âthe present labourers have been builders up of statistics ..... Historical data can tell us a great deal about ... developing the phenology website (www. 165 ...
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and soft fruit, but where slugs and snails can thrive on the soft shoots of emerging plants it can be disastrous in wetter years - my shredded dahlias, hostas and Lobelia cardinalis were all too obvious examples during the summer of 2001.
-(1998) Degrees of damage. J. R. Honk. SOC.,
Global warming
VIII Lindley, J. (1 842) Observations on the effects produced on plants by the frost which occurred in England in the winter of 1837-38. Trans. Hortic. SOC.,11, pp. 225-31 5 Manley, G. (1953) The mean temperature of central England, 1698-1952. Q. J. R. Meteorol. Soc., 79, pp. 242-26 1 -(1974) Central England temperatures: monthly means 1659 to 1973. Q. J. R. Meteorol. SOC.,100, pp. 389-405 Parker, D. E., Legg, T. P. and Folland, C. K. (1992) A new daily central England temperature series, 1772-1991. Int. J. Climatol., 12, pp. 317-342 Roach, W. T. and Brownscombe, J. L. (1984) Possible causes of the extreme cold during the winter 1981-82. Weather, 39, pp. 362-372 Royal Horticultural Society (1964) Frost and wind damage survey for winter 1962-3. J. R. Honk. SOC.,89, pp. 27-39 Wigley, T. M. L., Laugh, J. M. and Jones, P. D. (1984) Spatial patterns of precipitation in England and Wales and a revised, homogeneous England and Wales precipitation series. J. Climatol., 4, pp. 1-25
The wider question of potential global warming in the coming century does not alter these conclusions appreciably. The changes in the climate of the British Isles during the twentieth century have been broadly in line with the predictions of global warming. So if the forecasts of continued warming are correct, then the trends identified above are likely to be maintained in the coming decades. Both day-to-day management of our gardens and the longerterm planning to protect the wealth of species that we have will depend on exploiting the experience of our horticultural predecessors and maintaining a constant watch for new climatic threats. References Beckett, G. and Beckett, K. A. (1980) Hardy or not hardy. Plantsrnan, 2, pp. 20-30, 79-89 -(1982) Hardiness survey 1981/82. Plantsrnan, 4, pp. 2 19-228 -(1 983) Hardiness survey Part 2. Planrsrnan, 5, pp. 17-32 Burroughs, W. J. (1982) Frost damage during the winter of 1981/82. Weather, 37, pp. 346-352 -(1 996) Forecasting for rhe future. J. R. Hortic. SOC., 121, pp. 12-14
123, pp. 249-251 -‘(1999) The many faces of frost: Winter frieze. J. R. Hortic. SOC., 124, pp. 22-25 Harrow, R. L. (1948) Frost damage survey 1946-7. J. R. Hortic. SOC.,73, pp. 390-421,439-448 Hemslow, G. (1887) The frost report on the effects of the severe frosts on vegetation during the winters of 1879-80 & 1880-81. J. R. Honic. Soc.,
Correspondence to: Dr W. J. Burroughs, Squirrels Oak, Clandon Road, West Clandon, Surrey GU4 7uw. 0Royal Meteorological Society, 2002.
Is spring getting earlier? T. H. Sparks’ and
R. J. Smithers2
‘NERC Centre for Ecology and Hydrology, Huntingdon *The Woodland Trust, Grantham
What is spring and when does it commence? While spring, astronomically, is defined strictly by the position of the sun over the equator, the
general public think of spring and its beginning in terms of biological events. The Oxford English Dictionary includes both descriptions. 157
Weather Vol. 57 A cursory glance at any book of quotations reveals a large number of references to spring in English literature, and without exception couched in biological terms. What is the importance of spring? Historically, prior to agricultural improvement, stock that could not be fed were slaughtered before winter. People and animals often survived in close proximity through the winter, until spring brought the first fresh food for humans and fodder for animals. Spring does not have the same significance today but we still seem surprised and delighted by its annual return and grateful for relief from the depression of winter. In central and northern Europe the arrival of the skylark (Alauda arvensis) is seen as a sign of spring, yet this is not true in the UK as this species is resident through our milder winters. The distribution of species across Europe varies so it is not unexpected that different cultures identify different spring indicators. Even within the UK, spring may be perceived in a number of different ways. Ornithologists may perceive spring as when migrant birds start to return and nesting begins. Others may think of the first flowers of the year, such as snowdrops (Galanthus nivalis) and primroses (Primula vulgaris), as defining spring. Others, still, may consider spring in terms of when woodland starts to green up at budburst. Historically, there has been an emphasis on recording spring events rather than those of other seasons. The earliest surviving records known in the UK date from 1736 (Sparks and Carey 1995). This implies that phenology, the study of the timing of natural events, especially in relation to climate, is our longest written biological record. There is some debate as to whether phenology should include non-biological events, such as the thawing of lakes which has been recorded traditionally at higher latitudes. The Royal Meteorological Society (RMS) has a long history of supporting phenology. In 1875 (Anon. 1875) the RMS initiated a phenology network to study the timing of the seasons. The subsequent history of involvement was dodumented by Clarke (1936). At its peak about 600 recorders were involved. Despite remaining popular, the network ceased in 1947 on the retirement of the last co-ordinator and 158
May 2002 the failure of the RMS to find an alternative organisation to take over. Little had been done with the data; Clarke (1936) pointed out that “the present labourers have been builders up of statistics, looking for the coming of other labourers to reap a bounteous reward”. Phenology has now shaken off its dusty image as the harmless pastime of rural clerics and has taken on new importance in examining how species respond to changing climates. In 1998 the UK Phenology Network was revived by the Centre for Ecology and Hydrology and today is organised jointly with the Woodland Trust. Support for the paper-based and Internet-based (www.pheno1ogy.org.uk) scheme has grown rapidly from 74 recorders in 1998 to more than 3000 in 2001. It has become the most popular such scheme in Europe. In 1999 phenological events were accepted by the UK government as indicators of climate change (Cannell et al. 1999). The reasons why phenology is now seen as important are: (i) (ii) (iii) (iv) (v)
The growing consensus that greenhouse-gas emissions are causing global climate change. The realisation that phenological events can be very sensitive to climate fluctuations. Phenological events are cheap and easy to record. Phenology can motivate and enthuse a large body of committed recorders. Phenological events are excellent vehicles through which to demonstrate a changing climate to the general public.
