At a time of fire and drought, it’s hard to know whether the local trees are dying or not. We see pines and firs turning yellow and orange and wonder, shouldn’t they always be green? Why do portions of them look dead, and why is the ground littered with pine needles and fir branches? Until I learned about needle drop, also known as needle cast, I was certain the forest around our house was dying, convinced that the drought had won. But needle drop is a natural phenomenon, part of a tree’s life cycle.
Even though pines and firs are evergreens, they shed their needles every two to three years. In the spring, new needles grow at the tips of the branches, appearing a lighter green color than the rest of the tree. With the new growth, the older, inner needles become shaded, hindering photosynthesis and making them no longer suitable contributors to the tree’s growth. In the fall, the older leaves turn yellow-orange and then, approximately one to two weeks later, they die and drop to the ground.
Needle drop takes place in all conifers, which for our area includes ponderosa, Jeffrey, and lodgepole pines, and white and red firs. This happens in the fall, usually September. Pines tend to follow more of a regular pattern in losing their needles than firs because pines are less efficient at photosynthesis, meaning they lose their needles at a more regular rate. Firs, on the other hand, are more efficient at photosynthesis and are more shade tolerant, so they lose their needles more sporadically. The Latin name for pine is pinea, meaning pioneer. Pines “pioneer” an area, or dominate it, because they’re shade intolerant and don’t want other plants taking up the sun. The acidic nature of their needles also helps dominate their area, keeping other plants from growing underneath or near them and exploiting valuable resources.
Drought can accelerate color change and the shedding of needles, so it’s not always easy to determine if a tree is living out its natural cycle or dying from disease or bark beetle. The main clues to needle drop generally point to the inner needles turning color, the pine needle drop happening in the fall, and the fir needle drop taking place in late summer and fall.
During a windy day, it can seem like the sky is unleashing a rainstorm of pine and fir needles. You can hear the needles scratching at your windows or feel them pelting your back. The forest floor becomes covered with a layer of needles, sometimes as thick as a soft, plush carpet. Fall is definitely in the air.
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