Late Summer Temperatures Research Articles

Effects of Environmental Factors and Husbandry Practices on Summer Mortality Events in the Cultivated Pacific Oyster Crassostrea gigas in the North of Ireland

The Pacific oyster Crassostrea gigas (Thunberg, 1793) is an important part of the aquaculture industry in Europe; however, since 2008, oyster mortality events (>20%) have become a regular summer occurrence. This study monitored and recorded C. gigas mortality events during a 3-y period at a commercial oyster site in Lough Foyle, North of Ireland, and related these to environmental conditions, oyster physiology, and husbandry practices. Early summer temperature rises above 16°C were consistently correlated with large mortality events, but warmer temperatures in late summer did not cause mortalities, including in 1 y when there were no early summer mortalities. Mortalities were also correlated with a sharp early summer decrease in salinity from 22.2 to 16.9. In the laboratory, the combined effects of various temperatures and salinities on oyster stress levels were investigated using total hemocyte count and neutral red retention techniques. The cell membrane integrity and hemocyte density in C. gigas are sensitive to temperatures of 20°C or greater and at salinities of 20 or lower. This suggests that high temperature and low salinity combinations can negatively impact oyster stress levels and potentially increase oyster vulnerability to infections, including oyster herpes OsHV-1 µvar. Comparing survivorship in experimental bags simulating commercial growing conditions, these results equivocally support previous studies in which higher shore position was correlated with higher survivorship. Bags of oysters at lower density in lower shore positions were equally successful and may be more protected from climate-related stressors. Focusing on a single stressor is insufficient to predict future oyster mortalities, but balancing effects and relieving stress on oyster stocks through husbandry could limit the impacts of summer mortalities.

Unprecedented recent late-summer warm extremes recorded in tree-ring density on the Tibetan Plateau

Tree-ring records have shown a significant upward trend of late summer temperatures over the Tibetan Plateau (TP) in recent decades. More detailed instrumental observations over the TP have also shown an increase in warm extremes, especially in the high-altitude area. It is not clear whether the recent increase in occurrence of warm extremes on the TP reflects an amplification of recent temperature fluctuations or it relates to the long-term climate trend. This study aims to address the above question by analyzing long-term late summer (August–September) temperature extremes over the TP using temperature reconstructions derived from tree-ring maximum latewood density. Our results show that the recent frequency of late summer warm extremes was unprecedented over the past four centuries, while the occurrence of cold extremes in the instrumental interval was minimal. However, after the removal of long-term trend, the frequencies of both warm and cold extremes in the instrumental period are actually smaller than the pre-instrumental period, indicating a decreased variability of late summer temperatures. Thus, we conclude that the recent observed increase in warm extremes is related to the long-term warming trend, rather than an amplification of temperature variability. This finding implies that the persistent warming on the TP in the future might trigger much more frequent warm extremes with potential ecological and environmental effects.

Impact of precipitation, air temperature and abiotic emissions on gross primary production in Mediterranean ecosystems in Europe

Mediterranean ecosystems are significant carbon sinks and are particularly sensitive to climate change. However, the carbon dynamics in such ecosystems are still not fully understood. An improved understanding of the drivers of carbon fixation by vegetation is needed to better predict how these ecosystems will respond to climate change. In this study, a large dataset collected through the FLUXNET network is used to estimate how the gross primary production (GPP) of different Mediterranean ecosystems was affected by air temperature and precipitation between 1996 and 2013. We showed that annual precipitation and temperature were not significant drivers of annual GPP. However, inter-annual variations of GPP seemed largely controlled by the precipitation during early spring (March–April). Late spring and early summer temperature also had a positive effect on annual GPP. We furthermore show that GPP may also have been influenced by both summer rainfall pulses and abiotic emissions due to carbonates precipitation/dissolution. Finally, the sensitivity of GPP in the Mediterranean region to climate drivers seemed not to be ecosystem-type dependent. Our results can provide general information for modeling exercises and improve future biomass projections on a regional scale.

