The management and sustainable use of Central Australian rangelands for
livestock production and conservation requires improved knowledge of the
temporal and spatial distribution of primary production in this region. To provide
such information, this thesis investigated methods that could rapidly and efficiently
estimate regional herbage biomass production in these arid landscapes. Two
different approaches were examined, using (1) ground-based or (2) satellite-based
data sources.
Soil moisture and herbage growth data were collected over several growth
seasons and five landscape types in Central Australia, and the data used to develop
a model of soil moisture balance and herbage production for the region. The
model has few parameters and only requires inputs of rainfall and potential
evaporation to predict daily soil moisture and plant growth. Moisture loss in the
0-500 mm soil profile was modelled using a negative exponential function that
depends on available soil moisture and is driven by potential evaporation. The
growth of herbage, whilst soil moisture is above wilting point, is a linear function
of actual evapotranspiration, with the decay of plant material represented by a
logistic curve through time.
Soil moisture, herbage biomass and species composition assessments made
at hectare and square kilometre scales at four locations within Central Australia
were examined to determine if a small sample area could be used to accurately
describe the soil and plant conditions at a landscape scale. Moisture levels of the
0-200 and 0-500 mm soil profiles from nine samples were analysed for the
beginning and conclusion of a growth season, whilst herbage biomass and species
composition from 50 samples were compared at the end of the growth season.
Results suggest that mean soil moisture levels determined in a 1 ha area are
comparable with mean values in the surrounding 1 km2 area. Herbage biomass
and species richness for a square kilometre can be assessed at a hectare site for
some landscape types, but a larger sampling area (> 1 ha) is recommended for
most rangeland assessments.
Satellite data (NOAA-11) were examined for their potential application in
assessing primary productivity in Central Australia. Several image correction
techniques were tested to minimise the adverse effects of atmospheric
contamination and illumination. Two measures of atmospheric moisture: (1)
radiosonde data and (2) temperature differences between bands 4 and 5 of the
NOAA satellite (split-window) were used to explain variations in NOAA-11
normalised difference vegetation index (NDVI) on inert desert sites. The splitwindow
approach provided the best single factor relationship (r2=0.63) and, when
combined with scattering angle (illumination) effects, up to 81% of the variation
in NDVI data could be explained.
Field measurements of herbage biomass were correlated with four growth
indices derived from NOAA-11 NDVI data. The influence of preflight and sensor
degradation calibrations of Bands 1 and 2, and atmospheric correction techniques
were also tested. Correlations between temporal sums of NDVI and herbage
biomass data were relatively poor (r2<0.42) and unsuitable for herbage
assessment in Central Australia. However, correlations between atmospherically corrected
and background-adjusted maximum NDVI data and observed herbage
biomass were strong (r2=0.91), that will allow primary production in the arid
rangelands of Central Australia to be assessed rapidly and efficiently using
remotely-sensed information.
| Identifer | oai:union.ndltd.org:ADTP/219024 |
| Date | January 1994 |
| Creators | Hobbs, Trevor J., n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Trevor J. Hobbs |
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