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Conifers Shed Most Inefficient
Needles in the Fall
The article below is a portion of an article written by Peter Kolb (MSU Extension Forester). The article is available in full at the Chouteau County Extension office. The article explains the natural phenomenon of fall needle drop, insect management, and proper watering techniques for pine and spruce trees.
Every fall a lot of concern arises when conifers such as pines, spruces and firs start to drop their older needle cohorts in preparation for winter. This is essentially an energy conservation mechanism for surviving the winter as all living tissue on trees require stored sugars and water to survive during cold and dark periods.
Conifers, depending on species typically hold on to needles for 3 to 7 years. Pines up to 5 years with 3 years retention are considered healthy along with spruces and firs up to 7 years with 4 years retention are considered healthy. As needles age, they typically become less efficient at photosynthesis due to a number of factors including excess wax buildup, shading from newer branches, and needle formation. The wax formation increases needle resistance to water loss, an essential design component for surviving in low humidity and strong winds, but also restricts carbon dioxide flow into the needle. Similarly, conifer needles are designed to reflect excess sunlight and avoid overheating during hot summer months. Photosynthesis for northern hemisphere C3 plants typically reaches its maximum capacity at 25% of full sunlight and 75º Fahrenheit during the summer solstice. Shade from the same branches reduces sunlight intensity by an average 90%. Needles designed to shed excess sunlight, therefore, only get approximately 3% full sunlight in the shade, not enough to make them positive producers for the tree. The final result is that trees shed their most inefficient needles in the fall.
For further management information on insect management and proper water techniques for conifers, please contact the Chouteau County Extension office at 622-3751 or stop in at the green building next to the Chouteau County Courthouse.
Montana State University, U.S. Department of Agriculture and Montana Counties Cooperating. MSU Extension is an equal opportunity/affirmative action provider of educational outreach.
