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Update:November 2, 2020

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When sika deer want to eat leaves in high places, they break stems

Article title

Characteristics of Stem Breakage in Young Sugi (Cryptomeria japonica) Trees due to Sika Deer

Author (affiliation)

Haruto Nomiya (a), Hiromi Yamagawa (b), Hidetoshi Shigenaga (c), Satoshi Ito (d), Ryoko Hirata (d), Shuichi Hikichi (e)

(a) Kyushu Research Center, FFPRI, Kumamoto, Japan.

(b) Department of Forest Vegetation, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Department of Plant Ecology, FFPRI, Tsukuba, Ibaraki, Japan.

(d) University of Miyazaki, Miyazaki, Japan.

(e) Ooita District Forest Office, Forestry Agency, Ooita, Japan.

Publication Journal

Journal of Japanese Forestry Society, 102: 202-206(2020) DOI:10.4005/jjfs.102.202( External link )

Content introduction

In forestry, in order for young trees to grow faster than undergrowth, so-called "large saplings" of 160cm or more in height are sometimes planted. When such saplings are planted, it is known that sika deer will often eat branches and leaves at a height of around 100cm. However, it has been observed that when a deer wants to eat parts that are higher up, it will sometimes eat them after breaking the trunk (main stem). Therefore, we have been studying the condition of young trees that have been damaged in this way.

When a survey was made of 500 very large sugi cedar saplings averaging 160cm in height that had been planted, it was found that over a 2-year period, stem breakage from deer browsing on tips had occurred in 70 of the trees. Damage tended to be concentrated between 100cm and 130cm in height (Fig. 1), and the maximum diameter of broken sections was 16mm (average 12mm) (Fig. 2). At the study site, stem breakage occurred in the 1st and 2nd years after planting, and the growth of damaged sugi trees was noticeably slower (Fig. 3). In addition, a diameter of 16mm at a height of 130cm would be the equivalent of a 200cm-high sapling, so it is thought that the greatest risk for breakage to occur would be in growth up to that height. Therefore, even if large 160cm-high saplings are planted, it appears that they would still go through a dangerous period for a while after planting.

This study has enabled the relationship between damage from deer browsing and young sugi cedar trees to be quantitatively demonstrated, and will provide useful information for incorporating deer countermeasures into forestry plans, such as time frames for formulating measures to counter damage.


Figure1:View of stem breakage
Figure1:View of stem breakage (left photo), and diagram showing the number of trees that were damaged at various breakage heights (right figure). The yellow background in the right figure indicates the height range at which deer can cause damage by eating tips of branches. (For more detailed information, please refer to the study result "How high can deer eat Sugi saplings?").


Figure 2:View of the point of breakage and diagram showing

Figure2:View of the point of breakage (left photo) and diagram showing the distribution of stem diameters at the point of breakage or failed breakage (right figure).


Figure 3:Tree growth up to the 4th year after planting

Figure3:Tree growth up to the 4th year after planting

Growth was noticeably slower in trees whose main stem had been broken, and even in the 4th year such trees were significantly smaller than undamaged individuals. The bars show the standard deviation.