Agriculture Reference
In-Depth Information
Chapter 6
Agroforestation of Grasslands in Southeast
Asia: WaNuLCAS Model Scenarios
for Shade-Based Imperata Control
During Tree Establishment
Meine Van Noordwijk 1 *, Ni'matul Khasanah 1 , Kurniatun Hairiah 2 ,
Didik Suprayogo 2 , Demi Macandog 3 , Betha Lusiana 1 , and Georg Cadisch 4
Abstract In the stage of land use evolution where smallholder tree-based systems
are desirable as replacement of Imperata cylindrica (and similar) grasslands, agro-
forestry can provide a gradual and rewarding approach to the transition. There tends
to be, however, a gap between the last opportunity for food crop interplanting and
canopy closure providing shade-based control of grass and weed growth. In such
period, regrowth of Imperata enhances the risk of fire and failure of tree establish-
ment. We analyzed the duration of this ' Imperata regrowth window', for a range of
planting patterns and choice of tree species in Lampung (Indonesia) and northern
Mindanao (the Philippines). Simulations of agroforestation scenarios with the
WaNuLCAS model ('water, nutrient and light capture in agroforestry systems')
focuss on the Imperata regrowth window as the period between 50 percent and
15 percent of ground-level light availability.
The simulation results first of all confirm a well-known fact: young trees of most
species are not able to compete with Imperata and partial weeding around the tree
stem base is absolutely necessary to get most trees started, with the possible excep-
tion of Paraserianthes falcataria . Although Acacia mangium is a fast growing tree,
a more intensive weeding regime will double tree growth. The improvement of ini-
tial tree growth speeds up tree canopy closure and reduces subsequent Imperata
regrowth window by two to more than five years according to the model, with
periods longer than five years associated with slow initial growth rates. There is,
according to the model, only limited opportunity to reduce risk exposure by modifying
tree spacing.
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