Growing Season Temperature Research Articles

Recent changes in forest structure and growth at the alpine‐treeline ecotone in the Rocky and Columbia Mountains of central British Columbia, Canada

AbstractAimGlobally, forests at the alpine‐treeline ecotone (ATE) are considered sensitive to warming temperatures; however, responses to recent climate change show high variability and many underlying processes remain unclear. This study aims to provide further insight into possible ATE forest responses to climate change by examining spatiotemporal patterns in recent tree regeneration and growth responses to climate across treeline forms.LocationThis study is situated at the ATE in the Rocky Mountain and Columbia Mountain ranges in central British Columbia, Canada.TaxonGymnosperms – subalpine fir (Abies lasiocarpa Hooker (Nutall)).MethodsWe collected tree and stand data from 48 plots across five study sites. Plots were distributed across three treeline stand types: (i) islands; (ii) abrupt; and (iii) fringes of regeneration adjacent to tree islands. We used a dendrochronological approach to analyse the ages of recently established trees in fringe stand types, detect long‐term trends in annual tree growth and quantify climate‐growth relationships.ResultsSeedling recruitment adjacent to tree islands occurred over a period of approximately 40 years (1960–2000), with two regeneration “pulses” in the late 1970s and 1980s. Abrupt and fringe trees showed a similar age structure and annual radial growth has increased in most trees over the past 30 years. Across the study region and stand types, summer temperature has the strongest influence on radial growth. Over the past 70 years, growth in tree islands has become increasingly correlated with growing season temperature variables.Main ConclusionsForest growth and structure have changed in coherent spatial and temporal patterns over recent decades at the ATE in central BC. Projections for sustained warming in this region will likely result in increased tree growth and potential continued expansion of forests into untreed areas below the treeline. These changes will have implications for hydrological regimes, wildlife habitat and carbon sequestration.

Substituting readily available nitrogen fertilizer with controlled-release nitrogen fertilizer improves crop yield and nitrogen uptake while mitigating environmental risks: A global meta-analysis

ContextControlled-release nitrogen fertilizer (CRN) is considered as an efficient tool for improving crop total uptake of N (TUN) and crop yield by providing better synchronization of crop N demand, but its effects on crop productivity, greenhouse gases (GHG) emissions and N loss are variable across agroecosystems. Objective and methodsHere, we conducted a meta-analysis by synthesizing 8874 observations from 240 published studies to address the effects of substituting CRN for readily available N fertilizer on crop yield, TUN, profit, GHG emissions, and N loss in rice, maize, wheat, soybean, and rape, with focus on cereals. ResultsOverall, CRN could increase crop productivity (crop yield, 5.1 %; profit, 8.2 %; TUN, 7.1 %) and reduce environmental pollution (GHG emissions, −3.6 % to − 18.6 %; N loss, −32.6 % to −49.1 %). These efficacies varied among crops but showed similar trends in general. The effect of CRN on crop yield was modulated by the N rate and the ratio of CRN. The optimal N rate and CRN ratio to obtain higher crop yields and profits also varied with crops. The CRN efficacies for decreasing GHG emissions and N loss depended on the mean growing season temperature, mean growing season precipitation, background soil total organic carbon content and pH values, the regions, and the CRN ratio and coating materials. A synergy of CRN with other crop management practices, such as mulching and efficient irrigation, was an effective strategy for increasing both crop productivity and environmental benefits. ConclusionsSubstituting readily available nitrogen fertilizer with CRN could produce more food and obtain higher profits with less environmental risk in crops, especially in cereals. ImplicationsThis study provides new insights into the effect of plant-soil-climate-management systems on crop productivity and environmental benefits for Sustainable Development Goals.

High Growing Season Temperatures Limit Winter Recovery of Grapevines from Xylella fastidiosa Infection - Implications for Epidemiology in Hot Climates.

