Trees for Tennessee Landscapes - Maintaining and Protecting
The answer to “Why do trees die?” follows a reverse chronological sequence. Trees die because respiration terminates. Respiration terminates because carbohydrate production ceases and stored carbohydrates are depleted. Carbohydrate production ceases because photosynthesis discontinues. Photosynthesis discontinues because the factors necessary for photosynthesis are interrupted or obstructed. Those factors include: sunlight, water, nutrients, temperature, CO2 and O2. Factors for photosynthesis are interrupted because of human activities or environmental changes. Many are summarized here.
"SP615 Why Do Trees Die?," The University of Tennessee Agricultural Extension Service, SP615-12M-7/03 R12-4910-034-006-04, http://trace.tennessee.edu/utk_agexfores/73