Douglas-fir climate sensitivity at two contrasting sites along the southern limit of the European planting range

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is an important exotic tree species that was planted across a large part of Europe during the last century. In both experimental trials and conventional forest plantations, the trees grow at a high rate and produce high-quality timber. The present study investigated climate-growth relationships of Douglas-fir at two Italian sites that contrast in climate: a Mediterranean area in southern Italy (Mercurella site) and a cooler, moister site in the northern Apennines without summer aridity (Acquerino). The relationship between tree-ring chronologies and monthly climatic variables was evaluated by a moving average and correlation analysis. Results showed that the minimum temperature in February and in March play a key role for Douglas-fir at both sites, with a positive effect on growth. At the northern site, it is also highly sensitive to late summer temperatures (negative correlation) and spring–summer precipitation (positive correlation). Growth rates in southern latitudes were high even in Europe and in the Mediterranean environment, with low sensitivity to climatic fluctuation. On the basis of our results, further common garden experiments should test adaptation and the interaction between genetics and environment of second- or third-generation seeds from old stands across Europe such as done by the old International Union of Forest Research Organizations (IUFRO) or the European Douglas-fir Improvement Research Cooperative (EUDIREC) experimentation programmes.

Seasonal epilimnetic temperature patterns and trends in a suite of lakes from Wisconsin (USA), Germany, and Finland

ABSTRACTEpilimnetic temperatures from early 1980s through 2017 were analyzed for 12 Wisconsin (USA), German, and Finnish lakes. Seasonal temperature metrics exhibited large interannual variability with trends differing among regions. In the Wisconsin lakes, only late summer and fall temperatures increased significantly. In the 2 northeastern German lakes, temperatures increased in all seasons (not all significantly). The 3 Finnish lakes exhibited large spring temperature increases influenced by earlier ice-out; summer and fall temperatures also increased except for Konnevesi (central Finland) in early summer and polar Kevojärvi in midsummer. Kevojärvi also exhibited no increase in maximum recorded temperatures. Earlier records from 4 lakes were analyzed to elucidate longer-term epilimnetic temperature patterns. For Lake Mendota (southern Wisconsin), spring and late fall temperatures have increased modestly but significantly since 1894; summer temperatures have also increased modestly because of higher frequency of warm temperatures in recent summers and not from new record high temperatures. Trout Lake (northern Wisconsin) exhibited warm temperatures in some summers during the 1930s–1940s, similar to warm temperatures in some recent summers. Air–water temperature relationships coupled with long-term regional air temperature data also indicated summer epilimnetic temperatures in the study lakes were likely as warm in the 1930s–1940s as in recent years. Lake data confirmed cooler epilimnetic temperatures occurred in many summers during the 1950s–1980s coincident with cooler air temperatures. Because epilimnetic temperatures have not increased monotonically since 1900, our study supports continued temperature monitoring in lakes with extensive historical data to better understand and predict future effects of climate change on lake ecosystems.

Glacier Dynamics in Changme Khangpu Basin, Sikkim Himalaya, India, between 1975 and 2016

This study provides a high resolution glacier database in the Changme Khangpu Basin (CKB) using LANDSAT 8 (2014) and Sentinel-2A image (2016), mapping of 81 glaciers that cover a 75.78 ± 1.54 km2 area. Composite maps of land surface temperature, slope and Normalized differential Snow Index have been successfully utilized in delineating near accurate debris cover boundary of glaciers. The cumulative controlling parameters of aspect, elevation, slope, and debris cover have been assessed to evaluate the nature of glacier distribution and dynamics. The local topographic settings seem to have significantly determined the glacier distribution in the CKB. Almost 20% area erstwhile under glacier cover has been lost since 1975 at an average rate of −0.453 ± 0.001 km2a−1. The recent decade (2001–2016) has witnessed a higher rate of area shrinkage (−0.665 ± 0.243 km2a−1), compared to a relatively lower rate of recession (−0.170 ± 0.536 km2a−1) between 1988 and 2001. The lower rates of glacial recession can most likely be induced regionally due to relatively cooler decadal late summer temperatures and peak in the monsoon spell. Glaciers with western and north-western aspects showed more vulnerability to area loss than the rest of the aspects. Lower altitude glaciers have receded faster than ones perched up on higher elevations. The rate of glacier area recession has been nearly twice that on clean glaciers as compared to debris-covered glaciers in the CKB.

