Mother Nature's calendar has been showing increasingly less resemblance to the seasonal patterns of the past, with tangible effects on both humans and the natural environment. Pollen-releasing grasses, shrubs and trees have started to appear earlier, expanding the hay fever season. Drought, forest fires and invasive alien species have caused serious damage to some of the world's most vulnerable ecosystems.

The science that deals with annually or periodically recurring natural events is called phenology. Examples of phenological observations include flowering, ripening of fruits, unfolding leaves, hatching eggs, and bird migrations. Correlations between these seasonal events (or phenophases) and the changing climate have been suggested by scientists for a long time. A recent study of more than 542 plant and 19 animal species in 21 European countries confirmed a popular but previously unproven assumption: the leafing, flowering and fruiting of more than 75% of all plant species had advanced as a result of rising temperatures. Spring and summer now arrive 2.5 days earlier each decade, and it seems that our natural environment has responded quickly.

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Box 1: The Oak Processionary Caterpillar Marches On


Figure 1: Trends in Caterpillar distribution, The Netherlands

The urticating (burning) hairs of the Oak processionary caterpillar (Thaumetopoea processionea) have been serious causing health problems (skin irritation, respiratory distress) in Central and Western Europe for decades. Once only found in Central Europe, the caterpillar is now swiftly moving in north-eastward direction, due to increasing spring temperatures (figure 1 shows the spatial distribution in The Netherlands). Eight of the ten hottest years ever recorded in The Netherlands occurred during the last decade (figure 2: blue line); the last cold ("normal") winter of ‘96/’97 resulted in a dramatic decrease of caterpillar observations (figure 2: green bars).


Figure 2: Graph showing Annual Temperature and Caterpillar distribution trends in The Netherlands

Source: Alexander van Oudenhoven, Environmental Systems Analysis Group, Wageningen University.
Data: Alterra, Wageningen UR. Photo: L. Moraal, Alterra, Wageningen UR

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Phenology and climate change are closely related, and we can measure the effects locally by observing the health of our ecosystems. Data can be observed by satellite images or even in the backyard; once aggregated, the composite indicators can offer a wealth of information. Observations can provide data on the timing of natural events (as mentioned above) or indicate the spatial distribution of plant and animal species (see Box 1: The Oak Processionary Caterpillar Marches On). Moreover, the integration of phenological observations and climate models creates a powerful tool for adaptation to the impacts of climate change.

The impacts of phenological change to both ecosystems and public health are severe. For years, dengue fever was confined to Central/South America, Africa and large parts of Asia. But in recent years more and more tiger mosquitoes (which carry dengue fever) have been reported in the southern United States as well as Spain, France and even Switzerland. The cuckoo is an endangered species in some parts of the world. But its unfortunate breeding behaviour has made its future even grimmer. The cuckoo relies on the nests of other migrating birds to incubate her eggs. However, other birds have started to return to their nesting grounds up to three weeks earlier, leaving the late-arriving cuckoo mother with no place to lay her eggs anymore and a scarce food supply.

Citizen Science Enables Phenological Observations
Many local climate variations and shifting species patterns could not have been measured without a large number of volunteer observers. The potential for phenology as a “Citizen Science” is enormous; as successful projects in Western Europe, Canada and the U.S. have shown, phenology is an excellent way of bringing scientists and the general public together.

For example, ten thousands of volunteers report numerous signs of changing natural seasons and species distributions through the Nature's Calendar project in The Netherlands and Great Britain, has been able to. Projects in the U.S. (Project Budburst, Plant Watch), Canada (Nature Watch), Australia, China and other countries are either emerging or have been set up successfully. Anyone can be a part of the experts’ team by simply observing and reporting what happens in one’s own backyard, in the park or in the forest nearby.

There are many applications for phenology that have not yet been explored; phenological observations can improve weather forecasting, and more observation networks need to be established in the future, particularly in developing countries. A Chinese proverb says that “seasons are sooner recognised by plants than by men.” With a combination of expert research and citizen science, though, we can observe the behaviour of the plants and animals around us and better understand our changing climate.

RELATED LINKS:

Overview of Phenological Networks Worldwide

Nature: "Extinction Risk from Climate Change"

Science: "Phenology: Responses to a warming world"

AVAILABLE DATA:

New Indicators Will Track Progress Towards Reversing Global Biodiversity Loss

Scientists Struggle to Estimate Number of Species Threatened by Climate Change

UNEP-WCMC: Known and Treatened Species

Searchable Databases: Life Cycles Phenology, Nature's Calendar (UK)