July 21, 2019 | 83° F

Leaves fall behind schedule due to unusually warm weather, Rutgers scientists say

Photo by Dustin Niles |

Rutgers scientists have determined that leaves changed colors for the fall approximately a week and half later than usual, this they said was due to the lingering warm weather earlier in the semester. 

Leaves took longer to change colors this fall than in years past, and unusually warm weather earlier this semester is to blame, Rutgers scientists said.

They changed approximately a week and a half later than usual, to be exact, said Pamela Zipse, Rutgers Urban Forestry Outreach coordinator. 

Zipse and Jason Grabosky, a professor in the Department of Ecology, Evolution and Natural Resources, discussed this fall’s unusual weather patterns. 

Grabosky said there are two main types of trees, deciduous and coniferous, also known as evergreens. Their differences lie in their cell system. Deciduous trees, whose leaves change color, have cell systems that move more fluid than evergreens, whose leaves are mostly green during the colder months. 

As a result, the leaves of deciduous trees have a faster turnover rate, lasting for only a year before dropping. The leaves of coniferous trees last longer, around three or four years, so they retain their green color and take longer to fall, Grabosky said. 

Trees grow and feed themselves through the process of photosynthesis or taking energy from the sun and water from its roots to turn carbon dioxide into sugar, Zipse said. Their leaves contain a chemical pigment called chlorophyll, which both absorbs the sun’s energy and reflects light to give leaves their green color. 

Due to the temperature drop and shorter days in autumn, the chlorophyll breaks down and all that is left are the pigments that reflect yellow, orange and red light. 

“Chlorophyll is the dominant color in most leaves … so when it breaks down, you start to see the other colors,” she said. 

The resulting crunchiness of fallen leaves is caused by lack of moisture. Since the tree is not going through the process of photosynthesis, it is closing off connections to the leaves instead of putting water into them, Zipse said.

As a part of the urban forestry program, Zipse works with forest management, which involves growing trees and working with local government to harvest and sell them. She said the field is important because it affects stormwater management, air pollution and energy usage. 

“Urban forestry is a career,” she said. “It’s where trees meet people. We’re all occupying the same living space, so we need people to take care of the trees.”

Catherine Nguyen

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