Tree Phenology

Jean Combes’s love of nature as a child led her to note the signs of starting spring. Her long-term records are now part of a vital growing citizen science dataset that starkly shows how climate change is shifting the timing of the natural world.

Shifts in phenology can impact organism fitness, ecosystem function, and goods and services from nature. Climate change management must better integrate phenology to optimize conservation outcomes as these impacts increase.

Phenological shifts due to climate change can desynchronize the timings of life history events between species, but predicting the consequences is challenging. Changes to current methodologies would allow testing of the widely used Cushing hypothesis and improve predictions of climate change impacts.

The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.

The authors conduct a meta-analysis to reveal mismatches in above- and belowground plant phenological responses to warming that differ by plant type (herbaceous versus woody). The work highlights a need for further research and consideration of under-represented belowground phenological changes.

Our knowledge of long-term changes in vegetation activity is incomplete, hindering understanding of Earth system dynamics. A comprehensive global assessment of vegetation phenology now shows that vegetation activity changed severely on 54% of the global land surface between 1981 and 2012.

The authors use central European observations of leaf unfolding date (LUD) for six tree species. They demonstrate antagonistic and heterogenous effects of winter chilling and spring thermal accumulation on leaf phenology, with the latter having greater explanation (61% versus 39%) for LUD advancement.

Climate-induced changes in phenology have the potential to push trophic relationships out of synchrony, but evidence of this phenomenon is scant, particularly in the Arctic. A long-term (1996–2009), spatially replicated data set from high-Arctic Greenland now indicates a climate-associated shortening of the flowering season, and a concomitant decline in flower visitor abundance.

Autumn leaf senescence has later onset, higher phenological plasticity and a stronger climatic response under warm compared to cold autumns. While night-time warming delays senescence, drought induced by daytime warming advances it, which may lead to loss in growing season under global warming.

Phenological shifts due to warming extend the growing season for plants, with implications for ecosystem productivity. Carbon uptake through photosynthesis is limited by radiation, particularly in autumn, which explains contrasting regional responses of autumn carbon uptake to rising temperatures.

Climate change has led to earlier spring leaf-out in northern temperate and boreal regions. This advanced leaf-out causes warming in the Northern Hemisphere due to the combined effects of water vapour, cloud and snow-albedo feedbacks on the surface energy budget.

Spring phenology is influenced by chilling, forcing and photoperiod cues; the phenological response to warming from anthropogenic climate change may be slowed by chilling or photoperiod. Plant species respond to all cues in experiments but under environmental conditions, forcing predominates.

Changes in precipitation remains an understudied factor that can impact leaf onset date (LOD) under climate change. The authors show that decreasing precipitation frequency has contributed to LOD advancement, and that incorporating precipitation data projects earlier LOD than currently predicted.