Agroforestation of Grasslands in Southeast Asia: WaNuLCAS Model Scenarios for Shade-Based Imperata Control During Tree Establishment - Smallholder Tree Growing for Rural Development and Environmental Services - page 133

Keywords Indonesia, Philippines, tree-crop interaction, tree plantation, tree spac-
ing, weed control
6.1 Introduction
Imperata cylindrica (and other coarse grasses) dominated vegetation tends to occur
as the interlude between the loss of natural tree cover by logging and similar enter-
prises, and the return of (managed) tree cover, often in forms of agroforestry. Fire
maintains the grasslands and slows down succession to woody vegetation (Chazdon
2003; Lavorel et al. 2007). Chomitz (2007) related to three landscape phases as
'core forests', 'forest margins' with rapid loss of forest cover and contests over land
use rights, and 'mosaic forests' in the (partial) recovery phase after land rights were
established. In the literature on 'forest transitions' (Mather 1992, 2002; Rudel et al.
2005; Geist et al. 2006; Angelsen 2007; Mather 2007; Rudel 2007) two possible
pathways are discussed for advancement of tree cover. One is the “economic devel-
opment route”, where the agricultural population declines as industrialisation and
urban migration proceed, and abandoned agricultural land is spontaneously refor-
ested (this has happened in parts of Europe and N America; it is less common in
densely populated Asia; Chokkalingam et al. 2002; Lamb et al. 2005). The other is
the “forest scarcity pathway”, where scarcity of forest products drives up price and
stimulates tree planting within an agricultural context. In an intermediate form,
where urban and service jobs relieve some of the pressure on land, timber-based
agroforestry can become an economically attractive land use.
Garrity et al. (1997) estimated that there was about 35 million hectare of
Imperata (and other coarse grasses) dominated lands in Asia at the time of assess-
ment, and the number has probably increased since. In the Philippines, pure grass-
lands occupy 1.8 million hectare and another 10.8 million hectare (33 percent of the
country's total land area) is under extensive cultivation mixed with grasslands and
shrub (Menz et al. 1999). Presently, conversion of these grassland areas into upland
farms planted to annual crops and perennial trees is proliferating at a fast rate
(Schuren and Snelder, Chapter 3, this volume). This is triggered by interacting fac-
tors of rapidly increasing population, the prevailing system of landholdings, scar-
city of non-agricultural jobs, and declining arable area in the lowlands. Predo and
Francisco (Chapter 14, this volume) analyzed land use options in northern
Mindanao and concluded that tree-based systems are profitable but risky for small-
holders. Bertomeu (2004; see also Bertomeu, Chapter 8, this volume) showed that
profitability depends on the silvicultural management of the trees and the price the
lumber can attract. In Indonesia, however, most of the grasslands are in the 'forest
zone' where land ownership is contested (Contreras-Hermosilla and Fay 2005) and
conversion is constrained by social and political factors. Current interest in increas-
ing terrestrial carbon stocks in the grasslands has lead to renewed attention (Tomich
et al. 1997; Menz and Grist 1997; Tomich et al. 2001; Wise and Cacho 2004;
Roshetko et al. 2007) to the transformation of grassland into tree-based land use