A 1200+ year reconstruction of temperature extremes for the northeastern Mediterranean region

Proxy evidence is necessary to place current temperature and hydroclimatic changes in a long‐term context and to assess the full range of natural and anthropogenic climate forcings. Here, we present the first millennium‐length reconstruction of late summer (August–September) temperature variability for the Mediterranean region. We compiled 132 maximum latewood density (MXD) tree‐ring series of living and relict Pinus heldreichii trees from a network of four high‐elevation sites in the Pindus Mountains of Greece. Forty series reach back into the first millennium and the oldest sample dates to 575 CE. At annual to decadal scales, the record correlates significantly with August–September temperatures over the Balkan Peninsula and northeastern Mediterranean (r1950–2014 = 0.71, p < 0.001). We produce two reconstructions emphasizing interannual and decadal scale variance over the past millennium. Analysis of temperature extremes reveals the coldest summers occurred in 1035, 1117, 1217, 1884 and 1959 and the coldest decades were 1061–1070 and 1811–1820. The warmest summers occurred in 1240 and 1474, and the warmest decades were 1141–1150 and 1481–1490. Comparison of this new reconstruction with MXD‐based summer temperature reconstructions across Europe reveals synchronized occurrences of extreme cool summers in the northeastern Mediterranean, and an antiphase‐relationship with warm summer temperatures over the British Isles and Scandinavia. This temperature dipole is related to anomalies in the latitudinal position of the North Atlantic Jet. Despite the representation of common atmospheric forcing patterns, the occurrence of warm extremes is limited to few events, suggesting potential weaknesses of MXD to record warm temperature anomalies. In addition, we acknowledge problems in the observational data to capture local temperature variability due to small scale topographic differences in this high‐elevation landscape. At a broader geographical scale, the occurrence of common cold summer extremes is restricted to years with volcanically induced changes in radiative forcing.

A Pinus cembra L. tree-ring record for late spring to late summer temperature in the Rhaetian Alps, Italy

Ongoing climate change strongly affects high-elevation environments in the European Alps, influencing the cryosphere and the biosphere and causing widespread retreat of glaciers and changes in biomes. Nevertheless, high-elevation areas often lack long meteorological series, and global datasets cannot represent local variations well. Thus, proxy data, such as tree rings, provide information on past climatic variations from these remote sites. Although maximum latewood density (MXD) chronologies provide better temperature information than those based on tree-ring width (TRW), MXD series from the European Alps are lacking. To derive high-quality temperature information for the Rhaetian Alps, Pinus cembra L. trees sampled at approximately 2000 m a.s.l. were used to build one MXD chronology spanning from 1647 to 2015. The MXD data were significantly and highly correlated with seasonal May-September mean temperatures. The MXD chronology showed a generally positive trend since the middle of the 19th century, interrupted by short phases of climatic deterioration in the beginning of the 20th century and in the 1970s, conforming with the temperature trends. Our results underline the potential for using Pinus cembra L. MXD to reconstruct mean temperature variations, especially during the onset and latter part of the growing season, providing additional information on parts of the growing season not inferred from TRW. Future studies on MXD for this species will increase the availability of temporal and spatial data, allowing detailed climate reconstructions.

Time series analysis of temperature and rainfall-based weather aggregation reveals significant correlations between climate turning points and potato (Solanum tuberosum L) yield trends in Japan

