To understand why or how trees die, we must first understand the processes by which they live. Broadly, these processes can be categorized under physiology, which is the branch of science dealing with the functions of living organisms and their parts. Major physiological processes in trees include photosynthesis, respiration and translocation.
The process of photosynthesis combines carbon dioxide with water in the presence of the sun’s energy to produce simple sugars (known as carbohydrates) and oxygen. This chemical reaction for photosynthesis occurs in leaves and can be written as:
Photosynthesis is the most essential and basic physiological process, inasmuch as tree growth is dependent upon successful conversion of the sun’s energy into carbohydrates. Kramer and Kozlowski (1960) make the following observations about carbohydrates:
they are the substances by which all other organic compounds are synthesized,
they are the chief building blocks of cell walls,
they form the starting point for synthesis of fats and proteins
they are oxidized in respiration, and
any amount still remaining after all these processes accumulates as stored food reserves.
Carbohydrates are transported from the leaves to the stem and roots via phloem cells for use in respiration and other physiological processes, including growth. Excess carbohydrates not used in growth and respiration are stored in roots, buds, stems and cambium.
Respiration is the oxidization of carbohydrates to provide energy to keep cells alive and to fuel growth. Respiration essentially works in reverse order of photosynthesis, whereby the synthesized carbohydrates react with oxygen to produce carbon dioxide, water and energy; e.g., food is oxidized and energy is released. The chemical reaction for respiration can be written as:
Unlike photosynthesis, which is seasonal in most climates, at least some respiration occurs at all times (even during the dormant season). This is why the production of carbohydrates through photosynthesis must exceed the oxidation of carbohydrates through respiration. Without a ....