Global climate change is predicted to have large impacts on the phenology and reproduction of alpine plants, which will have important implications for plant demography and community interactions, trophic dynamics, ecosystem energy balance, and human livelihoods. In this article we report results of a 3-year, fully factorial experimental study exploring how warming, snow addition, and their combination affect reproductive phenology, effort, and success of four alpine plant species belonging to three different life forms in a semiarid, alpine meadow ecosystem on the central Tibetan Plateau. Our results indicate that warming and snow addition change reproductive phenology and success, but responses are not uniform across species. Moreover, traits associated with resource acquisition, such as rooting depth and life history (early vs. late flowering), mediate plant phenology, and reproductive responses to changing climatic conditions. Specifically, we found that warming delayed the reproductive phenology and decreased number of inflorescences of Kobresia pygmaea C. B. Clarke, a shallow-rooted, early-flowering plant, which may be mainly constrained by upper-soil moisture availability. Because K. pygmaea is the dominant species in the alpine meadow ecosystem, these results may have important implications for ecosystem dynamics and for pastoralists and wildlife in the region.

Phenology studies the cycle of events in nature that are initiated and driven by an annually recurring environment. Plant phenology is expected to be one of the most sensitive and easily observable natural indicators of climate change. On the Tibetan Plateau (TP), an accelerated warming since the mid-1980s has resulted in significant environmental changes. These new conditions are accompanied by phenological changes that are characterized by considerable spatiotemporal heterogeneity. Satellite remote sensing observed widespread advance in the start of the plant growing season across the plateau during the 1980s and 1990s but substantial delay over 2000–2011 in the southwest although it continued to advance in the northeast regions of the TP. Both observational studies and controlled experiments have revealed, to some extent, the positive role of higher preseason temperature and even more precipitation in advancing the leaf onset and first flowering date of the TP. However, a number of rarely visited research issues that are essential for understanding the role of phenology in ecosystem responses and feedback processes to climate change remain to be solved. Our review recommends that addressing the following questions should be a high priority. How did other phenological events change, such as flowering and fruiting phenology? What are the influences from environmental changes other than temperature and precipitation, including human activities such as grazing? What are the genetic and physiological bases of plants phenological responses? How does phenological change influence ecosystem structure and function at different scales and feedback to the climate system? Investigating these research questions requires, first of all, new data of the associated environmental variables, and consistent and reliable phenological observation using different methodologies (i.e. in situ observations and remote sensing).

Organisms' life cycles consist of hierarchical stages, from a single phenological stage (for example, flowering within a season), to vegetative and reproductive phases, to the total lifespan of the individual. Yet phenological events are typically studied in isolation, limiting our understanding of life history responses to climate change. Here, we reciprocally transfer plant communities along an elevation gradient to investigate plastic changes in the duration of sequential phenological events for six alpine species. We show that prolonged flowering leads to longer reproductive phases and activity periods when plants are moved to warmer locations. In contrast, shorter post-fruiting leaf and flowering stages led to shorter vegetative and reproductive phases, respectively, which resulted in shorter activity periods when plants were moved to cooler conditions. Therefore, phenological responses to warming and cooling do not simply mirror one another in the opposite direction, and low temperature may limit reproductive allocation in the alpine region.

Start of growing season advanced by 9.4 ± 2.2 and 8.3± 2.0 days during 1982-1999 and 2000-2020 respectively, whereas its end delayed only by 8.2 ± 1.9 days during 2000-2020.Current models project an advance in season start by 8.8 days and a delay in season end by 14.0 days in 2086-2100 relative to 2000-2014 under Shared-Socioeconomic-Pathway 5-8.5. Warming and increasing precipitation are the main climatic drivers of advancing spring phenology (start of vegetative growing season and first flowering) and delaying end of the growing season. The direction and magnitude of responses of phenophases to temperature depend on soil water availability, with greater temperature sensitivity of the start and end of the season under wetter conditions.First flowering date is more sensitive to temperature on the Qinghai-Tibetan Plateau than in Arctic grasslands.The temperature sensitivities of the start and end of the growing season are greater than those of Arctic grasslands, but smaller than those of mid-latitude alpine and subalpine grasslands.

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Alpine meadows on the Tibetan Plateau comprise the largest alpine ecosystem in the world and provide critical ecosystem services, including forage production and carbon sequestration, on which people depend from local to global scales. However, the provision of these services may be threatened by climate warming combined with land use policies that are altering if and how pastoralists can continue to graze livestock, the dominant livelihood practice in this region for millennia. We synthesized findings from a climate warming and yak grazing experiment with landscape-level observations in central Tibet to gain insight into the trajectories of change that Tibet's alpine meadows will undergo in response to expected changes in climate and land use. We show that within 5 years, experimental warming drove an alpine community with intact, sedge-dominated turfs into a degraded state. With removal of livestock, consistent with policy intended to reverse degradation, a longer-term shift to a more shrub-dominated community will likely occur. Neither degraded nor shrub meadows produce forage or sequester carbon to the same degree as intact meadows, indicating that climate warming and drying will reduce the ability of Tibet's alpine meadows to provide key ecosystem services, and that livestock reduction policies intended to counteract trajectories of land degradation instead endanger contemporary livelihoods on the Tibetan Plateau.

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Change in individual species phenology is often unsuitable for predicting change in community phenology because of different responses of different species to temperature change. However, few studies have observed community phenological sequences in the field. Here we explore the changes in timing and duration of the community phenological sequence (i.e. onset of leaf-out (OLO), first flower bud (FB), first flowering (FF), first fruiting-set (FFS), post-fruiting vegetation (OPFV), first leaf-coloring (FLC) and complete leaf-coloring (CLC)) along an elevation gradient from 3200 to 3800 m in an alpine meadow on the Tibetan plateau. Our results indicate that OLO and FFS significantly advanced and other timings of phenological events significantly delayed at 3200 m compared with higher elevations (3600 and 3800 m). The flowering duration of the community was shortest and other phenological durations (except budding stage and post-fruiting vegetation stage) were longest at 3200 m. The duration of the growing season decreased as elevation increased, and the ratio of the durations of the reproductive period and growing season was smallest at 3200 m. There were negative correlations between the proportion of early-spring flowering functional group plants and FB, and the durations of leafing and post-fruiting vegetation of the community. Positive correlations were found between the proportion of midsummer flowering functional group plants in the community and these variables. There were significant negative correlations between flowering duration of the community and annual mean air temperature and soil moisture. 4 Therefore, our results suggest that different community compositions might respond differently to climate change.