Research area: Thailand
Mae Sa Mai (Chiang Mai Province)
This area is
located in Mae Rim district, Chiang Mai province, and covers 10.5km2.
It extends from N 18° 51’ 01’’ to 53’ 55’’ and from E 98° 50’ 44’’ to
Mae Sa watershed with the Mae Sa Mai research area. Full
area is characterised by steep slopes, which are dissected by V-shaped
valleys.At middle slope position isolated hills occur, representing
remnants of former crests. The elevation ranges from 616m asl up to
1540m asl. The lowest point is located at the north-eastern boundary of
the area, where the Mae Sa Noi creek joins Mae Sa stream. The highest
point is found on a mountain peak at the southern boundary. The average
elevation of the area is approximately 1000m asl. The average annual
precipitation measured for 2001/2002 and 2004 at 820m asl was 1419mm
accompanied by an average mean temperature of 21.7°C. For 2005 an
average discharge of 11l s-1 km-2
within the lower part of the Mae Sa Noi catchment (SFB 564 database –
unpublished data) which corresponds to 347l m-2 a-1
runoff and percolation. Almost half of the area is covered with forest
with the primary forest on the eastern side degraded, but
intact. Deciduous trees and bamboo dominate the forest below 1000m asl;
above it consists mainly of evergreen trees, some pine trees, and
bamboo. Along the streams evergreen trees occur. There is no evidence
about human activities in this area before 1965. The two Hmong villages
Mae Sa Mai and Mae Sa Noi are situated in this subcatchment. Nowadays,
the subcatchment is influenced by Hmong people in the upper part and by
the activities of Thai people (Queen Sirikit Botanical Garden
single households) in the lower part. The Hmong originated from the
mountainous southern provinces of China. The movement of the Hmong into
Northern Thailand has started 1885 (Cooper 1995). In 1965 the Hmong
village in the study area was founded under the name Mae Sa Noi at a
higher elevation than the present village. In 1975 the villagers moved
to the present position due to water scarcity, and the name was changed
to Mae Sa Mai (Maxwell personal communication). In 2004 the village was
subdivided into Mae Sa Mai and Mae Sa Noi. Nowadays both
have together more than 2000 inhabitants (Sangkapitux et al. 1999).
Traditionally, the Hmong farming system consisted of swidden
farming, mainly growing maize, opium, and upland rice. During the 1970s
opium was cultivated as cash crop, maize for stock feed, and mainly
rainfed rice for subsistence (Irwin 1976). Since the 1980s various cash
crops were introduced. Nowadays lychee orchards dominate the
cultivation area. Only a very small area is covered with mango,
“Chinese” peach, or coffee plantations. The plantation of fruit trees
went along with irrigation activities.
Sa Mai research area.
Some areas have been reforested
with pine trees and some Eucalyptus sp. during the 1990s and with
native trees on ridges since 1998 (Maxwell personal communication). Due
to pressure by the Royal Forest Department a protected forest area has
been established in the south-eastern part of the subcatchment
(Sangkapitux et al. 1999).
Mae Sa Mai area roughly consists of 90% migmatite, 9% marble, and to
approximately 1% freshwater limestone. The predominant migmatite can be
subdivided into a granite dominated migmatite (20% of the area) and a
paragneiss dominated one (70% of the area). The paragneiss and granite
were dated by the German Geological Mission (1979) as Precambrian and
Palaeozoic, respectively. Within the paragneiss bodies of marble and
(very small) quartzite were found. While the paragneiss dominates the
central and northern part of the subcatchment, granite is merely found
in the northern part. Paragneiss bodies of variable sizes are preserved
within the granite. Paragneiss and granite have as common minerals
microcline, muscovite, and orthoclase. Additionally, the granite
contains albite and anorthite. The quartz content of the
paragneiss is around 6% higher than in the granite. This indicates
reduced weathering rates for paragneiss in comparison to granite.
respect to geomorphology the weak granites are found in valleys, like
the Mae Sa valley
in the north, while stronger paragneiss builds up the
surrounding mountain ranges.
are often covered with a thick and highly weathered regolith. Despite
this, the regolith
on paragneiss is mostly shallow and not so intensively weathered.
rates for the upper part of granite can be assumed. The different clay mineral contents also show the
different weathering intensities. Kaolinite and vermiculite
were developed in paragneiss and gibbsite in granite.In the western
part of the watershed marble was found in the paragneiss with body
sizes ranging from little veins up to a thickness of more than 10
meters. This marble shows clear karst features such as karren and
caves. At one site, freshwater limestone is precipitated below a karst
spring in the paragneiss-marble contact. The Quaternary freshwater
limestone also showed clear karst features in the form of a cave with
speleothems. Many prints of leaves and branches are preserved in the
freshwater limestone. The marble and freshwater limestone consists to
more than 98% of calcite.
The soil cover in the Mae Sa Mai area is
dominated by Acrisols covering about 70% of the surface, while the
remaining 25% are represented by Cambisols,Anthrosols, Chernozems,
Gleysols, Leptosols, and Regosols (see Figure below).
map of the Mae Sa Mai area.