Timing Of Phenological Events Research Articles

Spring to summer transition timing influences zooplankton phenology and temporal niche partitioning in the coastal zone of the White Sea

Climatic changes are manifested through temporal shifts of seasonal events in environment, which may be critical for planktonic organisms. Temporal shift of seasonal warming curve in high latitudes affects phenology of aquatic organisms. Significant correlation between timing of phenological events in the life cycles of planktonic copepods and spring-summer temperature transition dates was revealed by canonical correlation analysis. We analyzed the long-term zooplankton and temperature time series (1961–2018) from the White Sea (66°19'50"N; 33°40'06"E, near the White Sea Biological Station of the Zoological Institute of the Russian Academy of Sciences). Two types of seasonal abundance dynamics of copepod juveniles and four types of the spring to summer transition were revealed. Each species demonstrated specific dynamics in response to each type of spring to summer transition. Species with similar ecological traits differed in their phenological response to the changes in the temperature dynamics. This phenomenon was explained, at least partly, by niche partitioning, when temporal niches of ecologically similar species were separated as a result of shifting the phenological events in time. The latter, in turn, was the result of organisms’ response to changes of spring to summer transition dynamics from year to year. We hypothesize that such separation may be one of the solutions of the “Paradox of the plankton”, favouring success of species-rich planktonic communities in high-latitude ecosystems, characterized by relative paucity of food resources and short productive season.

The Impact of Systematic Insecticides Against Emerald Ash Borer on Phenology of Urban Ash Trees.

The continued threat of emerald ash borer (Agrilus planipennis; EAB) to North American ash trees (Fraxinus spp.) has necessitated the use of systemic insecticide treatments as a primary control strategy against EAB in urban centers. Altered tree phenology due to systemic insecticides could mediate nontarget effects on other insect species, such as seed weevils or leaf-feeders, but whether such injections alter phenological events has not been studied. This study assessed the effects of systemic injections of emamectin benzoate or azadirachtin relative to untreated controls on the spring and fall phenology of mature green ash trees in Saint Paul, MN, USA from fall 2017 to spring 2019. EAB was first detected in this area in 2009. Trees showed minor, visible signs of EAB infestation at study initiation, but not mortality. We examined six phenological events: bud swelling, budburst, flowering, leaf out, leaf color change, and leaf abscission using a visual survey protocol. The timing of phenological events was similar across the different treatments for all but two of events; budburst and flowering. Budburst and flowering occurred 7 d and 5 d earlier, respectively, in treated trees than untreated trees. Given symptoms observed, we posit that delays in these events in untreated trees were due to infestations of EAB and the treatments of emamectin benzoate or azadiractin simply preserved the original phenology. The results from this study suggest that systemic insecticides may mitigate changes in ash tree phenology such as delayed leaf out that may be early symptoms of emerald ash borer.

Timing of phenological events and fruit ripening in Ficus palmata forssk. In the Mid Himalayan Region

Timing of phenological events and fruit ripening in Ficus palmata forssk. In the Mid Himalayan Region

Warming reduced flowering synchrony and extended community flowering season in an alpine meadow on the Tibetan Plateau.

The timing of phenological events is highly sensitive to climate change, and may influence ecosystem structure and function. Although changes in flowering phenology among species under climate change have been reported widely, how species-specific shifts will affect phenological synchrony and community-level phenology patterns remains unclear. We conducted a manipulative experiment of warming and precipitation addition and reduction to explore how climate change affected flowering phenology at the species and community levels in an alpine meadow on the eastern Tibetan Plateau. We found that warming advanced the first and last flowering times differently and with no consistent shifts in flowering duration among species, resulting in the entire flowering period of species emerging earlier in the growing season. Early-flowering species were more sensitive to warming than mid- and late-flowering species, thereby reducing flowering synchrony among species and extending the community-level flowering season. However, precipitation and its interactions with warming had no significant effects on flowering phenology. Our results suggest that temperature regulates flowering phenology from the species to community levels in this alpine meadow community, yet how species shifted their flowering timing and duration in response to warming varied. This species-level divergence may reshape flowering phenology in this alpine plant community. Decreasing flowering synchrony among species and the extension of community-level flowering seasons under warming may alter future trophic interactions, with cascading consequences to community and ecosystem function.

