(2024/01/24)

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Sika Deer Overpopulation Endangers Beech Forests in Southern Kyushu, JapanA new study reveals how soil erosion caused by sika deer foraging reduces the growth of thebeech trees.
Fukuoka, Japan—Kyushu University researchers have found that beech trees in the forests ofsouthern Kyushu have seen reduced growth, due to soil erosion caused by the overpopulationof sika deer (Cervus nippon). Their findings, which were published in the journal Catena,
could help in the development of new strategies for forest conservation.
Conservation is more than just preserving forests; it's about protecting the diverse web of life.
One area where conservation has become critical is a beech forest in Shiiba Village, in theremote mountains of Southern Kyushu. The Japanese beech tree (Fagus crenata) is aprominent and iconic species in Japan's cool-temperate forests, spanning all across Japan
from Honshu to Southern Kyushu.
However, in recent years, the beech forest in Shiiba Village has have been on the decline,
believed to be driven by the rapid growth of the sika deer population between the 1980s tothe early 2000s.
"Due to their overpopulation and subsequent foraging, dwarf bamboo (Sasamorphaborealis)—the dominant understory vegetation in this area—was lost. This destabilized thesoil and led to soil erosion, exposing the roots of the beech trees," explains Hayato Abe aPh.D. student in Kyushu University's Graduate School of Agriculture and first author of thestudy. "We wanted to see if soil erosion was playing a role in the decline of the beech forest."
Abe and his team conducted an ecological survey on 12 beech trees at a research site in
Shiiba Forest, established by Kyushu University in 1939. They investigated tree growth bymeasuring the production of leaves, stems, and roots. Tree ring samples were also obtained
and used to compare the growth of the trees throughout the years. Their analysis revealed aconcerning decline in tree growth since 1997 – around the same time that the understory
vegetation has been lost due to deer foraging.
Suspecting soil erosion as the primary driver for reduced tree growth, the team looked for alink by measuring the length of the exposed beech tree roots. They found that trees withmore exposed roots showed lower growth rates and produced fewer new leaves.
To understand this link, the researchers also investigated how the trees use water. They
found that trees that struggled to take up water were growing at a slower pace. A likely
explanation, Abe says, is that the parts of the roots that remain in the soil retain water better,as they are exposed to less extreme temperatures. In contrast, the exposed roots arevulnerable to water loss due to freezing or drought and are unable to transport water
efficiently.
"Our results suggest that soil erosion possibly leads to water stress in the trees, affecting

their growth and health. These trees are also more vulnerable to damage from strong winds,
climate change, and pests, which means they are also more likely to wither or die," says Abe.
The scientists also fear that due to fewer leaves growing, the leaf litter on the forest floor will
also decrease, further exacerbating soil erosion and leading to a negative spiral. Ultimately,
the study highlights the delicate relationship between forests and the wildlife that inhabit
them, and the cascading impacts that occur when the ecosystem is out of balance.
"The Japanese government has been taking steps to reduce the local deer population. Up
until the 1980s, the hunting tradition in Shiiba Village had a key role in controlling the sika
deer population. But as time went on, the number of hunters decreased. Compounded by thelack of natural predators in the area, the deer population exploded, leading to the situation
today," continues Abe. "The government is supporting local hunters but it's a short-term
solution. They have also considered exclusion fences to restrict deer to a limited region.
Unfortunately, due to the remoteness of Shiiba Village, setting up such facilities can be costly
and time-consuming."
Solving problems in conservation is never an easy task and requires multifaceted andmultidisciplinary approaches.
"As scientists, we can work to find the root causes of the problems and even developsolutions. But implementation will require working with other researchers and with the larger
community," concludes Abe.
(By Negar Khalili)###For more information about this research, see "Soil erosion under forest hampers beech
growth: Impacts of understory vegetation degradation by sika deer," Hayato Abe, Tomonori
Kume, Fujio Hyodo, Mimori Oyamada, Ayumi Katayama, Catena,https://doi.org/10.1016/j.catena.2023.107559
About Kyushu University
Kyushu University is one of Japan's leading research-oriented institutes of higher education
since its founding in 1911. Home to around 19,000 students and 8,000 faculty and staff, Kyushu
U's world-class research centers cover a wide range of study areas and research fields, fromthe humanities and arts to engineering and medical sciences. Its multiple campuses—including
one of the largest in Japan—are located around Fukuoka City, a coastal metropolis on thesouthwestern Japanese island of Kyushu that is frequently ranked among the world's mostlivable cities and historically known as Japan's gateway to Asia. Through its Vision 2030, Kyushu
U will 'Drive Social Change with Integrative Knowledge.' Its synergistic application of knowledge
will encompass all of academia and solve issues in society while innovating new systems for abetter future.

Fig. 1. Increase in sika deer population damages
the environment. Researchers found that theincrease in sika deer population led to soil erosion
and subsequent reduction in beech tree growth.
(Kyushu University/Samantha Sastrawidjaja)[Contact]
Ayumi Katayama, Associate Professor
Department of Agro-environmental Sciences
Faculty of Agriculture
Tel: +81 92-948-3112
E-mail: ayumi@forest.kyushu-u.ac.jp

Fig. 2. How Sika Deer overpopulation
leads to reduced tree growth. Outline
on how Sika Deer overpopulation leads
to reduced tree growth. Sika Deer
overpopulation leads to thedegradation of understory vegetation,
which in turn leads to soil erosion. This
causes the tree roots to be exposed
leading to water stress in trees andeventual reduction of tree growth.
(Kyushu University/Samantha
Sastrawidjaja)