Rosanne Cull, age 11, of Toronto, Ont., Canada, for her question:
WHY DON'T PINE TREES SHED THEIR NEEDLES?
Every summer countless visitors arrive to admire the scenic beauty of Ontario. However, the late comers who arrive in the fall have a chance to behold the beauteous autumn colors. Then the maples are decked in papery scarlet and the white‑legged birches are hung with golden pennies. And among the dazzling rainbow colors stand the pines with their same old evergreen boughs.
When you walk among shady evergreen pines, you notice a fresh, tangy fragrance. It comes from the gummy resins in the needles and wood of these conifer trees. Some of it comes from the living trees, but most of it comes from the ground. There you walk on a springy carpet of old fallen needles, turning brown as they slowly decay.
A pine tree does not don candy colors in the fall and shed its needles as the maples and birches shed their leaves. But it does shed some of its needles. So do all the wide‑leafed tropical evergreens, though they do not shed them all at once and go bare through the winter.
The papery leaves of maples and birches are too fragile to withstand the wintry weather. The frost would penetrate their thin cell walls and turn their liquid sap to ice. Daggers of ice would tear the delicate cells apart. This is why the deciduous trees shed their leaves in the fall. The leaves of a pine tree are tough needles with coats of resin, thick enough to seal out the frost.
This is one reason why a pine tree can keep its leaves all year. Another reason is its shape. Those thick furry boughs slope down like the pointed roof of a house, which is just right for shedding a heavy load of snow. So the pine tree does not have to lose all its sturdy leaves in the fall. However, even those tough green needles grow old and useless.
The average pine needle may stay in good working condition for two or three years. Then it falls to the ground and new ones grow in to replace it. This may happen at any time of the year, though it usually happens in the spring when evergreen trees put on tufts of new growth to bear their cones.
In the fall the maples and birches strew thick layers of old rusty leaves on the ground. But come spring they have decayed and disappeared. Not so the old pine needles. Those tough little needles are slow to decay. Some of the fallen needles under a pine tree may have been there for six or seven years. And this year a few more will be added to the springy brown carpet.