Potato (Solanum tuberosum L) yield per unit area in Hokkaido, Japan used to be the highest in the world; however, it has levelled off recently. The objectives of this study were to determine how recent climate variations drive potato yields and to understand the causes for this tendency of yield to level off. We used the 1-km mesh resolution for meteorological data; aggregation was performed for each municipality based on annual potato cultivation area; yield data were obtained from crop statics of Tokachi and Okhotsk regions in Hokkaido for the years 1986–2014. Potato yield was not only determined by temperatures during plant growth, as expected, but also by temperatures before planting. Probable yield inflexion point corresponded with increase in late summer temperature from the year 2000 onward. The negative correlation between spring and summer temperatures during the years 2000–2014 resulted from patterns of warm spring/cool summer or cool spring/hot summer, linked to the Inter-decadal Pacific Oscillation. A cool spring delayed planting and germination, whereas a hot summer shortened the growth period, causing the lowest yield in the year 2010. High temperatures in summer have encouraged farmers in Japan to implement adaptation strategies, such as earlier planting. As early plantation does not necessarily reduce time to sprout nor does it promote a longer growth period, the recent climate trend exacerbated potato yield responsiveness to summer temperature. As a result, increasing temperatures in summers from the late 2000s and unaltered spring temperatures as well as a shift in cultivars have caused potato yields in eastern Hokkaido to drop below those of other countries where potato yields are high. Detection of decadal climate shift as a planned-scale strategy and enhancement of drainage as a farm-scale strategy could effectively improve regional potato yield despite climate change.

Climate-sensitive radial increment model of Norway spruce in Tyrol based on a distributed lag model with penalized splines for year-ring time series

A novel methodological framework is presented for climate-sensitive modeling of annual radial stem increment using year-ring width time series. The approach is based on a generalized additive model with penalized regression splines together with a distributed time lag model taking into account smooth nonlinear effects of a series of monthly temperature and precipitation values, as well as their interactions. Climate effects are also assumed to vary smoothly with time lag. The model framework enables both the detrending of the individual time series and the regression modeling to be performed simultaneously in a single model step. The approach is applied to year-ring width time series of Norway spruce (Picea abies (L.) H. Karst.) trees in Tyrol, Austria. The marginal response curves show that tree growth is mainly promoted by high temperatures in late spring and early summer and by precipitation in fall and winter. Summer drought does not have a negative influence on the current year’s radial increment; however, when it is associated with high temperatures, it lowers the increment in the subsequent growth period. Higher winter precipitation in conjunction with lower temperatures has a positive effect. A significant non-climate related long-term growth trend is demonstrated, probably reflecting NOx and SO2 emission trends in Austria.

Diurnal foraging of a wild coral-reef fish Parapercis australis in relation to late-summer temperatures.

In situ observations of diurnal foraging behaviour of a common site-attached shallow reef mesopredator Parapercis australis during late summer, revealed that although diet composition was unaffected by seawater temperature (range 28.3-32.4°C), feeding strikes and distance moved increased with temperature up to 30.5°C, beyond which they sharply declined, indicative of currently living beyond their thermal optimum. Diel feeding strikes and distance moved were however, tightly linked to ambient temperature as it related to the population's apparent thermal optimum, peaking at times when it was approached (1230 and 1700 h) and declining up to four fold at times deviating from this. These findings suggest that although this population may be currently living beyond its thermal optimum, it copes by down regulating energetically costly foraging movement and consumption and under future oceanic temperatures, these behavioural modifications are probably insufficient to avoid deleterious effects on population viability without the aid of long-term acclimation or adaptation.

Recent spring warming limits near‐treeline deciduous and evergreen alpine dwarf shrub growth

AbstractWarming may lead to a cover increase of tundra shrubs and a north‐ and upward shift of treelines. The latter may be inhibited by a densification of shrub stands. However, the climatic drivers of near‐treeline shrub growth are relatively unexplored, especially that of shrub species from different functional groups growing intertwined, in competition for light and resources. We measured ring widths from two dominant dwarf shrubs species, the deciduous Betula nana and the evergreen Empetrum nigrum ssp. hermaphroditum from a near‐treeline alpine ridge in the Central Norwegian Scandes, and tested the influence of on‐site and regional climate, and changes therein, over the past 55 yr. Radial growth of B. nana was found to be negatively influenced by early summer (June–July) precipitation, possibly related to low amounts of photosynthetically active radiation and nitrogen leaching, and positively by July temperatures. That of E. hermaphroditum was positively correlated with late summer (July–August) temperatures. In recent decades, the influence of summer climate on both species’ growth has declined and been replaced by a negative influence of May temperatures. Rising spring temperatures in recent decades have likely advanced key phenology events in B. nana and E. hermaphroditum, such as budburst and flowering. This may have left the shrubs’ soft tissues vulnerable to late frost events, which in recent decades occur more frequently after the advanced start of the growing season, resulting in suppressed growth.

