In the forests of northeastern U.S. cities, leaves decompose quickly, much more quickly than they do in more natural settings. This might seem counterintuitive because city soils are disturbed, of low quality, and polluted. City trees also grow tough, decay-resistant leaves to fight water loss, pollution, and the mouths of herbivorous insects. Soil organisms, however, play a huge role in starting leaf breakdown, notably earthworms, which are more abundant in urban soils than in natural soils. The greater warmth of urban soils is favorable to earthworms and other agents of decay, but the greater abundance of worms in U.S. city soils also reflects their alien origins. Most earthworms are not native to the United States; they came from Europe as settlers brought in plants and horticultural soils from their native homelands.
Some of the most familiar invaders, such as "night crawlers" and "red wigglers," are clearly enhancing soil fertility and even helping stem climate change. . . . Carbon is also quickly stripped from the decaying plant matter by worms and stored in the soil. This may be the worm's greatest gift. Increasing the capacity of our soils to sequester carbon is a significant step that helps counter the carbon we release into the atmosphere.John M. Marzluff, Welcome to Subirdia: Sharing Our Neighborhoods with Wrens, Robins, Woodpeckers, and Other Wildlife (New Haven: Yale Univ. Press, 2014), p. 167