How Sika Deer’s Overpopulation Led To Forest Decline in Kyushu

Sika deer ate away the understorey vegetation of Kyushu’s Beech forest, leading to soil erosion and exposed roots in the area.

AsianScientist (Apr. 13, 2024) – Researchers from Japan have found that the unchecked growth of the Sika deer (Cervus nippon) is causing soil erosion in beech forests of southern Kyushu, which in turn is reducing the growth of iconic Japanese beech trees (Fagus crenata). This indicates how ecological balance can be altered with the increase or decrease of a single species. The study was published in the journal Catena.

In nature, different species interact with each other and their physical environment directly or indirectly in the form of food chains and food webs. Any change in a food chain can alter the ecological balance and have serious consequences.

The overpopulation of Sika deer has led to the degradation of dwarf bamboo, which is the dominant understorey vegetation in Southern Kysushu forests. “Due to their overpopulation and subsequent foraging, dwarf bamboo was lost. This destabilized the soil and led to soil erosion, exposing the roots of the beech trees,” said  Hayato Abe, the first and corresponding author of the study at Kyushu University’s Graduate School of Agriculture, in an interview with Asian Scientist Magazine.

Soil erosion, catalyzed by the degradation of understory vegetation, rendered beech tree roots vulnerable, hindering their capacity to absorb water and nutrients efficiently. Abe elaborated, “Our findings strongly indicate that soil erosion contributes to water stress in the trees, significantly impacting their growth and vitality.”

Ecological surveys and careful tree ring analysis showed that the growth of beech trees has been slowly decreasing since 1997. This is around the same time that the deer have been foraging the understory plants. Abe and his colleagues carefully measured the length of open beech tree roots and found a strong link between higher levels of exposed roots and slower growth rates. “To learn more about this connection, we looked into how the trees absorb water.” The trees with exposed roots absorb less water, which slows down their growth. This shows how soil erosion, tree health, and water availability are interconnected in a complicated manner. “Our research showed that trees that had difficulty absorbing water grew slowly,” Abe said.

“When the growth of beech trees is slowed down, it has multiple consequences. As leaf growth slows down, there is less leaf litter on the forest floor. This makes soil erosion faster, which starts a negative feedback loop,” Abe told Asian Scientist Magazine. “These weakened trees are also more susceptible to damage from strong winds, climate fluctuations, and pest infestations, increasing the likelihood of their death.”

Overpopulation of Sika deers in the Southern Kyushu forests is also hampering the attempts to conserve the forest. Until 1980s, Sika deer hunters helped control their population but gradually the number of hunters decreased, leading to increase the Sika population. Absence of their natural predators in the area contributed to the problem. The Japanese government has tried to restrict the Sika deer to particular areas, but creating such facilities in remote places like Shiba village of Southern Kyushu is difficult.

To solve the problem, scientists, politicians, and people from the community must work together in cross-disciplinary teams.

Source: Kyushu University ; Image: Shuterstock

The article can be found at: Soil erosion under forest hampers beech growth: Impacts of understory vegetation degradation by Sika deer.

Disclaimer: This article does not necessarily reflect the views of Asian Scientist or its staff.



Parvaiz Yousuf is a science journalist and researcher based in Kashmir, India.

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