Climate Change’s Impact on Japan’s Cherry Trees

Climate Change causes global warming, and Japan’s Cherry Trees are a demonstration of this climate crisis

Savannah Strome OSC
Zawadzki
July 6, 2022

Climate Change’s Impact on Japan’s Cherry Trees

Japan’s cherry trees, also referred to as Yoshino Cherries, have been some of the first organisms studied to demonstrate microevolution in response to climate change. As climate change becomes more globally prominent, scientists have begun to study the effect it has on organisms and their response to global warming. Climate change and its subsequent global warming are increasing at a rate at which most plants and animals are struggling to adapt to. In the past, the Earth has experienced organic climate changes that were brought upon gradually, thus animals had time to adapt and evolve to their changing habitats. In the present, climate change brought upon by humans has continued at a rapid pace that does not allow organisms the time to safely evolve. Because of this pressure to evolve faster than their transforming environments, scientists are starting to observe specific changes animals and plants were forced to make in order for their species to survive. In particular, experts are studying Japan’s cherry blossom trees as an example of a microevolutionary reaction to climate change. For decades, Japan has hosted annual cherry blossom festivals, which laid the foundation for this experiment to take place. Years of documentation of blossoming Yoshino Cherries compared to the increase in urbanization and temperature, highlight new forming adaptations (Higuchi, Miller-Rushing, & Primack, 2009). On a small scale, cherry trees within cities like Tokyo and Osaka were recorded to have different flowering dates than those located in remote areas. Studied by Dr. Yasuyuki Aono and Yukio Omoto, they discovered that the Urban Heat Island Effect, warming that develops due to urbanization, affects the trees within that urban area thus, they flower early. While in remote, cooler areas, cherry tree flowering dates are later in the spring. Urbanization, a form of climate change, increases the temperature in the city and so, high temperatures were found to be the cause for the early flowering dates (Higuchi et al., 2009).

Documents starting in the 1950’s find that cherry blossoms planted at the same time in urban and rural locations, all flowered within a similar time frame. The temperature in both locations remained similar and constant, along with their blossoming rate. 50 years later, urban suburban, and rural cherry blossoms progressively began to differentiate in flowering times. Similarly, throughout those 50 years, Japan was undergoing industrialization and urbanization, which increased the temperature in springtime when the Yoshino Cherries flower. By the 1980’s, warmer temperatures within cities had changed flowering patterns to 5 to 8 days earlier in Tokyo, Osaka, and Kyoto compared to remote areas. The investigation focused on Osaka city in 1989, where 80 cherry trees were placed at various distances away from the city’s center. Flowering near the city was recorded starting on March 22nd, while flowering near the outskirts had begun by the 27th. Flowering times in Osaka city corresponded to the temperature rise of 1 to 1.5oC. This study demonstrates how cherry blossoms have evolved due to urbanization via climate change and global warming. As urbanization and temperature increase, the flowering dates of cherry blossom trees shifted days earlier (Don Lee, Higuichi, Ishii, Katsuki, Miller-Rushing & Primack, 2007). On a larger scale, a series of experiments were conducted on Yoshino Cherries planted in the remote location of Mt. Takao in Japan. The untouched location of Mt. Takao removes the temperature increase variable from urbanization, so the impact of global climate

change could be witnessed. The experiment was performed over a 25 year period, where 97 cherry trees were observed at relatively similar locations. Scientists found that the tree’s peak flowering day was, on average, 5.5 days earlier than what was first recorded. This shift in flowering dates was explained by an increase of 1.8oC in the months of February to March, which is the optimal time for flowering (Don Lee et al., 2007). The change in flowering dates because of the temperature increase from global warming, suggest that cherry blossoms are also affected by climate change on a larger global scale.

