Geography Reference
In-Depth Information
af ected by urbanization. In the forests of northeastern U.S. cities, leaves de-
compose 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
i ght water loss, pollution, and the mouths of herbivorous insects. Soil or-
ganisms, however, play a huge role in starting leaf breakdown, notably earth-
worms, 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 rel ects
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 wig-
glers,” are clearly enhancing soil fertility and even helping stem climate change.
As worms decompose leaves, they accelerate the conversion of nitrogen from
ammonia to nitrate, making this natural fertilizer available to plants. This con-
version spurs plant growth, though it may also favor some quick-growing, non-
native, weedy plants over slower growing natives. Either way, the nitrogen
cycling facilitated by worms and other soil microorganisms is an essential ser-
vice that allows our plants to sustain themselves in the city. 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 signii cant step that helps counter the carbon we re-
lease into the atmosphere. Releasing carbon stored long ago in soils by burning
fossil fuels increases global temperatures, so by storing new carbon in today's
soils, worms are, in ef ect, helping us combat global climate change.
To some species the storage of leaf carbon in the soil that worms enhance
is occurring too ei ciently. Ovenbirds are small warblers that nest on the l oor
of midwestern and eastern U.S. forests. Their bright song, an increasingly
loud
Chertee Chertee Chertee,
is always one of the i rst to enliven woodlands in
