Berkeley ESPM H196 - Trap Crops’ Influence on Biodiversity in Agroecosystems

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Trap Crops’ Influence on Biodiversity in Agroecosystems Nathaniel Allen Abstract In agricultural systems natural self-regulating processes, like pest control and nutrient cycling, are aided by biodiversity. Modern commercialized farming practices, using expansive monocultures, have reduced biodiversity in agroecosystems. This study assesses the influence trap crops along the edge of a field have on the arthropod diversity and richness levels through out the field. A radish/mustard blend and an alfalfa/alyssum blend of trap crops along field edges are tested for their abilities to attract and enhance arthropod diversity and richness levels through out the strawberry crops. Pitfall trapping along the trap crops and in field interiors were used to assess the diversity and richness levels of foraging arthropods through out the three treatment and control sites. Using two-way ANOVAs, no statistically significant differences were found between diversity (0.481 P-value) and richness (0.704 P-value) levels in the fields with and with out trap crops. However, differences in diversity and richness levels between edges and interiors of the strawberry crops were close to statistical significance for large field experiments with P-values of 0.103 and 0.109 respectively.Introduction Biodiversity is the variety of all flora and fauna living and interacting in an ecosystem. Biodiversity has an intricate role in the functioning of natural and agricultural ecosystems. In natural ecosystems plant diversity, in the form of vegetative cover, helps to protect topsoil from wind and water erosion, while reducing flood hazards to the ecosystem by enhancing infiltration and reducing runoff (Johnson, 2000; Granger, 2000). In agricultural systems natural renewal processes such as: nutrient recycling, control of microclimate, regulation of local hydrological processes, regulation of the abundance of undesirable organisms, and detoxification of noxious chemicals are largely biological processes, and therefore aided by biodiversity (Altieri, 1994). Many traditional farming systems have utilized biodiversity. For example, intercropping, where multiple crops are grown in the same field, have been used extensively in Latin American countries where 70-90% of their bean crops are grown with maize, potatoes, and other crops (Francis, 1986). However, since the development of industrialized farming systems, during the “Green Revolution,” ecologically sustainable polycultures have been replaced with large input dependent monocultures. Modern agriculture is highly dependent on huge inputs of fertilizers, pesticides, and fossil fuels to maintain the same levels of output (Johnson, 2000). Monocultures can interrupt the self-regulating characteristics of natural communities, like pest control and nutrient cycling, and consequently can become dependent on inputs. In effect, biodiversity’s role in agroecosystem processes has been replaced with human inputs in modern agricultural systems. The decline of biodiversity in modern agricultural systems has become a growing concern for agroecologists. Previous studies have shown that agroecosystem instability is linked to the expansion of crop monocultures and the decline in local habitat diversity (Altieri and Letourneau, 1982). When plant communities are manipulated for human use they become more susceptible to insect pests. The self-regulating characteristics of natural communities, like pest control and nutrient cycling, are lost when ecosystem interactions are disrupted by human modification (Altieri, 1999). However, the self-regulating characteristics of natural communities can be restored or repaired, agroecologists maintain, by the addition of biodiversity (Altieri, 1994). Biodiversity can improve the natural regulation of pests in agroecosystems. If biodiversity promotes the natural regulation of insect pests and other beneficial processes, then how can it be improved in modern agricultural systems? Previous studies have found improved biodiversity in organic or ecological agricultural. Organic agricultural systems havebeen linked to increases in biodiversity of arable fields and grasslands and have been shown to support higher number of endangered species (van Elsen, 2000). Organic systems utilize many methods to promote biodiversity and pest regulation. For example, integrated pest management (IPM) was shown to maintain harvest quality and high productivity with less inputs than conventional practices (Brown, 1999). Organic agriculture is a crucial component of biodiversity in agroecosystems; however, field margins/edges and proximity to natural habitats has also been linked to increases in biodiversity in agroecosystems. A study in Hungary found that near the edge of an orchard the species richness and density of epigeic spiders were higher (Bogya and Marko, 1999). Field edges potentially provide shelter and alternative food sources for natural enemies of pests. A study on birds in Southern Ontario also found that most bird species used field edges consistently more often than expected with regards to the edge/interior ratio (Boutin, Freemark, and Kirk, 1999). Natural field edges are shown to have positive effects on all trophic levels. Given that the type of agricultural system (organic or conventional), the types of field edge, and proximity to natural habitat all affect biodiversity levels in agroecosystems; the aim of this study is to determine if biodiversity in agroecosystems can be enhanced by trap crops. Trap crops are used to attract and accumulate pest insects along the edge of a field and prevent them from infesting the major crop (Naito, 2000). Could increased insect pest levels in the trap crops bordering a field attract more beneficial insect predators into the field? I hypothesize that trap crops result in the accumulation of more arthropod species at the edge of a field and that the increased arthropod diversity and richness will spread through out an associated field crop. This hypothesis was tested in three organic strawberry fields in Watsonville, California. Methods Study Site The study will be conducted in three fields, Murphy, Eagle, and Coke Farms, in the vicinity of Watsonville, California. Watsonville is located on the Central Coast of California in the Pajaro river valley. Watsonvilles' coastal fog, year round mild temperatures, and a growing season of 245 days is ideal for commercial agriculture. The


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