Above: Figure 1. The allocation of Carbon into structure, storage, and defense in lodgepole pine. Tree components with low numbers represent strong priorities for C allocations, whereas components with high numbers indicate a low priority for C allocation. Source: Ecological Society of America.
Trees are amazing organisms. They can live for hundreds of years, and tolerate a variety of environmental stresses. Similar to humans, they too need some nourishment from their environment in order to survive and live healthy lives. Trees obtain their energy, not from the supermarket, but instead from a process called photosynthesis. Leaves utilize the ingredients that include: water, carbon dioxide (CO2), light and chlorophyll in order to fix carbon (C). The opposite of photosynthesis is respiration. Whereas photosynthesis creates energy or carbohydrates from C, respiration uses C in the form of carbohydrates. Trees require significant energy in order to stay alive and healthy especially since they are large organisms that can live a considerable amount of time. Trees therefore require large amounts of fixed C in order to re-foliate leaves each year, grow and maintain roots, branches, boles, reproductive structures, and defend against herbivory. The most successful and healthiest trees are those that are able to fix more C from photosynthesis, than C lost from respiration. A tree that fixes more C from photosynthesis than is respired will have a positive net photosynthetic balance.
Trees are very careful where to allocate the sun’s energy or fixed carbon within its structure. Energy cannot be wasted on structures that will not help to produce a positive net photosynthetic balance. Therefore, trees prioritize in importance where this energy is allocated. Figure 1 illustrates the priority of carbon allocation. Notice that the greatest priority component is the leaves. This makes sense since this is where energy is manufactured. Following the leaves are the roots and buds. Roots are probably just as important as the leaves, but biologists have a more difficult time quantifying carbon allocation there since they are hard to monitor and are underground. Roots are extremely important in water and nutrient uptake, especially nitrogen. Buds are where vegetative production occurs for growth and sexual parts for regeneration. Only after these important priorities are met does a tree then allocate energy to storage, diameter growth and finally defense against herbivory.
The aforementioned priorities of carbon allocation can be used to better prioritize forest management practices. Whether a tree is growing on a poor site or good site photosynthesis levels are limited under low-light levels. This means even when a tree is growing in fertile soil with adequate soil moisture and nutrients, photosynthesis will be limited if the stand of trees is crowded and competing for sunlight. Carbon will be allocated first to leaf and root growth at the expense of diameter growth, storage, and protective chemicals for protection against herbivory. Trees in such a crowded state are therefore more susceptible to insect attack, wind, drought, sunscald, frost-cracking, ice-rime damage, and an array of diseases. In addition, diameter growth is diminished, lengthening the time, or perhaps preventing any harvest for potential wood products. In this way, trees can only be fat and happy if they have extra energy from the sun to work with.
Forest landowners who want healthy, fast-growing trees should thin out their forest. Thinning prescriptions under the supervision of a trained Forester will result in increased light availability. More light will be available to the remaining trees further reducing competition. Trees under less competition will be able to grow faster, and be less susceptible to stress.
Thinning prescriptions will most likely become more of a priority for the forests of the Catskill region since most stands are crowded. The priority is made even more significant since society demands a renewable product in the form of wood, as well as the increasing threats from insects and diseases from abroad. Threats include the Asian Long-Horned Beetle, Emerald Ash Borer, and Hemlock Wooly Adelgid. Currently, Beech Bark disease, Chestnut Blight, and Dutch Elm Disease have reeked havoc on our forests with some trees such as the chestnut disappearing. Native pests such as the Forest Tent Caterpillar may also increase its impact in a forest that is crowded, and more susceptible as a result of light scarcity.
Healthier trees from thinning also mean more carbon is fixed and stored within the tree for its health and ours. A healthier tree will be able to store more carbon thus reducing a greenhouse gas, while growing a renewable energy and wood product for society to use. Casting more sunlight upon trees can also make us healthier by literally bearing more fruit. Fruit and nut trees that receive plenty of light produce far more apples, acorns, or serviceberries than their shady counterparts – benefitting both wildlife and humans.
Other environmental factors such as soil, water, and nutrient availability are important. However, trees compete the most for sunlight – which makes it the most limiting factor. As forest managers, landowners, or forest enthusiasts, this is one limiting factor that we can all easily provide. Let the light shine in! www.catskillforest.org
