Abstract The hydrological and geomorphological impacts
of traditional swidden cultivation in Montane Mainland
Southeast Asia are virtually inconsequential, whereas the
impacts associated with intensified replacement agricultural
systems are often much more substantial. Negative perceptions
toward swiddening in general by governments in the
region beginning half a decade ago have largely been based
on cases of forest conversion and land degradation associated
with (a) intensified swidden systems, characterized by
shortened fallow and extended cropping periods and/or (b)
the widespread cultivation of opium for cash after the
Second World War. Neither of these practices should be
viewed as traditional, subsistence-based swiddening. Other
types of intensive agriculture systems are now replacing
swiddening throughout the region, including semi-permanent
and permanent cash cropping, monoculture plantations, and
greenhouse complexes. The negative impacts associated with
these systems include changes in streamflow response,
increased surface erosion, a higher probability of landslides,
and the declination in stream water quality. Unlike the case
for traditional swiddening, these impacts result because of
several factors: (1) large portions of upland catchments are
cultivated simultaneously; (2) accelerated hydraulic and
tillage erosion occurs on plots that are cultivated repetitively
with limited or no fallowing to allow recovery of key soil
properties, including infiltration; (3) concentrated overland
flow and erosion sources are often directly connected with
the stream network; (4) root strength is reduced on
permanently converted hillslopes; (5) surface and ground
water extraction is frequently used for irrigation; and (6)
and pesticides and herbicides are used. Furthermore, the
commercial success of these systems relies on the
existence of dense networks of roads, which are linear
landscape features renowned for disrupting hydrological
and geomorphological systems. A new conservation focus
is needed to reduce the impacts of these intensified upland
agricultural practices.