The Full Picture

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been described and studied. It is also necessary for them to

develop a working, mappable classification system that

covers all vegetation, ecosystem and land cover classes.

An example of a rapid assessment is a recent scien-

tific investigation to map a globally significant

occurrence of a freshwater/groundwater inland lowland

swamp forest in the Kompong Thom, Kratie, Stung

Treng and Preah Vihear Provinces west of the Mekong

River in Cambodia. There is scant description of this

type of forest, being mentioned previously only by

Béjaud in 1932 (translated from the French):

“On sandy humic soils in the places constantly moist,

which Cambodians call

Chom

(literally source or spring)

develops a shrubby vegetation dominated by the rattans

Phdau Som

, the

Prinh Kantuoy Chke, Chom

“In certain ponds that never completely dry, one finds

the

Smach Chanluos

of the rear mangrove. They do not

reach the large dimensions as when in their real habitat;

even sometimes their growth remains shrubby.

Cambodians then call them

Smach Tachak

. On other areas

occurs a corky plant

Chamrong Pras Ream

.”

Expert opinion concurs that Prey Long represents a glob-

ally, regionally and locally significant occurrence of this

previously unidentified swamp forest. The Prey Long forest,

however, is under increasing pressure from logging.

Conversion and selective logging have an impact not only

on the ecological integrity of the forest and the services

that they provide in terms of water and soil conservation;

it also impacts the livelihood of the local peoples who make

their living from sustainable use of the forest resources,

especially from resin tapping. The GEO ten-year plan calls

specifically for the continuity of high-resolution imagery

for monitoring logging concessions in areas with high

biodiversity concentrations, as well as for biodiversity

conservation and ecosystem protection.

The objective of this study was to perform a systematic,

rapid assessment of the groundwater swamp forests of the

Prey Long region, to map their extent and condition and

to detect changes in forest cover due to land conversion.

Landsat Thematic Mapper data were obtained for 2002

and 2004, and used to detect changes in forest cover.

Systematic flight lines were laid out, and the aerial survey

collected digital colour photographs of the study area.

While Landsat data are generally acceptable for mapping

forests, in this case they could not be used to locate the

sparse palm trees indicative of the wetland forests. These

were readily detectable in the aerial photographs. Global

Positioning System coordinates that were collected simul-

taneously with the aerial photographs were used to guide

the field team to the location of specific patches of forest,

and even individual trees.

In conclusion, rapid assessments take advantage of

current and historic satellite data because of their synop-

tic cover, and spatial and spectral resolution. Aerial data

provide the intermediate resolution between the satellite

perspective and the field observation needed to under-

stand the vegetation condition. It is therefore an invaluable

tool for biologists and resource managers.

significant investment in assembling these datasets so that they may

be used in tandem to predict vegetation and ecosystems occurrences,

and processes. Rapid assessments also require technological capacity

and integration of many types of data.

Rapid assessments also require that biologists and ecologists conduct

a complete review of the literature on the site’s biology and ecology. This

enables them to understand what vegetation and ecosystem types have

The Global Positioning System coordinates and aerial photographs were

used to guide the field team to the location of specific patches of forest, and

even individual trees

Photo: Douglas Muchoney

While Landsat data are generally acceptable for mapping forests, in this case

they could not be used to locate the sparse palm trees indicative of the wetland

forests. These were readily detectable in aerial photographs

Photo: Eva Galabru

OCIETAL

ENEFIT

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COSYSTEMS