Determinants of spring molt in bighorn sheep: life-history, plasticity and phenology.

Anthropogenic climate change and habitat alterations increase the importance of understanding the causes and consequences of variation in phenological traits. Although the timing of phenological events may vary in response to both direct and mediated effects, methods to measure and distinguish direct and mediated effects have seldom been used. We used a Bayesian structural equation model (SEM) to evaluate potential direct and mediated effects of intrinsic individual and environmental factors on the timing and progression of spring molt in bighorn sheep. The SEM showed that molt phenology varied across years, was earlier in prime-aged and in heavier individuals, slower in males, and later in lactating ewes, especially if they were light. These results highlight how individual variation in intrinsic traits and life-history leads to substantial variation in a phenological trait. Indirect effects in the SEM predicted a delay in sheep molt phenology at high population density mediated through negative density effects on body mass and lactation probability. Cooler temperatures in late spring were also predicted to delay molt phenology via a negative effect on body mass. Finally, lactation reduced ewe mass which was predicted to delay molt phenology. This mediated effect thus increased the total delay (sum of direct and mediated effects) in molt phenology experience by lactating ewes. Our results underline the importance of estimating direct and indirect effects when modeling phenological traits. Because indirect effects could substantially affect estimates of total plasticity, they should be critically important to accurately predict phenological mismatches and demographic consequences of environmental change.

Functional traits influence patterns in vegetative and reproductive plant phenology - a multi-botanical garden study.

Phenology has emerged as key indicator of the biological impacts of climate change, yet the role of functional traits constraining variation in herbaceous species' phenology has received little attention. Botanical gardens are ideal places in which to investigate large numbers of species growing under common climate conditions. We ask whether interspecific variation in plant phenology is influenced by differences in functional traits. We recorded onset, end, duration and intensity of initial growth, leafing out, leaf senescence, flowering and fruiting for 212 species across five botanical gardens in Germany. We measured functional traits, including plant height, absolute and specific leaf area, leaf dry matter content, leaf carbon and nitrogen content and seed mass and accounted for species' relatedness. Closely related species showed greater similarities in timing of phenological events than expected by chance, but species' traits had a high degree of explanatory power, pointing to paramount importance of species' life-history strategies. Taller plants showed later timing of initial growth, and flowered, fruited and underwent leaf senescence later. Large-leaved species had shorter flowering and fruiting durations. Taller, large-leaved species differ in their phenology and are more competitive than smaller, small-leaved species. We assume climate warming will change plant communities' competitive hierarchies with consequences for biodiversity.

Extreme temperatures help in identifying thresholds in phenological responses

AbstractAimThe aim was to investigate temperature drivers of the spring phenology of 12 flowering events and six leafing events. Boreal phenology has previously exhibited only a modest response to temperature, but record‐breaking temperatures in March 2020 led to some extreme phenological timing and provided the opportunity for a more rigorous look at the nature and complexity of the relationship between temperature and phenology.LocationBoreal habitat in the Tatarstan Republic of Russia.Time period1989–2020.Major taxa studiedEighteen plant species.MethodsWe examined changes over time in the timing of phenological events and the relationship with temperature drivers using a range of regression techniques. Extreme temperatures caused some extreme phenology and visually suggested temperature thresholds, which were investigated using segmented regression (broken stick models). The performance of these models was subsequently compared with more complex alternatives based on accumulated daily temperatures.ResultsTemperatures in March 2020 were the warmest for this month in a record covering 200 years and were 5.9°C above the 1989–2020 average. Significant advances over time were detected for only seven of the events, but all events demonstrated significant relationships with temperature variables. Segmented regression identified significant temperature thresholds for 13 of the events with substantially stronger temperature relationships above these thresholds. Segmented regressions outperformed models based on accumulated daily temperatures for 12 of 18 events.Main conclusionsThe threshold models were a significant improvement over a linear response to temperature for 13 of the 18 events. The presence of thresholds explains, in part, why the response of boreal phenology to temperature previously seemed lower than in, for example, Western Europe. Responses to temperature above the identified thresholds were closer to those widely published from milder locations.

