Earlier Onset Of Spring Research Articles

Culicoides-borne Orbivirus epidemiology in a changing climate.

Orbiviruses are of significant importance to the health of wildlife and domestic animals worldwide; the major orbiviruses transmitted by multiple biting midge (Culicoides) species include bluetongue virus, epizootic hemorrhagic disease virus, and African horse sickness virus. The viruses, insect vectors, and hosts are anticipated to be impacted by global climate change, altering established Orbivirus epidemiology. Changes in global climate have the potential to alter the vector competence and extrinsic incubation period of certain biting midge species, affect local and long-distance dispersal dynamics, lead to range expansion in the geographic distribution of vector species, and increase transmission period duration (earlier spring onset and later fall transmission). If transmission intensity is associated with weather anomalies such as droughts and wind speeds, there may be changes in the number of outbreaks and periods between outbreaks for some regions. Warmer temperatures and changing climates may impact the viral genome by facilitating reassortment and through the emergence of novel viral mutations. As the climate changes, Orbivirus epidemiology will be inextricably altered as has been seen with recent outbreaks of bluetongue, epizootic hemorrhagic disease, and African horse sickness outside of endemic areas, and requires interdisciplinary teams and approaches to assess and mitigate future outbreak threats.

Multiple environmental drivers across life stages influence Yukon River Chinook salmon productivity

Recent declines of Yukon River Chinook salmon ( Oncorhynchus tshawytscha) populations have severely impacted people residing in the Yukon and Alaska. Evidence-based conservation strategies focused on stock recovery and adaptation are urgently needed but are limited by our understanding of what is driving declines, particularly in Canadian portions of the Yukon River basin. We examined how multiple environmental drivers may be influencing Canadian-origin Yukon River Chinook salmon productivity for eight populations over a 28-year period. We found that productivity was related to various environmental and ecosystem processes acting cumulatively over multiple life stages and across broad geographic scales. Productivity decreased in association with warmer upriver migration temperatures, wetter freshwater juvenile rearing habitats, and increasing abundances of potential marine competitors. In contrast, productivity increased in years with warmer and snowier winters and earlier spring onset. We found that different populations had similar relationships with environmental drivers, with potentially negative implications for regional fisheries stability. Our findings provide insight into how Chinook salmon are responding to rapid environmental change and can help inform salmon conservation initiatives and sustainable harvest strategies.

Changes in phenological events and long‐term seasonality in response to climate change and the ecological restoration in China's Loess Plateau

AbstractPhenology is highly responsive to environmental changes, particularly in ecologically vulnerable regions that have undergone significant anthropogenic management and rapid climate change. While previous research has mainly focused on interannual variations of specific phenological events such as the start (SOS), peak (POS), and end (EOS) of growing season, little attention has been given to abrupt shifts in long‐term phenological seasonality resulting from land management. In this study, we utilized full temporal details of Moderate Resolution Imaging Spectroradiometer‐derived normalized difference vegetation index to investigate how phenological metrics and seasonality have changed within the Loess Plateau. Our results indicated an earlier initial phase (SOS‐POS) and a prolonged POS‐EOS phenophase. Earlier spring onset was dominated by increasing water availability from the previous autumn, and earlier SOS led to an earlier POS but no significant carryover effect on EOS. In addition, spring onset of grassland was sensitive to precipitation while forest community was strongly influenced by temperature. We also reported significant changes in phenological seasonality across the plateau, and this shift in long‐term seasonality was mainly controlled by growing season precipitation. Moreover, land use/land cover change also played a role with increasing importance after the abrupt change in seasonality. In sum, our findings highlight the importance of water availability in shaping phenological patterns across this semiarid plateau and illuminate shifts in phenological seasonality that are indispensable to a comprehensive understanding of phenology dynamics.

MONITORING OF DURATION OF COLD AND WARM SEASONS FOR THE PERIOD 1925-2022 AND ARBORICULTURE IN SAINT PETERSBURG

For the period 1925-2022, the earliest date of winter beginning in Saint Petersburg was 11 October 1941, and the latest date was 26 January 2019. The longest winter was in 1941/42 (178 days), and the shortest one - in 2019/20 (14 days). There is a tendency towards an earlier onset of spring, from 3 April (calculated for the period 1925-1934) to 4 March (for the period 2013-2022). The date of beginning of winter in 1986-1995 was the earliest one in the 20th century, with considerable increasing of autumnal period after it, with changing the date of beginning of winter till 19 December (2011-2020). The duration of winter period in 30-years period 1925-1954 comparing with similar period 1992-2022 has shortened from 130 days (36 % of the year) to 105 days (29 % of the year). On prolonging the vegetative period and the period without frosts woody plants have the opportunity to prepare more successfully for wintering. This creates better conditions for their reproductive ability, growth and development. The assortment of trees and shrubs promising for city planting has been enlarging.

