5 Causes of the Death of a Tree

Trees have an extraordinary ability to withstand many damaging agents that are ever-present in their environment. Trees have evolved over millions of years to ward off many stressors that bite and burn and starve and rot their roots, trunk, limbs, and leaves. It is amazing how a tree compartmentalizes itself to seal off dead wood and disease, defoliates to reduce the effect of drought and bleeds to extract harmful insects. We know that all trees do eventually die. There are many hundreds of seedlings and saplings that succumb for every mature tree left in the forest. All ages of trees eventually die to the same agents and only the most adaptive (and often lucky) individuals make it to old age. There are 5 factors to which a tree eventually succumbs: death from its environment, death from harmful insects and diseases, death from a catastrophic event, death from age-related collapse (starvation) and of course, death from harvest. In most cases, death is the result of several, if not all of these conditions taking place simultaneously. Lets take a look at each of these. Adverse Environment Ground and site conditions on which a tree lives ultimately determines the environmental stressors placed on that tree. If a drought-sensitive tree lives on a dry site during drought conditions, it may indeed die from lack of water. But that same tree can also be more susceptible to every other life-threatening factor placed upon it. For example, a disease that appears to be killing the tree may in effect be only a secondary issue to the initial environmental problem. Examples of adverse environments to trees are poorly draining soils, salty soils, droughty soils, air and ground pollution, extreme sun heating or cold spots and many, many others. It is particularly important to understand a tree species genetic tolerance to environmental conditions when planting. Many trees adapt very well to poor sites, but you need to understand which species fits where. Harmful Insects and Disease Virulent diseases like Dutch elm disease and the chestnut blight have caused sudden death to entire forests in North America. However, the most common diseases are more subtle in their work, killing many more trees in total than virulent types and cost forest and yard tree owners billions of dollars in forest product and specimen tree value. These common diseases include three bad ones: Armillaria root rot, oak wilt, and anthracnose. These pathogens invade the tree through leaves, roots and bark wounds and damage a trees vascular system if not prevented or treated. In natural forests, prevention is the only economic option available and is a significant part of a foresters silvicultural management plan. Harmful insects are opportunistic and often invade trees under stress from environmental problems or disease. They not only can directly cause tree death but will spread harmful disease fungi from a host tree to surrounding trees. Insects can attack a trees cambial layer by boring for food and nesting cavities, or they can defoliate a tree to the point of death. Bad insects include pine beetles, the gypsy moth, and emerald ash borers. Catastrophic Events A catastrophic event is always possible in a vast forest as well as in an urban setting. All property, including trees, are subject to being damaged or destroyed. In many cases, trees are not killed but are damaged to the point where their vigor is lost, and insects and disease take advantage of a trees loss of resistance. Significant tree losses can occur during a forest fire or when exposed to tornado-strength winds. Trees take a terrible hit when heavy ice is deposited on species sensitive to limb weight which results in breakage. Floods that do not recede quickly can cause root oxygen levels to diminish to the point where tree damage can occur. Extraordinary drought makes quick work of moisture-loving tree species and can harm all trees when extended over a long period. Old Age For trees who beat the odds and live through maturity to old age, there is a slow dying process that may take centuries to complete (in long-lived species). The modular tree compartmentalizes around damage and infected areas and continues to grow. Still, growth starts slowing after a tree matures, the ability of the plant to support itself diminishes and incurs the loss of adequate foliage for hydration and food. New immature branches, called epicormic sprouts, try to assist in maintaining an old trees vigor but are weak and are insufficient to sustain life for very long. A mature tree slowly collapses under its weight and crumbles to become the nutrients and topsoil for future trees. Timber Harvests Well remind you that trees do die to the ax. Trees via their wood have supported humankind and civilization for millennia and continue to be a necessary part of the human condition. The practice of forestry through professional foresters work continually with much success to provide a sustained flow of available wood volume and at the same time, ensure a surplus of trees. Some consider deforestation a growing global crisis.