Vegetation classification system using remotely sensed
data for Viet Nam's condition
Existing methods of vegetation classification
Plant communities have many characteristics features, that it is not possible to use them all in devising a method to classify vegetation. In the last about 100 years, various systems have been developed to describe and to classify vegetation cover. Schimper's vegetation classification system was the first one (Schimper, 1898). During the last century, many classification systems of vegetation have been given to describe and to classify vegetation on the world as well as regions and countries. However, it would be impracticable within the framework of this report to discuss them in detail. Here follows the list of the main vegetation classification systems which have been given during the last century: Warming (1909) , Tansley and Chipp (1926) Kuchler (1949), Elenberg (1956) Densereau (1957), Fosberg (1958, 1961) Trochain (1957, 1961), Gaussen (1959, 1967) Holdrige (1967) Elenberg and Mueller-Dombois (1967, 1974)............etc and at the global level -UNESCO'S International classification and mapping of Vegetation (UNESCO, 1973) provides a comprehensive framework for the more important categories to be used in vegetation maps at scale of 1/1,000,000 or smaller . In their work, P.Legris,F.Blasco (CNRS, University of Toulouse, France) and K.D.sing (FAO,Rome,1985)have summarized of existing classification systems for vegetation in Asia and Pacific Region.
In Vietnam, we can mainly refer to the vegetation classification systems by Chevalier (1918) , P.Maurand (1943) Rollet (1962) M.Schmid (1956,1974) Thai Van Trung (1963, 1970, 1978) , Tran Ngu Phuong 1970 and Phan Ke Loc (1984).
However, such classification can not be used in interpreting
ACRS D-7-3
Remotely sensed data. It can provide general indicative information about the nature of vegetation types.
Based on Raunkiaer's life-forms, Howard (1969) developed and classification based on remote Sensing to describe vegetation formations and sub-formations in Eastern Australia andEast-Africa using Serial photographs. Howard,J.A. and Shade, J. (1982) introduced a standardized hierarchical classification of vegetation for remote sensing. Howard , J.A.,Z.D. Kalensky and F. Blasco (1985) presented conee-concepts for Global Mapping of woody vegetation using Remote sensing data. Anderson and other (1976) , Maling Greau (1977) introduced land cover/ land use classification use with Remote Sensing data in Indonesia…….
However, these vegetation classification are not suitable for Viet nam's conditions.
Vegetation classification system of Viet Nam
Viet nam is situated in the East of the Indochina peninsula, in the tropical monsoon area of South East Asia. The annual average rainfall varies from one region to another, from 1,500 mm to 2,500 mm(min. about 600 mm, and max about 45 00 mm ) The landform is complex . Average temperature changes from 23 oc to 27 oc . Because of its intermediate position , Viet nam contains elements of the floras of Indonesia, Malaysia, Myanma, China and India. This is results in an abundant and varied flora and vegetation in the country. However, after the prolonged destruction of the war and human impact, the natural ecosystem of Vietnam have been destroyed and have changed former vegetation into a complex mosaic of secondary vegetation replacement communities .The application of the classification systems mentioned above proved unsuitable for the classification and the mapping of actual vegetation of Viet nam.
- General principle classification of vegetation using Remotely Sensed data
In general, principle classification of vegetation using remotely Sensed data is based on the spectral nature of remote sensing data. The spectral nature of remote sensing data is one of the major element for their application to vegetation studies. Remote sensing is usually concerned with the characterization of plant formations in terms of stand height and crown cover. The height of the stand is considered to be most consistent physiognomic parameter to describe a formation (Raunkiaer,1934; Kuchler, 1967). When remotely sensed data are the principal data for mapping purposes which is normally the case for large area mapping programmes, the information about land cover that can be directly derived from the imagery should form
the basis for a classification system. A vegetation classification system should be designed according to the following principle:
- The classification system should have categories that could be directly interpreted from imagery, taking advantage of the ground information as well as the ancillary information available.
- The level of interpretation accuracy should be high.
- The results can be repeated by a number of interpreters using imagery of different seasons
The distinctions based on height classes are as follows
(FAO, 1982) :
|
>7m | Forest |
| 0,5cm to 7m |
Scrubs |
The crown cover classes are listed below :
|
>40 percent | Closed forest |
| 10-40 percent | open forest |
| <10 Per cent | Non-forest |
The each unit of classification of vegetation was described by its physiognomic structural characteristics with some supplementary ecological information .The units of vegetation were interpreted has based on the different intensities of the colour tone of the image and each one was described according to the results of the field check.