Conformance of sowing dates for maximizing heat use efficiency and seed cotton yield in arid to semi-arid cotton zone of Pakistan.

Pakistan is placed among the most vulnerable countries with relation to climate change and its impacts on agricultural productivity. Cotton is staged as the cash crop of the country and the main source of raw material for textile, oil, and feed industry. Varying environmental attributes have significant effects on the duration of vegetative and reproductive stages of cotton crop. To evaluate the potential impacts of varied temperatures regimes in different sowing times, field experiments were carried out throughout the cotton growing areas of Pakistan from Faisalabad in Central Punjab to RYK in Southern Punjab and Sakrand in Sindh to Dera Ismail Khan in Khyber Pakhtunkhwa (KPK) Province. Crop was sown on six different sowing dates starting from 1st March towards 15th May with 2-week intervals for two crop seasons (2016 and 2017). The timing of phenological events like emergence, squaring, flowering, and boll opening was recorded on calendar days and cumulative heat units (GDDs) were calculated for flowering and boll opening stages. Heat use efficiency for these sowing times was estimated. Data regarding yield-related parameters like opened bolls per plant, average boll weight, and seed cotton yield were also recorded during the study. Results revealed that duration of the growth stages was significantly affected by variation in mean thermal kinetics in varied sowing times in all four different environments. Seed cotton yield and heat use efficiency were also varied among the locations and sowing dates. The maximum seed cotton yield was recorded in Sakrand location at 15th April sowing date. The dependence of the phenological advancement on temperature and negative impacts of higher thermal stress on cotton productivity were also confirmed throughout the cotton growing zone of Pakistan.

Climate changes and trends in phenology of Cassia fistula L. in Agra (India)—1965-2019

Aim. The phenological observations help in identifying how plant species respond to regional climatic changes in particular such as ambient temperature. The study of trends in phenology of Cassia fistula L. (Caesalpiniaceae, Fabaceae) to climate changes in Agra (India) was the aim of the researches. Methods. The data on the average annual temperature in India and Agra were collected for 1965 to 2019 from the Meteorological Department. Commencement of leaf fall, time of new flush of leaves, flowering period (initiation, full bloom, and end) and the rest of phenophases in trees planted at Raja Balwant Singh College (Agra, Uttar Pradesh, India) were recorded from 25 marked trees during 1965–2019. Results. In C. fistula trees leaf fall started in the second and third week of February. Trees became completely leaf-less at the beginning of March. Flowering commenced in the first week of March, and the trees were in full bloom during the second week of March. Flowering continued till the beginning of May, and it was over in the second week of June. Fruiting commenced in December and continued till April. The timing of phenological events was consistent in 1965–2000. However, after 2001, there was a gradual shift recorded, and the shift was evident in 2009–2019. During the period 1965–2008, the average annual temperature ranged between 23.23o–25.13oC there was a liner increase in the temperature. The increase in average yearly temperature became more pronounced in 2009, and this trend is rising in temperature continued till 2019. In Agra in 2009–2019, temperature increase by 0.75–1.0oC had been recorded. The shift of phenoevents in C. fistula is correlated with the rise in annual average temperature. Conclusions. The shift in the timing of various phenoevents is the trees of C. fistula at Agra (India) are influenced by the change in the climate and rise in temperature. It is suggested that a phenological model should be developed to estimate the impact of climate change on fruit trees, horticultural plants and crops development in different regions of India.

Best environmental predictors of breeding phenology differ with elevation in a common woodland bird species.

