Fall comes with the expectation, and often hopeful anticipation, that the leaves on deciduous trees, such as sassafras, white oak, and American beech, will transition to a beautiful array of yellows, oranges and reds before being shed for the season. But pine trees, including our local pitch pines (Pinus rigida) and white pines (Pinus strobus), retain their needles throughout the year. This quality led to the use of the term “evergreen” to describe these trees.  But if pine trees are truly evergreen, what’s going on with the enormous amount of orange-brown pine needles that drop from their branches and collect on the ground below in October? 

While pine trees are in fact evergreen, each individual needle has a finite lifespan – typically spanning only two to three years. Each fall, pines shed their oldest class of needles. This is a normal part of the plant’s cycle and is no cause for alarm. This natural occurrence can, however, be exaggerated by current environmental conditions. In times of drought, such as we experienced this year, needle browning can be particularly noticeable as slightly more-than-normal needles are shed in response to environmental stress. Even in non-drought years, however, white pines display one of the most dramatic changes of all the evergreens during their needle drop period. This is often the most noticeable after a windy day – the next day your previously clear lawn will be blanketed in shed needles. 

But why retain leaves/needles at all for the winter? Rather than shed all their leaves at once, as their deciduous neighbors do, by shedding only a portion of their leaves conifers are able to photosynthesize all winter whenever temperatures are above freezing. The leaves of conifers are typically needled-shaped and waxy, which helps to prevent excessive moisture loss – an important adaptation during a time of year when roots cannot readily take up water from frozen ground. Snow accumulation is also a concern for trees that retain their leaves throughout the winter. Just observe the effects of an early season snowfall, prior to leaf-drop in deciduous trees, to understand how damaging that extra weight can be for trees – those conditions are a recipe for downed limbs and trees. To avoid these impacts, the shape of most conifers and the arrangement of their branches are such that they facilitate the shedding of heavy snow loads. These adaptations have resulted in a situation where it’s an advantage rather than a danger for conifers to be evergreen (even if sometimes they look a little orange). 

Were you able to observe the white pine needle drop this year?