Earthworm population density and diversity in different-aged urban systems

Earthworms are known to play important roles in soil profile development, nutrient cycling, and plant productivity where their population densities are high. Our objective was to understand the impact of disturbance and management intensity within different-aged urban landscapes on earthworm population density and diversity. Our study was conducted in Moscow, ID, USA. Earthworms and soils were collected from open turf in three residential yards less than 10 years old, three residential yards greater than 75 years old, and in three urban parks greater than 75 years old. Mean earthworm density was significantly different among urban park (437 individuals m−2), old residential (121 individuals m−2), and young residential sites (26 individuals m−2). Bulk density of the 0–10 cm depth was significantly higher in young residential sites (1.59 g cm−3) than in urban park (1.30 g cm−3) or old residential sites (1.30 g cm−3). Mean total soil C in the first 30 cm of soil was significantly different among the three landscape types (3.6 kg C m−2 in urban parks, 2.9 kg C m−2 in old residential, and 1.4 kg C m−2 in young residential sites). Total soil N content followed the same trend as soil C across landscape types. Fertilizer additions in urban park sites were associated with increases in earthworm density and total soil C and N content. Overall, high bulk density due to soil compaction in young landscapes may directly and indirectly limit earthworm density. Bulk density, however, tends to decrease while soil C and N content increase as urban systems mature and these changes are associated with increases in earthworm population density.