CC8 Pollen season

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Development

The beginning of birch pollen season has been measured in southern Finland (Turku), in central north Finland (Oulu) and in northernmost Finland (Utsjoki) since mid-1970s. In Turku birch pollen season starts approximately two weeks earlier than it used to, in Oulu a week earlier and in Utsjoki there is only a slight change or no change at all. It is unclear why the timing of the pollen season has not changed in the northern parts of the country while in the south the change is relatively strong.

Impact on biodiversity

Phenology or periodic life cycle events of many species have altered during the latest decades. For example migratory birds arrive earlier because of climate warming and some changes have occured in timing of birch pollen season and coming into leaf.

Birch is in the beginning of food chain and as such it affects a great deal the nutrition and reproduction of many species. For instance the caterpillars feed on birch leaves and the abundance of caterpillars benefits the reproduction of insectivores such as the Passeriformes. The abundance of Passeriformes further improves the nutrition of birds of prey,    e. g. Eurasian Pygmy Owl and Eurasian Sparrowhawk.

Different species and populations react to climate change in different ways. In addition to warming, the phenology of species is affected by many other phenomena such as anomalous weather conditions and photoperiodicity, the seasonal variation of light, which is not dependent on the climate. Because of climate change, some species might mistime their life cycle events, e. g. reproduction. This might cause asynchrony between different species and thus have significant effects on different levels of the food chain.

In Oulu region both the peak of the caterpillars and the willow tit nesting have occured earlier and earlier during the last two decades because of rising spring temperatures. The caterpillars are the most important nutrition source for willow tits during their nest feeding period. Because of the climate warming, the timing of the caterpillar peak has become more favourable for nest feeding willow tits. This has slightly improved the willow tit nesting success.

Similar studies have been made in Central Europe and the results vary a great deal. In some areas climate warming has not caused mistiming between species' life cycles, but in others the caterpillar peak has appeared earlier while the willow tit nesting period has not. This has hindered the willow tit nesting and increased nest mortality.

On the whole the climate change affects different populations and species in varying ways. In order to really see the big picture, plenty of research needs to be made on various food chain levels, climate zones and habitats.