Management of widespread plant pathogens is challenging as climatic differences among crop-growing regions may alter key aspects of pathogen spread and disease severity. Xylella fastidiosa is a xylem-limited bacterial pathogen that is transmitted by xylem sap-feeding insects. Geographic distribution of X. fastidiosa is limited by winter climate, and vines infected with X. fastidiosa can recover from infection when held at cold temperatures. California has a long history of research on Pierce's disease and significant geographic and climatic diversity among grape-growing regions. This background in combination with experimental disease studies under controlled temperature conditions can inform risk assessment for X. fastidiosa spread and epidemic severity across different regions and under changing climate conditions. California's grape-growing regions have considerable differences in summer and winter climate. In northern and coastal regions, summers are mild and winters are cool, conditions which favor winter recovery of infected vines. In contrast, in inland and southern areas, summers are hot and winters mild, reducing likelihood of winter recovery. Here, winter recovery of three table grape cultivars (Flame, Scarlet Royal, and Thompson Seedless) and three wine grape cultivars (Sauvignon Blanc, Cabernet Sauvignon, and Zinfandel) were evaluated under temperature conditions representative of the San Joaquin Valley, an area with hot summers and mild winters that has been severely impacted by Pierce's disease and contains a large portion of California grape production. Mechanically inoculated vines were held in the greenhouse under one of three warming treatments to represent different seasonal inoculation dates prior to being moved into a cold chamber. Winter recovery under all treatments was generally limited but with some cultivar variation. Given hot summer temperatures of many grape-growing regions worldwide, as well as increasing global temperatures overall, winter recovery of grapevines should not be considered a key factor limiting X. fastidiosa spread and epidemic severity in the majority of cases.

Distance to a River Modifies Climate Legacy on Vegetation Growth in a Boreal Riparian Forest

Inter-annual variability in growing season temperature and precipitation, together with snow coverage duration, determine vegetation growth in boreal ecosystems. However, little is known about the impact of concurrent and antecedent climate, particularly snow cover duration, on vegetation growth in a boreal riparian forest. Additionally, significant uncertainty exists regarding whether the distance to a river (as a proxy of groundwater availability) further modifies these climatic legacy effects on vegetation growth. To fill this knowledge gap, we quantified the responses of different vegetation types (shrub, deciduous coniferous and broadleaf forests) to concurrent and antecedent climate variables in a boreal riparian forest, and further determined the magnitude and duration of climate legacies in relation to distance to a river, using MODIS-derived NDVI time series with gridded climate data from 2001 to 2020. Results showed that higher temperature and precipitation and longer snow cover duration increased vegetation growth. For deciduous coniferous forests and broadleaf forests, the duration of temperature legacy was about one year, precipitation legacy about two years and snow cover duration legacy was 3 to 4 years. Further, distance to a river modified the concurrent and antecedent temperature and snow cover duration legacy effects on vegetation growth, but not that of precipitation. Specifically, temperature and snow cover duration legacies were shorter at the sites near a river compared to sites at greater distance to a river. Our research highlights the importance of snow cover duration on vegetation growth and that closeness to a river can buffer adverse climate impacts by shortening the strength and duration of climate legacies in a boreal riparian forest.

Organic layers preserved in ice patches: A new record of Holocene environmental change on the Beartooth Plateau, USA

Growing season temperatures play a crucial role in controlling treeline elevation at regional to global scales. However, understanding of treeline dynamics in response to long-term changes in temperature is limited. In this study, we analyze pollen, plant macrofossils, and charcoal preserved in organic layers within a 10,400-year-old ice patch and in sediment from a 6000-year-old wetland located above present-day treeline in the Beartooth Mountains, Wyoming, to explore the relationship between Holocene climate variability and shifts in treeline elevation. Pollen data indicate a lower-than-present treeline between 9000 and 6200 cal yr BP during the warm, dry summer and cold winter conditions of the early Holocene. Increases in arboreal pollen at 6200 cal yr BP suggest an upslope treeline expansion when summers became cooler and wetter. A possible hiatus in the wetland record at ca. 4200–3000 cal yr BP suggests increased snow and ice cover at high elevations and a lowering of treeline. Treeline position continued to fluctuate with growing season warming and cooling during the late-Holocene. Periods of high fire activity correspond with times of increased woody cover at high elevations. The two records indicate that climate was an important driver of vegetation and treeline change during the Holocene. Early Holocene treeline was governed by moisture limitations, whereas late-Holocene treeline was sensitive to increases in growing season temperatures. Climate projections for the region suggest warmer temperatures could decrease effective growing season moisture at high elevations resulting in a reduction of treeline elevation.

