Plant phenology shifts under climate warming: a systematic review of recent scientific literature

Climate warming-driven temporal shifts in phenology are widely recognised as the foremost footprint of global environmental change. In this regard, concerted research efforts are being made worldwide to monitor and assess the plant phenological responses to climate warming across species, ecosystems and seasons. Here, we present a global synthesis of the recent scientific literature to assess the progress made in this area of research. To achieve this, we conducted a systematic review by following PRISMA protocol, which involved rigorous screening of 9476 studies on the topic and finally selected 215 studies for data extraction. The results revealed that woody species, natural ecosystems and plant phenological responses in spring season have been predominantly studied, with the herbaceous species, agricultural ecosystems and other seasons grossly understudied. Majority of the studies reported phenological advancement (i.e., preponement) in spring, followed by also advancement in summer but delay in autumn. Methodology-wise, nearly two -third of the studies have employed direct observational approach, followed by herbarium-based and experimental approaches, with the latter covering least temporal depth. We found a steady increase in research on the topic over the last decade with a sharp increase since 2014. The global country-wide scientific output map highlights the huge geographical gaps in this area of research, particularly in the biodiversity-rich tropical regions of the developing world. Based on the findings of this global synthesis, we identify the current knowledge gaps and suggest future directions for this emerging area of research in an increasingly warming world.