Temperatures in mountain areas are increasing at a higher rate than the Northern Hemisphere land average, but how fauna may respond, in particular in terms of phenology, remains poorly understood. The aim of this study was to assess how elevation could modify the relationships between climate variability (air temperature and snow melt‐out date), the timing of plant phenology and egg‐laying date of the coal tit (Periparus ater). We collected 9 years (2011–2019) of data on egg‐laying date, spring air temperature, snow melt‐out date, and larch budburst date at two elevations (~1,300 m and ~1,900 m asl) on a slope located in the Mont‐Blanc Massif in the French Alps. We found that at low elevation, larch budburst date had a direct influence on egg‐laying date, while at high‐altitude snow melt‐out date was the limiting factor. At both elevations, air temperature had a similar effect on egg‐laying date, but was a poorer predictor than larch budburst or snowmelt date. Our results shed light on proximate drivers of breeding phenology responses to interannual climate variability in mountain areas and suggest that factors directly influencing species phenology vary at different elevations. Predicting the future responses of species in a climate change context will require testing the transferability of models and accounting for nonstationary relationships between environmental predictors and the timing of phenological events.

‘Variations in phenological and functional traits in Thapsia garganica populations in Al Jebel Al Akhdar, Libya’

AbstractThapsia garganica is a herbaceous perennial in the Apiaceae, distributed around the Mediterranean and traditionally used in North Africa as a remedy for arthritis, herpes, hair‐fall, hypertension, rheumatic, eczema and scabies. T. garganica is the source of thapsigargin: known for killing cancer cells. Seven populations were studied in sites differing in aspect and elevation within Al Jebel Al Akhdar in Libya. We studied the within‐population size distribution of individuals, the timing of the phenological events, and vegetative and reproductive traits.Thapsia garganica showed high flexibility of functional traits and shifts in the timing of phenological events in response to elevation and aspect (north‐ or south‐facing slopes). Local soil properties, together with effects due to altitude and aspect, could be direct causes of the observed differences in terms of population size and phenological traits. The phenological patterns detected also provide insights into the species response to climate change. Despite this phenotypic flexibility, and good growth in sites at 300–700 m a. s. l. on south‐facing slopes, most sites in this study have an unstable size‐structure, with few small individuals. This raises concerns about the long‐term persistence of the other populations of this species in Al Jebel Al Akhdar.

Vegetation Phenological Characterization of Alluvial Plain Shorea robusta-dominated Tropical Moist Deciduous Forest of Northeast India Using MODIS NDVI Time Series Data

The current study attempts to extract the phenological variables of alluvial plain Shorea robusta-dominated tropical moist deciduous forest of Northeast India using threshold-based method. A total of 230 Moderate Resolution Imaging Spectroradiometer (MODIS) MOD13Q1 time series normalized difference vegetation index (NDVI) datasets (year 2006–2015) has been used. Time series NDVI datasets were fitted to an adaptive Savitzky–Golay filter for smoothing. Important phenological matrices, namely start of season (SOS), end of season (EOS), length of season (LOS), peak of season (POS), seasonal amplitude, seasonally integrals (large and small integral), were evaluated. SOS varied from 106 to 120 day of year (DOY) (average of 110 ± 17.6), and EOS varied from 425 to 441 DOY (average of 431 ± 14.33). POS reaches in the month of September and October (average 262 ± 15). In the current study, a mean amplitude of 0.35, lower value of small integral (4.70 ± 0.34) and higher value of large integral (16.24 ± 0.25) signify that the studied forest is highly productive ecosystem, with semievergreen or moist deciduous canopy. Strong linear relationship of NDVI with temperature and rainfall was witnessed, particularly with a 1–2 month time lag. Also, NDVI-temperature correlation was found stronger than NDVI-precipitation correlation, suggesting that the area being a humid subtropical region, temperature plays a greater role in the timing of phenological events than rainfall and can act as a crucial factor for growth of the species under the climate changing scenario.

