The resource budget hypothesis is widely accepted as a physiological explanation of masting, which is characterized by highly variable, synchronous reproduction within a population across years. According to the hypothesis, when resources are depleted by a large reproductive output, it takes more than one year to replenish them. This results in intermittent mass flowering and seed production. The key resources depleted by a single reproduction have been identified in several woody species but rarely in herbaceous species. Here, we examined the adequacy of the resource budget hypothesis for masting in the herbaceous species Veratrum album subsp. oxysepalum and identified the key resources. Over an 11-year period, we investigated stem volume as an indicator of resource availability and flowering in 52 plants tagged in the 2013 mast year in a population in northern Japan. We compared the concentrations and masses of carbon and nitrogen in the aboveground and belowground parts of flowering and non-flowering plants. Stem volume decreased in the year after reproduction and gradually recovered in subsequent years. Flowering occurred again once the plant had grown to a large size. These results support the predictions of the resource budget hypothesis. Flowering plants had greater concentrations and masses of carbon in their aboveground parts than non-flowering plants, but smaller concentrations and masses in their belowground parts. Conversely, there were no consistent differences in nitrogen concentration or mass between flowering and non-flowering plants. Therefore, carbon is the key limiting factor in reproduction for this species.

Flowering phenology of alpine plant communities and seasonal dynamics of flower visitors have been scarcely studied in the tropical/subtropical alpine regions. We report flowering phenology, flower production, and flower-visiting insects in the alpine site of central Taiwan. Throughout the research period (2017–2018), we recorded flowering phenology of 130 plant species, flower production of 81 species, and 15,127 insects visiting alpine flowers. Most of the alpine plants were visited by dipteran insects and/or hymenopteran insects. The seasonal patterns of flowering were more apparent in bee-visited plants compared to fly-visited plants in which the flowering of bee-visited plants clearly increased as the season progressed. About 63% of flower visitors were dipteran insects (syrphid and non-syrphid flies), and 30% were hymenopteran insects (mostly bumble-bee workers). Although the seasonal trend in fly abundance was less clear between years, bumble-bee abundance consistently increased in the middle to late seasons, reflecting colony development. There was a positive correlation between bee abundance and the number of flowering species of bee-visited plants, but there was no correlation between fly abundance and the number of flowering species of fly-visited plants throughout the season. These results suggest that the flowering phenology of subtropical alpine communities is influenced by the seasonal availability of pollinators. Bumble bees, syrphid flies, and non-syrphid flies had wide ranges of foraging flowers, but their niche overlap was relatively small. Because cold-adapted bumble bees are threatened by climate change in Taiwan, plant–pollinator interactions may be disturbed by global warming.