Shifting climatic responses of tree rings and NDVI along environmental gradients

Variations in the growth of aboveground biomass compartments such as tree stem and foliage significantly influence the carbon cycle of forest ecosystems. Yet the patterns of climate-driven responses of stem and foliage and their modulating factors remain poorly understood. In this study, we investigate the climatic response of Norway spruce (Picea abies) at 138 sites covering wide spatial and site fertility gradients in temperate forests in Central Europe. To characterize the annual growth rate of stem biomass and seasonal canopy vigor, we used tree-ring chronologies and time-series of NDVI derived from Landsat imagery. We calculated correlations of tree-ring width and NDVI with mean growing season temperature and standardized precipitation evapotranspiration index (SPEI). We evaluated how these climate responses varied with aridity index, soil category, stand age, and topographical factors. The results show that the climate-growth responses of tree rings shift from positive to negative for SPEI and from negative to positive for temperature from dry (warm) to wet (cold) areas. By contrast, NDVI revealed a negative response to temperature across the entire climatic gradient. The negative response of NDVI to temperature likely results from drought effects in warm areas and supporting effects of cloudy conditions on foliage greenness in wet areas. Contrary to NDVI, climate responses of tree rings differed according to stand age and were unaffected by local topographical features and soil conditions. Our findings demonstrate that the decoupling of stem and foliage climatic responses may result from their different climatic limitation along environmental gradients. These results imply that in temperate forest ecosystems, the canopy vigor may show different trends compared to stem growth under ongoing climate change.

Environmental Factors Affecting Volume Growth of Yellow Poplar Plantations in South Korea

South Korean forests need hardwood tree species that can produce timber, as global warming progresses and the habitats of conifers dwindle. For the past 30 years, exotic yellow poplar (Liriodendron tulipifera) has been planted to replace some of the pine-dominated forests, as there is a lack of native hardwood tree species that produce large and good quality timber. However, yellow poplar growth has varied among planting sites across the country. We studied how environmental factors affect the growth of 49 stands of yellow poplar trees, with 945 dominant trees across 129 plots. To identify the optimal conditions for yellow poplar growth, we assessed 28 environmental variables, including geographic, climatic, topographic, and soil properties, for their correlation with volume growth. We estimated the optimal conditions for yellow poplar growth by averaging the values of the variables for the top five performing stands. To calculate the relative distance of any stand from the optimal conditions, we divided the difference between the stand’s values for the environmental variables and the optimal conditions by the standard deviation of those variables. We then calculated Spearman rank correlation coefficients between these distances and volume growth rankings. Wind exposure (WE), growing season temperature (GT), Latitude (LN), soil phosphorus pentoxide (P2O5) content, low extreme temperature during January and February (LT), and spring humidity (SH) were the most important environmental factors governing growing sites for yellow poplar in Korea, with WE being the most critical. Some variables showed synergistic effects and correlated slightly more strongly with volume growth when combined with the WE variable. Our study provides crucial insights for optimizing plantation management and site selection in non-native ranges, enhancing overall success in establishing yellow poplar plantations in South Korea.

The functioning of alpine grassland ecosystems: Climate outweighs plant species richness

AbstractThe biodiversity–ecosystem functioning relationship has received significant attention in recent decades. It has been widely demonstrated that plant diversity plays a crucial role in enhancing the functioning of terrestrial ecosystems. However, few studies have tested the influence of plant species richness in mediating the impacts of climate on ecosystem functions at large spatial scales.To address this gap, we utilized data from field surveys across broad climatic gradients at the Qinghai–Tibetan Plateau, China. Our goal was to examine the importance of plant species richness for the functioning of alpine grassland ecosystems, specifically productivity and soil carbon sequestration.Our results showed strong positive correlations between ecosystem functioning and growing season precipitation as well as species richness. In contrast, there was a negative correlation with growing season temperature. Notably, the positive effect of growing season precipitation on ecosystem functioning outweighed the negative effect of growing season temperature. The indirect effects of growing season precipitation and temperature on ecosystem functioning through changes in species richness were weak. Furthermore, the inclusion of climate factors in the model weakened the relationships between species richness and ecosystem functioning.Synthesis. Our findings demonstrate that climate factors are more important than species richness for the provisioning of ecosystem functions at large spatial scales. In summary, our study underscores the importance of considering climate factors alongside species richness when assessing ecosystem functioning across extensive geographical areas.

