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. Phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle. Examples include the date of emergence of leaves and flowers, the first flight of butterflies, the first appearance of migratory birds, the date of leaf colouring and leaf fall in deciduous trees, the dates of egg-laying of birds, etc. Because many such phenomena are very sensitive to small variations in climate, phenological records can be a useful proxy for temperature in historical climatology, especially in the study of climate change. Changes in timing affect ecosystem functioning. Plant phenology has been proposed as an indicator of climate change by the European Environmental Agency and the Intergovernmental Panel on Climate Change. Changes in the timing of phenological events may influence biological processes and species distribution.
The data used for this release were obtained directly from Met Éireann and the National Botanic Gardens. The CSO integrated the annual observations from each garden into one integrated file. The full time-series of available data back to 1966 has been used.
In this report, an observation is defined as a single date for one phenological stage for one tree at one location. In some cases, multiple dates were available for the same event e.g. where a plant was cloned at the same garden. If the observer had combined the cloned observations into a single date for the phenophase then that was used. The number of observations recorded per station and per phenophase is shown in Table A. An example of a Phenological Observations Sheet can be found on the Methodology section of this release here: Methodology
Some phenological events must precede other events. However there are known errors in the microdata used for this report. These errors have not been corrected. It is hoped that it may be possible to recheck some of the data or to obtain access to the original data.
The number of days between the beginning of leaf unfolding and leaf fall dates has been used in some graphs as an approximation for the length of the growing season.
The full time series of observations has been made available on the CSO PxStat database. Users should note that the series has not been smoothed to correct errors in the observation dates.
Beginning of leaf unfolding (bud burst): 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.
St John’s sprout: The first sprouts of oaks and mountain ashes are regularly followed by a second sprout, the St John’s sprout. Buds that are already developed for the next year are caused to sprout prematurely by weather conditions. These second sprouts can be recognised by their fresh colour. The state of the first leaf unfolding is repeated: the first leaves of the sprout have their typical forms but not yet the final size of the fully developed leaves.
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.
The International Phenological Gardens is a network of gardens that was formed to record standardised phenological observations. All IPGs are situated in similar surroundings (mainly plain surface with meadows and some trees). Data are collected using a detailed observation-guide. In order to eliminate the hereditary variability, cloned species of all trees and shrubs have been planted in the IPGs. To enable this, a parent garden doing the vegetative propagation, breeding, and dispatch was established. The IPG network in Ireland has four sites (Valentia Observatory (Co. Kerry), John F. Kennedy Arboretum (Co. Wexford), Johnstown Castle (Co. Wexford) and the National Botanic Gardens (Dublin)) with phenological data records extending as far back as 1966. Observers record and monitor phenophases such as leaf unfolding, flowering, leaf fall, etc. for a range of species.
Observations from six Irish gardens were available for inclusion in this report:
- Data for Enniscoe House in Mayo (West) for 2013-2020 were used in this report (8 years)
- Data for Glenveagh National Park in Donegal (North-West) for 2007-2020 were used in this report (14 years)
- Data for John F. Kennedy Arboretum in Wexford (South-East) for 1967-1988 and 1990-2011 were used in this report (44 years)
- Data for Johnstown Castle in Wexford (South-East) for 1967-1979, 1982-2000, and 2011-2020 were used in this report (42 years)
- Data for National Botanic Gardens in Dublin (East) for 1966-1974, 1976-1992, 1994, 1997-2009, and 2011-2020 were used in this report (50 years)
- Data for Valentia Observatory in Kerry (South-West) for 1966-2020 were used in this report (55 years)
The main objective of PEP725 is to promote and facilitate phenological research by delivering a pan European phenological database with open data access for science, research and education purposes.
The records maintained at Irish gardens include the following species:
Code Plant species name English name
[111] Larix decidua* (Germany) European larch
[112] Larix decidua (E-France) European larch
[113] Larix decidua (S-Poland) European larch
[114] Larix decidua (Czech Republic) European larch
[115] Larix decidua (N-Italy) European larch
[121] Picea abies (early)* (Germany) Norway spruce
[122] Picea abies (late)* (Germany) Norway spruce
[123] Picea abies (northern) (Norway) Norway spruce
[124] Picea abies (late) (E-Poland) Norway spruce
[125] Picea abies (average) (E-Poland) Norway spruce
[126] Picea abies (E-Germany) Norway spruce
[127] Picea abies (E-France) Norway spruce
[128] Picea abies (N-Scandinavia) Norway spruce
[129] Picea omorika (Croatia) Serbian spruce
[131] Pinus sylvestris* (Poland) Scots pine
[132] Pinus sylvestris (E-France) Scots pine
[133] Pinus sylvestris (N-Scandinavia) Scots pine
[211] Betula pubescens* (Germany) Downy birch
[215] Betula pendula (N-Poland) Silver birch
[216] Betula pendula (N-Scandinavia) Silver birch
[221] Fagus sylvatica (Hardegsen)* (Germany) European beech
[222] Fagus sylvatica (Düdelsheim) (Germany) European beech
[223] Fagus sylvatica (Trippstadt) (Germany) European beech
[224] Fagus sylvatica (Denmark) European beech
[226] Fagus orientalis (Balkan) Oriental beech
[231] Populus canescens (Germany) Grey poplar
[235] Populus tremula* (Germany) European aspen
[236] Populus tremula (E-Poland) European aspen
[237] Populus tremula (S-Finland) European aspen
[238] Populus tremula (Ireland) European aspen
[239] Populus tremula (Greece) European aspen
[241] Prunus avium (Bovenden)* (Germany) Wild cherry
[242] Prunus avium (Lutter) (Germany) Wild cherry
[251] Quercus petraea (Zell/Mosel) (Germany) Sessile oak
[253] Quercus petraea (Croatia) Sessile oak
[256] Quercus robur (Wolfgang)* (Germany) Pedunculate oak
[257] Quercus robur (Barlohe) (Germany) Pedunculate oak
[258] Quercus robur (Croatia) Pedunculate oak
[261] Robinia pseudoacacia* (USA) Black locust
[271] Sorbus aucuparia* (Czech Rep.) Rowan / Mountain ash
[272] Sorbus aucuparia (N-Scandinavia) Rowan / Mountain ash
[281] Tilia cordata* (Germany) Small-leaved lime
[311] Ribes alpinum* (Austria) Alpine currant
[321] Salix aurita* (Germany) Eared willow
[323] Salix acutifolia* (Germany) Siberian violet-willow
[324] Salix smithiana* (Germany) Silky-leaf osier
[325] Salix glauca (Greenland) Grayleaf willow
[326] Salix viminalis* (Germany) Osier willow
[331] Sambucus nigra* (Germany) Elder
[411] Corylus avellana* Common hazel
[421] Forsythia suspensa (Fortunei)* Weeping forsythia
[431] Syringa x chinensis (Red Rothomagensis)* Chinese lilac
