps. The vegetation
characteristics and other relevant information
such as landform pattern and forest density were
also recorded for each of the sites visited
during this trip.
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