For purposes of classification, the committee used both biological and cultural criteria to recognize six major classes of agroecosystems. In the context of agronomic crop production, biological constraints differ between perennial systems—which include silviculture, orchards and vineyards, forages and turf—and annual systems—which include row crops, vegetables, and cereals. Stored-products systems have unique attributes; climate and temperature are factors for all of the systems, but manifest themselves in unique ways in that stored-products systems are often indoors and spatially constrained. Animal-production systems (including those for swine, ruminants, poultry, such nonfood animals as horses and llamas, and aquaculture) present a different set of biological constraints. Urban pest-management systems—indoors for vermin, structural pests, and companion animals; and outdoors for lawn, garden, golf courses, ornamentals, rights of way, and nuisance insects—present cultural and biological constraints that differentiate the process of management from that in other systems. Finally, wildland systems (including rangelands, forests, conservation holdings, and aquatic systems) often present species-conservation priorities that make nontarget effects important in pest-management strategies.

Perennial Cropping Systems

The longevity of perennial crop plants (particularly trees) creates a distinctive challenge in that both time and vegetational structure promote biological diversity (Lawton and Gaston 1989). Thus, management decisions in these systems targeted at particular pests often have community-level implications. For example, use of conventional pesticides for control of major pests can preclude adoption of nonchemical alternative methods of controlling other pests (Brunner 1994); use of conventional pesticides remains heavy in these agroecosystems. In 1995, over 90% of acres on which the five most widely grown fruit crops (grapes, oranges, apples, grapefruits, and peaches) were grown were treated with at least one pesticide, and most of the acres received herbicide, fungicide, and insecticide treatment (Economic Research Service 1995).

Explanations for the heavy reliance on conventional pesticides are numerous and include shortages of trained consultants, institutional limits on information transfer, and unavailability of pesticides with appropriate specificity (Brunner 1994). Cultural factors enter in as well; because of consumer aesthetic concerns, crops grown for fresh market receive more intensive pesticide use to ensure quality. Among perennial crops,

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