Changes in temperature sensitivity of spring phenology with recent climate warming in Switzerland are related to shifts of the preseason

Abstract

The spring phenology of plants in temperate regions strongly responds to spring temperatures. Climate warming has caused substantial phenological advances in the past, but trends to be expected in the future are uncertain. A simple indicator is temperature sensitivity, the phenological advance statistically associated with a 1°C warmer mean temperature during the "preseason", defined as the most temperature-sensitive period preceding the phenological event. Recent analyses of phenological records have shown a decline in temperature sensitivity of leaf unfolding, but underlying mechanisms were not clear. Here, we propose that climate warming can reduce temperature sensitivity simply by reducing the length of the preseason due to faster bud development during this time period, unless the entire preseason shifts forward so that its temperature does not change. We derive these predictions theoretically from the widely used "thermal time model" for bud development and test them using data for 19 phenological events recorded in 1970-2012 at 108 stations spanning a 1600 m altitudinal range in Switzerland. We consider how temperature sensitivity, preseason start, preseason length and preseason temperature change (i) with altitude, (ii) between the periods 1970-1987 and 1995-2012, which differed mainly in spring temperatures, and (iii) between two non-consecutive sets of 18 years that differed mainly in winter temperatures. On average, temperature sensitivity increased with altitude (colder climate) and was reduced in years with warmer springs, but not in years with warmer winters. These trends also varied among species. Decreasing temperature sensitivity in warmer springs was associated with a limited forward shift of preseason start, higher temperatures during the preseason and reduced preseason length, but not with reduced winter chilling. Our results imply that declining temperature sensitivity can result directly from spring warming and does not necessarily indicate altered physiological responses or stronger constraints such as reduced winter chilling.

Climatic Warming Increases Spatial Synchrony in Spring Vegetation Phenology Across the Northern Hemisphere

“…We tested this hypothesis by applying four chilling-based models for 2080-2099 but kept the winter temperature (S3) or the spring temperature (S4) constant and then assessing their difference to simulations based on varying winter and spring temperatures (S5; Figures S10a-S10h; see section 2). Experimental studies comparing phenology in regions at lower and higher elevations have reported similar findings (Gusewell et al, 2017;Vitasse et al, 2018). The predicted SOSs across most of the NH (mainly at higher latitudes) did not differ significantly between these two simulations (p > 0.05).…”

Sensitivity of Deciduous Forest Phenology to Environmental Drivers: Implications for Climate Change Impacts Across North America

“…Despite the wider range of spring temperature anomalies at cold sites (3.2 °C vs. 2.9 °C in warm sites), we observed less variability in the timing of green‐up (7.8 days in cold sites vs. 9.8 days in warm sites). Our findings do not necessarily contradict previous studies finding higher photoperiod sensitivity in lower latitudes (Zohner et al, ), as higher temperature sensitivity and higher photoperiod sensitivity could co‐occur and photoperiod limitation may not explain spatial patterns of temperature sensitivity of green‐up (Güsewell et al, ; Zhang et al, ).…”

Climate change fingerprints in recent European plant phenology

“…It was not the aim of our paper to disentangle the contribution of the obvious reasons for this result, but the moving window approach clearly showed that spring and winter warming trends exhibited very similar variation overtime, that is, the strongest trends in the 1980-2010 period. Thus, it is more likely that a reduction in forcing conditions has driven the decrease in the advance of spring and summer phenology (as reported by Güsewell et al, 2017 for Switzerland) than a lack of chilling (e.g. .…”

“…However, there are also contrasting opinions for example, by Wang et al (). Güsewell, Furrer, Gehrig, and Pietragalla () showed that for Switzerland there are still no indications of a lack of chilling leading to altered temperature sensitivities. Changes in temperature sensitivities are reported as not uniform over time (Chen et al, ) and, in particular, a weakened temperature response was observed since 2000 (Fu et al, ).…”