Seasonal and inter-annual variation in exposure to peregrines (Falco peregrinus) for southbound western sandpipers (Calidris mauri)

BackgroundThe western sandpiper (Calidris mauri) is an early southbound migrant species in North America. The ‘peregrine avoidance’ hypothesis proposes that this timing evolved to reduce exposure to their main predator, the peregrine (Falco peregrinus), along the Pacific flyway.MethodsI evaluate this hypothesis based on 16 years of near-daily (June – October) measures of peregrine presence made on the Fraser River estuary, a major stopover in the Pacific northwest.ResultsExposure to peregrines is lowest for the earliest southbound western sandpipers, and rises steeply as peregrines en route from northern breeding areas begin to arrive in late July or August. Peregrine arrival timing varies greatly between years, shifting in step with the onset of spring along coastal Alaska. Peregrine presence on the Fraser estuary on any date is higher in years with earlier spring onset. On the median adult sandpiper passage date (day-of-year 198) this increases 17-fold over the inter-annual range between the earliest and latest peregrine arrival dates.ConclusionThe pattern of strong and predictable changes in the seasonal pattern of danger quantified here provides a further test of the hypothesis that danger affects migratory timing. Western sandpipers appear to anticipate the exposure level of southward migration, perhaps because they are able to observe spring onset on their Alaskan breeding grounds. They adjust the duration of parental care and length of the breeding season to keep the date of migratory departure from the Arctic relatively invariant in spite of large interannual variation in spring onset. While underway they also adjust aspects of migratory behavior. These observations support the ‘peregrine avoidance’ hypothesis, and suggest that western sandpipers are able to counter, at least partially, the higher migratory danger of early spring years.

Advanced roe deer (Capreolus capreolus) parturition date in response to climate change

AbstractIn temperate habitats, the vegetation onset in spring affects the life cycle activities of large herbivores. For one species of large herbivore, roe deer (Capreolus capreolus), parturition is tied to peak resource availability. However, recent long‐term studies of the parturition date of roe deer found only limited support for its earlier occurrence with an earlier onset of spring. In this study, data from a long‐term project (1973–2019) in southern Germany (Baden‐Württemberg; elevation 101–1036 m; 16,130 tagged roe deer fawns) were used to investigate whether the advance in the roe deer parturition date reflected different environmental conditions and was thus explained by temporal and spatial factors. Our results showed a consistent advance toward an earlier parturition date (between 0.16 and 0.33 d/yr), especially for elevations above 750 m, that coincided with an advance in plant phenology. Up to 37% of the variance of the detrended time series of the mean annual parturition was accounted for by the detrended time series of the flowering date of forsythia. Our results suggest a plasticity that allows roe deer to cope with climate‐induced changes along environmental gradients.

Spatiotemporal Variations of Spring Indices in China and Their Physical Mechanisms

AbstractSpring indices refer to the onset date of Spring, which quantify the phenological events in Spring. The average spring index (Avg‐SI) is defined as the average of the first leaf index (the date of early spring) and the first bloom index (the date of late spring) in this study. This study calculated the Avg‐SI in China for 2,780 weather stations during 1951–2014. The long‐term mean Avg‐SI suggested that the spring onset gradually delayed with the increase of latitudes and altitudes. The long‐term trend indicated earlier onset of spring in nearly all sub‐regions in China. The spatiotemporal variations of Avg‐SI were analyzed using the empirical orthogonal functions (EOF) method. The first EOF mode suggested a homogenous pattern across China. This mode is closely linked to the Atlantic Multidecadal Oscillation (AMO), which impacts the atmospheric circulation and temperature across Eurasia. Warm phase of AMO is associated with positive geopotential height (HGT) anomalies and warmer spring in China. The second EOF mode suggested a north‐south zonal pattern, which is linked to the Arctic Oscillation (AO) and the East Asian Trough Strength. Positive phases of AO lead to positive HGT anomalies over the northern China but negative HGT anomalies over the southern China. Together they lead to a weaker East Asian Trough and less cold air intrusions to the northern China, which in turn cause earlier onset of spring in this region.