Tree-ring reconstruction of late summer temperatures in northern Sikkim (eastern Himalayas)

The Sikkim region of the Himalayas is among one of the most highly sensitive hotspots to climate change due to its fragile mountainous environment and rapidly growing population, which exert significant impacts on regional ecosystem factors, including biodiversity and hydrology. Limited observational data coverage in space and time for the high-altitude mountainous region impedes our understanding of climate change and its impact on the environment. In this paper, we develop a 437-year tree-ring width index chronology of Tsuga dumosa (D.Don) Eichler in northern Sikkim as a climate proxy. The substantial dendroclimatic potential of this proxy is evidenced in various statistics computed from the tree-ring chronology. An analysis of the tree-ring chronology indicates a strong negative relationship between late-summer mean temperatures (July–August–September; JAS) and tree growth. This relationship enables us to reconstruct the JAS mean temperature over northern Sikkim since 1705 C.E. The 304-year (1705–2008 C.E.) reconstructed temperature series shows similar warm and cool epochs, which have been observed in many other temperature reconstructions in the region and other proxy records of glacial fluctuations. An overall steady decreasing trend in the regional surface temperature is observed since 1705 C.E., while an increasing trend with intermittent, short and cool epochs are noticed from 1850 C.E. to the present. Prior to the observational period (before 1901 C.E.), cold conditions (X̄ - 1σ) prevailed during 1816–1819, 1831–1837, 1856–1859, and 1884–1887 C.E, with extremely cold conditions (X̄ - 2σ) occurring in 1816, 1817, 1832, 1833, 1857, 1877, 1884, and 1885 C.E; Warm conditions (X̄ + 1σ) prevailed during 1713–1735 and 1823–1827 C.E, with extremely warm (X̄ + 2σ) conditions occurring in 1724, 1823, 1824, and 1825 C.E. Global teleconnections of the reconstructed temperature variations indicate the important roles of the Pacific Decadal Oscillation (PDO), El Niño Southern Oscillation (ENSO), and volcanic eruptions as drivers of temperature variations in the Sikkim region of the Himalayas.

Late summer temperature reconstruction based on tree-ring density for Sygera Mountain, southeastern Tibetan Plateau

Abstract Although several tree-ring density-based summer/late summer temperature reconstructions have been developed on the Tibetan Plateau (TP), the understanding of the local/regional characteristics of summer temperature fluctuations on a long-term scale in some regions is still limited. To improve our understanding in these aspects, more local or regional summer temperature reconstructions extending back over several centuries are required. In this study, a new mean latewood density (LWD) chronology from Abies georgei var. smithii from the upper tree line of Sygera Mountain on the southeastern TP was developed to reconstruct the late summer temperature variability since 1820 CE. The bootstrapped correlation analysis showed that the LWD chronology index was significantly and positively correlated with the late summer (August-September) mean temperatures (r1950–2008 = 0.63, p

Climate signals in a multispecies tree-ring network from central and southern Italy and reconstruction of the late summer temperatures since the early 1700s

Abstract. A first assessment of the main climatic drivers that modulate the tree-ring width (RW) and maximum latewood density (MXD) along the Italian Peninsula and northeastern Sicily was performed using 27 forest sites, which include conifers (RW and MXD) and broadleaves (only RW). Tree-ring data were compared using the correlation analysis of the monthly and seasonal variables of temperature, precipitation and standardized precipitation index (SPI, used to characterize meteorological droughts) against each species-specific site chronology and against the highly sensitive to climate (HSTC) chronologies (based on selected indexed individual series). We find that climate signals in conifer MXD are stronger and more stable over time than those in conifer and broadleaf RW. In particular, conifer MXD variability is directly influenced by the late summer (August, September) temperature and is inversely influenced by the summer precipitation and droughts (SPI at a timescale of 3 months). The MXD sensitivity to August–September (AS) temperature and to summer drought is mainly driven by the latitudinal gradient of summer precipitation amounts, with sites in the northern Apennines showing stronger climate signals than sites in the south. Conifer RW is influenced by the temperature and drought of the previous summer, whereas broadleaf RW is more influenced by summer precipitation and drought of the current growing season. The reconstruction of the late summer temperatures for the Italian Peninsula for the past 300 years, based on the HSTC chronology of conifer MXD, shows a stable model performance that underlines periods of climatic cooling (and likely also wetter conditions) in 1699, 1740, 1814, 1914 and 1938, and follows well the variability of the instrumental record and of other tree-ring-based reconstructions in the region. Considering a 20-year low-pass-filtered series, the reconstructed temperature record consistently deviates < 1 °C from the instrumental record. This divergence may also be due to the precipitation patterns and drought stresses that influence the tree-ring MXD at our study sites. The reconstructed late summer temperature variability is also linked to summer drought conditions and it is valid for the west–east oriented region including Sardinia, Sicily, the Italian Peninsula and the western Balkan area along the Adriatic coast.