Temperature variability during the growing season affects the quality attributes of table grapes in Pothwar-insight from a new emerging viticulture region in South Asia.

Rising air temperature due to climate change has posed a mammoth challenge to global viticulture and key berry quality traits are compromised. Exploring the effects of seasonal temperature variability on berry ripening and quality attributes in different viticulture regions may help in sustainable viticulture industry. The present research was designed to explore the effect of temperature variables on key quality attributes of table grape cultivars in Pothwar region of Pakistan. Key berry quality traits such as total soluble solids (TSS), titratable acidity (TA), maturity indices (MI), ascorbic acid, sugars, total polyphenol contents (TPC) and total anthocyanin contents (TAC) were unlocked for four important table grape cultivars under varying environmental conditions at Chakwal and Islamabad districts for two consecutive vintages of 2019 and 2020. The district Chakwal has up to 0.92 °C, 1.35 °C, 1.12°C and 0.81°C higher Tmin, Tmax, Tmean anddiurnal temperature variation (DTV)respectively, compared to Islamabad particularly for the 2019 vintage. The results of the present study revealed that the warmer site (Chakwal) has significantly (P ≤0.05) higher juice pH, TSS (°brix) and maturity indices (MI) particularly for the relatively hotter vintage of 2019. Interestingly, MI was 33% higher for the relatively warmer vintage of 2019 compared to 2020 with relatively lower acidity (up to 38%). Moreover, higher titratable acidity (11.2%), ascorbic acid (28.5%), polyphenols (20.3%) and anthocyanins (10.6%) were noticed for the colder Islamabad compared to Chakwal. Although elevated temperature for warmer location and vintage favoured berry ripening, however key biochemical attributes such as titratable acidity, ascorbic acid, polyphenols and anthocyanins were negatively affected. The findings of the present research provide useful insight into the impact of growing season temperature on key berry attributes and may help devise adaptation strategies to improve berry quality.

Response of resin canal area of Pinus tabuliformis with different ages to climate change in Taiyue Mountains, China.

To investigate the responses of resin canal area of Pinus tabuliformis with different ages to climate change, we analyzed the relationship between the resin canal area and climate factors from 1972 to 2017 in P. tabuliformis plantation at young age, middle age, near-mature, mature, and over-mature periods in Taiyue Mountains, Shanxi Province. The results showed that 55.7% to 75.2% of resin canal occurred in earlywood. The mature and over-mature periods had the largest resin channel area, sequentially followed by near mature, middle age, and young age periods. Annual mean latewood resin canal area increased significantly in near-mature period and mature period, but not in other periods. There was a significant negative correlation between earlywood resin canal area and minimum temperature during the growing season (May to July) for trees at middle age period. Earlywood resin canal area of mature trees showed significant negative correlation with minimum temperature during the growing season, but significant positive correlation with drought (PDSI) in the non-growing season (previous September to current April). The total area of earlywood resin canal at the young, near-mature, and mature periods was less influenced by climate than other periods. The minimum growing season temperature was a limiting factor to earlywood resin canal growth, while the non-growing season drought gradually became a limiting factor for earlywood resin canal with increasing tree age. The total area of earlywood resin canal decreased with increasing non-growing season drought and increasing growing season minimum temperature. In the context of global warming, the earlywood resin canal area may gradually decrease at all five periods, and the most reduction in the over-mature stage.

