27 May 2021
Go to release: Plant Phenology 2020
The Central Statistics Office (CSO) has today (27 May 2021) published Plant Phenology 2020. Phenology is the study of annual seasonal changes in plants and animals such as the flowering of plants, the emergence of insects and the migration of birds. This report analyses changes in the timing of the beginning of leaf unfolding, general flowering, first ripe fruits, Autumn colouring, and leaf fall. Because many such phenomena are sensitive to variations in our climate, these records are a useful proxy for temperature in the study of climate change.
The report found that the length of the phenological season for Betula pubescens (Downy birch) at Valentia Observatory in Kerry during the period 1969-2020 varied from 168 days in 1979 to 236 days in 2014. The length of the phenological season is defined as the number of days between the beginning of leaf unfolding in Spring and leaf fall in Autumn. However, while the data suggest that the season may be getting longer, the earliest date for the beginning of leaf unfolding of Betula pubescens (Downy birch) at Valentia Observatory was on 13 March 1975.
Statistician in the Environment and Climate Division Paul McElvaney commented: “The observations are from six Irish phenological gardens. They were made available to the CSO by Met Éireann and the National Botanic Gardens. Some of the series start as far back as the mid-1960s and the long time-series are a tribute to the observers who carefully recorded the timing of these annual seasonal changes. Phenology represents the scientific collection and analysis of seasonal changes in nature that people would recognise in their own lives such as when daffodils flower, leaves appear on trees in Spring and leaf fall in Autumn as well as butterfly and bird migrations. These seasonal events are often used to introduce school pupils to methods of observing the Natural World.”
The six Irish gardens contributing data to this report are: Enniscoe House in Mayo; Glenveagh National Park in Donegal; John F. Kennedy Arboretum in Wexford; Johnstown Castle in Wexford; the National Botanic Gardens in Dublin; and Valentia Observatory in Kerry. These gardens are part of a broader International Phenological Gardens of Europe network. The participating gardens across Europe all use cloned plants to ensure the observations can be compared. Examples of the plants being monitored in Irish gardens are: Betula pubescens (Downy birch); Ribes alpinum (Alpine currant); Tilia cordata (Small-leaved lime); Prunus avium (Wild cherry); Larix decidua (European larch); and Fagus sylvatica (European beech).
The following phenological stages are recorded as appropriate for each plant:
Beginning of leaf unfolding: This phase occurs when the first regular surfaces of leaves become visible in three to four places. This is when the first leaf of a plant has pushed out of the bud up to its leaf stalk.
May shoot: This is the first Spring sprout of the conifers. The buds are open, and the protective sheath comes off the bud edges. The needles have not yet expanded at this point.
Beginning of flowering: This is when the first regular flowers have opened in three to four places on the observed plant.
General flowering: This occurs when more than half of the blossoms are open.
First ripe fruits: This phase is observed when the first fruits have ripened in several places (about three or four) on the observed plant.
Autumn colouring: More than half of the leaves of the observed plant have changed their colour, including those leaves which have fallen in large quantities.
Leaf fall: This is recorded when more than half of the leaves of the observed plant have fallen.
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