Frank-M. Chmielewski

Response of tree phenology to climate change across Europe

To investigate the impact of recent climatic changes on the plant development in Europe, this study uses phenological data of the International Phenological Gardens for the period 1969–1998. For this study, the leafing dates of four tree species (Betula pubescens, Prunus avium, Sorbus aucuparia and Ribes alpinum) were combined in an annual leaf unfolding index to define the beginning of growing season. The end of growing season was defined using the average leaf fall of B. pubescens, P. avium, Salix smithiana and R. alpinum. A nearly Europe-wide warming in the early spring (February–April) over the last 30 years (1969–1998) led to an earlier beginning of growing season by 8 days. The observed trends in the onset of spring corresponded well with changes in air temperature and circulation ( North Atlantic Oscillation Index (NAO-index)) across Europe. In late winter and early spring, the positive phase of NAO increased clearly, leading to prevailing westerly winds and thus to higher temperatures in the period February–April. Since the end of the 1980s the changes in circulation, air temperature and the beginning of spring time were striking. The investigation showed that a warming in the early spring (February–April) by 1 ◦ C causes an advance in the beginning of growing season of 7 days. The observed extension of growing season was mainly the result of an earlier onset of spring. An increase of mean annual air temperature by 1 ◦ C led to an extension of 5 days.

Climate changes and trends in phenology of fruit trees and field crops in Germany, 1961-2000

Distinct changes in air temperature since the end of the 1980s have led to clear responses in plant phenology in many parts of the world. In Germany phenological phases of the natural vegetation as well as of fruit trees and field crops have advanced clearly in the last decade of the 20th century. The strongest shift in plant development occurred for the very early spring phases. The late spring phases and summer phases reacted also to the increased temperatures, but they usually show lower trends. Until now the changes in plant development are still moderate, so that no strong impacts on yield formation processes were observed. But further climate changes will probably increase the effect on plants, so that in the future stronger impacts on crop yields are likely.

Impact of weather on yield components of winter rye over 30 years

Abstract This study examines the relationships between atmospheric influences and grain yields as well as yield components: crop density (ears m −2 ), number of kernels per ear and kernel weight of winter rye. The study uses data of a long-term field experiment at Berlin-Dahlem for the period between 1962 and 1996. The crop density and kernel number of winter rye were positively influenced by warm and sunny weather in autumn. An early start of the growing season after winter was also important for the satisfactory development of these components. Moderate temperatures prior to the beginning of shooting prolonged the period of spikelet formation and led to an increased number of spikelets and finally to a high number of kernels per ear. The kernel weight was negatively influenced by high temperatures and drought during the ripening stage. This weather situation reduced the duration of the grain filling period and thus the kernel weight. The yield of winter rye increased continuously from the mid 1980s as a result of a higher crop density and kernel number. Probably this is a positive climate change effect. Particularly the higher temperatures in winter time and an earlier beginning of the growing season seem to be favourable in this context.

The relationship between crop yields from an experiment in southern England and long-term climate variations

Abstract This study examines the relationships between meteorological variables (average monthly maximum and minimum air temperature, total monthly precipitation) and crop yields of a long-term field experiment in southern England. The aim is to determine whether the long-periodic changes in crop yields are associated with climatic variations. This investigation uses the grain and straw yields (from 1854 to 1967) of the Broadbalk winter wheat experiment at Rothamsted, UK, which is one of the oldest agricultural field experiments in the world. In this study the main techniques used to describe the crop/weather relationships are correlation analysis and multiple regression. The results show that the long-term changes in crop yields at Rothamsted are partially related to climate variations at this site. The main influence on grain yields is precipitation. In all months there are negative correlations between grain yield and rainfall. A weak positive correlation is found between precipitation and straw yield from April to June (stem elongation) whereas in the other months the correlation coefficients remain negative. The maximum air temperature is positively correlated with the straw yield in all months except May, June and July. Generally it is easier to explain the variability of straw yields by weather variations than it is that of grain yields. On the basis of simple multiple regression models it is possible to explain 33% of the grain and 50% of the straw yield variability by precipitation and temperature variations. Long periodic changes in rainfall and temperature are reflected in estimated crop yields. The lowest grain and straw yields are observed in wet/cold as well as in wet/warm years wheareas the highest grain yields are more frequent in dry or cold years and the highest straw yields in dry or warm years.

