Herbicides susceptible to that herbicide Research conducted to date has shown that herbicide-resistance in crops has a benign effect on weed abundance and diversity Instead, it is the weed control methods, including herbicides, as well as other management practices used in those crops that exert selection pressure for changes in weed abundance, composition, and dynamics, as discussed above Other Organisms By suppressing, removing, or destroying vegetation, weed control modifies the environment and habitat of other organisms In agroecosystems, crop pests as well as beneficial organisms can be affected by weed removal since weeds can serve as host plants or food sources for many types of organisms, including insects, fungi, and nematodes (Norris and Kogan, 2000) In some cases, a high diversity of weed species in an agricultural field has been shown to reduce the magnitude of insect attacks on crop plants because the weeds serve as alternate food for the insect pests or harbor beneficial organisms that feed on the pests In other cases, however, increased weed species diversity results in increased insect problems in a crop field because the weeds provide a food source or habitat so that the insect pest can remain in the field even during periods when the crop is absent In those cases, weed control to reduce the diversity of weeds in a particular field will decrease the incidence of insect pest damage to the crop, to the extent that herbicides affect weed biodiversity, therefore, their use will also indirectly affect insect organisms The response of fungal and nematode populations to weed species diversity has not been well studied In general, weed control practices result in a cleaner crop field, which usually leads to fewer disease and nematode problems However, it is also possible that large areas of crop monocultures with few weeds may be susceptible to widespread disease epidemics because of the lack of genetic diversity in response to the disease To date, little information is available to indicate how weed biodiversity or use of herbicides in weed control influence populations of fungal pathogens or nematode pests of crop plants As noted above, most herbicides are nontoxic to mammals, which lack most of the biochemical pathways in plants that are targeted by herbicides Aside from toxicology research required for registration, studies of herbicide effects on animals in field settings are limited One exception is aquatic communities, which have been relatively well studied since taxon diversity is usually high and pesticides can move more readily than in terrestrial ecosystems As expected, impacts on animals are pesticide specific While some insecticides have direct negative impacts on aquatic animals, such as zooplankton, insects, amphibians and others, any negative herbicide effects are generally indirect through a reduction in food or shelter for organisms at higher trophic levels One study showed direct negative effects on tadpoles of glyphosate herbicide when it was formulated with a surfactant additive; however, this additive is absent in the aquatic forms of the herbicide, which had no detrimental effects on tadpoles or other animals (Relyea, 2005) Thus, in both terrestrial and aquatic ecosystems, herbicides used properly appear to have only indirect 93 effects on nonplant organisms when weeds they rely on for food, habitat, or other uses are controlled The question whether weed biodiversity is an asset or a detriment to overall pest management and other ecosystem services in agriculture deserves serious attention by researchers This issue is particularly important in the UK and other countries where the majority of land is agricultural and wilderness areas are limited In some regions weeds are increasingly being considered an important component of healthy agroecosystems and worthy of conservation (Marshall et al., 2003) Evidence exists showing that agricultural intensification over the past century, including use of herbicides and inorganic fertilizers, has been accompanied by a reduction in populations of many insect groups and birds, presumably through reductions in weeds that they rely on (Storkey and Westbury, 2007) To understand the importance of weed biodiversity in agroecosystems, more information is needed on the effects of various weed control practices on both weed biodiversity and nonweed organisms With this information, the costs and benefits of weed control can be weighed against potential costs and benefits of alternative strategies to other organisms that are indirectly affected by weed control The question is complicated by the fact that in large-scale mechanized agricultural production, increases in weed species diversity complicate weed control efforts However, this problem could be offset if there were benefits to be gained from maintaining increased genetic diversity of weeds in a field, such as greater buffering against selection for herbicide resistance, enhanced pest control, improved nutrient cycling, or other ecosystem services In wildland situations where exotic weeds have replaced native vegetation, weed control is increasingly practiced to reduce weed invasions and restore the abundance and diversity of native plants The indirect result of these weed control activities is often a restoration of habitat for nonplant organisms, such as birds and small mammals In these situations, therefore, weed control, including use of herbicides, can result in increased diversity of other organisms that depend on native plant communities for habitat Wild Plants Weeds are managed in many situations to restore or preserve the biodiversity of native plant species The most common methods used for weed management in wildlands in the US are manual and mechanical weed removal, prescribed fire, release of biological control agents, use of grazing animals, encouragement of native competitors, and judicious use of herbicides (Clout and Williams, 2009) Weed management strategies in wildlands differ from those in agroecosystems because wildland managers must promote or protect large numbers of plant and nonplant species rather than one or a few crop species Thus, wildland weed management is generally approached with a desire to manage an entire plant community rather than to control a single weed species Although the same methods can be used in agricultural and nonagricultural habitats, wildland managers must minimize negative impacts to a wider range of nontarget species than must agricultural land managers Therefore, the methods used