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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University of California, San Diego1, Goddard Institute for Space Studies2, Lamont–Doherty Earth Observatory3, University of Connecticut4, United States Geological Survey5, North Dakota State University6, State Street Corporation7, McGill University8, University of British Columbia9, University of Maryland, College Park10, National Center for Atmospheric Research11, Lund University12, Swedish University of Agricultural Sciences13, University of California, Santa Barbara14, Denver Federal Center15, University of Maine16, University of Texas at Austin17, University of Plymouth18, University of Lausanne19, Swiss Institute of Bioinformatics20, University of Wisconsin–Milwaukee21
TL;DR: In this paper, the authors compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius).
Abstract: Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.
751 citations
01 Apr 2012
TL;DR: Warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations, which introduces uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.
685 citations
TL;DR: In this paper, the authors present an extensive O2/N2 data set which shows simultaneous trends in O 2 /N 2 in both northern and southern hemispheres and allows the O 2/N 2 gradient between the two hemisphere to be quantified, consistent with a budget in which, for the 1991-94 period, the global oceans and the northern land biota each removed the equivalent of approximately 30% of fossil-fuel CO2 emissions, while the tropical land biome as a whole were not a strong source or sink.
Abstract: THE global budget for sources and sinks of anthropogenic CO2 has been found to be out of balance unless the oceanic sink is supplemented by an additional 'missing sink', plausibly associated with land biota1,25. A similar budgeting problem has been found for the Northern Hemisphere alone2,3, suggesting that northern land biota may be the sought-after sink, although this interpretation is not unique2–5; to distinguish oceanic and land carbon uptake, the budgets rely variously, and controversially, on ocean models2,6,7, 13CO2/12CO2 data2,4,5, sparse oceanic observations of (ref. 3) or 13C/12C ratios of dissolved inorganic carbon,4,5,8 or single-latitude trends in atmospheric O2 as detected from changes in O2/N2 ratio.9,10 Here we present an extensive O2/N2 data set which shows simultaneous trends in O2/N2 in both northern and southern hemispheres and allows the O2/N2 gradient between the two hemispheres to be quantified. The data are consistent with a budget in which, for the 1991–94 period, the global oceans and the northern land biota each removed the equivalent of approximately 30% of fossil-fuel CO2 emissions, while the tropical land biota as a whole were not a strong source or sink.
609 citations
Harvard University1, University of Montana2, McMaster University3, Environment Canada4, Ohio State University5, Auburn University6, University of Toronto7, Centre national de la recherche scientifique8, Pennsylvania State University9, University of Wisconsin-Madison10, University of Illinois at Urbana–Champaign11, Indiana University12, Virginia Commonwealth University13, University of Alberta14, United States Forest Service15, Laval University16, Queen's University17, Cooperative Institute for Research in Environmental Sciences18, Oak Ridge National Laboratory19, Princeton University20, University of Colorado Boulder21, Ensenada Center for Scientific Research and Higher Education22, Ghent University23, University of New Hampshire24, University of California, Los Angeles25
TL;DR: In this article, the authors evaluate the representation of phenology, and the associated seasonality of ecosystem-scale CO2 exchange, in 14 models participating in the North American Carbon Program Site Synthesis.
Abstract: Phenology, by controlling the seasonal activity of vegetation on the land surface, plays a fundamental role in regulating photosynthesis and other ecosystem processes, as well as competitive interactions and feedbacks to the climate system. We conducted an analysis to evaluate the representation of phenology, and the associated seasonality of ecosystem-scale CO2 exchange, in 14 models participating in the North American Carbon Program Site Synthesis. Model predictions were evaluated using long-term measurements (emphasizing the period 2000–2006) from 10 forested sites within the AmeriFlux and Fluxnet-Canada networks. In deciduous forests, almost all models consistently predicted that the growing season started earlier, and ended later, than was actually observed; biases of 2 weeks or more were
578 citations
TL;DR: The aim of this study was to show that the most widely used models simulating vegetative or reproductive phenology of trees are particular cases of a more general model, which provides a standardized framework for phenological models, which is essential for comparative studies as well as for robust model identification.
464 citations