Differences in spatial versus temporal reaction norms for spring and autumn phenological events

For species to stay temporally tuned to their environment, they use cues such as the accumulation of degree-days. The relationships between the timing of a phenological event in a population and its environmental cue can be described by a population-level reaction norm. Variation in reaction norms along environmental gradients may either intensify the environmental effects on timing (cogradient variation) or attenuate the effects (countergradient variation). To resolve spatial and seasonal variation in species’ response, we use a unique dataset of 91 taxa and 178 phenological events observed across a network of 472 monitoring sites, spread across the nations of the former Soviet Union. We show that compared to local rates of advancement of phenological events with the advancement of temperature-related cues (i.e., variation within site over years), spatial variation in reaction norms tend to accentuate responses in spring (cogradient variation) and attenuate them in autumn (countergradient variation). As a result, among-population variation in the timing of events is greater in spring and less in autumn than if all populations followed the same reaction norm regardless of location. Despite such signs of local adaptation, overall phenotypic plasticity was not sufficient for phenological events to keep exact pace with their cues—the earlier the year, the more did the timing of the phenological event lag behind the timing of the cue. Overall, these patterns suggest that differences in the spatial versus temporal reaction norms will affect species’ response to climate change in opposite ways in spring and autumn.

Misunderstanding mismatch

This is a reponse to Kharouba and Wolkovich's (2020) review of consumer-resource phenological synchrony. They provide a valuable review and cogent advocacy for future work. However, they misunderstand and misinterpret examples from plant-insect interactions. Their detailed case study involves phenological synchrony/ asynchrony between spring hatching of Winter Moth eggs and budburst of their oak hosts. Published studies of this and other insect/plant systems are misinterpreted by applying a definition of phenological synchrony as "the situation in which the most energetically demanding period of the consumer's life cycle overlaps with the period of resource availability." This definition works well for ornithologists, since parent birds require high caterpillar abundance when their chicks are most demanding. But for Winter Moth the crucial phenological event occurs when larvae are just hatched and least demanding of energy, not most demanding (see below). The important role of phenological synchrony in most insect-plant systems is to fit the life cycle into the available time, not to synchronize peak resource demand with peak availability. The same is true of the Bay Checkerspot butterfly, for which baseline data are available from 1968-71 and 1983-5, showing that a fecundity-mortality tradeoff generated a persistent, adaptive, phenological asynchrony between the insect and its hosts, killing 70-80% of larvae each year.Kharouba HM, Wolkovich EM. 2020. Disconnects between ecological theory and data in phenological mismatch research. Nat Clim Chang 10: 406-415

New station-specific limits in phenology to improve data quality during online-data-entry

<p>The Swiss phenology network operated by MeteoSwiss counts approximately 160 stations where up to 69 phenological events are observed by private persons. Currently, 68% of the observer transmit their data online by a recently developed tool called Phenotool. In order to reduce typing errors during the entry of the data, the values are instantly checked by Phenotool. The observer receives a visual warning if the data exceeds defined limits of an expected time-period giving him the opportunity to verify the date entered. The defined limits need to be as suitable as possible for each station and phenological event as numerous false warnings reduce the sensitivity of the observers and cause them to ignore the warning. <br>Until June 2019, limits had been used for five altitudinal layers and for each phenological event resulting from the mean ± 2 SD (standard deviation) rounded to the nearest 10. However, for some stations these limits were not appropriate, therefore, we decided to calculate station specific limits as follows: The median and SD was calculated for each phenological series consisting of at least 10 observations. In a second step, the mean of all SDs < 20 days was calculated and 2.5 times SD added/subtracted from the median. This approach leads to the same range of the limits for each phenological event, while the start of the limits is specific for each stations depending on the previously calculated median. If we would have used a station-specific standard deviation, stations with high variability and often less accurate data, would have been “awarded” with a large range. <br>For new stations, data-series consisting of less than 10 observations or deviant data-series, we calculated the limits with the mean standard deviations as described above and a predicted median from a linear regression model showing the relationship between the medians of a specific phenological event and the station heights. Deviant data-series were recognized by a difference larger than 30 days between modelled and calculated median.<br>The comparison of the old and new limits revealed that the newly calculated limits have an average range which is 8.52 days smaller. 55 out of the 69 phenological events have a smaller range, two has the same, and the remaining 12 have a larger range. Using the previous limits, in average 8.12% of the data from 1985-2019 was outside the defined ranges, however, applying the new limits results in 3.98% of the observations not fitting the limits. Considering the fact that the new limits have in average a smaller range, this improvement becomes even more significant. To conclude, we can say that the new limits produce clearly less warnings and more appropriate warnings in Phenotool enhancing data quality.</p>

