Pine trees are members of the evergreen, or coniferous, family of trees. There are many different species of pine, and they are found on several continents in many different environments, ranging up to extreme altitudes and to the limits of arctic tree-lines. Like other evergreen trees, the pine tree is distinctive due to its foliage, which takes the form of narrow green needles.
The pine needle may look much different than the leaves seen on deciduous trees, but it performs exactly the same function and is simply an adaptation which occurred hundreds of millions of years ago. The shape of the pine needle enables the pine tree to retain water better than deciduous tree species and therefore tolerate dryer, colder conditions better.
The pine needle is ideally designed for water conservation. Its narrow shape means that it exposes less surface area to sunlight than other types of leaves, which reduces evaporation. In addition, the pine needle has a thicker skin and coating of waterproof wax which combats water loss. This is not the only adaptation the pine tree has undergone, however. Unlike deciduous trees, the pine tree is able to retain pine needles through the coldest months of the year. This is another energy and water-conserving feature which makes the pine tree and other evergreens so hardy.
Even though the pine tree retains green pine needles throughout the year, pine needles do eventually turn brown and fall just as deciduous leaves do. However, this may not be as noticeable because this needle loss tends to happen throughout the year. When these needles fall, they are replaced by new growth. The needles which are least exposed to light tend to fall more readily. Pine needles typically live for about two years, compared to spruce needles, which can live as long as 10 years.
Sometimes, it may appear as if a pine tree is dying or struggling with some type of disease because a high number of pine needles are turning brown and falling. This isn't necessarily the case. In extremely hot or dry conditions, a pine tree may shed a larger number of its needles than normal. The way to differentiate between natural needle loss and disease is the pattern of the needle loss. If the discolouration is gradual and affects the innermost needles from the top to bottom of the tree, the needle loss is likely natural. If outer needles and entire branches are affected, it may be disease.
A common pest of pine trees and other conifers is pine needle scale, which is an insect that directly targets the needles on young pine trees. Pine needle scales suck the sap from pine needles, turning them yellow and killing them. Severe infestations may kill or severely weaken a pine tree.
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