Vietnam War: Forest Fire as a Military Weapon - Paperless Archives

Technique"s for Kdlin, D•rming
and Compacting Fuels
S1ECRIET
Slashing:
tropical regions. 23J
-Slash and bum" is the clasic approach to preparing and burning vegetatin' as praciced by native peoples in
Their shifting agriculture depends on recycling of elements from the lower sod layers. This isaccomplished
by growing crops on an area for only one or two years. allowing deep-rooted native hardwood vegetation to regrow
for several years. and then felling and burning it to return the essential elements to the surface so•.
Fuel preparation involves cutting and dropping the brambles, shrubby plants. and many of the trees
This fallen
material makes an excellent fuel bed of fine particles, branches, anJ larger stems. The severed plants lose moisture as
rapidly as wea:her conditions permit. The slashing is done at least four months ahead of the period when driest weather
is expected for burning.
In Southeast Asia, burning of slashed areas in mixed hardwood forest types is done i:ear the end oaf the dry season.
mainly in late February and early March just before the monsoonal transition. The native tribesmen may select the actual
day of burning by ritualistic procedures but you can depend on it being done in clear weather with humidity near the
minimum for the year. We have observed and evaluated the burning of many small patches in V ietnam and Thailand, where
the fuel had been prepared by slashing. The vegetation burned readily and all but the largest tree trunks were consumed.
Fire did not spread from the small cleared patches into the dense forest. However, ground fires did creep through surrounding
open vegetation thpt was in an early stage of secondary plant succession.
In tropical regions with yearlong rainfall, prediction of favorable weather and final selection of the day for burning
are more difficult. But, slashed dry vegetation can be burned successful in any climate after a few days of clear weatler.
Crushing or Chaining:
These are more modern versions of the old slashing technique for severing or uprooting woody
vegetation and compacting it on the ground. They involve use of heavy equipment to crush or uproot plant& with a bulldozer
blade, with a roller or cutter drawn by a tractor, or with a heavy chain pulled between two tractors. These methods
are useful in shrub types or younger forests, but they are not suitable for clearing mature forests where the trees are too
large to be readily knocked down.
Successdependson the vegetation having rigid stems that can be broken off or pulled out by the roots. Fuel preparation
generally is not successful in vegetation with limber stems, unless the plants are chopped with a heavy cutter or scraped
loose at the soil surface with a bulldozer blade.
A drying period of a few months to a year is usually needed after crushing or chaining, although some shrub types
with unusually small stems can be burned within a week or so. If plants are scattered rather.then continuous, the preparation
treatment should be done early so that a stand of grass to carry fire can grow within the felled vegetation. If new
growth is mainly shrub sprouts instead of grass, an additional treatment with herbicides to kill this vegetation is advisable
before burning.
Combinations of felling, logging, and slashing have been used to prepare jungle or other forest types for burning, Bull.
dozer crushing can be used along with hand felling of trees or uprooting of trees with the bulldozer in both woodland and
forest types. All of the various combinations kill and compact the woody fuels, and they promote easy burning
23 This subject is very well covered in Batchelder, R. B. and H. F. Hit. Fire in Tropical Forests and Grasslands. U.S.
Army, Natick Lab. Tech. Rpt 67-41-ES. 380 pp., illus. June 1966.
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