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Phenology

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Phenology is the study of the times of recurring natural phenomena. The word is derived from the Greek Phainomai - to appear, come into view, and indicates that phenology has been principally concerned with the dates of first occurrence of natural events in their annual cycle. Examples include the date of emergence of leaves and flowers, the first flight of butterflies and the first appearance of migratory birds, the date of leaf colouring and fall in deciduous trees, the dates of egg-laying of birds and amphibia, the timing of the developmental cycles of honeybee colonies. Because many such phenomena are very sensitive to small variations in climate, especially to temperature, phenological records can be a useful proxy for temperature in the study of climate change.

Phenological Records from the past

Observations of phenological events have provided indications of the progress of the natural calendar since pre-agricultural times. Many cultures have traditional phenological proverbs and sayings which indicate a time for action: "When the sloe tree is white as a sheet, sow your barley whether it be dry or wet" or attempt to forecast future climate: "If oak's before ash, you're in for a splash. If ash before oak, you're in for a soak". But the indications can be pretty unreliable, as an alternative version of the rhyme shows: "If the oak is out before the ash, 'Twill be a summer of wet and splash; If the ash is out before the oak,'Twill be a summer of fire and smoke."

In Japan and China the time of blossoming of cherry and peach trees is associated with ancient festivals and some of these dates can be traced back to the eighth century. Such records form an important part of climate change research.

The pinot noir grape can also be used in historical phenology. Writing in Nature, Chuine et al. (2004) describe how French records of pinot noir grape-harvest dates in Burgundy can be used to reconstruct spring–summer temperatures from 1370 to 2003. Chuine found that 2003 summer temperatures were probably higher than in any other year since 1370 (see global warming). Chuine goes on to state

"The inferred anomaly for the summer of 2003 represents an unprecedented event. It was +5.86 °C warmer than the reference period (1960–1989), whereas the next highest anomaly during the whole period was +4.10°C in 1523. This confirms and refines the conclusions of previous studies about the exceptional warmth of the 2003 summer in France."

Gilbert White and William Markwick reported the seasonal events of more than 400 plant and animal species, Gilbert White in Selbourne, Hampshire and William Markwick in Battle, Sussex over a 25-year period between 1768 and 1793. The data, reported in a Natural History and Antiquities of Selborne are reported as the earliest and latest dates for each event over 25 years, so annual changes cannot therefore be determined.

Modern phenological recording

Robert Marsham is the founding father of modern phenological recording. Marsham was a wealthy landowner who kept systematic records of "Indications of spring" on his estate at Hevingham, Norfolk, from 1736. These were in the form of dates of the first occurrence of events such as flowering, bud burst, emergence or flight of an insect. Consistent records of the same events or "phenophases" were maintained by generations of the same family over unprecedentedly long periods of time, eventually ending with the death of Mary Marsham in 1958, so that trends can be observed and related to long-term climate records. The data show significant variation in dates which broadly correspond with warm and cold years. Between 1850 and 1950 a long-term trend of gradual climate warming is observable, and during this same period the Marsham record of oak leafing dates tended to become earlier.

After 1960 the rate of warming accelerated, and this is mirrored by increasing earliness of oak leafing, recorded in the data collected by Jean Combes in Surrey. Over the past 250 years, the first leafing date of oak appears to have advanced by about 8 days, corresponding to overall warming of the order of 1.5oC in the same period.

Towards the end of the 19th century the recording of the appearance and development of plants and animals became a national pastime, and between 1891 and 1948 a programme of phenological recording was organised across the British Isles by the Royal Meteorological Society. Up to 600 observers submitted returns in some years, with numbers averaging a few hundred. During this period 11 main plant phenophases were consistently recorded over the 58 years 1891-1948, and a further 14 phenophases were recorded for 20 years between 1929 and 1948. The returns were summarised each year in the Quarterly Journal of the RMS as “The Phenological Reports”. The 58-year data have been summarised by Jeffree (1960), and show that flowering dates could be as many as 21 days early and as many as 34 days late, with extreme earliness greatest in summer flowering species, and extreme lateness in spring flowering species. In all 25 species the timings of all phenological events are significantly related to temperature (Sparks et al., 2000), indicating that phenological events are likely to get earlier as climate warms.

The Phenological Reports ended suddenly in 1948 after 58 years, and Britain was without a national recording scheme for almost 50 years, just at a time when climate change was becoming evident. During this period, important contributions were made by individual dedicated observers. The naturalist and author Richard Fitter recorded the First Flowering Date (FFD) of 557 species British flowering plants in Oxfordshire between about 1954 and 1990. Writing in Science in 2002, Richard Fitter and his son Alistair Fitter found that "the average FFD of 385 British plant species has advanced by 4.5 days during the past decade compared with the previous four decades". They noted that FFD is sensitive to temperature, as is generally agreed, that "150 to 200 species may be flowering on average 15 days earlier in Britain now than in the very recent past" and that these earlier FFDs will have "profound ecosystem and evolutionary consequences".

In the last decade, national recording in Britain has been resumed by the UK Phenology network, run by Woodland Trust and the Centre for Ecology and Hydrology, and the BBC Springwatch survey. There is a USA National Phenology Network[1], in which both Professional scientists and lay recorders participate, a European Phenology Network[2] which has monitoring, research and educational remits, and many other countries such as Canada, China and Australia have phenological programs.

References

  • Chuine, I., Yiou, P., Viovy, N., Seguin, B., Daux, V. and Le Roy Ladurie, E. (2004). Grape ripening as a past climate indicator. Nature 432: 289-290.
  • Clark, M & Thompson, R (2004) Botanical records reveal changing seasons in a warmer world. Australian Science, Oct 2004, 37-39
  • Fitter, AH and Fitter RSR (2002) Rapid changes in flowering time in British plants. Science 296, 1689-1691
  • Jeffree, E.P. (1960) Some long-term means from the Phenological reports (1891-1948) of the Royal Meteorological Society. Quarterly Journal of the Royal Meteorological Society 86, 95-103
  • Sparks, TH & Carey, PD (1995) The responses of species to climate over two centuries: an analysis of the Marsham phenological record, 1736-1947. Journal of Ecology 83, 321-329
  • Sparks TH, Jeffree EP & Jeffree CE (2000) An examination of the relationship between flowering times and temperature at the national scale using long-term phenological records from the UK. International Journal of Biometeorology 44, 82-87
  • White, G. (1789) The natural history and antiquities of Selborne
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