The relationship between oak phenology and acorn production, and Formosan black bears in Yushan National Park, Taiwan

in International Symposium (Abstract oral presentation), 國際研討會(摘要口頭發表)
標題The relationship between oak phenology and acorn production, and Formosan black bears in Yushan National Park, Taiwan
AuthorsMei-Hsiu Hwang, 黃美秀
出版日期Nov 17 2009 12:0

Acorns present a high-nutrition food for many wildlife species, including bears throughout their geographical ranges. The seasonal acorn production results in fluctuation of food availability. The Fagaceae family is a main component of forests in sub-mountain and mountain zones of Taiwan. However, its phenology and acorn production, and their relationship with wildlife abundance are barely known. The objective of this study was to understand the phenology and acorn production of the ring-cupped oak (Cyclobalanopsis glauca) in Daphan of Yushan National park, a critical habitat for the locally endangered Formosan black bear (Ursus thibetanus formosanus). We would further explain the effect of the oak forest on the temporally relative abundance of the bears.
We observed 45 ring-cupped oak trees monthly for one year. Although fruiting started in June, acorn gradually ripened in late October until February. Most of the acorn fell off in November and December, when the peak of mature fruiting occurred according to the amount and dry weight of the acorns collected from 45 seed traps. The fruiting peak was consistent with the pressure of acorn predation by wildlife, when the removal rate was high, i.e., 10-12 acroms/m2. Most of the fallen acorns were consumed within a month, when the removal percentage of fallen acorns caused by animals continually increased from October to January (92-97%). By February, the amount of fallen acorns (0.5 acroms/m2) and the percentage (93%) of acorns used by wildlife diminished substantially.
We found that 49% of the oak trees (n=507) had bear claw marks, indicating enormous use of acorns by black bears in Daphan. Bear feeding signs on oak trees were classified by 3 classes: none, only claw marks, and broken branches damaged by bears. We found that the level of tree use by bears was related to acorn production (X2 = 59.3, df =8, P<0.005). Black bears tended to use the productive oak trees more than those with few or no acorns (Spearman correlation, r = 0.311, P<0.001).
We used passive infrared-triggered cameras to assess the occurrence of animals by an Occurrence Index (OI, number of individual-pictures taken per 1,000 camera working hours). The OI values for bears in 2008 were greater than that in both 2007 and 2006, which seems consistent with the acorn masting in 2008. The OI values for bears in acorn seasons (October to January) in 2008 and 2007 were 4.27±2.36 and 0.39±0.50, respectively, which were higher than those in non-acorn seasons (February to September), i.e., 0.25±0.48 and 0.04±0.09 (Mann-Whitney U test, P both <0.01). The seasonal variation of bear OI values was significant within the oak forest only, not in the surrounding non-oak forest. Bears also demonstrated a different activity pattern between seasons by increasing their nocturnal activity during acorn seasons.
The yearly and seasonal variation of relative bear abundance were also found in occurrence of bear signs, which in 2008 was 3.3 times that in 2007. In acorn seasons, the bear signs detected along transects per month*km in 2008 and 2007 were5.15±3.61 and 1.54±1.52, respectively, which were greater than in non-acorn seasons, both 0.09±0.20. The seasonal variation of relative abundance of bears across years seemingly fluctuated more in acorn seasons than in non-acorn seasons.
The result indicated that the acorn production in Daphan was mostly consumed by wildlife, and that it presented a critical seasonal food resource for bears and other large mammals. However, the effects of acorns on the relative abundance and activities of bears may vary by their specific ecological requirement, interspecific interaction, and large-scale distribution and abundance of other food resources.

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