It’s about November, but many trees are still green: how is that possible?

On Eddie Street, tree leaves are yellow on one side. But those are the acacia trees, the trees that change color for the first time in the fall. On the other hand, the leaves are still quite green.

Biologist Arnold van Vliet of Wageningen University says: Radio NOS 1 News. “Even beech, which should be completely discolored by this time. You see some color, but it’s still very minimal.”

The reason for the slow change of trees this fall is due to the heat in September and October, says Van Vliet. “We are in the top ten of the warmest months of September and October. Since there are no night frosts, the leaf color begins very slowly.”

Much more papers than before

As the weather gets colder, the trees should lose their leaves. Otherwise, they will dry out with frost because they can no longer absorb moisture while the leaves continue to evaporate moisture, van Vliet explains. “The fact that leaves will fall again is determined by frost, day length and temperature.”

Van Fleet has been observing this tree evolution for a number of years with Application, which creates time-lapse images of tree photos taken by a biologist from the same place on the same date. There are big differences.

“This year there was a little more color change than in 2016, when it was a bit warmer and greener. But compared to previous years, there are more leaves on the trees,” he notes.

The consequences for the environment

This phenomenon also affects the concentration of carbon dioxide, or carbon dioxide, in the air. Van Vliet also tracks it. “Around this time, the carbon dioxide concentration starts to rise again because trees stop absorbing it after they lose their leaves.”

Although trees absorb more carbon dioxide, that doesn’t work against global warming, says Van Villette. “These leaves fall off again, as they are digested in the soil and then the carbon dioxide is released again.”

care rowan

If trees keep their leaves longer, this will also have dire consequences for their environment. “Sunlight reaches the soil. Because the leaves fall off later, the interaction with soil organisms changes and the leaves continue to evaporate water longer.”

Not all tree species thrive in these conditions. “We’re worried, for example, about the rowan, but maybe also about the beech,” van Vliet says.

Other species can come back for this. Plane Trees, Walnut Trees, and Southern Species. According to the scientist, this dynamic is already changing amazingly, in plants and animals. “The question is how will that continue. I would say especially looking to the south.”

The intensity of autumn colors also depends on weather conditions. “Determined by the amount of sun, but also cool nights without a night frost. More nights of sun and cooler nights means more redness.”

A single autumnal storm could put an end to all the impressive fall colors, but that’s not the case, according to Van Fleet. “With all that green leaf on the tree, it’s going to take a while.”