Evergreen trees first came from cold climates. But you can find many in warm tropical rainforests too. They have very strong leaves rolled up tight, like long, thin needles. This shape allows the evergreens to conserve water, which is needed for photosynthesis. Because they have more water than their deciduous cousins, their leaves stay green, and stay attached longer. Evergreen needles also have a very waxy coating that also helps save water during summer and winter.
Christmas trees are generally evergreens like spruce, fir, or pine. My friend Bert Cregg is also very curious about the lives of trees. Cregg told me that evergreens have lots of needles, which are their leaves. We have even seen some trees, such as bristlecone pines, that have had the same needles for more than 16 years.
Each tiny needle on a great big evergreen is working hard to make food for the tree. It all happens through a process called photosynthesis. But the chlorophyll also has another important job.
The chlorophyll absorbs sunlight which the tree can use to turn carbon dioxide from the air and water into sugars. It is these sugars that help the tree grow and stay green. Evergreens have very strong leaves that are rolled up as long, thin needles. This special needle shape, along with a waxy coating, allows the evergreens to conserve water during summer and winter, which is needed for that continued photosynthesis process.
So because they can conserve more water than their deciduous counterparts, their leaves stay green and remain attached longer. Evergreens shedding needles happens mostly in the spring. But this goes largely unnoticed because they are growing new leaves at the same time as they shed their old ones.
While most conifers are evergreens, some lose more of their needles than others in the fall. And some cypress species even drop needles during the dry season as drought protection. While most evergreens follow these rules, there are always exceptions. The bald cypress, for instance, loses all of its needles every year. Just like their deciduous counterparts, this acts as winter protection, enabling them to conserve resources and grow under challenging conditions. Though pines and most other conifers are called evergreens, their needles do not stay alive and green forever.
The trees produce new needles every spring and summer that last for two to four or more years. Newer needles are always at the branch ends, while older needles are typically further back. But when do pine trees shed needles? As needles age, they conduct less photosynthesis for the tree. In addition, they become shaded by new needles.
New needles in most instances are there to replace the old ones. On some evergreens, like spruce or fir trees, this process is barely noticeable, while on other trees like white pines, the yellowing inner needles are easier to see beyond the green needles. If one-third to one-fourth of the needles on the inner parts of your evergreen fall off, this is usually a normal sign of aging.
Leaving those needles where they fall under the tree can also a good mulch layer. But if you notice that your beloved evergreen is losing needles at the branch tips, this could be a sign of trouble.
Looking to add more evergreens to your landscape?
0コメント