A long‐term perspective on microclimate and spring plant phenology in the Western Cascades

AbstractPhenology—recurring seasonal events in an organism's life cycle—is largely driven by local climates <1 km2 (microclimates), and changes in phenology are frequently used to indicate a species’ or community response to climate change. Phenological shifts can result in trophic asynchrony, population declines of higher‐level consumers, and reduction of plant fitness. While timing of phenological events is often correlated with elevation, studies have shown that microclimates created by areas of heterogeneous topography can be decoupled from regional climate patterns and that the distribution of microclimates does not always follow the elevation gradient. To examine the interaction between regional weather patterns and microclimate, and the subsequent effect of microclimate on phenology, we conducted standardized weekly spring phenology surveys of 18 native forest plants at the H.J. Andrews Experimental Forest in the Western Cascades from 2009 to 2016. We saw a high degree of inter‐annual variability of microclimate within and across sites, resulting in a changing pattern of microclimate diversity across the landscape from year to year. Most importantly, we saw that years with regional conditions predicted by continued climate change showed a loss of diversity in both microclimate and phenological events, with a more rapid advancement in bud break occurring at higher elevation sites. This study highlights the importance of understanding the interactions between regional and local processes that determine microclimate conditions and how those conditions influence patterns of plant phenology within forest communities, across mountain landscapes and over time, with implications for the capacity of mountainous regions to buffer local communities against the effects of climate change.

Phenological cues intrinsic in indigenous knowledge systems for forecasting seasonal climate in the Delta State of Nigeria.

Shifts in the timing of phenological events in plants and animals are cited as one of the most robust bioindicators of climate change. Much effort has thus been placed on the collection of phenological datasets, the quantification of the rates of phenological shifts and the association of these shifts with recorded meteorological data. These outputs are of value both in tracking the severity of climate change and in facilitating more robust management approaches in forestry and agriculture to changing climatic conditions. However, such an approach requires meteorological and phenological records spanning multiple decades. For communities in the Delta State of Nigeria, small-scale farming communities do not have access to meteorological records, and the dissemination of government issued daily to seasonal forecasts has only taken place in recent years. Their ability to survive inter-annual to inter-decadal climatic variability and longer-term climatic change has thus relied on well-entrenched indigenous knowledge systems (IKS). An analysis of the environmental cues that are used to infer the timing and amount of rainfall by farmers from three communities in the Delta State reveals a reliance on phenological events, including the croaking of frogs, the appearance of red millipedes and the emergence of fresh rubber tree and cassava leaves. These represent the first recorded awareness of phenology within the Delta State of Nigeria, and a potentially valuable source of phenological data. However, the reliance of these indicators is of concern given the rapid phenological shifts occurring in response to climate change.

Networked web-cameras monitor congruent seasonal development of birches with phenological field observations

Ecosystems’ potential to provide services, e.g. to sequester carbon, is largely driven by the phenological cycle of vegetation. Timing of phenological events is required for understanding and predicting the influence of climate change on ecosystems and to support analyses of ecosystem functioning. Analyses of conventional camera time series mounted near vegetation has been suggested as a means of monitoring phenological events and supporting wider monitoring of phenological cycle of biomes that is frequently done with satellite earth observation (EO). Especially in the boreal biome, sparsely scattered deciduous trees amongst conifer-dominant forests pose a problem for EO techniques as species phenological signal mix, and render EO data difficult to interpret. Therefore, deriving phenological information from on the ground measurements would provide valuable reference data for earth observed phenology products in a larger scale. Keeping this in mind, we established a network of digital cameras for automated monitoring of phenological activity of vegetation in the boreal ecosystems of Finland. Cameras were mounted at 14 sites, each site having 1–3 cameras. In this study, we used data from 12 sites to investigate how well networked cameras can detect the phenological development of birches (Betula spp.) along a latitudinal gradient. Birches typically appear in small quantities within the dominant species. We tested whether the small, scattered birch image elements allow a reliable extraction of colour indices and the temporal changes therein. We compared automatically derived phenological dates from these birch image elements both to visually determined dates from the same image time series and to independent observations recorded in the phenological monitoring network covering the same region. Automatically extracted season start dates, which were based on the change of green colour fraction in spring, corresponded well with the visually interpreted start of the season, and also to the budburst dates observed in the field. Red colour fraction turned out to be superior to the green colour-based indices in predicting leaf yellowing and fall. The latitudinal gradients derived using automated phenological date extraction corresponded well with the gradients estimated from the phenological field observations. We conclude that small and scattered birch image elements allow reliable extraction of key phenological dates for the season start and end of deciduous species studied here, thus providing important species-specific data for model validation and for explaining the temporal variation in EO phenology products.

