Kenny Evens, age 11, of Morenci, Arizona,for his question:
How can pine needles stay green all winter?
The delicate leaves of the oak, true ash and the elm cannot stand frosty weather. They shed their leaves before winter sets in, otherwise the frost would freeze the sap in their veins. The ice would tear their fragile cells and they would turn black and die. The pines and other evergreens keep their needles through the coldest weather. We see them piled deep in the snow with icicles and make snow hanging from dark green boughs. All these trees are equipped to cope with the cruelest of winters.
Lets study a single pine needle. We can see for ourselves some of the tricks it uses to combat the weather. Actually, of course, it is a leaf. Its cells are not too different from those of a delicate oak leaf. Also like the oak leaf, it has veins to carry the sap to and fro and quantities of green chlorophyll, However, whereas the oak leaf is papery thin, the pine needle is hard and sturdy Its outer surface is thick and glossy with wax.
The surface of a leaf is full of tiny pores through which air passes in and out. The greater the surface, the mere chance it has of losing its water vapor. During the summer this is fine, and a great oak tree loses gallons of water. vapor through its leaves every day. This extravagance doss not deprive the summery oak tree, for at this time of year plenty of liquid sap runs up to replace the last vapor.
During the cold weather, the pine needle cannot afford this loss of water vapor. A lot of tiny doors connected with the chilly outdoor air would be disastrous. Hence: the pine needle has a very small surface, In addition it is covered with a thick waxy skin. This helps to keep out the cold from the delicate leaf cells inside, for if the sap filled veins were to freeze.the solid ice would break and destroy them.
The shape of the pine needle is else designed to resist great piles of snow. When fully grown, a pins tree may have about seven million needles clustered together in furry boughs. The needles are sharp and slippery and they do not form a solid base on which the snow can settle. True, the snow may pile up high and among the pine trees during a blizzard. But it soon comes slipping and slithering down from those springy branches.
The leaves, cones, stem and roots of a pine tree contain quantities of tangy resin. This discourages insects and certain bacteria. It also provides a healing salve when the tree is wounded. This gooy resin: of course, also helps to preserve the needles. A pine needle may stay on the tree for maybe ten years. Finally it falls and is replaced by a new one. But the fallen needle does not decay rapidly, as does the delicate oak leaf. It stays on the forest floors helping to make a crisp carpet, with countless other old pine needles. The sturdy quality which protected it from the cold winter now work to prevent if from rotting away.