Divergent negative spring vegetation and summer runoff patterns and their driving mechanisms in natural ecosystems of northern latitudes

The reported wide change in natural vegetation growth in the Northern Hemisphere could have altered hydrological cycles in the past 30 years. However, it is hard to understand the underlying mechanisms for substantial variations in the magnitude and direction of runoff response to vegetation change. Models fail to clearly identify the underlying mechanisms due to limitations in accommodating all the driving factors of the extremely complex reality. This study used a data-driven approach to determine the linkages between Normalized Difference Vegetation Index (NDVI) and runoff in the spring and summer seasons of 1982–2015 in 3600 + northern mid/high-latitude (≥30 °N) catchments. The results suggested that a significant (p < 0.05) negative correlation existed between spring NDVI and summer runoff in the Rocky Mountains, the Great Lakes region, the northern Scandinavia and the Alps. In the southern Rocky Mountains, there was a significant increase in spring NDVI and a decrease in summer runoff due to loss of snowpack. In the Great Lakes region, significant decrease in spring NDVI was accompanied by increase in summer runoff. Earlier spring onset and consequent withering vegetation in late spring significantly reduced spring NDVI while slightly increased summer runoff in Northern Rocky Mountain. The warmer and wetter winter could have increased spring NDVI owning to better water/energy environment, and insignificantly reduced summer runoff in northern Scandinavia and the Alps. Both anthropogenic warming and Arctic amplification might influence the patterns of vegetation-runoff in the region. Our findings can help improving the understanding on how vegetation change affects runoff and enhancing the forecasting abilities of hydrological models.

Time‐varying trends in frost indicators in the U.S. Southern Great Plains

AbstractClimatic frost indicators, including the dates of the last spring frost (LSF), the dates of the first fall frost (FFF), and the length of the frost‐free season (FFSL), are critical factors in anthropogenic and natural ecosystem management and can be directly calculated from daily minimum temperatures. Daily minimum temperature from the Applied Climate Information System was used to determine long‐term trends of frost indicators across the U.S. Southern Great Plains. The results demonstrated statistically significant trends of earlier LSF in eastern Kansas, western and eastern Oklahoma, and eastern Texas from 1950 to 2017. However, significantly later FFF trends and longer FFSL trends were mainly identified in eastern Oklahoma and eastern Texas. Overall, the region was characterized by the trends toward earlier LSF, later FFF, and longer FFSL from 1950 to 2017. In addition, the choice of time period in the climatic time series played an important role in LSF, FFF, and FFSL trends. Furthermore, the results from the correlation analysis of LSF and FFF with multiple climate indices indicated that the increasing trends in the spring Arctic Oscillation (AO) were consistent with the earlier onset of spring in Kansas and Texas, and the fall Atlantic Multidecadal Oscillation (AMO) was positively correlated with the later FFF dates in Kansas.

Response of barren-ground caribou to advancing spring phenology.

Phenological shifts are occurring in many ecosystems around the world. The capacity of species to adapt to changing phenology will be critical to their success under climate change scenarios. Failure to adjust migratory and reproductive timing to keep pace with the earlier onset of spring has led to negative demographic effects for populations of species across a variety of taxa. For caribou, there have been concerns that earlier spring green-up on calving areas might not be matched by earlier migration and parturition, potentially leading to a trophic mismatch with nutritional consequences for parturient and lactating caribou cows. However, there is limited evidence supporting these concerns. Here, we investigate the response of barren-ground caribou to changing spring phenology using data from telemetry and satellite imagery. From 2004 to 2016, we found that the average start of green-up on the calving area advanced by 7.25days, while the start of migration advanced by 13.64days, the end of migration advanced by 6.02days, and the date of peak calving advanced by 9.42days. Despite the advancing onset of green-up, we found no evidence for the development of a trophic mismatch because the advancing green-up coincided with earlier migration and calving by caribou. Changing snow cover on the late winter and migratory ranges was the most supported driver of advancing migratory behavior. The ability of caribou to adjust the timing of migratory and reproductive behavior in response to changing environmental conditions demonstrates the potential resilience of the species to some aspects of climate change.

Ongoing seasonally uneven climate warming leads to earlier autumn growth cessation in deciduous trees.