Using ground observations of a digital camera in the VIS-NIR range for quantifying the phenology of Mediterranean woody species

The spectral reflectance of most plant species is quite similar, and thus the feasibility of identifying most plant species based on single date multispectral data is very low. Seasonal phenological patterns of plant species may enable to face the challenge of using remote sensing for mapping plant species at the individual level. We used a consumer-grade digital camera with near infra-red capabilities in order to extract and quantify vegetation phenological information in four East Mediterranean sites. After illumination corrections and other noise reduction steps, the phenological patterns of 1839 individuals representing 12 common species were analyzed, including evergreen trees, winter deciduous trees, semi-deciduous summer shrubs and annual herbaceous patches. Five vegetation indices were used to describe the phenology: relative green and red (green\\red chromatic coordinate), excess green (ExG), normalized difference vegetation index (NDVI) and green-red vegetation index (GRVI). We found significant differences between the phenology of the various species, and defined the main phenological groups using agglomerative hierarchical clustering. Differences between species and sites regarding the start of season (SOS), maximum of season (MOS) and end of season (EOS) were displayed in detail, using ExG values, as this index was found to have the lowest percentage of outliers. An additional visible band spectral index (relative red) was found as useful for characterizing seasonal phenology, and had the lowest correlation with the other four vegetation indices, which are more sensitive to greenness. We used a linear mixed model in order to evaluate the influences of various factors on the phenology, and found that unlike the significant effect of species and individuals on SOS, MOS and EOS, the sites' location did not have a direct significant effect on the timing of phenological events. In conclusion, the relative advantage of the proposed methodology is the exploitation of representative temporal information that is collected with accessible and simple devices, for the subsequent determination of optimal temporal acquisition of images by overhead sensors, for vegetation mapping over larger areas.

Phenological sensitivity to climate across taxa and trophic levels.

Differences in phenological responses to climate change among species can desynchronise ecological interactions and thereby threaten ecosystem function. To assess these threats, we must quantify the relative impact of climate change on species at different trophic levels. Here, we apply a Climate Sensitivity Profile approach to 10,003 terrestrial and aquatic phenological data sets, spatially matched to temperature and precipitation data, to quantify variation in climate sensitivity. The direction, magnitude and timing of climate sensitivity varied markedly among organisms within taxonomic and trophic groups. Despite this variability, we detected systematic variation in the direction and magnitude of phenological climate sensitivity. Secondary consumers showed consistently lower climate sensitivity than other groups. We used mid-century climate change projections to estimate that the timing of phenological events could change more for primary consumers than for species in other trophic levels (6.2 versus 2.5-2.9 days earlier on average), with substantial taxonomic variation (1.1-14.8 days earlier on average).

Artificial Selection Reveals High Genetic Variation in Phenology at the Trailing Edge of a Species Range.

Species responses to climate change depend on the interplay of migration and adaptation, yet we know relatively little about the potential for adaptation. Genetic adaptations to climate change often involve shifts in the timing of phenological events, such as flowering. If populations at the edge of a species range have lower genetic variation in phenological traits than central populations, then their persistence under climate change could be threatened. To test this hypothesis, we performed artificial selection experiments using the scarlet monkeyflower (Mimulus cardinalis) and compared genetic variation in flowering time among populations at the latitudinal center, northern edge, and southern edge of the species range. We also assessed whether selection on flowering time yielded correlated responses in functional traits, potentially representing a cost associated with early or late flowering. Contrary to prediction, southern populations exhibited greater responses to selection on flowering time than central or northern populations. Further, selection for early flowering resulted in correlated increases in specific leaf area and leaf nitrogen, whereas selection for late flowering led to decreases in these traits. These results provide critical insights about how spatial variation in the potential for adaptation may affect population persistence under changing climates.

