City Trees Grow Faster, But Seedlings Struggle to Take Root – Scientific American Blog Post
Urban areas are growing in size–and with them, the number of trees influenced by city life. While development often leads to deforestation, there are still a significant number of trees growing in the shadow of cities. According to a report released in 2000, 2.8% of tree canopy cover in the U.S. is in cities, and nearly one-quarter lies in the surrounding metropolitan areas (urban counties).
City trees have to deal with very different growing conditions than trees in more rural areas or old forests. Cities are notorious heat islands: the asphault and dark rooftops absorb enough heat to raise summertime nighttime temperatures by 2-5°F on average–and as much as 22°F on clear nights–compared to the surrounding non-urban areas. Hotter nights mean more evaporation, potentially draining the soil of moisture. Carbon dioxide levels are higher due to greater car exhaust. And the prevalence of cars and fertilizers increases pollution runoff, altering the soil’s nutrient availability.
How do trees, adapted to non-urban lifestyles, fare under these circumstances? According to the results of a study published in Urban Ecosystems, western red-cedars (Thuja plicata), coniferous trees common in the U.S. Pacific Northwest, grow more quickly but produce fewer seedlings, potentially putting these urban forest ecosystems on an unpredictable long-term trajectory.
Read more: City Trees Grow Faster, But Seedlings Struggle to Take Root — Scientific American blog Culturing Science
Photo: Evan Leeson