Expansion and intensification of cultivation are among the predominant global changes of this century. Intensification of agriculture by use of high-yielding crop varieties, fertilization, irrigation, and pesticides has contributed substantially to the tremendous increases in food production over the past 50 years. Land conversion and intensification, however, also alter the biotic interactions and patterns of resource availability in ecosystems and can have serious local, regional, and global environmental consequences. The use of ecologically based management strategies can increase the sustainability of agricultural production while reducing off-site consequences.

Agricultural ecosystems provide humans with food, forage, bioenergy and pharmaceuticals and are essential to human wellbeing. These systems rely on ecosystem services provided by natural ecosystems, including pollination, biological pest control, maintenance of soil structure and fertility, nutrient cycling and hydrological services. Preliminary assessments indicate that the value of these ecosystem services to agriculture is enormous and often underappreciated. Agroecosystems also produce a variety of ecosystem services, such as regulation of soil and water quality, carbon sequestration, support for biodiversity and cultural services. Depending on management practices, agriculture can also be the source of numerous disservices, including loss of wildlife habitat, nutrient runoff, sedimentation of waterways, greenhouse gas emissions, and pesticide poisoning of humans and non-target species. The tradeoffs that may occur between provisioning services and other ecosystem services and disservices should be evaluated in terms of spatial scale, temporal scale and reversibility. As more effective methods for valuing ecosystem services become available, the potential for ‘win–win’ scenarios increases. Under all scenarios, appropriate agricultural management practices are critical to realizing the benefits of ecosystem services and reducing disservices from agricultural activities.

Invasive plant species both threaten native biodiversity and are economically costly, but only a few naturalized species become pests. Here we report broad, quantitative support for two long-standing hypotheses that explain why only some naturalized species have large impacts. The enemy release hypothesis argues that invaders' impacts result from reduced natural enemy attack. The biotic resistance hypothesis argues that interactions with native species, including natural enemies, limit invaders' impacts. We tested these hypotheses for viruses and for rust, smut and powdery mildew fungi that infect 473 plant species naturalized to the United States from Europe. On average, 84% fewer fungi and 24% fewer virus species infect each plant species in its naturalized range than in its native range. In addition, invasive plant species that are more completely released from pathogens are more widely reported as harmful invaders of both agricultural and natural ecosystems. Together, these results strongly support the enemy release hypothesis. Among noxious agricultural weeds, species accumulating more pathogens in their naturalized range are less widely noxious, supporting the biotic resistance hypothesis. Our results indicate that invasive plants' impacts may be a function of both release from and accumulation of natural enemies, including pathogens.