Timing of rice maturity in China is affected more by transplanting date than by climate change

The phenological development of rice is a critical element affecting grain yield. The phenophases of rice development from transplanting through heading to maturity have often been linked to climatic factors, such as temperature and solar radiation. In contrast, the effects of physiological processes on the timing of rice maturity have not been well investigated. In this study, we examined shifts in the timing of transplanting, heading, and maturity of single, early, and late rice in China during the period 1991–2012; we used in situ records assembled at 113 agricultural stations, and explored the correlations between changes in the timing of phenological events and (i) climatic and (ii) physiological factors. We detected a significant warming trend through whole growing seasons (from transplanting to maturity) for all three rice varieties; this trend had negative impacts on the dates of maturity. The durations of the growing seasons over the period were extended by 4.1±2.0, 1.8±2.9, and 2.2±1.9 days for single, early, and late rice, respectively. However, for single rice, the extension was related to delayed dates of transplanting and maturity, whereas for early and late rice, it was attributed to advances in the dates of transplanting and maturity. The timing of maturity in all rice types was most closely related to transplantation and heading dates; climatic factors were of secondary importance. We hypothesize that internal regulation processes operating via carbohydrate content or leaf/cell longevities likely influence rice phenological processes through hormonal mechanisms. Early-season phenological events clearly influence the timing of plant maturity; the dates of early season events are shifting. Therefore, current protocols for global and regional crop modeling that use fixed planting dates are unlikely to accurately account for the impacts of climate change on croplands.

Response of grapevine phenology to recent temperature change and variability in the wine-producing area of Sremski Karlovci, Serbia

SUMMARYThe historical temperature (1981–2007) and phenological (1986–2011) data were analysed for the region of Sremski Karlovci, one of the oldest grapevine growing areas in Europe, with the aim of detecting trends of changes in the data, evaluating the sensitivity of grapevine phenology to temperature and revealing diversity among cultivars in their response to observed changes in temperature. The onset dates of four major phenological stages (budburst, flowering, veraison and harvest), along with the corresponding growth intervals between them, were examined for 20 wine grape cultivars. A number of climatically important parameters for viticulture were calculated for the calendar year, growing season and different grapevine growth periods. Significant increases were detected in average and heat-related extreme temperature indices. The greatest rate of change in temperature variables across the growing season was observed during the period from the beginning of flowering to the beginning of veraison and the smallest during the ripening period. Linear trends indicated that all phenological stages, except budburst, have advanced significantly. Averaged across all cultivars, detected trends were –0·4, –0·7 and –0·6 days/year for the beginning of flowering, the beginning of veraison and harvest date, respectively. Observed warming and change in the timing of phenological events did not significantly affect the duration of the growth intervals, which can be explained by significant inter-correlation between the phenological stages’ onset. Ripening was occurring under warmer conditions due to earlier flowering and veraison, rather than because of considerably higher temperatures preceding harvest or shortening of the ripening period. Most of the variation in phenology timing (74–90%) can be explained by a linear relationship between the onset date of phenological stage and temperature, with mean and maximum temperatures being more important than minimum temperatures. According to the current results, a 1 °C increase in the most influential temperature variable during the most relevant periods for the onset of phenological stages led to an advancement in the beginning of budburst, the beginning of flowering, the beginning of veraison and harvest by 3·6, 3·1, 5·2 and 7·4 days, respectively, on average for all cultivars. Among the cultivars studied, Pinot Noir displayed the greatest phenology advancement in response to increased temperature.