Gloomy scales reproduce only once per year, giving birth to live young. So Dale collected gloomy scales at each site he was monitoring and dissected them to see how many young they were about to produce.
"At the coolest sites 18.26 degrees Celsius (64.87 Fahrenheit) the females were producing approximately 20 young," Dale says. "At the warmest sites 20.12 degrees Celsius (68.22 Fahrenheit) the females were producing around 60 young. That supports the differences we saw in scale insect abundance on the trees. Populations at the warmest sites were over 200 times more abundant than those at the coolest sites."
"We don't know all of the variables that contribute to the higher abundance, but higher reproduction rates are clearly part of the picture," Frank says. "When we look at abundance, we're looking at an accumulation of generations of scales."
The researchers also found a second factor in urban heat's adverse impact on red maples. Specifically, the researchers found that higher temperatures increase stress on red maples by making it harder for them get water from their roots to their leaves.
To get a sense of the overall impact of heat on red maples, the researchers evaluated the condition of 2,780 trees in Raleigh, North Carolina, and compared the condition against a heat map of the city.
"This work tells us that urban planners and foresters may need to change the way they decide which trees to plant, and select trees that are better suited to hotter conditions," Dale says.
"This also tells us that we need to plant more trees and vegetation in cities, increasing shade on impervious surfaces and limiting the 'heat island' effect," Frank says. "It would also
|Contact: Matt Shipman|
North Carolina State University