Researchers Primack and Higuchi questioned the purpose of the evolutionary response to the increase in temperature on both small and larger scales in Japan. Plants successfully flowering is a vital part of their life cycle, as it helps attract bees, butterflies, and other insects to pollinate. Pollination is extremely important to all plant species, as it allows blooming plants to reproduce offspring. Plants generate pollen and ovules, which house genetic material to create seeds when combined together. The insects help carry and distribute the pollen to support the spread, continuation, and distribution of plants. If organisms are unable to flower, they could not produce offspring, and eventually their species would die out and extinction would occur. While pollination in a plant’s life process is crucial, other factors like spring temperatures, amount of sunlight, and cycles of other symbiotic organisms play a key role in a plant species’ survival. Trees and plants undergo a type of hibernation during the cold winter temperatures, as they conserve their energy until spring when the temperature rises. The increase in temperature and sunlight that comes with the new season, alerts the organism to stop hibernation and to begin blossoming, thus to start the reproduction cycle (Belyeu, 2019). In the cherry tree example, the earlier flowering dates allow for their species to become more successful when producing offspring (Don Lee et al., 2007). The rise in temperature in early spring signals to cherry trees to commence its reproduction process, which explains the differecianting flowering dates. Cherry blossoms flower annually within the same time frame, meaning that late flowering trees will always flower late and similar with early flowering trees (Don Lee et al., 2007). The cherry trees that flower late and do not produce offspring in high temperatures will die out, leaving the early flowering trees to thrive due to their adaptation. The studies analyzed by Dr. Primack and Higuchi find that changes in early flowering can extremely impact the species’ carbon intake and reproduction (Don Lee et al., 2007). The adaptation to higher temperatures allows for the organism to continue to reproduce and prosper thus that the cherry tree species will continue to survive. This process of evolution on Japan’s cherry trees is a form of natural selection that sprouted from the effects of global warming due to local and worldly climate change.

If climate change, urbanization and global warming continue to raise temperatures for Japan’s Yoshino Cherries, they may be in danger of extinction. As the population exponentially increases, cities like Tokyo and Osaka will continue to urbanize at a greater rate. As urbanization increases, local temperatures will directly increase following the expansion of cities to support additional people. The gap in flowering dates of trees located in populated cities compared to rural and suburban areas will continue to differentiate due to the estimated development of cities (Higuchi & Primack, 2007). Although trees in remote areas will still encounter climate change, but on a larger scale that will nevertheless alter their flowering patterns. The cherry trees unfortunately subject to the Urban Heat Island Effect near cities are more vulnerable to faster rates of temperature increase than those affected by global warming in isolated areas. Earlier and earlier flowering dates for the cherry blossoms may notably take time away from the plant’s hibernation. Significant time dedicated for a tree’s hibernation during the winter is essential to flowering and reproduction, as the tree conserves its energy to be used in the spring. Hibernation

is important because it allows for the plant to become protected and dormant in the winter, and collect and store carbon. Carbon consumption generates energy to be used for flowering in the spring, thus a shorter hibernation will not provide the tree with sufficient energy to bloom, live long, and successfully reproduce (Belyeu, 2019). This defensive response to survival in the face of rapidly accelerating climate change will help the cherry blossom species survive longer and adapt efficiently to further increases in temperature. But if global warming, mostly in cities, continues, then the population may be at risk. Although this prediction of eventual extinction is far in the future, that does not mean that the cherry trees are already threatened. All throughout Japan, the varying flowering dates of the cherry blossom trees prolong with the continuation of urbanization and global warming. This adaptation as microevolution on both a minor and major scale is evidence to support the increasing global climate crisis, and how it is severely impacting all levels of life.

Bibliography

Belyeu, S. (2019, November 22). Why Are Flowering Plants Important to the Earth & Humans? Sciencing. Retrieved July 5, 2022, from https://sciencing.com/flowering-plants-important-earth-humans-6628704.html

Primack, R., & Higuchi, H. (2007). Climate Change and Cherry Tree Blossom Festivals in Japan. Arnold Arboretum of Harvard University. http://bigtime.arboretum.harvard.edu/pdf/issues/2007-65-2-Arnoldia.pdf#page=16

Primack, R., Higuchi, H., & Miller-Rushing, A. (2009). The Impact of Climate Change On Cherry Trees and Other Species in Japan (9th ed., Vol. 142). Biological Conservation. https://doi.org/10.1016/j.biocon.2009.03.016.

Primack, R., Miller-Rushing, A., Katsuki, T., Ishii, Y., Don Lee, S., & Higuchi, H. (2007, September 1). Impact of Global Warming on a Group of Related Species and Their Hybrids. American Journal of Botany, 94(9), 1470-1478. https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/ajb.94.9.1470