Shortrotation Woody Crop Systems

SRWC systems are essentially tree plantations that combine traditional agricultural and forestry practices. Most tree plantings usually are done with minimal site preparation following a timber harvest; however, intensive site preparation occurs prior to planting SRWC systems. Site preparation includes tillage to break up the soil, herbicide applications to reduce existing weeds, pre-emergent herbicides to reduce weeds during tree establishment, and the addition of lime or granular fertilizer to increase the pH or nutrient availability of the soil (Dickmann and Stuart 1983). Irrigation or fertigation is often provided, allowing SRWC systems to be grown on less than optimal soils. Typically, trees are planted in a grid pattern; spacing depends on the desired product. Narrow spacing (e.g. 1.5 x 1.5 m) often is used in coppice plantations, where the end product can be used for pulp or energy (Kenney etal. 1993, Peterson etal. 1996, Hughes 1997). Wider spacing (e.g. 3 * 3 m) is used for pulp production and for saw timber where rotation ages are greater (Peterson et al. 1996, Zsuffa et al. 1996, Eaton 2000b). As the phrase implies, harvest intervals in SRWC systems are much shorter than in traditional forestry and usually range between 1 and 15 years.

Tree species commonly used in SRWC systems are fast growing, early successional species such as Populus, Salix, Platanus, Liquidambar, Eucalyptus, and Pinus. These genera provide species and hybrids that are very shade intolerant; weeds must be kept to a minimum throughout the establishment period by tilling or herbicide applications. Weeds have been shown to have a major negative impact on Populus growth in SRWC systems (Hansen et al. 1984, Schuette 2000). Most of the species used in SRWC systems are quite susceptible to insect and disease pests. This is common in fast growing tree species, as the majority of the available resources are invested in growth rather than defense (Kozlowski et al. 1991). Currently, the most common solution for pest problems in SRWC systems is pesticides. This chapter examines alternative pest management strategies, primarily host plant resistance, that can be used in SRWC systems. Our review is primarily limited to research conducted on Populus and Salix species in temperate zones;

selections and hybrids from these two genera are the most widely planted trees in temperate SRWC systems.

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