Leaf onset in the northern hemisphere triggered by daytime temperature
TL;DR: This work shows that the interannual anomalies of LUD during 1982–2011 are triggered by daytime (Tmax) more than by nighttime temperature (Tmin), and suggests a new conceptual framework of leaf onset using daytime temperature to improve the performance of phenology modules in current Earth system models.
Abstract: Recent warming significantly advanced leaf onset in the northern hemisphere. This signal cannot be accurately reproduced by current models parameterized by daily mean temperature (Tmean). Here using in situ observations of leaf unfolding dates (LUDs) in Europe and the United States, we show that the interannual anomalies of LUD during 1982–2011 are triggered by daytime (Tmax) more than by nighttime temperature (Tmin). Furthermore, an increase of 1 Ci nTmax would advance LUD by 4.7 days in Europe and 4.3 days in the United States, more than the conventional temperature sensitivity estimated from Tmean. The triggering role of Tmax, rather than the Tmin or Tmean variable, is also supported by analysis of the large-scale patterns of satellite-derived vegetation green-up in spring in the northern hemisphere (430N). Our results suggest a new conceptual framework of leaf onset using daytime temperature to improve the performance of phenology modules in current Earth system
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01 Jan 2009
TL;DR: In this paper, the authors assess 10 start-of-spring (SOS) methods for North America between 1982 and 2006 and find that SOS estimates were more related to the first leaf and first flowers expanding phenological stages.
Abstract: Shifts in the timing of spring phenology are a central feature of global change research. Long-term observations of plant phenology have been used to track vegetation responses to climate variability but are often limited to particular species and locations and may not represent synoptic patterns. Satellite remote sensing is instead used for continental to global monitoring. Although numerous methods exist to extract phenological timing, in particular start-of-spring (SOS), from time series of reflectance data, a comprehensive intercomparison and interpretation of SOS methods has not been conducted. Here, we assess 10 SOS methods for North America between 1982 and 2006. The techniques include consistent inputs from the 8km Global Inventory Modeling and Mapping Studies Advanced Very High Resolution Radiometer NDVIg dataset, independent data for snow cover, soil thaw, lake ice dynamics, spring streamflow timing, over 16000 individual measurements of ground-based phenology, and two temperature-driven models of spring phenology. Compared with an ensemble of the 10 SOS methods, we found that individual methods differed in average day-of-year estimates by ! 60 days and in standard deviation by ! 20 days. The ability of the satellite methods to retrieve SOS estimates was highest in northern latitudes and lowest in arid, tropical, and Mediterranean ecoregions. The ordinal rank of SOS methods varied geographically, as did the relationships between SOS estimates and the cryospheric/hydrologic metrics. Compared with ground observations, SOS estimates were more related to the first leaf and first flowers expanding phenological stages. We found no evidence for time trends in spring arrival from ground- or model-based data; using an ensemble estimate from two methods that were more closely related to ground observations than other methods, SOS
828 citations
TL;DR: It is suggested that future studies should primarily focus on using new observation tools to improve the understanding of tropical plant phenology, on improving process-based phenology modeling, and on the scaling of phenology from species to landscape-level.
Abstract: Plant phenology, the annually recurring sequence of plant developmental stages, is important for plant functioning and ecosystem services and their biophysical and biogeochemical feedbacks to the climate system. Plant phenology depends on temperature, and the current rapid climate change has revived interest in understanding and modeling the responses of plant phenology to the warming trend and the consequences thereof for ecosystems. Here, we review recent progresses in plant phenology and its interactions with climate change. Focusing on the start (leaf unfolding) and end (leaf coloring) of plant growing seasons, we show that the recent rapid expansion in ground- and remote sensing- based phenology data acquisition has been highly beneficial and has supported major advances in plant phenology research. Studies using multiple data sources and methods generally agree on the trends of advanced leaf unfolding and delayed leaf coloring due to climate change, yet these trends appear to have decelerated or even reversed in recent years. Our understanding of the mechanisms underlying the plant phenology responses to climate warming is still limited. The interactions between multiple drivers complicate the modeling and prediction of plant phenology changes. Furthermore, changes in plant phenology have important implications for ecosystem carbon cycles and ecosystem feedbacks to climate, yet the quantification of such impacts remains challenging. We suggest that future studies should primarily focus on using new observation tools to improve the understanding of tropical plant phenology, on improving process-based phenology modeling, and on the scaling of phenology from species to landscape-level.
750 citations
Cites background from "Leaf onset in the northern hemisphe..."
...For example, it was found that spring phenology is more responsive to warming during daytime than to nighttime warming, at both species‐ and ecosystem levels (Piao et al., 2015; Rossi & Isabel, 2017)....
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...Considering the faster nighttime warming over the past decades (Davy, Esau, Chernokulsky, Outten, & Zilitinkevich, 2017), the absence of such asymmetric warming effects in models might lead to underestimations of the temperature sensitivity of spring phenology (Piao et al., 2015)....
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TL;DR: The results provide empirical evidence for a declining ST, but also suggest that the predicted strong winter warming in the future may further reduce ST and therefore result in a slowdown in the advance of tree spring phenology.
