What satellites and treetop ‘phenocams’ tell us about Ireland’s changing seasons

Michael Viney: This is the new face of phenology, the age-old study of the timing of changes in nature

The morning trudge to the rain gauge in my warmest wellies wears tracks in the grass that the windswept beech has filled with golden leaves. Its thin twigs are hung with last night’s rain, each drop a sudden jewel as the sun slides out of the mountain.

The rain to be measured has run into a bottle beneath a bronze funnel, set into the lawn to the prescription of Met Éireann. I pour it into a crystal tube engraved with successive millimetres up to 10.5cm. Last night’s measured a modest 6.6cm.

The original leaflet of instructions, prepared in ancient days, enjoined me to take heed of the meniscus, the curved upper surface of a liquid in a tube. That was before rain came in from the ocean in such obese and supersaturated clouds, to fill the measuring glass several times over.

Wild swings of weather, the local dumps of rain, can seem to mock the need for such precise recording. On one September morning in 2015, it took eight pours to empty the bottle, for a total of 83.5cm, or about as much rain as might fall in a whole month of spring.

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Meanwhile, the sun has held to its annual descent, delivering splendid textures and smouldering colours on the land. Unlike parts of these islands where heat and drought made trees drop their leaves too soon, most of those on the Wild Atlantic Way have waited for the winds.

The autumn colour of deciduous trees is chemical. It leads with the progressive loss of intensely green chlorophyll. As it fades, the orange-yellows and browns of carotenoids shine out, and the reds and purples of anthocyanins can glow in autumn light

The length of the growing season has increased, you’d think, since the earlier springs of climate change prompted trees to burst their buds earlier. But Swiss researchers suggest their autumn leaves will age and die faster. This governs how much carbon they will absorb that would help to slow climate change.

The autumn colour of deciduous trees is chemical. It leads with the progressive loss of chlorophyll, whose intensity of green has masked the colours of the leaf’s other pigments. As it fades, the orange-yellows and browns of carotenoids shine out, and the reds and purples of anthocyanins can glow in autumn light.

The intensity of green in the explosive growth of spring, the response to droughts and heat during summer, the changes of colour as the season fades, are all measured now in high-tech analysis of satellite scans from above Earth and scrutiny by “phenocams”. These are cameras mounted to peer across the upper canopy of trees at close range. They take successive digital images in all weathers that measure leaf activity and growth.

All this is the new face of phenology, the age-old study of the timing of changes in nature — changes that reach out from tree growth into the lives of insects and birds.

Records of Ireland’s tree life, from budburst to fruiting to leaf fall, are produced in 16 phenological gardens across the country, planted with clones of European tree species as part of an international network. Eleven more gardens grow Ireland’s native species alone.

In the late 1990s, when it was clear that climate change was producing an earlier spring, I joined the efforts of citizen scientists to record the progress of budburst, year by year, among the trees of the acre.

I visited the same branches each morning, from March to mid-June, to mark a card with a number for the stage of their progress, from the very first swelling of tight-clenched winter buds to the full four leaves out and a confetti of bud scales on the ground.

The advance of spring was thus made visible and recordable, but as a recent Irish research report observes, such ground observations became “time-consuming and unreliable” in autumn, when tree colours change as leaves enter senescence and finally fall.

The PhenoClimate project found that moth caterpillars were ahead of tree growth in responding to warmer springs

In a report for the Environmental Protection Agency, a science team at UCC describes a project called PhenoClimate. Led by Prof Astrid Wingler, this used satellite sensing and phenocams to chart the impact of climate change on the length and timing of the growing season for different types of woodland.

Among its tree species were native birch, hazel, spindle and hawthorn, and the study extended to wildlife that relies on trees for food.

The project drew in ground observations by citizen scientists to monitor the related phenology of migrant birds, butterflies and moths. It found, for example, that moth caterpillars were ahead of tree growth in responding to warmer springs — a significant mismatch between food supply and demand.

To help promote citizen science for phenology, the Nature Watch website was established by the National Biodiversity Data Centre. And the centre’s wider citizen science portal has just reached its millionth submitted record — a striped ladybird, Myzia oblongoguttata, in Co Carlow. This orange- and cream-spotted beetle is the rarest and most elusive of conifer ladybirds, feeding on the aphids of pines.