Have you ever wondered whether trees can die from old age like humans?
After all, trees are living organisms, and like most living things, it wears and deteriorates over time. Would it then be reasonable to assume that trees also pass away from old age?
Trees do not die from old age in the manner that humans do. Instead, trees go through development stages until they reach a mature phase. In favorable conditions, trees can live indefinitely until their physiological processes are disrupted by environmental and other external factors, leading to their deaths.
The hypothesis of tree immortality has grown popular in the past 20 years as researchers report having found little to no evidence of senescence in trees.
This article will look at what we currently know about age-related processes in trees and the factors they’re more likely to die from.
Do Trees Have Senescence?
Studies indicate that trees may experience senescence (the deterioration process with age), but there is a lack of evidence to confirm this. There is currently no proof to show that trees will reach an eventual death by a certain age or harmful genetic mutations.
The study observes that there may be a relationship between fecundity decline in large trees, which is consistent with physiological decline. As trees become larger and mature, their capabilities to produce seeds reduce, which is a similar behavior that we see in female humans.
The authors assert that:
“trees produce proportionately fewer seeds per diameter and per crown area as they increase in size at the species level, consistent with age-related decline.”
This is also consistent with studies in species of Quercus where fecundity plateaus and declines were found.
In an article by Barbara J. Bond, she states that woody perennials do not go through a defined senescence phase, but instead, go through predictable developmental stages. These age-related changes include:
- Reduced photosynthesis and stomatal conductance
- Thickened leaf-bearing-stems
- Thickened and smaller leaves
- Capped growth in height
Signs of possible senescence are seen in maturing trees as their reproductive efforts, photosynthetic capability, and xylem growth rates are reduced over time.
Trees Are More Likely to Die From Physiological Disruptions Than Old Age
Trees die when their physiological processes are disrupted. The primary tree functions are photosynthesis, respiration, and translocation. When one of these functions terminates, the tree loses its ability to produce food for itself (carbohydrates) and therefore dies over time.
In an article by R.H Waring, the author recognizes several different stresses that can disrupt a tree’s physiological functions:
- Shade-induced stress
In dense forests, trees compete for sunlight by spreading their canopies. Shorter trees are more likely to die before reaching old age.
Larger trees are at higher risk of dying if they cannot reach sunlight because they have larger body structures to support. The maintenance cost of additional living cells to constantly photosynthesize and maintain their volume is far greater than its saplings.
- Drought-induced stress
Prolonged drought conditions halt photosynthesis and deplete carbohydrate reserves, eventually reducing the amount of canopy. Shallow-rooted trees are most susceptible to drought conditions as they cannot reach water in the deep ground.
- Stress by mechanical abrasion
Mechanical forces such as strong winds, heavy snow, and fire threaten a tree’s survivability. For example, tree branches and leaves are damaged in the event of a hurricane. Prolonged flooding can cut off oxygen within the soil, weakening tree root systems and leading to death.
- Stress through nutrient deficiencies or imbalance
Canopy closures in dense forests may allow permafrost to form throughout the soil. This restricts decomposition rates and root growth in trees.
When trees are injured, they rely on resources to produce new growth.
Likely Causes of Death in Trees
Empirical evidence suggests that trees are much more likely to die from conditions caused by weather and human activities. This includes:
|Cause of Death||Explanation|
|Drought||Prohibits absorption of sufficient moisture for photosynthesis|
|Fire||Wildfire is one of the leading causes of tree death in dryer climates.|
|Unfriendly Microbes||What is often unseen to us humans is the biological warfare that occurs beneath the surface where the tree’s roots and core is. An unsuspecting tree could become a victim of a biotic or abiotic organism with sinister plans to kill off the tree for its own benefit.|
|Humans||Human intervention in tree death varies from logging, purposeful wildfire setting, accidental, and so on.|
|Logging||Humans will cut down, process, and sell wood from trees eliminating trees in the thousands during this process.|
|Pests||Pests often feed on sap and leaves until the tree is depleted of its own sustenance.|
|Forest clearing for land use||Clearing large swaths of forests filled with long-living and thriving trees is becoming an increasing phenomenon. This is done to accommodate population growth.|
Unfavorable weather conditions often lead to soil problems such as excessive or poor drainage. This leads to root respiration issues and therefore risks the tree’s survivability. Human activity, such as deforestation, leads to hundreds of tree deaths.
Trees do not die from old age like humans do – skin damage, weakened bones, loss of muscle, deteriorated immunity, and so on, making it difficult to recover from illnesses.
The physiological changes that occur between trees and humans are fundamentally different. Trees undergo a developmental process in which they reach an ‘old growth’ phase. It is probably more accurate to use the term ‘aging’ than ‘senescence’ to describe the age-related change in trees.
Deaths in trees are more likely to be caused by external factors rather than physiological deterioration. At the time of writing (Jan 2023), there is no solid evidence for the claim that trees die from senescence or ‘old age.’
Qiu et al, Is there tree senescence? The fecundity evidence. Proc Natl Acad Sci U S A. 2021 Aug 24;118(34):e2106130118. doi: 10.1073/pnas.2106130118. PMID: 34400503; PMCID: PMC8403963.
Bond BJ. Age-related changes in photosynthesis of woody plants. Trends Plant Sci. 2000 Aug;5(8):349-53. doi: 10.1016/s1360-1385(00)01691-5. PMID: 10908880.