Ongoing global warming is causing phenological shifts that affect photosynthesis and growth rates in temperate woody species. However, the effects of seasonally uneven climate warming-as is occurring in much of Europe, where the winter/spring months are warming twice as fast than the summer/autumn months-on autumn growth cessation (completion of overwintering buds) and leaf senescence, and possible carry-over effects between phenophases, remain under-investigated. We conducted experiments in which we exposed saplings of canopy and understory species to 4°C warming in winter/spring, summer/autumn, or all year to disentangle how the timing of bud break, bud set completion, and leaf senescence is affected by seasonally uneven warming. All-year warming led to significantly delayed leaf senescence, but advanced bud set completion; summer/autumn warming only delayed leaf senescence; and winter/spring warming advanced both bud set and senescence. The non-parallel effects of warming on bud completion and leaf senescence show that leaf senescence alone is an inadequate proxy for autumn growth cessation in trees and counterintuitively suggest that continued uneven seasonal warming will advance cessation of primary growth in autumn, even when leaf senescence is delayed. Phenological responses to warming treatments (earlier spring onset, later autumn senescence) were more than twice as high in understory species than in canopy species, which can partly be explained by the absence of carry-over effects among phenophases in the former group. This underscores the need to consider differences among plant functional types when forecasting the future behaviour of ecosystems.

Long-term phenoclimatic averages of the Yuganskiy Nature Reserve territory and changes for 1961-2016

In light of the observed global climate changes in recent decades, we studied the local climate indicators and explored the possible links between the spring and autumn phenophases and climate data changes in the Yuganskiy nature reserve (N 600 17’; E74054’ – N590 23’; E74000’) in 1982-2016. The collected climate data include daily average, maximum and minimum temperatures, daily precipitation amount and intensity, and number of days with precipitation of 0.1mm or more, monthly average of snow depths, dates of first and last occurrence of daily mean temperatures 0, +5, +10°С through the year. Timing of sap movement and leaf fall start were used as the spring and autumn indicators of birch (Bétula péndula ) phenology. The mean value of weather averages in the 30-year period of 1961-1990 was used as reference. Trends were calculated using linear least squares regression. Statistical significance was determined by calculating the standard error of the trend estimate.&#x0D; We found that the annual mean temperature has increased from –1.9°С (1961-1990) to –0.8° С (1982-2016), with corroborating indicators including increased temperature of the coldest night of the year from –53°С (1961-1990) to –51.3° С (1982-2016) and increased frequency of significant positive temperature anomalies from 21% (1961-1990) to 37% (1982-2016). May, June, August and October nights have become successively warmer. The air temperature increase was not accompanied by a corresponding increase in precipitation.&#x0D; Statistically significant trends toward earlier onset of spring and summer from 1982 to 2016 were observed. The date of the last spring freeze has been advancing by 6.1 days per decade since 1982. A freeze-free season has lengthened by 7.7 days per decade. Linear trend of the snowmelt timing was –3.7 days per decade. Permanent snow cover period has been shortening by 7.7 days per decade. The date of the first occurrence of the daily mean temperatures of +10° С has been advancing by 5.1 days per decade. However, the 0 -+5° С lag has been lengthening significantly by 9.2 days per decade, and the number of biologically effective degree days (base +5C) has not statistically changed.&#x0D; Sap flux and leaf fall timing of B. pendula have been advancing almost simultaneously by 4.0 and 4.2 days per decade since 1985. Sap flux beginning and last spring freeze date have been found to be linearly correlated (r=0.904). The average lag of them was 5±1 days and has been lengthening by 3 days per decade (1985–2016).

Exploring relationships of spring green-up to moisture and temperature across Wyoming, U.S.A

ABSTRACTVegetation green-up signals the timing of available nutritious plants and shrubs providing high-quality forage for ungulates. In this study, we characterized spatial and temporal patterns of spring phenology and explored how they were related to preceding temperature and moisture conditions. We tested correlations between late winter weather and indicators of the onset and the length of the spring growing period with 250-m resolution time-series satellite data (2001 – 2013) for Wyoming, USA. In western Wyoming mountains, drier and warmer conditions during late winter were associated with earlier spring green-up onset of growth in forests, shrubs, and grasses. In the northeast mountains, onset of spring correlated positively with preceding warmer temperatures, but not with precipitation. In most basin and plains shrublands and grasslands, spring onset was not correlated with temperature, although earlier onset of spring was correlated with drier conditions in 25% of shrub/scrub areas. Results about the length of spring were less definitive, with warmer temperatures related to longer green-up time for 12–30% of the land cover in western mountains but to shorter green-up time periods for 10–20% of the grasses and shrubs in basins and plains. Complex phenological patterns are likely to affect ungulate foraging behaviour on a local scale.

