Full text: Proceedings of the Symposium on Global and Environmental Monitoring (Pt. 1)

2. STUDY AREA 
2.1. Location 
Mengyang Nature Reserve (99733 ha) is 
located in the Xishuangbanna Dai 
autonomous prefecture in th south of 
Yunnan province in the South est of the 
People's Republic of China. The study 
area forms part of the Xishuangbanna 
Nature Reserve, a discontinuous series 
of forest blocks totalling S'.me 200.000 
ha (Figure 1). 
Mengyang is shaped like a figure of 8 
on its side with the central 
constriction being where a major road 
cuts through. There are numerous 
villages and clearings in this central 
sector. 
Its landforms vary from riverine val 
leys (about .49%), hills (6.71%), low 
mountains (.89%), medium mountains 
(51.33%) and high plateau (40.58%). 
Most of the land lies between 1100 - 
1300 m a.s.l., but the highest hills 
reach over 1700 m. 
2.2. Vegetation types 
According to the physical regions clas 
sification by Ren Mei'e (1985), the 
test area forms part of the Southern 
Yunnan Intermontane Basin. The variety 
in relief and soil types, the latter 
mostly of the red soil type, combined 
with its location in the subtropical 
region, yields an exceptional richness 
of vegetation types. 
Mountains and rivers mainly run in a 
north-south direction favouring the 
penetration of humid and warn air cur 
rents from the south. 
The region features no marked contrast 
in seasons, but there ai e notable 
differences in rainfall. The wet season 
lasts from the end of May till the end 
of October, and brings 9C% of the 
annual rainfall. A somewhat cooler 
spring period lasts from the beginning 
of november till the end of March, and 
a warm spring period lasts only six 
weeks between early April and the mid 
dle of May. Fog is very common in the 
dry season. The resulting high air 
moisture content allows true tropical 
vegetation species to survive at a 
higher latitude than expected. 
The vertical distribution of forest 
types in Xishuangbanna is rather clear: 
1. Tropical seasonal rainforests below 
800 m 
2. Montane rainforest betweei, 800 m and 
1000 m 
3. Monsoon everqreen broadluaf 
between 1000 m and 1800 m 
4. Mossy evergreen broadle if 
above 1800 m 
Owing to the complexity of geo 
morphology, soil distribution and the 
variation in bioclimate in 
Xishuangbanna, the numerous vegetation 
types may criss-cross each 
even duplicate in transition 
The vegetation of Mengyang 
forest 
forest 
other and 
belts. 
reserve is 
mostly sub-tropical evergreen broadleaf 
forest. The most important species 
belong to the Fagaceae, with 
Castanopsis sp., Lithocarpus sp. and 
Cyclobalanopsis sp. This forest type 
has a somewhat discontinuous canopy. 
The trees are lower than in the ever 
green rainforest, and the diameters are 
seldomly larger than 40 cm (Verbist 
1990) . This forest type is mixed with 
bamboo in the western part of Mengyang. 
In the eastern part this forest type 
features open areas covered with grass, 
the weed Eupatorium sp. or scrub. 
Mengyang has small areas (1254 ha) of 
seasonal evergreen rain forest. The 
primary forest has an uneven, but 
closed canopy and, besides the upper 
layer, a secondary tree layer, a layer 
with small trees and shrubs, and the 
ground cover (Wang 1961). There is no 
dominance of single species. Important 
key species are: Terminalia bellirica, 
Barringtonia pendula and Antiaris 
toxicaria (Verbist 1990). 
There are extensive areas of bamboo 
forest (with Dendrocalamus sp.), 
especially in the western sector along 
the Lancang river. The occurrance of 
limestone hill monsoon forest, with key 
species Cleistanthus sumatranus and 
Celtis wightii, should also be 
mentioned. 
A long history of shifting cultivation 
has resulted in a patchiness of forest 
condition with many extensive cleared 
areas around the larger villages. These 
areas, which have lost their natural 
forest vegetation, are now classified 
as tall grasslands (with Imperata 
cylindrica, the telltale fire climax 
species), warm savannah scrub, economic 
plantations (mostly rubber) and agri 
cultural lands (MacKinnon 1988). 
3. MATERIALS AND METHODS 
3.1. Field data 
During field trips conducted in the 
summer of 1988, as much different 
vegetation classes as possible were 
indicated on enhanced pseudo-coloured 
hard copies of the TM image described 
below. Some classes yielding few re 
presentative pixels were dropped from 
further analysis. On the other hand, 
areas with particular homogeneous co 
lour, but that could not be visited, 
were selected from existing, albeit 
crude, vegetation maps of Mengyang. 
Additionally, some classes had to be 
divided into sub-classes due to their 
different aspect. 
3.2. Image material and preprocessing 
The image available was a Landsat-5 
Thematic Mapper image recorded on 2 
February 1988 (frame 139/45). Its co 
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