World Agroforestry Systems

For example, leeks, corn, and strawberries are grown in peach orchards in Ontario, Canada; oats are grown in some New York apple orchards; and potatoes, grains, soybeans, squash, and peaches have been planted in pecan (Carya illinoensis) orchards in the southern United States (Williams and Gordon, 1991). Approximately 10% of all fruit and nut orchards in Washington State (USA) are intercropped with vegetables for home use, and in another 25% of the orchards cattle or sheep are grazed during part of the year (Lawrence et al., 1992).

One of the most widely intercropped group of trees is the poplar species (Populus spp.) and their hybrids; these species were traditionally planted for short rotation fiber and fuel production. Poplar plantations in Europe and eastern Canada have been interplanted with corn, potatoes, soybeans, and other cereal and tuber crops, in different temporal sequences, for the first three to six years after tree establishment (Gold and Hanover, 1987). Many of the poplar plantations are only grown for an additional five to ten years after crop harvest before harvesting and establishment of the next rotation. In China, sesame, soybeans, peanuts, cotton, indigo, and various vegetable crops are grown in both hybrid poplar (Figure 25.2) and Paulownia tomentosa plantations (Figure 25.3); the poplars are widely planted in a variety of other crop-border configurations (Farmer, 1992). In Australia, various melon and squash crops are grown for two years, followed by permanent pasture, with cattle grazing on both the pasture and branches lopped from the poplars. Poplar is also frequently planted on plot boundaries of wheat and barley fields in northern India and Pakistan.

The vast majority of research on silvopastoral systems in North America has focused on pine forest with deliberate management of both pasture and trees. These systems are most important in the Southern Coastal Plain under slash pine (Pinus elliottii), and longleaf pine (Pinus palustris); they are popularly known as “pine-and-pasture” or “cattle-under-pine” systems. The earliest studies on pasture improvement in these systems, initiated in the 1940s, indicated that mechanical site preparation and fertilization were essential for forage establishment, and that production of established pasture declined with increasing tree-canopy closure (Lewis and Pearson, 1987). Among the most productive pasture species were Pensacola bahiagrass (Paspalum notatum), annual lespedeza (Lespedeza striata), and white clover (Trifolium repens), with Pensacola bahiagrass being the most shade tolerant.


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