Temperature-manipulated dynamics and phenology ofMindarus abietinus(Hemiptera: Aphididae) in commercial Christmas tree plantations in Québec, Canada

AbstractThe balsam twig aphidMindarus abietinusKoch (Hemiptera: Aphididae) is a major pest of economic importance for the Christmas tree industry. Global warming during the 21st century could potentially increase local population densities and reinforce the pest status of this aphid in commercial fir (AbiesMiller; Pinaceae) plantations in Québec, Canada. During this study, we tested the effects of a warmer environment on colony growth rates ofM. abietinusand aphid morph composition during the second generation of its cycle, which is key to colony size growth and potential damage to Christmas trees. We monitoredM. abietinuspopulations on two host fir species and one host fir variety, in order to understand the early season dynamics of this aphid and its host tree. It was possible to distinguish the two overlapping generations of winged aphids leaving colonies, which led to observing a much higher proportion of wingless daughters, produced by the stem mother, than what had previously been reported. Colony growth rates were significantly higher in a warmer environment than in the nearby plantation, suggesting that warmer temperatures in late spring and early summer may provide the suitable conditions required forM. abietinuscolonies of greater density.

Climate Response of Larch and Birch Forests across an Elevational Transect and Hemisphere-Wide Comparisons, Kamchatka Peninsula, Russian Far East

Kamchatka’s forests span across the peninsula’s diverse topography and provide a wide range of physiographic and elevational settings that can be used to investigate how forests are responding to climate change and to anticipate future response. Birch (Betula ermanii Cham.) and larch (Larix gmelinii (Rupr.) Kuzen) were sampled at eight new sites and together with previous collections were compared with monthly temperature and precipitation records to identify their climate response. Comparisons show that tree-ring widths in both species are primarily influenced by May through August temperatures of the current growth year, and that there is a general increase in temperature sensitivity with altitude. The ring-width data for each species were also combined into regional chronologies. The resulting composite larch chronology shows a strong resemblance to a Northern Hemisphere (NH) tree-ring based temperature reconstruction with the larch series tracking NH temperatures closely through the past 300 years. The composite birch ring-width series more closely reflects the Pacific regional coastal late summer temperatures. These new data improve our understanding of the response of forests to climate and show the low frequency warming noted in other, more continental records from high latitudes of the Northern Hemisphere. Also evident in the ring-width record is that the larch and birch forests continue to track the strong warming of interior Kamchatka.

Historical vegetation–environment patterns for assessing the impact of climatic change in the mountains of Lesotho

Climate change will probably profoundly impact the Maloti Mountains in Lesotho, which are likely to have a warmer, wetter and more CO2-enriched (eCO2) atmosphere in the future. Intensive smallstock grazing could exacerbate the effects of climate change on the mountain grasslands. Vegetation composition data collected in ca. 1990 in the eastern and western Maloti provide a baseline for assessing historical and future shifts in the abundance of functional groups such as C3 and C4 grasses and encroaching unpalatable dwarf Karroid shrubs. C3/C4 grasses had a skewed topographic distribution with the 50% floristic crossover from C4 to C3 grasses occurring approximately at 2 900 m above sea level (asl) on northerly slopes and 2 700 m asl and 2 400 m asl on south-facing slopes in the east and west, respectively. Shrubs were restricted to low, warm and dry slopes. C3/C4 grass patterns were most strongly correlated with modelled daily temperatures in early spring (October) and late summer (February), whereas winter temperatures and evaporation appeared important for shrubs. Warming would favour C4 grasses but eCO2 might benefit C3 grasses, whereas unpalatable C3 shrubs would be promoted by warming, eCO2 and grazing and should expand their distribution. Monitoring functional groups by remote sensing is recommended.

