The strongly incised mountain landscape of northern Thailand has changed dramatically during the last few
decades due to increased population pressure, agricultural commercialization, limitation to use old fallows and
reforestation of upper catchments. The traditional shifting cultivation with fallow periods of 7 years and longer
was gradually replaced by 1 to 4 year fallow periods. As a result, in high population areas the landscape became
dominated by fields planted to rainfed upland crops, wetland rice terraces, fallow vegetation, and patches of
secondary forest. This new land-use system seems to have triggered new land degradation processes that are
easy to observe when travelling through this landscape.
The objective of this research was to assess the multiple effects of land-use intensification in a tropical
steepland environment on land degradation processes. A case studywas conducted at Pakha village (located in
Thailand's northern most Chiang Rai province), which is dominated by steepland with average slope gradients
ranging from 30 to 70%. Soil erosion processes were monitored in a selected catchment for 2 years, and informal
interviews were conducted to elucidate farmers' perceptions regarding land degradation processes.
The rapid land-use changes at the Dze Donglo catchment (164 ha) resulted in severe and accelerated land
degradation, including tillage erosion (386 ton/year), inter-rill and rill erosion (502 ton/year), gully erosion
(423 ton/year), and landslides (7572 ton during 1994). Water erosion is most common in intensively farmed
areas. The combination of runoff-generating areas, runoff-concentrating features and connectivity led to
extensive gully erosion. Landslides were most common in steep fallows and in wetland terraces along incising
streams. Many of these steepland degradation processes interacted with each other (i.e. rills with gully erosion,
tillage erosion with water erosion, gullies with landslides). The observed land degradation processes matched
very well with farmers' perceptions. This study enabled to identify potential land degradation hotspots and
indicates the necessity to analyze steepland degradation processes in a holistic way.