From comparison of a wealth of historical records with observations in recent years, it is apparent that the timing of biological events is experiencing significant change in response to variations in spring temperatures. In this paper a number of examples of phenological data, held by the UK Phenology Network, that demonstrate evidence of climate change are discussed. Historical examples
Some species make better ‘indicators of climate
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March CET Fig. 1 National meanfirstflowering date of wood anemone relative to March Central England Temperature ( C E ~"C). Open circles represent data from 58years of the Royal Meteorological Sociery phenological reports, filled circles are data for 1998-2000fiom the UK Phenology Network.
change' than others and perhaps should be chosen because they: (i) (ii)
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Are thought to respond strongly to changes in seasonal temperaures. Are fairly common across the UK thereby ensuring widespread recording that enables us to compare changes in response to different temperatures at different locations. Are widely recognised and well loved to encourage as many people as possible to participate and so increase the accuracy of records and awareness of climate change. Are found in both rural and urban situations encouraging the widest range of people to become involved with their natural world. Have been recorded extensively in the past, meaning that any new observations can be used immediately to assess trends without having to wait years until sufficient records have been collated.
Figure 1 displays the relationship between wood anemone (Anemone nemorosa) flowering and March temperature, with historical RMS and current data identified separately. A similar relationship for common hawthorn (Crataegus monogyna) flowering is shown in Fig. 2. In gen-
eral terms, flowering and leafing events are advanced by 6-8 days for every 1 degC rise in temperature, and Figs. 1 and 2 suggest that current timings still fit in with the relationship observed from historical data. This very important finding gives much greater value to historical data and implies that we can use these to predict future change to species recorded historically. Figure 3 demonstrates the general synchrony between the recorded first flowering dates of coltsfoot (Tussdugo fat$ara) at three locations. The relationship is very strong between sites (all pairwise correlations p 53%) and suggest a response to a 1 degC increase in mean temperature of 9.4, 8.5 and 8.2 days respectively. Figure 5 is a similar example but using a common hawthorn flowering date. The response to temperature in this p gives the level of statistical significance and r is the correlation coeficient.
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example, as judged by the smoothed lines, appears to be nonlinear in support of the theoretical response suggested by Sparks et al. (2000); for example, flowering cannot get infinitely earlier in a seasonal climate and must reach an equilibrium. Thus far, we have demonstrated a temperature response in flowering events of plants at the national and site level. The more observant would remark at this point that we are just calculating correlations and have not proved a response to temperature per se. Whilst this is 160
true, there is so much evidence of significant correlation with temperature, backed up by results from controlled temperature environments, that we have little doubt that we are witnessing a response in the true sense of the word. Certainly, some aspects of the life cycle of plants and animals are controlled by day length rather than temperature, but day length is not changing. If we look at photographs taken by John Willis (Willis 1944) of the same clump of daffodils (Narcissus pseudo-narcissus) on 1 February 1916 and 1 February 1933
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Fig. 11 Mean arrival times ojthe sand martin at three Wekh islands (Skomer, Skokholm and Bardsey); smoothed line. superimposed
increasingly early spring events are not just evidenced by recent observation of plants. They are also apparent from records of when birds nest (Crick and Sparks 1999), butterflies emerge (Roy and Sparks 2000), amphibians breed (Reading 1998), and birds migrate. There has been a big shift in recent years in bird arrival times, particularly in those species that arrive first, and this pattern has been repeated across the British Isles (Sparks 1999) and Europe (Sparks et al. 1999). Figure 11 demonstrates mean sand martin (Riparia rzparia) arrival times at three Welsh bird observatories: Skomer, Skokholm and Bardsey. The 164
correlation of arrival time with mean February-April temperature is -0.53 (p= 0,001). The slightly later period of arrival in the late 1970s coincides with a period of cooler springs, and this feature is apparent in many biological time-series. Common frog ( R a m temporaria) spawning dates vary in relation to temperature; advancing by 5-7 days for every ldegC increase. They are also later in the north and earliest in the milder south-west, as we might expect. Figure 12 displays the relationship with temperature for four independent records from Cumbria (r = -0.86, p
