A new scientific study shows that tree leaf fall in the fall has become occurring earlier in the season, compared to past decades due to climate change, and that is contrary to what was expected.
These results indicate - according to the scientists - that forests have a limit in the amount of carbon they can absorb each year, which reduces their ability to cope with greenhouse gas emissions.
Warming and defoliation
Botanists have long studied the factors that control the timing of the periodic processes of the tree, such as the growth of leaves in the spring and their fall in the fall, and they found a strong relationship between the rise in temperatures in the beginning of the spring as a result of climate change and the early growth of buds.
But the trees ’behavior in the fall remained relatively incomprehensible to them.
Scientists agree that the lower temperatures in the fall and the shrinking of the sunny period per day are the main factors that determine when trees drop their leaves.
Deciduous trees - which shed their leaves seasonally - resort to discarding their leaves, which become a burden due to the decrease in photosynthesis and cold weather, and spend the winter months consuming the sugars stored in them.
Therefore, scientists previously believed that high temperatures would stimulate trees to shed their leaves with a delay than usual between two and three weeks by the end of this century.
But the results of the new study, published recently in the journal Science, completely contradict what scientists previously believed. A team of researchers from the Institute of Integrative Biology, ETH Zurich, found that leaves fall in autumn. Ahead of its usual time.
For their study, the researchers used data from the Pan European Phenology Project, a long-term project to monitor central European trees.
This project provided them with information on 3,855 forest sites that include 6 types of trees, some dating back 65 years, and related to budding and leaf fall rates, photosynthesis rates, in addition to climatic information.
And unlike old models that assumed the length of growing seasons determines how much carbon trees absorb from the atmosphere, the new study instead looked at how changing carbon absorption affects trees ’production of leaves during the growing season.
In this study, the researchers conducted several experiments, one of which was to shade some trees and compare the growth of their leaves to another group that receives natural sunlight, and they noticed that the fall of the leaves of those that live in the shade was delayed for more than a week.
Leaves are falling off earlier than before (Beekshair)
In another experiment, the team found that trees that were kept in a warm climate or given an excessive amount of carbon dioxide (or both), shed their leaves earlier than trees that had not been treated.
The study authors concluded that the trees shed their leaves the sooner there was an increase in photosynthesis.
They found that for every 10% increase in photosynthesis activity during the spring and summer seasons, it corresponds to an 8-day advance in the time the trees shed their leaves compared to the average date recorded during the past decades.
The team estimated that by the end of the century, the trees will drop their leaves during the fall 3 to 6 days early.
On the other hand, the study indicates that even with an abundance of light and warmth, trees have limits in the amount of carbon they can convert into sugars, leaves and roots in a given growing season.
According to the researchers, these limits are related to the amount of nitrogen available. The more productive trees, the faster their nitrogen reserves are depleted, leading to an early halt in productivity.
Trees have a specific ability to absorb carbon from the atmosphere every season (Bikshair)
So rather than delay dropping their leaves as temperatures rise, deciduous species of trees will become barren early in the season, reducing their ability to cope with greenhouse emissions.
Fall deciduous leaves are no longer just a sign of seasons change, but a dangerous sign of climate change, the researchers say.