IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002
interpretation from both original and texture processing allowed
mapping of the following land cover categories: bare sand,
sparsely cover sand , sand covered by medium density of shrubs
and areas of high shrub density. Individual trees and areas of
Acacia saligna were recognized by combining field assessment
and visual interpretation techniques.
Figure 1: Aerial Photographs of the study area from two dates
4. RESULTS
Over the research time frame of 34 years, the area covered in
acacia grew from 36.7 ha in 1965 to 97.8 ha in 1999, an
increase of 166% at an average annual growth rate of 2.92%.
The growth rate of the area covered by indigenous vegetation
increased during this period from 179 ha in 1965 to 314 ha in
1999, or a total increase of 75% at an annual average growth
rate of 1.67%.
Beyond to the distinctive difference between the overall rates of
expansion a significant insight could be gained by looking at the
average yearly rates between the photographs’ dates (Table 1)
for four cover categories: Dense Acacia/indigenous vegetation,
total Acacia / indigenous vegetation
Table 1 : Average Yearly rates of growth
1965 1974 1982 1990
Years/Veg. Type to to to to
1974 1982 1990 1999
Dense Acacia 0.2% 2.4% 5.3% 5.9%
Total Acacia 1.2% 3.9% 2.8% 3.5%
Total Ind. Veg. 1.7% -0.3% 4.4% 1.7%
Dense Ind. Veg. 1.7% -2.1% 11.6% 1.4%
Differentiating between the dense and the total vegetation cover
classes infer also regarding the role of the sparse and vegetation
f medium cover density. Looking at the increase in the total area
of the Acacia reveal the two phase behavior of the Acacia’s
expansion: the slow down between 1982 and 1990 represents
the exploitation of the growth from sand disturbed areas (the
first phase) and the initiation of the penetration into the dense
indigenous vegetation, then the second increase n the rate of
expansion is representing the massive spread into the areas of
indigenous vegetation areas in general and the dense vegetation
in particular. The fact that the dense indigenous vegetation is
the main cover type which is replaced at the domination phase
of the Acacia invasion is apparent both from its drastic decrease
in expansion between 1990 and 1999 and from a GIS overlay
analysis.
S. CONCLUSIONS
A remote sensing study using historical aerial photographs
allowed better understanding of the landscape changes in
general and of the rates and modes of the Acacia saligna
invasion in particular. Although the awareness to the high rates
and the consequences of biological invasions are well
appreciated there are not many studies, which reveal the mode
and temporal patterns of such invasion. Describing the invasion
utilizing two phase model is relatively new, and could
contribute to the management decisions concerning control
measures over the spread of vegetation in the sand dunes areas
to allow the survival of shifting dunes in the coastal zone.
6. REFERENCES
Arnold, D, 2002, The photogrammetry of shifting Dunes:
volumetric changes in the Coastal Dunes of Nizanim 1956-
1999. MA Thesis , Environmental Information Laboratory, Bar-
Ilan University, Israel.
Baker, H.G. 1986. Patterns of plant invasion in North America.
In: H.A. Mooney and J.A. Darke (eds.). Ecology of Biological
Invasions of North America and Hawaii. Springer-Verlag, New
York, NY. Pp. 44-56.
Barzilay, E., Tsoar, H. & Blumberg, D., 1998. Dynamics and
morphological changes that occurred in the Ashdod sands over
the past 50 years. Proceedings of Israel Geographic Conference,
December 16-18, 2000, Bar-Ilan University, Ramat Gan, Israel
(in Hebrew).
Cohen, O, 2002, Vegetation cover changes in the Coastal Dunes
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Geography), Bar-Ilan University, Israel.
Goldberg, C. 1999. Killer Algae: The True Tale of Biological
invasion. Science News 156 (21): 322.
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