Abstract: Spring leaf unfolding has been occurring earlier in the year because of rising temperatures; however, long-term evidence in the field from 7 European tree species studied in 1,245 sites shows that this early unfolding effect is being reduced in recent years, possibly because the reducing chilling and/or insolation render trees less responsive to warming. Spring leaf unfolding has been occurring earlier in the year because of rising temperatures, but some experimental evidence has suggested that the effect is becoming less marked because trees are not receiving the necessary chilling required to trigger leaf unfolding. Shilong Piao and colleagues present evidence based on long-term field observations of seven European tree species studied in 1,245 locations across Europe confirming that a weakening of temperature sensitivity of leaf unfolding is indeed occurring. The authors provide model-based evidence that the chilling effect is at least partially responsible. Earlier spring leaf unfolding is a frequently observed response of plants to climate warming1,2,3,4. Many deciduous tree species require chilling for dormancy release, and warming-related reductions in chilling may counteract the advance of leaf unfolding in response to warming5,6. Empirical evidence for this, however, is limited to saplings or twigs in climate-controlled chambers7,8. Using long-term in situ observations of leaf unfolding for seven dominant European tree species at 1,245 sites, here we show that the apparent response of leaf unfolding to climate warming (ST, expressed in days advance of leaf unfolding per °C warming) has significantly decreased from 1980 to 2013 in all monitored tree species. Averaged across all species and sites, ST decreased by 40% from 4.0 ± 1.8 days °C−1 during 1980–1994 to 2.3 ± 1.6 days °C−1 during 1999–2013. The declining ST was also simulated by chilling-based phenology models, albeit with a weaker decline (24–30%) than observed in situ. The reduction in ST is likely to be partly attributable to reduced chilling. Nonetheless, other mechanisms may also have a role, such as ‘photoperiod limitation’ mechanisms that may become ultimately limiting when leaf unfolding dates occur too early in the season. Our results provide empirical evidence for a declining ST, but also suggest that the predicted strong winter warming in the future may further reduce ST and therefore result in a slowdown in the advance of tree spring phenology.
583 citations
Chinese Academy of Sciences1, University of California, Los Angeles2, University of Gothenburg3, Ohio State University4, University of Maryland, College Park5, Fudan University6, University of California, Santa Barbara7, Peking University8, Japan Agency for Marine-Earth Science and Technology9, University of Tsukuba10, Nanjing University11, San Diego State University12, University of Twente13, National Center for Atmospheric Research14, Texas A&M University15, Pacific Northwest National Laboratory16, Chengdu University of Information Technology17
TL;DR: The Third Pole (TP) is experiencing rapid warming and is currently in its warmest period in the past 2,000 years as mentioned in this paper, and the latest development in multidisciplinary TP research is reviewed in this paper.
Abstract: The Third Pole (TP) is experiencing rapid warming and is currently in its warmest period in the past 2,000 years. This paper reviews the latest development in multidisciplinary TP research ...
530 citations
TL;DR: It is argued that inconclusive, unexpected, or counter-intuitive results should be embraced in order to understand apparent disconnects between theory, prediction, and observation, and that the need for ecologists to conduct community-level experiments in systems that replicate multiple aspects of ACC is highlighted.
337 citations
Cites background from "Leaf onset in the northern hemisphe..."
...While remote-sensing techniques have been effective in discerning and analysing differences among years and regions in community metrics, such as ‘green-up’ (Fitchett et al., 2015; Piao et al., 2015), they cannot effectively distinguish between component species within ecosystems....
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...…Jeong et al., 2011), flowering and fruiting (Fitter and Fitter, 2002; Cook et al., 2012; Xia and Wan, 2013), and general green-up of the northern hemisphere (Piao et al., 2015) have all advanced in concert with regional warming trends (Menzel et al., 2006; Parmesan, 2007; Poloczanska et al., 2013)....
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References
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TL;DR: In this paper, the seasonal vegetation response to the recent climatic variation on the Mongolian steppes, the third largest grassland in the world, was examined using time-series analysis of advanced very high resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) biweekly composite data collected between January 1982 and December 1991.
302 citations
01 Jan 2002
302 citations
TL;DR: The springtime extension of the photosynthetic and potential growing seasons has apparently stimulated earlier and stronger net CO(2) uptake by northern ecosystems, while the autumnal extension is associated with an earlier net release of CO( 2) to the atmosphere.
Abstract: We combine satellite and ground observations during 1950-2011 to study the long-term links between multiple climate (air temperature and cryospheric dynamics) and vegetation (greenness and atmospheric CO(2) concentrations) indicators of the growing season of northern ecosystems (>45°N) and their connection with the carbon cycle. During the last three decades, the thermal potential growing season has lengthened by about 10.5 days (P 0.05). The photosynthetic growing season has closely tracked the pace of warming and extension of the potential growing season in spring, but not in autumn when factors such as light and moisture limitation may constrain photosynthesis. The autumnal extension of the photosynthetic growing season since 1982 appears to be about half that of the thermal potential growing season, yielding a smaller lengthening of the photosynthetic growing season (6.7 days at the circumpolar scale, P < 0.01). Nevertheless, when integrated over the growing season, photosynthetic activity has closely followed the interannual variations and warming trend in cumulative growing season temperatures. This lengthening and intensification of the photosynthetic growing season, manifested principally over Eurasia rather than North America, is associated with a long-term increase (22.2% since 1972, P < 0.01) in the amplitude of the CO(2) annual cycle at northern latitudes. The springtime extension of the photosynthetic and potential growing seasons has apparently stimulated earlier and stronger net CO(2) uptake by northern ecosystems, while the autumnal extension is associated with an earlier net release of CO(2) to the atmosphere. These contrasting responses may be critical in determining the impact of continued warming on northern terrestrial ecosystems and the carbon cycle.
288 citations
01 Jan 1990
255 citations
Peking University1, Centre national de la recherche scientifique2, University of Exeter3, Lund University4, Chinese Academy of Sciences5, National Center for Atmospheric Research6, University of Sheffield7, Oak Ridge National Laboratory8, Boston University9, Max Planck Society10, University of Maryland, College Park11, Princeton University12
TL;DR: This article showed that the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient RNDVI-GT) declined substantially between 1982 and 2011.
Abstract: Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient RNDVI-GT) declined substantially between 1982 and 2011. This decrease in RNDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in RNDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.
245 citations