Tillage and fertilizing effects on sandy soils. Review and selected results of long‐term experiments at Humboldt‐University Berlin

The Humboldt-University of Berlin conducts several long-term field trials designed to assess the effects of tillage methods, crop rotations, organic fertilization, mineral nitrogen, phosphorus, and potassium fertilizers, liming, irrigation, and weather conditions. On silty sand soils shallow ploughing resulted in a distinct accumulation of soil organic matter and phosphorus in the tilled soil layer while potassium and pH values were unaffected. On average shallow ploughing increased yields, with a tendency for higher yields in spring crops and lower yields in winter cereals. Different amounts of organic and mineral fertilizers applied over 30 years resulted in a great differentiation in soil organic matter content. In the following 32 years this variation stayed more or less unchanged, but with an overall reduction in the carbon content. In variants in which phosphate and potassic fertilizers were omitted, 16 kg ha—1 P and 15 kg ha—1 K per year were still being mobilized in the soil after 60 years. In treatments with mineral fertilization, the phosphorus is nearly balanced whilst only 60 % of the potassium is withdrawn from the soil. Additional organic fertilizers, given as farm yard manure, led to a nutrient surplus of 19 kg ha—1 a—1 P and 99 kg ha—1 a—1 K. Omitted liming caused an acidification of the soil to such an extent that crop production became impossible. Bodenbearbeitungs- und Dungeeffekte in Sandboden — Ubersicht der Dauerfeldversuche an der Humboldt-Universitat zu Berlin Die Humboldt-Universitat zu Berlin verfugt uber langjahrige Dauerfeldversuche, mit denen die Wirkungen unterschiedlicher Bodenbearbeitung, Fruchtfolge, organischer Dungung, mineralischer Stickstoff-, Phosphor- und Kalidungung, Kalkung, Beregnung sowie der Witterung gepruft werden. Dauerhaft verminderte Pflugtiefe hat auf mittel-schluffigem Sandboden in Berlin-Dahlem zur Humus- und Phosphoranreicherung in der bearbeiteten Krume gefuhrt, wahrend der Kaliumgehalt und der pH-Wert davon weitgehend unbeeinflusst blieben. Bei flacher Bodenbearbeitung wurden im Mittel tendenziell hohere Ertrage erzielt, wobei Fruchtarten der Sommerung Mehrertrage erreichten und Wintergetreide eher negativ reagierte. Differenzierte organisch-mineralische Dungung am Standort Thyrow hat im Verlauf von 30 Versuchsjahren zu Unterschieden im Gehalt an organischem Kohlenstoff von bis zu 75% gefuhrt. Nach sechs Jahrzehnten unterlassener P- und K-Dungung wurden jahrlich durchschnittlich noch 16kg ha—1 P und 15 kg ha—1 K mobilisiert. Bei ausschlieslicher Mineraldungung war die P-Bilanz nahezu ausgeglichen, wahrend die gedungte K-Menge nur zu 60 % entzogen wurde. Zusatzliche organische Dungung als Stallmist fuhrte im langjahrigen Mittel zu Nahrstoffuberschussen in Hohe von 19 kg ha—1 a—1 P und 99 kg ha—1 a—1 K. Bei unterlassener Kalkung des Bodens versauerte der Boden so stark, dass seine pflanzenbauliche Nutzung nicht mehr moglich ist.

Phenology and Agriculture

This chapter deals with both traditional aspects of phenology in agriculture (length of growing season and different applications of phenological data in agriculture) as well as modern aspects, which focus on impacts of climate change on phenophases of field crops and fruit trees.