The extreme warmth of the Central European spring in 2018 and its effects on fruit ripening phenology in Austria – a 251 year perspective

<p>The exceptional warmth of spring and early summer of 2018 caused the earliest beginning of fruit ripening dates in Austria since 1946 of black elder and red currant, the second earliest of apricot, as well as the shortest period between the beginning of flowering and fruit ripening for all three species (same as 1956 for red currant). These phenological extremities of the 2018 spring correspond with the highest Austrian preseason (temperatures before the phenological event) April/May/June average since 1768.</p><p>In order to put the spring of 2018 into a long term perspective, the above mentioned phenological time series were extended back to 1768 by the much longer homogenised HISTALP temperature time series. This was achieved by multiple regression driven by preseason mean monthly temperatures. In order to accommodate for the uncertainty of the regression model, the lower (5%) and upper (95%) bounds of the confidence intervals were added to the reconstructed time series. Even when considering the lower bounds, the 2018 entry date of black elder beginning of fruit ripening remains the earliest since 1768. The 2018 entry date of apricot comes fourth (after 1811, 1794, 1797 and same as 1822) and that of red currant third (after 1811 and 1794). In order to evaluate the phenological variability since 1970 a 11 year moving average and a 41 year moving trend were calculated for the combined time series consisting of the modelled (from 1768 to 1945) and observed (from 1946 – 2018) sections. Neither the level of the 11 year averages nor the level of the 41 year trend values since 1970 have occurred during any other period since 1768.</p><p>These results contribute to the discussion of the temperature sensitivity of phenological phases. In spite of the unprecedented spring and early summer temperature level our phenological data do not indicate that lower bounds of the time period between flowering and fruit ripening have yet been reached. The fruit ripening phenology of the mid latitudes is still sensitive enough to faithfully record temperature trends and extreme events supplementing the instrumental record.</p>

Trend Evolution of Vegetation Phenology in China during the Period of 1981–2016

The trend of vegetation phenology dynamics is of crucial importance for understanding vegetation growth and its responses to climate change. However, it remains unclear how the trends of vegetation phenology changed over the past decades. By analyzing phenology data including start (SOS), end (EOS) and length (LOS) of growth season with the Ensemble empirical mode decomposition (EEMD), we revealed the trend evolution of vegetation phenology in China during 1981-2016. Our study suggests that: (1) On the national scale, with EEMD method, the change rates of SOS and LOS were increasing with time, while that of EOS was decreasing. Moreover, the EEMD rates of SOS and LOS exceeded the linear rates in the early-2000s, while that of EOS dropped below the linear rate in the mid-1980s. (2) For each phenological event, the shifted trends took up a large area (~30%), which was close to the sum of all monotonic trends, but more than any monotonic trend type. The shifted trends mainly occurred in the north-eastern China, eastern Qinghai-Tibetan Plateau, eastern Sichuan Basin, North China Plain and Loess Plateau. (3) For each phenological event, the areas in the high-latitude experienced the contrary trends to the other. The amplitude and frequencies of phenology variation in the mid-latitude were stronger than those in the high-latitude and low-latitude. Meanwhile, LOS in the high-latitude was induced by SOS. (4) For each phenological event, the trend evolution varying with longitudes can be divided into eastern region (east of 121°E), central region (92°E–121°E) and western region (west of 92°E) based on the evolution of trends varying with longitudes. The east experienced a delayed SOS and a shorten LOS, which was different from the other areas. The magnitude of delayed trends in EOS and the prolonged trends in LOS were stronger from east to west as longitudes changes. The variation characteristics of LOS with longitude were mainly caused by SOS in the eastern region and by SOS and EOS together in the western and central region. (5) Each land cover types, except Needleleaf Forests, experienced the same trends. For most land cover types, the advance of SOS, delay of EOS and extension of LOS began in the 1980s, the 1990s, and the 1990s, respectively and enhanced several times. Moreover, the magnitudes of Grasslands in SOS and Evergreen Broadleaf Forest in EOS were much greater than the others, while that of croplands was the smallest in each phenological event. Our results showed that the analysis of trend evolution with nonlinear method is very important to accurately reveal the variation characteristics of phenology trends and to extract the inherent trend shifts.