Энергоэффективные биопозитивные конструкции в зданиях гражданского назначения для условий Санкт-Петербурга

Objective: Development of technical solutions for improving energy efficiency in residential buildings. Methods: Field experiment, thermal inspection of residential buildings. Results: In the conditions of rising global mean annual temperature over the last century, changed climatic parameters of St. Petersburg city. The duration of the winter period decreased by 13 days compared to the first half of the XX century due to the earlier onset of spring. The shift of the winter end has shifted to a colder part of the year and beginning remained unchanged. The winter in the district of St. Petersburg became colder. The change of climatic parameters of St. Petersburg affects the efficiency of the housing stock built since the late 90s. using the technology of monolithic housing construction. In the work conducted thermal survey of residential buildings of monolith structures in St. Petersburg. The result revealed the following defects: the formation of cold bridges in the construction of the pairing of the slabs with wall enclosing structures; disturbance of temperature and humidity conditions in residential areas; a deterioration of living conditions in the apartments; in some cases, the growth of education fungi. To create favorable conditions for human habitation designed a constructive solution that improves the thermal performance of the exterior walls. The technical solution is the use of the valve, in the thickness of the wall and provides or prevents the penetration of outside air in the air layer. Practical importance: The application of the proposed constructive solution after additional experimental studies will improve the energy efficiency of residential buildings in the context of changing climatic parameters.

Spring plant phenology and false springs in the conterminous US during the 21st century

The onset of spring plant growth has shifted earlier in the year over the past several decades due to rising global temperatures. Earlier spring onset may cause phenological mismatches between the availability of plant resources and dependent animals, and potentially lead to more false springs, when subsequent freezing temperatures damage new plant growth. We used the extended spring indices to project changes in spring onset, defined by leaf out and by first bloom, and predicted false springs until 2100 in the conterminous United States (US) using statistically-downscaled climate projections from the Coupled Model Intercomparison Project 5 ensemble. Averaged over our study region, the median shift in spring onset was 23 days earlier in the Representative Concentration Pathway 8.5 scenario with particularly large shifts in the Western US and the Great Plains. Spatial variation in phenology was due to the influence of short-term temperature changes around the time of spring onset versus season-long accumulation of warm temperatures. False spring risk increased in the Great Plains and portions of the Midwest, but remained constant or decreased elsewhere. We conclude that global climate change may have complex and spatially variable effects on spring onset and false springs, making local predictions of change difficult.

Temporal and geographical variation in the onset of climatological spring in Northeast China

Indications of earlier onset of spring have been observed in behavior of diverse animal and plant species in the Northern Hemisphere in response to recent climate warming. Knowledge of changes in the spring onset is a critical requirement for understanding ecosystem adaption to climate change, especially for agricultural regions. In this study, we present a climatological approach for detecting the temporal and spatial variability in onset of spring with particular emphasis on how they vary along geographical parameters. Yearly dates for spring onset were computed for 71 climate stations in Northeast China based on daily surface air temperature records. These analyses were conducted for the two study periods (1960–2004 and 1979–2004). We also examined the boundary shifts of spring onset for three selected dates between the periods of 1960–1978 and 1979–2004. The results showed that advancement of spring onset was more pronounced for the period of 1979–2004 than for the period of 1960–2004 (4.0 vs. 2.2 days/decade). For the 22 stations where the spring advancement was statistically significant in the two periods, the mean rate of advancement was −0.6 days/decade during the period of 1960 to 1978. The trends of advancement of spring onset decreased with both increasing latitude and altitude up to 300 m above sea level, and these geographical effects were clearer during 1979–2004. Analysis of boundary shifts of three specific dates revealed that the spring onset has moved to higher latitudes for each date with an average shift of about 1° of latitude (about 110 km). Our results suggest that attempts to address how ecosystems will adapt to spring advancement associated with climate warming should consider the differences in response rates and geographical effects across the study area.

