International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
signature of a species difficult to define. It is not however
practically feasible to determine the ideal wavelengths for
discrimination when large numbers of invasive species are
present. Furthermore, if the presence of number of invasive
species per pixel increases, the difficulty in identifying the
individual components that contribute to the mixed spectrum
also increases. These problems will be further aggravated if
species variability in spectral signatures is high. For large scale
direct remotely sensed monitoring of several invasive species,
the possibility of correctly identifying all individuals through
direct mapping thus appears doubtful.
5. SUMMARY AND CONCLUSIONS
In this article, we attempted to evaluate the potential of remote
sensing and GIS techniques for the critical task of invasion
mapping. Although the use of RS and GIS techniques for
mapping invasive species and invaded ecosystems is increasing
rapidly, the literature on means and methods for invasive
species mapping remains scattered and often contradictory.
Most of the IUCN's worst invasive species fall under our class
IV species, in which straightforward application of remote
sensing is almost impossible. Recent remote sensing and GIS
applications on detecting invasive species were mainly dealing
with species belonging to class I (Graph 3).
60 r-——————
7 OIUCN y mS 1
BRS & GIS
No. of species
| Il Hi IV
Species catagory
Graph 3. Classification of 100 world's worst invasive species
included in the list of International Union for Conservation of
Nature and Natural Resources (IUCN) and 100 world's invasive
species addressed in GIS and RS literatures (RS & GIS)
For instance, most of the understory species that have been
declared as the world's worst invaders by the ecologists have
not caught the attention of remote sensing experts. In the same
way species such as Melaleuca quinquenervia or Tamarix
ramosissima, which dominate entire ecosystems forming a
monotypic dense canopy, do not necessarily need the use of
high spectral resolution imagery and vice versa. It is not clear
whether RS and GIS techniques will prove equally strong for
mapping mobile invasive species such as Acridotheres tristis
(Bird), Aedes albopictus (mosquito) or Boiga irregularis
(snake). This needs further testing in the near future.
The status of many exotic species with respects to their
invasiveness is not well documented. Therefore the ability of
remote sensing and GIS techniques to monitor changes in
different ecosystems may be crucial if the effect as well as the
cause of rarity are to be assessed. Cases of actual applications
are still not much more than the traditional investigations.
Rapidly shifting interest in remote sensing and IGIS of bio-
invasion mapping has resulted in the development of a diverse
range of mapping techniques. But, the technology needs further
development in terms of real world applications in the mapping
of invasive species. Moreover, mapping, modelling and
predicting biological invasion will still be a major challenge for
ecologists because the biological processes involved are very
complex. This complexity makes it difficult to retrieve or
delineate invasions which occur in diverse ecosystems. As
Specter and Gayle (1990) pointed out the proliferation of new
technologies does not guarantee their application to real world
problems.
Although restricted to few taxa, studies revealed the potential of
remote sensing and GIS application in mapping and modelling
invasive species. Possibly, the greatest impacts of invaders are
caused by plant species that come to dominate entire ecosystems
as remarked by Simberloff et al. (1996). There are possibilities
of generating in-depth information in detecting, mapping and
analyzing the impact of invasion on an area or entire ecosystem
and species level properties. To enhance the result of invasion
mapping, there is a clear need of combined use of remote
sensing, GIS and expert knowledge. Management dealing with
invasive species requires accurate mapping and modelling
techniques at relative low costs. Development of those will be a
valuable step towards conservation of native biodiversity.
6. DIRECTIONS FOR FUTURE RESEARCH
The increasing number of sensors have provided spatial
ecologists with tremendous opportunities to advance the
application of RS and GIS techniques in mapping and
modelling the distribution of invasive species. Yet progress has
been slow. Application of remote sensing is strongly limited
when dealing with world’s worst understory plant species and
most of the animal species. In our view, progress will be
hastened if ecologists and remote sensing experts adopt
integrated approaches to their studies of invasions, including
GIS and RS techniques, modelling, meta-analysis exploration of
existing concepts, and full utilization of available pre- and post
invasion models to test emerging concepts. We argue that
spatial, spectral and temporal image analysis holds particular
promise since ecosystem boundaries can be delineated; species
biometry, expert knowledge and environmental data often
incorporate pre- and post-invasion phases.
7. REFERENCES
Allen, T. R., & Kupfer, J. A., 2000. Application of spherical
statistics to change vector analysis of landsat data: Southern
appalachian spruce - Fir forests. RS. Env, 74(3), 482-493.
Anderson, G. L., Everitt, J. H., & Escobar, D. E., 1996.
Mapping leafy spurge (Euphorbia esula) infestations using
aerial photography and geographic information systems.
Geocarto International, 11(1), pp. 81-89.
Anderson, G. L., Everitt, J. H., Richardson, A. J., & Escobar, D.
E., 1993. Using satellite data to map false broomweed
(Ericamera | austrotexana) infestations on south Texas
rangelands. Weed Technology, 7, pp. 865-871.
Barrett, E. C., 1980. Satellite monitoring of conditions
conducive to the upsurge of insect pests. in: Satellite remote
sensing. Applications to rural disasters. Proc. joint
ESA/FAO/WMO training course, Rome.
674
Inte
Bel
mal
47.
Ber
pho
Mai
Bre
rela
Mu:
Bry
Nev
Inte
Bud
L..
(Dr
Bay
213
Cars
of y
Tec]
Cog
spat
edit«
scal
Czec
of s]
116-
Dral
Krug
Biol
Wile
Eav,
phot
of F
ENV
Vers
Epp,
using
data
mant
Ever
Davi
range
pp. 9
Ever
Refle
range
Elect
Everi
M. F
plain