Implications of an exceptional autumn bud flush on subsequent cold tolerance of Garry oak (Quercus garryana)

In the fall of 2016, an unusual phenological event occurred in Quercus garryana Douglas ex Hook. in Victoria, British Columbia. After normal autumn leaf drop, some trees burst bud and leafed out prematurely in late October. This allowed a comparison of the cold hardiness of the prematurely flushed and non-flushed trees over the following year. Cold hardiness of five tree pairs (premature fall flush and non-flush) in three locations in Victoria was assessed bi-weekly over the dehardening period in January–March 2017 and again over the hardening period in September–December 2017. Cold hardiness of 10 non-flushed trees from the most northerly population of Q. garryana was also assessed twice in spring 2017. Between January and March, all trees dehardened, but cold hardiness was greatest in non-flushed trees on the first sampling date, and thereafter, the non-flushed trees dehardened more rapidly than the prematurely flushed trees. Index of injury was consistently 10% greater in Victoria than in northern trees. In fall 2017, trees that had flushed prematurely in fall 2016 had the same cold hardiness as non-flushed trees. Hardiness of all trees decreased from mid-September to the end of October, followed by rapid hardening in November and December of 2017.

An experimental manipulation of species’ phenologies overturns competitive hierarchies

Ecological theory produces opposing predictions about whether differences in the timing of life history transitions, or ‘phenology’, promote or limit coexistence. Phenological separation is predicted to create temporal niche differences, increasing coexistence, yet phenological separation may competitively favour one species, increasing fitness differences and hindering coexistence. We experimentally manipulated relative germination timing, a critical phenological event, of two annual grass species,Vulpia microstachysandV. octoflora, to test these contrasting predictions. We parameterized a competition model to estimate within-season niche differences, fitness differences, and coexistence, and to estimate coexistence when among-year fluctuations of germination timing occur. Increasing germination separation caused parallel changes in niche and fitness differences, with the net effect of weakening within-year coexistence. Both species experienced a competitive advantage by germinating earlier, strongly enough to allow the generally inferior competitor to exclude the other with at least a four day head start. The overall consequence of germination separation was to limit coexistence within a given year, although among-year variation in relative timing of germination was sufficient to support long-term coexistence. Our results clarify how phenological differences structure competitive interactions, and highlight the need to quantify among-year variation in these differences to better understand species coexistence.

Checking the Consistency of Volunteered Phenological Observations While Analysing Their Synchrony

The increasing availability of volunteered geographic information (VGI) enables novel studies in many scientific domains. However, inconsistent VGI can negatively affect these studies. This paper describes a workflow that checks the consistency of Volunteered Phenological Observations (VPOs) while considering the synchrony of observations (i.e., the temporal dispersion of a phenological event). The geographic coordinates, day of the year (DOY) of the observed event, and the accumulation of daily temperature until that DOY were used to: (1) spatially group VPOs by connecting observations that are near to each other, (2) define consistency constraints, (3) check the consistency of VPOs by evaluating the defined constraints, and (4) optimize the constraints by analysing the effect of inconsistent VPOs on the synchrony models derived from the observations. This workflow was tested using VPOs collected in the Netherlands during the period 2003–2015. We found that the average percentage of inconsistent observations was low to moderate (ranging from 1% for wood anemone and pedunculate oak to 15% for cow parsley species). This indicates that volunteers provide reliable phenological information. We also found a significant correlation between the standard deviation of DOY of the observed events and the accumulation of daily temperature (with correlation coefficients ranging from 0.78 for lesser celandine, and 0.60 for pedunculate oak). This confirmed that colder days in late winter and early spring lead to synchronous flowering and leafing onsets. Our results highlighted the potential of synchrony information and geographical context for checking the consistency of phenological VGI. Other domains using VGI can adapt this geocomputational workflow to check the consistency of their data, and hence the robustness of their analyses.

Relationships between Cabernet Sauvignon phenology and climate in two Spanish viticultural regions: observations and predicted future changes

The aim of the current research is to analyse potential changes in the phenology of Cabernet Sauvignon under future climate change scenarios. The study compares results from two areas with different climatic conditions in Spain: Ribera del Duero and Penedès. Phenology data for budbreak (BB), bloom (BL), veraison (V) and maturity (M) were analysed for the period 2004–2015 in Ribera del Duero and for 1996–2012 in Penedès. Thermal requirements to initiate the growing cycle and to reach each phenological event were evaluated. Simulated data of changes in climate from eight models provided by Agencia Estatal de Meteorología (AEMET) of Spain, and for two Representative Concentration Pathways (RCP) (greenhouse gas concentration trajectories) – RCP4.5 and RCP8.5 by 2030, 2050 and 2070 were used. Differences of approximately 6 days for BL and about 12 days, on average, for V existed between the two areas. Based on the predicted changes of temperature and the accumulated degree days needed to reach each stage, future changes in phenology were modelled. The results indicate potentially greater changes in the warmer region (Penedès), particularly for the later growth stages, which is in agreement with greater temperature increases in Penedès. The advance of BB, BL, V and M by 2070 could be up to 5, 11, 17 and 24 days, respectively, under the RCP4.5 emission trajectory, and up to 50% higher in some stages under the RCP8.5 emission trajectory.