Title Page

To maximize biodiversity conservation within cities, transmission lines and other underused urban grassy spaces could be restored and managed as critically endangered ecosystems such as tall-grass prairies. However, it is unclear whether conserving these ecosystems requires a reduction in mowing and spraying to control weeds, because mowing and spraying reduce numbers and cover of many plant species and resources for animals. Further, it is unknown whether urban sites can be restored as self-sustaining tall-grass prairies, as surrounding urban lands might prevent or deter plants and animals from settling along and benefiting from new wildlife habitats along transmission lines. Since urban transmission lines are frequently mowed and sprayed to control weeds, the separate effects of mowing, spraying, and degree of surrounding urbanization on biodiversity along transmission lines might be confounded with each other in purely observational studies. Experimental habitat manipulation can be used to decouple effects of mowing and surrounding urban land on biodiversity, but is rare in urban ecology studies. I compared effects of mowing and surrounding urban lands upon plants and animals along 48 transmission lines in Winnipeg, Manitoba (2007 – 2009). Surveys at 20 of these 48 lines were conducted before and after an experimental one-year adjustment to the mowing regime at eight of the sites. Increases in urban land within 100 m (20 and 40 %) were associated with 20 % and 35 % fewer plant species, 34 % and 56 % less arthropods in pitfall traps, 26 to 75 % fewer territories of grass-nesting birds, and lower numbers per species per visit of some butterflies. Frequent mowing and spraying reduced numbers of other numbers per visit of other butterfly