Effects of Global Warming on Grapevine Berries Phenolic Compounds—A Review

The steadfast propensity to global warming has had a severe impact on overall viticulture. Given the observed increase in growing season temperatures in Europe (+1.7 °C from 1950 to 2004), between 2000 and 2049, it is assumed that temperatures for major wine regions will increase on average by about +0.42 °C per decade and will generally increase by +2.04 °C. Phenolic compound development is affected by environmental parameters such as ultraviolet (UV) radiation, sunlight, maximum and minimum temperatures, and grapevine water status. Proanthocyanidins, flavan-3-ol monomers, and other pigmented polymers are impacted by soil management and canopy handling strategies, as well as obtaining a microclimate around the developing bunch. This review, after a necessary summary of the synthesis of phenolic compounds in the berry (flavonoids and non-flavonoids) to let the lector delve into the topic, describes the impact of climate change and therefore of environmental factors on their accumulation and storage throughout ripening and harvesting. For example, high berry temperatures can reduce the total concentrations of skin anthocyanin; a 35 °C temperature entirely obstructed anthocyanin synthesis, and instead quercetin 3-glucoside could be enhanced with exposure to solar radiation. In addition, increments via water deficit in the relative abundance of methoxylated anthocyanins were also found. The vineyard management strategies to mitigate the degradation of phenolic compounds and preserve their concentration are also further discussed. Finally, it is believed that it is necessary today to establish an elastic and variable approach towards the single wine year, moving away from the concept of product standardization.

Growing season temperature and precipitation affect nutrient resorption in herbaceous species through a foliar stoichiometric control strategy

Growing season temperature and precipitation affect nutrient resorption in herbaceous species through a foliar stoichiometric control strategy

Responses of phenology, yield attributes, and yield of wheat varieties under different sowing times in Indo-Gangetic Plains.

A field experiment with wheat was conducted at Pusa (25.98°N, 85.67°E, 52m amsl), Bihar (middle Gangetic plains of India), to assess the responses of phenology, yield attributes, and yield to growing season temperature and heat stress. For this purpose, wheat was planted on five dates (viz., 15 November, 25 November, 5 December, 15 December, and 25 December) for three consecutive years (viz., 2014-2015, 2015-2016, and 2016-2017) with three prominent cultivars of the region (viz., RAU-3711, HD-2824, and HD-2733). Five dates of sowing represent different wheat-growing micro-environments as imposed by varying sowing dates encompassing the entire sowing window. The study observed the significant effect of sowing dates on phenophase duration. In general, with progress in the date of sowing, tiller initiation was delayed, while the reverse trend was observed for later growth phases. Sowing environments significantly influenced the number of effective tillers m-2. Average numbers of effective tillers (ET) m-2 for the wheat sown during 15-25 November were almost 11.6% higher than those of the 25 December sown crop. Grain filling duration (GFD) showed a declining trend with the advancement of sowing dates due to increased thermal load on the crop during the reproductive period. 15 November planted crop exhibited the highest GFD (47 days), which was shortened significantly beyond 25 November, signifying agrometeorological non-suitability of wheat sowing beyond this window. Wheat sown on 25 November recorded the highest grain yield (3.21 Mg ha-1), 48.61% higher than the 25 December sown crop due to the congenial thermal regime. In this context, we have identified optimal and sub-optimal conditions to escape heat stress for higher wheat productivity. Moreover, the sum of deviation of temperature from optimum thresholds, computed for sensitive growth phases (50% flowering to physiological maturity), helped us to identify heat stress and its impact on wheat. Genotype-by-environment (GGE) biplot analysis revealed that RAU-3711 was found to be the most stable cultivar. A decrease in the yield of wheat by 4.9% to 12.0%, sown during November, and 33.8% to 42.4%, sown during December, is predicted in 2050-51 and 2080-81, respectively, under RCP 4.5.

Central European Agroclimate over the Past 2000 Years

Abstract Central Europe has experienced a sequence of unprecedented summer droughts since 2015, which had considerable effects on the functioning and productivity of natural and agricultural systems. Placing these recent extremes in a long-term context of natural climate variability is, however, constrained by the limited length of observational records. Here, we use tree-ring stable oxygen and carbon isotopes to develop annually resolved reconstructions of growing season temperature and summer moisture variability for central Europe during the past 2000 years. Both records are independently interpolated across the southern Czech Republic and northeastern Austria to produce explicit estimates of the optimum agroclimatic zones, based on modern references of climatic forcing. Historical documentation of agricultural productivity and climate variability since 1090 CE provides strong quantitative verification of our new reconstructions. Our isotope records not only contain clear expressions of the medieval (920–1000 CE) and Renaissance (early sixteenth century) droughts, but also the relative influence of temperature and moisture on hydroclimatic conditions during the first millennium (including previously reported pluvials during the early third, fifth, and seventh centuries of the Common Era). We conclude that Czech agricultural production has experienced significant extremes over the past 2000 years, which includes periods for which there are no modern analogs. Significance Statement As temperatures increase, droughts are becoming a growing concern for European agriculture. Our study allows recent extremes to be contextualized and helps to better the understanding of potential drivers. Stable carbon and oxygen isotopes in oak tree rings were analyzed to reconstruct year-to-year and longer-term changes in both temperature and moisture over central Europe and the past 2000 years. We combine these proxy-based climate reconstructions to model how well crops were growing in the past. The early fifth and the early sixteenth centuries of the Common Era were most likely characterized by extreme conditions beyond what has been experienced in recent decades. Our reconstructions of natural variability might be used as a baseline in projections of future conditions.

