Why do some trees have needles?
Why do some trees have needles instead of broad, flat leaves?
The short answer is: survival.
In general plants like it hot and humid—such as in rain forests near the Equator (or in greenhouses). But about 250 million years ago, the Earth’s climate was going in the opposite direction: colder and drier. (Blame it on Pangaea.) Plants needed new tactics to survive. Conifers, or cone-bearing trees, evolved to have needles that retain more water and seeds that could hang out until there was enough moisture to take root.
It may not seem like it, but needles are leaves. They do the same job that broad leaves do—capture sunlight, “inhale” carbon dioxide, and “exhale” oxygen—providing the tree with food and air for us to breath. Instead of shedding every fall, though, needles can last three or four years!
Conifers in many ways are more primitive than flowering, broad-leafed trees that evolved more recently. But their needles still offer some nifty advantages over leaves—especially in tough climates or soil conditions:
- Needles have a thick, waxy coating that retains more water than a regular leaf.
- Since needles don’t shed each fall they can capture sunlight for nearly the entire year.
- Needles can survive ice and snow.
- Needles have lower wind resistance than big, flat leaves, so they’re less likely to make the tree fall over during a big storm.
- Needles are tough for insects to eat.
Today a host of conifers like Douglas fir, Ponderosa Pine, and Western red cedar can thrive in our neighborhoods and green spaces, especially if they’re given enough space to grow and enough water (even in our climate) during the first few summers.