Physiological Response of Trees to Temperature Extremes
Like other living organisms, trees are greatly influenced by the conditions of their surroundings, particularly temperature. Extreme temperatures, whether hot or cold, can significantly impact trees' health, growth, and overall functioning, ultimately affecting their survival.
Response to High Temperatures
Transpiration Increase: Trees increase transpiration and water evaporation from the leaf surface in response to high temperatures. This acts as a cooling mechanism akin to sweating in humans. However, this can lead to water stress if water uptake from the roots does not compensate for the loss.
Photosynthesis Alteration: Elevated temperatures can enhance photosynthesis up to a point. Beyond the optimal temperature range, the process becomes less efficient as the enzymes involved in photosynthesis become less effective.
Respiration Rate Increase: Heat causes an increase in the respiration rate of trees. While this initially may boost growth, prolonged increased respiration can deplete energy reserves, reducing growth and vitality.
Cellular Structure Stress: Prolonged exposure to high temperatures can lead to stress on cellular structures. This can cause cell death in extreme cases, leading to leaf scorch, branch dieback, or even whole-tree mortality.
Response to Low Temperatures
Dormancy Induction: Trees, particularly in temperate zones, enter a state of dormancy in response to decreasing temperatures. This physiological state reduces metabolic activity, conserving energy and protecting the tree from cold weather stresses.
Cell Membrane Stability: Cold temperatures can affect the fluidity of cell membranes. Trees acclimate by altering the composition of lipids in the membrane, thereby maintaining membrane function and preventing damage from freezing.
Frost Damage Avoidance: Trees produce specific proteins and sugars that act as antifreeze, lowering the freezing point of cell sap and preventing ice crystal formation within cells, which can be lethal.
Reduced Growth Rate: As temperatures drop, the rate of growth in trees significantly slows down. This is a survival strategy, as the energy demand of growth could be unsustainable during periods when resources (like water and sunlight) are limited.
Frost Crack Development: Sudden temperature fluctuations in winter can cause the outer layer of wood to contract more rapidly than the inner layer, leading to frost cracks. This can be a pathway for pathogens and weaken the tree's structural integrity.
Adaptive Mechanisms
Trees have evolved various adaptive strategies to cope with extreme temperatures. These include changes in leaf orientation and surface characteristics to minimize heat absorption, shedding leaves to reduce water loss, and developing thicker bark to insulate against cold. Some species have also developed the ability to enter a state of dormancy, where growth stops. Still, physiological activities continue at a minimal level, allowing the tree to survive until favorable conditions return.
Conclusion
Extreme temperatures can significantly impact trees' physiology, affecting growth, development, and survival. Arborists and tree care professionals must understand these responses, especially in changing global climates with increasingly frequent and severe temperature anomalies. This knowledge helps develop strategies for tree care, selection, and management to ensure the health and longevity of trees in our changing world. In conclusion, understanding the impact of extreme temperatures on trees is essential for their well-being and survival.
Additional Reading
Teskey, R., Wertin, T., Bauweraerts, I., Ameye, M., McGuire, M. A., & Steppe, K., Responses of tree species to heat waves and extreme heat events. Plant, Cell & Environment, 38(9), 1699-1712. University of Georgia, Athens, GA, USA. (2015). Retrieved January 19, 2024, from https://doi.org/10.1111/pce.12417
Michael G. Ryan, Temperature and tree growth, Tree Physiology, Volume 30, Issue 6, June 2010, Pages 667–668, https://doi.org/10.1093/treephys/tpq033