Detecting spatiotemporal changes of peak foliage coloration in deciduous and mixedforests across the Central and Eastern United States

The timing of fall foliage coloration, especially peak coloration, is of great importance to the climate change research community as it has implications for carbon storage in forests. However, its long-term variation and response to climate change are poorly understood. To address this issue, we examined the long-term trends and breakpoints in satellite derived peak coloration onset from 1982 to 2014 using an innovative approach that combines Singular Spectrum Analysis (SSA) with Breaks for Additive Seasonal and Trend (BFAST). The peak coloration trend was then evaluated using both field foliage coloration observations and flux tower measurements. Finally, interannual changes in peak coloration onset were correlated with temperature and precipitation variation. Results showed that temporal trends in satellite-derived peak coloration onset were comparable with both field observations and flux tower measurements of gross primary productivity. Specifically, a breakpoint in long-term peak coloration onset was detected in 25% of pixels which were mainly distributed at latitudes north of 37°N. The breakpoint tended to occur between 1998 and 2004. Peak coloration onset was delayed before the breakpoint while it was transformed to an early trend after the breakpoint in nearly all pixels. The remaining 75% of pixels exhibited monotonic trends, 35% of which revealed a late trend and 40% an early trend. The results indicate that the onset of peak coloration experienced a late trend during the 1980s and 1990s in most deciduous and mixed forests. However, the trend was reversed during the most recent decade when the timing of peak coloration became earlier. The onset of peak coloration was significantly correlated with late summer and autumn temperature in 55.5% of pixels from 1982 to 2014. This pattern of temperature impacts was also verified using field observations and flux tower measurements. In the remaining 44.5% of pixels, 12.2% of pixels showed significantly positive correlation between the onset of peak coloration and cumulative precipitation during late summer and autumn period from 1982 to 2014. Our findings can improve understanding of the impact of changes in autumn phenology on carbon uptake in forests, which in turn facilitate more reliable measures of carbon dynamics in vegetation–climate interactions models.

Prediction of Arctic plant phenological sensitivity to climate change from historical records.

The pace of climate change in the Arctic is dramatic, with temperatures rising at a rate double the global average. The timing of flowering and fruiting (phenology) is often temperature dependent and tends to advance as the climate warms. Herbarium specimens, photographs, and field observations can provide historical phenology records and have been used, on a localised scale, to predict species’ phenological sensitivity to climate change. Conducting similar localised studies in the Canadian Arctic, however, poses a challenge where the collection of herbarium specimens, photographs, and field observations have been temporally and spatially sporadic. We used flowering and seed dispersal times of 23 Arctic species from herbarium specimens, photographs, and field observations collected from across the 2.1 million km2 area of Nunavut, Canada, to determine (1) which monthly temperatures influence flowering and seed dispersal times; (2) species’ phenological sensitivity to temperature; and (3) whether flowering or seed dispersal times have advanced over the past 120 years. We tested this at different spatial scales and compared the sensitivity in different regions of Nunavut. Broadly speaking, this research serves as a proof of concept to assess whether phenology–climate change studies using historic data can be conducted at large spatial scales. Flowering times and seed dispersal time were most strongly correlated with June and July temperatures, respectively. Seed dispersal times have advanced at double the rate of flowering times over the past 120 years, reflecting greater late‐summer temperature rises in Nunavut. There is great diversity in the flowering time sensitivity to temperature of Arctic plant species, suggesting climate change implications for Arctic ecological communities, including altered community composition, competition, and pollinator interactions. Intraspecific temperature sensitivity and warming trends varied markedly across Nunavut and could result in greater changes in some parts of Nunavut than in others.