Climate Change and National Security

Abstract Climate change is increasingly recognized as having national security implications, which has prompted dialogue between the climate change and national security communities—with resultant advantages and differences. Climate change research has proven useful to the national security community sponsors in several ways. It has opened security discussions to consider climate as well as political factors in studies of the future. It has encouraged factoring in the stresses placed on societies by climate changes (of any kind) to help assess the potential for state stability. And it has shown that changes such as increased heat, more intense storms, longer periods without rain, and earlier spring onset call for building climate resilience as part of building stability. For the climate change research community, studies from a national security point of view have revealed research lacunae, such as the lack of usable migration studies. This has also pushed the research community to consider second- and third-order impacts of climate change, such as migration and state stability, which broadens discussion of future impacts beyond temperature increases, severe storms, and sea level rise and affirms the importance of governance in responding to these changes. The increasing emphasis in climate change science toward research in vulnerability, resilience, and adaptation also frames what the intelligence and defense communities need to know, including where there are dependencies and weaknesses that may allow climate change impacts to result in security threats and where social and economic interventions can prevent climate change impacts and other stressors from resulting in social and political instability or collapse.

Enhanced growth of Juniperus thurifera under a warmer climate is explained by a positive carbon gain under cold and drought

Juniperus thurifera L. is an endemic conifer of the western Mediterranean Basin where it is subjected to a severe climatic stress characterized by low winter temperatures and summer drought. Given the trend of increased warming-induced drought stress in this area and the climatic sensitivity of this species, we expect a negative impact of climate change on growth and ecophysiological performance of J. thurifera in the harsh environments where it dominates. To evaluate this, we measured long- and short-term radial growth using dendrochronology, photosynthesis and water-use efficiency in males, females and juveniles in three sites in Central Spain. Climate was monitored and completed with historical records. Mean annual temperature has increased +0.2 °C per decade in the study area, and the main warming trends corresponded to spring (+0.2 °C per decade) and summer (+0.3 °C per decade). Radial growth and maximum photosynthesis peaked in spring and autumn. Positive photosynthetic rates were maintained all year long, albeit at reduced rates in winter and summer. Radial growth was enhanced by wet conditions in the previous autumn and by warm springs and high precipitation in summer of the year of tree-ring formation. Cloud cover during the summer increased growth, while cloudy winters led to impaired carbon gain and reduced growth in the long term. We argue that maintenance of carbon gain under harsh conditions (low winter temperatures and dry summer months) and plastic xylogenesis underlie J. thurifera's ability to profit from changing climatic conditions such as earlier spring onset and erratic summer rainfall. Our results highlight that not only the magnitude but also the sign of the impact of climate change on growth and persistence of Mediterranean trees is species specific.

Spring-season changes during the Late Pleniglacial and Bølling/Allerød interstadial

Earlier spring onset and the associated extension of the growing season in high latitudes belong to the most obvious consequences of global warming. The natural dynamics of growing-season properties during past climate shifts however, are extremely difficult to reconstruct since temperature reconstructions are hardly ever seasonally resolved and the applied proxies such as chirinomid or pollen analysis are mainly sensitive to summer temperatures. Here we apply a newly developed leaf cuticle-based proxy to reconstruct growing degree-days (GDD) in a quantitative way and to estimate changes in the timing of spring onset over the last deglaciation. Cuticle analyses of fossil birch leaves preserved in lake sediments from southern Germany reveal extremely low GDD values during the Late Pleniglacial, which are rapidly increasing at the onset of the Bølling/Allerød interstadial. While temperature and GDDs show a simultaneous warming during deglaciation, a GDD decline precedes lowering of summer temperatures during the Older Dryas cooling. Later bud-burst dates support the hypothesis of a shortening the growing season during this cool pulse.

Influence of climate change on phenological phases in Latvia and Lithuania

To investigate the impact of recent climatic changes on plant development, this study used phenological data of the volunteer networks in Latvia and Lithuania from the 1971-2000 period. The phenological calendar method was applied. Phenological seasons were described using data on 6 phenological phases at 10 stations. The growing season was described using birch Betula pendula as an example. Correlation analysis, linear regression and non-parametric Mann-Kendall trend tests were applied to establish the relationship between phenological phases and meteorological factors (temperature, precipitation) and the North Atlantic Oscillation (NAO). The results indicate a statisti- cally significant trend toward earlier onset of spring and summer phases. The study found that, unlike the majority of trends observed in Europe, on average the onset of phenological autumn in Latvia and Lithuania also started earlier. The observed trends in spring correlated well with temperatures in the preceding months and with the NAO. A strong correlation (in 12 cases out of 20) was found between spring phenophases and precipitation in February.