AgMIP-Wheat multi-model simulations on climate change impact and adaptation for global wheat

The climate change impact and adaptation simulations from the Agricultural Model Intercomparison and Improvement Project (AgMIP) for wheat provide a unique dataset of multi-model ensemble simulations for 60 representative global locations covering all global wheat mega environments. The multi-model ensemble reported here has been thoroughly benchmarked against a large number of experimental data, including different locations, growing season temperatures, atmospheric CO2 concentration, heat stress scenarios, and their interactions. In this paper, we describe the main characteristics of this global simulation dataset. Detailed cultivar, crop management, and soil datasets were compiled for all locations to drive 32 wheat growth models. The dataset consists of 30-year simulated data including 25 output variables for nine climate scenarios, including Baseline (1980-2010) with 360 or 550 ppm CO2, Baseline +2oC or +4oC with 360 or 550 ppm CO2, a mid-century climate change scenario (RCP8.5, 571 ppm CO2), and 1.5°C (423 ppm CO2) and 2.0oC (487 ppm CO2) warming above the pre-industrial period (HAPPI). This global simulation dataset can be used as a benchmark from a well-tested multi-model ensemble in future analyses of global wheat. Also, resource use efficiency (e.g., for radiation, water, and nitrogen use) and uncertainty analyses under different climate scenarios can be explored at different scales. The DOI for the dataset is 10.5281/zenodo.4027033 (AgMIP-Wheat, 2020), and all the data are available on the data repository of Zenodo (http://doi.org/10.5281/zenodo.4027033). Two scientific publications have been published based on some of these data here.

Sensitivity of varve biogenic component to climate in eastern and central Finland

Biogenic varves as well as the biogenic component of clastic–biogenic varves have great potential as climate and environmental proxies but the response of biogenic lamina thickness to variations in growing-season climate is not well known. The connection of biogenic lamina thickness with growing-season or open-water season climate has been the focus of a limited number of studies. We examined biogenic laminae deposited during the past 100 years in five Finnish lakes representing different catchment types. We compared variations in biogenic lamina thicknesses with growing-season temperature records and open-water-season precipitation records. Statistical analyses for the whole study period reveal that the studied lakes generally respond positively to variations in growing-season temperature and open-water season precipitation. This suggests that warm summers intensify primary production while precipitation enhances transportation of allochthonous biogenic material and nutrients into the lake. Both mechanisms lead to enhanced biogenic lamina thickness. Two lakes reveal a more complex relationship to climate. Biogenic lamina thicknesses record a distinguishable climate signal despite human activities in the catchments, such as peatland drainage and forest cutting. We conclude that variations in biogenic lamina thickness of such boreal (clastic)–biogenic varves show potential for growing-season climate reconstructions. However, the response of each lake to climate parameters should be tested and understood separately.

Large herbivore diversity slows sea ice-associated decline in arctic tundra diversity.

Biodiversity is declining globally in response to multiple human stressors, including climate forcing. Nonetheless, local diversity trends are inconsistent in some taxa, obscuring contributions of local processes to global patterns. Arctic tundra diversity, including plants, fungi, and lichens, declined during a 15-year experiment that combined warming with exclusion of large herbivores known to influence tundra vegetation composition. Tundra diversity declined regardless of experimental treatment, as background growing season temperatures rose with sea ice loss. However, diversity declined slower with large herbivores than without them. This difference was associated with an increase in effective diversity of large herbivores as formerly abundant caribou declined and muskoxen increased. Efforts that promote herbivore diversity, such as rewilding, may help mitigate impacts of warming on tundra diversity.

