Plant phenology

Phenological sensitivity to temperature changes

Note: In a study of 254 national records across nine countries, most phenological changes correlated significantly with mean monthly temperatures of the previous two months

Data source:

Menzel, A.; Sparks, T. H.; Estrella, N.; Koch, E.; Aasa, A.; Ahas, R.; Alm-Kübler, K.; Bissolli, P.; Braslavská, O.; Briede, A.; Chmielewski, F. M.; Crepinsek, Z.; Curnel, Y.; Dahl, Å.; Defila, C.; Donelly, A.; Filella, I.; Jatczak, K.; Måge, F.; Mestre, A.; Nordli, Ø.; Peñuela, J.; Pirinen, P.; Remišová, V.; Scheinfinger, H.; Stríž, M.; Susnik, A.; Van Vliet, A. J. H.; Wiegolaski, F.-E.; Zach, S.; Zust, A., 2006. European phenological response to climate change matches the warming pattern. Global Change Biology 12: 19691976.

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Oak (Quercus sp) leafing date in Surrey (United Kingdom) 1950-2008

Note: Annual observations (connected by straight lines); black line: average change in leafing date (showing advancement).

Data source:

Nature's Calendar, UK. www.naturescalendar.org.uk/ climate+change/past.htm.

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Past trends

There is clear evidence of changing phenology across Europe in recent decades (Parmesan and Yohe, 2003; Root et al., 2003; Menzel et al., 2006) (Figure 1). Overall, 62 % of the observed variability in the timing of life cycle events can be explained by climate (van Vliet, 2008).  However, variability differs between events, with those occurring earlier (i.e. spring) being more variable than later events (Menzel et al., 2006). For example:

78 % of all leaf unfolding, flowering and fruiting records across Europe show an advancing trend and only 3 % a significant delay. The average advance of spring/summer phenological events is occurring at a rate of 2.5 days per decade (Menzel et al., 2006).

The pollen season currently starts on average 10 days earlier and is of longer duration than 50 years ago.

In Britain, the first flowering date for 385 plant species has advanced by 4.5 days on average during the past decade in comparison with the previous four decades (Fitter and Fitter, 2002); oak leafing has advanced three weeks in the last 50 years (DEFRA, 2007) (Figure 2).

In the Arctic, rapid climate-induced advancement of spring phenomena (e.g. flowering, egg laying) has been observed during the last 10 years. The strong responses of Arctic ecosystems and large variability within species illustrate how easily biological interactions can be disrupted by climate change (Høye et al., 2007).

Projections

Phenological changes will alter growing seasons, ecosystem production, population-level interactions and community dynamics (Fitter and Fitter, 2002). Different species show different phenological responses; for example, annuals and insect-pollinated species are more likely to flower early than perennials and wind-pollinated species (Fitter and Fitter, 2002). Ecological research is evaluating these response thresholds to better understand what the wider effects might be. While advancing trends in seasonal events will continue as climate warming increases in the years and decades to come, it is uncertain how different species will respond when temperature thresholds are reached and whether linear relationships between temperature and growing season will be realised in the future.