Dafen of the Yushan National Park (YNP) is a critical habitat for locally endangered Formosan black bears (Ursus thibetanus formosanus). The phenology and acorn production of the dominant ring-cupped oaks (Cyclobalanopsis glauca) potentially influence temporal and spatial movement, activity and relative abundance of bears. The objective was to explore the dynamics and acorn production of ring-cupped oak, and the relationship between acorns and the relative abundance, activity of black bears in Dafen oak forest. The study was further designed to estimate the size and genetic variation of the YNP population and provide guidelines for representative data sampling. The acorn production estimated by two visual survey methods both indicated 2010 was after 2008. From 2006 to 2009, seed traps revealed the same pattern with visual survey. There were positive correlation relationships among the three methods of estimating acorn production. The average amount of intact acorns, damaged acorns and total acorns collected by seed traps (85 cm* 85 cm, n=195) was highest in November and December, followed by October and January. The fallen acorns during the acorn season in 2010 was 21 acorns/m2. The damaged acorns were 46% of the total acorns collected in seed traps, and its proportion decreased with the total amount of acorns. The acorn removal rate on ground was 4-5 acorns/m2 in November and December, followed by 1-2 acorns/m2 in October and January-February. Most (69%-96%) of the monthly fallen acorns were consumed, indicating the very high pressure of acorn predation by wildlife in Dafen. Using hair samples snared from baited traps with lures and fecal samples which were collected during February 2008-January 2009 in Dafen, microsatellite DNA analysis was applied to distinguish bear individuals. We analyzed 112 hair and 290 fecal samples, which yielded 62% and 54% of the successful DNA amplification rates, respectively. The genotyping based on 7 microsatellite primers for individual identification indicated 37 and 73 individuals, from hair and fecal samples, separately. Thus, a total of 100 different individuals were indentified and the population estimation was further conducted and discussed. The average number of alleles per locus was 8.7, ranging from 5 to 19. The overall observed heterozygosity was 0.762, which was close to the expected heterozygosity (0.761). The overall FIS value was 0.001. The result revealed the acceptable level of genetic diversity of the YNP population. Among all bear individuals identified from genetic samples, 7% of them were only detected in the non-acorn season (October up to next January), and 90% were only detected in the acorn season. The masting season of ring-cupped oak in 2008 likely attracted a highly dense congregation of bears. Considering the bear movement pattern for seeking food and our result that all the effective samples collected in non-acorn season were hair samples, we suggested that hair traps should be technically feasible and suitable for areas with sparsely distributed populations. On the other hand, if a seasonal high-density benchmark like our study area can be identified, scat sampling tends to provide an appropriate representative of DNA sampling methods.