why do trees lose leaves in autumn
In temperate regions of the world, autumn is marked by the brightly colored foliage that slowly drops from
and to carpet the ground. But why do some plants shed their leaves before winter? It turns out autumnal leaf drop is a form of self-protection. While in cold climates have thick waxes and resins to protect their leaves from freezing and fracturing, deciduous species generally have thin leaves that are susceptible to cold temperatures. Since water expands when frozen, the tender leaf would rupture during the winter, making them useless for.
Without dropping these leaves, such a tree would be stuck with thousands of unproductive appendages and no way to make food! As if that weren't reason enough, the surface area of all those leaves would also pose a threat to the plantвs physical integrity. Winter months are often windier than other seasons, and the wind against the broad leaves on a cold, brittle tree could cause major breakage. The same goes for the weight of collecting on all those leaves. Finally, by the end of summer, many leaves are insect-eaten, diseased, or otherwise damaged.
Dropping them gives the plant a fresh start in the spring, and the nutrients from the decaying leaves are recycled to help grow the next leafy generation. Interestingly, autumn leaves are not simply blown off trees but are separated from the plants in a highly controlled process. As day length shortens and temperatures cool, hormones within the plant are activated to begin the abscission process. production stops and the pigment starts to degrade, often revealing showy reds and yellows that were masked by green. The vessels that carry water to the leaf and sugars to the rest of the plant are closed off, and a layer of cells, known as the abscission layer, starts to grow between the leaf stalk and the twig holding it.
These cells serve to slowly cut the leaf from the plant without leaving an open wound. As the leaves fall, the plant enters, saving its energy for the great bud burst of spring. Asked by: Barry Cull, by email Deciduous trees shed their leaves as an active process that evolved to conserve resources and protect the tree from being blown over in the windier winter months.
The process is controlled by the plant hormone auxin. As light levels and temperatures drop, the flow of auxin to the leaves slows and levels of another hormone, ethene, rise. This signals the cells at the base of the leaf to weaken their cell walls, at the same time as other cells expand to break the connections between the weakened cells. The result is like tearing perforated paper, and the leaf drops to the ground. Subscribe to for fascinating new Q As every month and follow on Twitter for your daily dose of fun facts.
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why do trees shed their leaves in winter
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