Bioclimate change across the protected area network of Finland

Protected areas (PAs) are crucial in conserving biodiversity under climate change. In boreal regions, trends of biologically relevant climate variables (i.e., bioclimate) in PAs have remained unquantified. We investigated the changes and variability of 11 key bioclimatic variables across Finland during the period 1961–2020 based on gridded climatology. Our results suggest significant changes in annual mean and growing season temperatures over the entire study area, whereas, e.g., annual precipitation sum and April–September water balance have increased especially in the central and northern parts of Finland. We found substantial variation in bioclimatic changes over the 631 studied PAs; in the northern boreal zone (NB) the number of snow-covered days has decreased on average by 5.9 days between 1961–1990 and 1991–2020, while in the southern boreal zone (SB) the corresponding decrease has been 16.1 days. The number of frost days in spring with absent snow cover has decreased in the NB (on average −0.9 days) while increasing in the SB (0.5 days), reflecting the changing exposure of biota to frost. The observed increases in accumulation of heat in the SB and more frequent rain-on-snow events in the NB can affect drought tolerance and winter survival of species, respectively. Principal component analysis suggested that the main dimensions of bioclimate change in PAs vary across vegetation zones; for example, in the SB the changes are related to annual and growing season temperatures, whereas in the middle boreal zone the changes are linked to altered moisture and snow conditions. Our results highlight the substantial spatial variation in bioclimatic trends and climate vulnerability across the PAs and vegetation zones. These findings provide a basis for the understanding of the multifaceted changes the boreal PA network is facing and help to develop and direct conservation and management.

Responsiveness to long days for flowering is reduced in Arabidopsis by yearly variation in growing season temperatures.

Conservative flowering behaviours, such as flowering during long days in summer or late flowering at a high leaf number, are often proposed to protect against variable winter and spring temperatures which lead to frost damage if premature flowering occurs. Yet, due the many factors in natural environments relative to the number of individuals compared, assessing which climate characteristics drive these flowering traits has been difficult. We applied a multidisciplinary approach to 10winter-annual Arabidopsis thaliana populations from a wide climactic gradient in Norway. We used a variable reduction strategy to assess which of 100 climate descriptors from their home sites correlated most to their flowering behaviours when tested for responsiveness to photoperiod after saturation of vernalization; then, assessed sequence variation of 19 known environmental-response flowering genes. Photoperiod responsiveness inversely correlated with interannual variation in timing of growing season onset. Time to flowering appeared driven by growing season length, curtailed by cold fall temperatures. The distribution of FLM, TFL2and HOS1 haplotypes, genes involved in ambient temperature response, correlated with growing-season climate. We show that long-day responsiveness and late flowering may be driven not by risk of spring frosts, but by growing season temperature and length, perhaps to opportunistically maximize growth.

Modelling growing season carbon fluxes at a low-center polygon ecosystem in the Mackenzie River Delta

A temporal upscaling study was conducted to estimate net ecosystem exchange (NEE) of carbon dioxide and net methane exchange (NME) for a low-center polygon (LCP) ecosystem in the Mackenzie River Delta, for each of the 11 growing seasons (2009–2019). We used regression models to create a time series of flux drivers from in situ weather observations (2009–2019) combined with ERA5 reanalysis and satellite data. We then used neural networks that were trained and validated on a single growing season (2017) of eddy covariance data to model NEE and NME over each growing season. The study indicates growing season NEE was negative (net uptake) and NME was positive (net emission) in this LCP ecosystem. Cumulative carbon (C) uptake was estimated to be −46.7 g C m−2 (CI95% ± 45.3) per growing season, with methane emissions offsetting an average 5.6% of carbon dioxide uptake (in g C m−2) per growing season. High air temperatures (>15 °C) reduced daily CO2 uptake and cumulative NEE was positively correlated with mean air growing season temperatures. Cumulative NME was positively correlated with the length of the growing season. Our analysis suggests warmer climate conditions may reduce carbon uptake in this LCP ecosystem.