Long‐term climate variability in a simple, nonlinear atmospheric model

A nonlinear, baroclinic, hemispheric, low-order model of the atmosphere with nonzonal orographic and zonal thermal forcings has been constructed. The model is used to investigate the long-term climate variability by running it over 1100 years. The model runs show a chaotic behavior in a realistic parameter range. With and without a seasonal cycle in the thermal forcing, the model generates decadal climate variations which are of the same order as interannual variations. The maximum variability is found in a broad range of periods between 3 and 44 years. Empirical orthogonal function analysis reveals that these fluctuations are predominantly caused by the interaction between the orographically excited standing wave and the mean zonal flow. The computed power spectra of the principal component time series stress the importance of the high-frequency transients in long-term climate variability.

Models for the beginning of sour cherry blossom

Seven different model approaches to calculate the onset of sour cherry blossom for the main growing regions in Rhineland-Palatinate (Germany) were compared. Three of the approaches were pure forcing models (M1, M2, M2DL) and the remaining four models were combined sequential chilling-forcing (CF) models. Model M1 was the commonly used growing degree day (GDD) model in which the starting date of temperature accumulation (t1), the base temperature (TBF) and the forcing requirement F* were optimized on the basis of observed data. Because of a relatively late optimal starting date (t1 = 1 March), the model can be applied only to calculate the onset of cherry blossom for present climate conditions. In order to develop forcing models that could possibly be used to estimate possible shifts in the timing of cherry blossom due to climate change, the starting date t1 of the models was intentionally set to 1 January (M2, M2DL). Unfortunately, model M2 failed in both the optimization and validation period. The introduction of a daylength term (DL) in model M2DL improved model performance. In order to project possible shifts in the timing of plant phenological events, combined CF-models are preferred over pure GDD-models. For this reason four CF-models were developed with (M3DL, M4DL) and without (M3, M4) consideration of daylength in the GDD-approach. The chilling requirement was calculated using chilling hours (M3, M3DL) and chill portions (M4, M4DL). Both models without daylength estimated implausible model parameters and failed model validation. However, models M3DL and M4DL showed meaningful model parameter estimations and the error between modelled and observed data was markedly reduced. Moreover, the models optimized and validated (internal validation) for one sour cherry growing region in Germany, were applied successfully to calculate the beginning of the blossom period in other regions in Europe and even at one station in North America (external validation).

The Global Phenological Monitoring Concept

In recent years, the Global Phenological Monitoring network has steadily increased in size. Set-up issues have been thoroughly explored, and sites successfully implemented in different parts of the world. GPM has demonstrated that it can play a significant role in standardization of phenological networks, as the BBCH-coding system is being adopted by other phenological networks. The first phase of the GPM network also improved cooperation between groups all over the world, and formed the basis for several successful initiatives, such as reviving the Dutch phenological network and the European Phenology Network. GPM will continue to contribute to the further expansion of existing networks, and the establishment of new networks, both to improve the use of phenological information, and improve cooperation and communication between the many actors involved in phenology. The program is now poised for future expansion into other parts of the world. Hopefully, GPM will be just as successful in gaining acceptance from phenologists internationally, as BBCH has been in worldwide agricultural experiments.

International Phenological Observation Networks: Concept of IPG and GPM

International phenological observation networks are of great importance for many applications in phenology. Data from these networks generally have a high quality standard (genetically identical plants, standardized observation guidelines, etc.) and cover different climatic regions. In this chapter we introduce two networks, the International Phenological Gardens in Europe (IPG) and the Global Phenological Monitoring Programme (GPM). Both observation networks are coordinated by the Humboldt-University of Berlin (Germany). These networks allow a phenological monitoring across lager geographical areas. At the end of each paragraph, we show some examples how these data can be used for scientific applications. They are of great importance to describe relationships between observed climate variability/change and plant development and they can be used to develop or validate phenological models which are able to project possible future shifts in plant development.