The factors that affect tree cover also play a role in natural regeneration. Precipitation, air temperatures, surrounding natural vegetation type, and the distribution of land use types in the city all influence how much seed source exists and whether seedlings grow. Land use plays a role in whether seedlings are mowed down or whether paved surfaces prevent seedling establishment, and ultimately affect a city's need for tree planting to sustain tree cover.
"Before we can say how many trees we need to plant, we need to know how many trees are regenerating naturally and how many are dying," according to Nowak. "Planting programs to sustain tree cover can be greatly improved with long-term monitoring data to show how the urban forest is changing."
Researchers evaluated the magnitude of natural regeneration or tree planting across an entire city system by randomly locating 0.04-hectare field plots in each city and recording tree measurements as well as an estimate of whether a sampled tree was planted or occurred through natural regeneration. Crews based their estimates on surrounding conditions. For example, trees along fence lines or in unmaintained areas were generally classified as naturally regenerated, while trees in maintained lawn areas or street trees were typically classified as planted. Residential and commercial/industrial areas have the highest proportion of planted trees, 74.8 percent and 61.2 percent respectively, while trees found in parks, cemeteries, golf courses, open space/vacant land, agricultural fields and wetlands are predominately the result of natural regeneration.
The study also evaluated two
|Contact: Jane Hodgins|
USDA Forest Service - Northern Research Station