Reuters

Most city trees aren't the result of tree-planting programs.

Trees seem to know how to make forests better than we do. According to new research from the U.S. Forest Service, an average of two-thirds of all trees in cities are the result of natural regeneration. Only one-third of trees are deliberately planted.

By looking at randomly located plots in 12 North American cities, the researchers found that the vast majority of the urban tree population is naturally occurring growth. Trees are reproducing and filling in empty spaces far more efficiently than any tree planting program ever could.

The amount of planted trees does vary from city to city, according to the research, published in the journal Urban Forestry and Urban Greening. Cities located in grassland-type areas have much higher rates of planted trees than cities in forested areas. And the proportion of planted trees increases in cities with higher population densities and amounts of impervious ground cover. Planted trees ranged from about 11 percent in Hartford, Connecticut, to nearly 90 percent in Los Angeles.

Trees, like any species, are in the business of reproduction. But that doesn't mean high-profile round-numbered tree planting programs and urban forestry managers can just take the rest of the week off. In looking at specific tree populations in Syracuse, the researchers found that exotic invasive species made up the bulk of new natural tree growth. Unless urban forests are managed, they could begin to shift more heavily toward these non-native species. And while non-native trees are better than no trees, the researchers point out that non-natives tend to have shorter life spans, and their invasiveness can often crowd out longer-lived native trees.

So while it's unsurprisingly impressive that nature can efficiently regenerate tree populations, the researchers argue this sort of data should become a more important part of the job of managing urban forests. But given the much higher rate of naturally regenerated trees, maybe we should start to think of it as assistant managing.

Photo credit: Mariana Bazo / Reuters

About the Author

Most Popular

  1. A cyclist rides on the bike lane in the Mid Market neighborhood during Bike to Work Day in San Francisco,
    Perspective

    Why We Need to Dream Bigger Than Bike Lanes

    In the 1930s big auto dreamed up freeways and demanded massive car infrastructure. Micromobility needs its own Futurama—one where cars are marginalized.

  2. Life

    Why U.S. Tech Inventors Are So Highly Clustered

    New research finds that high-tech inventors are significantly more productive when they work in large clusters—but there are drawbacks.

  3. a photo of the Maryland Renaissance Festival
    Life

    The Utopian Vision That Explains Renaissance Fairs

    What’s behind the enduring popularity of all these medieval-themed living-history festivals?

  4. Maps

    A Comprehensive Map of American Lynchings

    The practice wasn’t limited to the South, as this new visualization of racial violence in the Jim Crow era proves.

  5. A photo of a police officer in El Paso, Texas.
    Equity

    What New Research Says About Race and Police Shootings

    Two new studies have revived the long-running debate over how police respond to white criminal suspects versus African Americans.

×