“Come with me into the woods, where spring is advancing, as it does, no matter what….” Mary Oliver, Poet
With the lengthening days and Easter upon us spring is definitely in the air and accelerating in pace. The start of spring though is open to interpretation depending on how you measure it and for what purpose. The meteorological spring, for instance, is based on 4 three-month periods using annual temperature cycles providing consistent markers between the seasons to enable comparative observations and forecasting. So, for weather forecasters in Exeter, spring began at the start of March as it does every year.
The official start of spring in the UK marked by the spring equinox, 12 hours of daylight and darkness – give or take where you are and a few other factors – has just been and gone, marked this year on March 20th. This astronomical measurement of the seasons relates to the tilt of the Earth’s axis and its orbit around the Sun therefore the date varies. The spring equinox is marked when the sun crosses the celestial equator, an imaginary line above the Earth’s equator from south to north, and the reverse line of travel marks the autumn equinox. The spring equinox is oft referred to as the vernal equinox, a historic term for spring.
Daffodils at Rudge Meadow: a marker of spring
Phenology, the study of reoccurring biological lifecycles and natural phenomena, such as the emergence of leaves and the first butterfly, observes the gradual but inexorable arrival of new life in spring reflecting how the season gradually arrives and blurs from winter into summer. Here, we have the earliest of springs within the UK, as flowering and other phenological events follow a spring temperature line across the country from the southwest to the northeast with, for instance, the first leafing of oak travelling at 1.3mph across the country.
Much of the woodland stirs in the pre-vernal season, well before the official spring date, when the trees are not in leaf and the ground flora and its associated invertebrate wildlife reap the benefit of sunshine and rain through the open canopy. This year, those early woodland changes were missed by all but local people, so as we move into official springtime here is a look back at some of those early spring transformations…
January is still mid-winter but harbingers of spring make an early appearance. Frog spawn appeared in mid January this year, early even for Devon, and having survived temperature fluctuations and transient ice coverings the tadpoles are now active. The delicate white flowerheads of snowdrops, often seen by watercourses, have been and gone but are another species that copes well with early spring temperatures, their hardened leaf tips able to break through frozen ground. Although not officially recorded as growing wild in the UK till the 1700s, they were likely present before then, as they may have been introduced from ecclesiastical plantings where they were used for Candlemass in the Catholic church, or may simply have crossed the Channel from their native Brittany.
At the same time as frogspawn was laid, the new leaf growth of the common hedgerow plant Alexander Smyrnium olusatrum, so named as it was a pot herb for the Romans who introduced the plant to the UK, was breaking through in the hedgerow banks. In flower since early February, it’s flat lime green umbellifer heads attract a proliferation of flies, an understated but important group of pollinators. However, the common name of ‘Spring Messenger’ was historically given to the lesser celandine Ranunculus ficaria, being considered one of the earliest spring flowers. Carpeting the glades and track edges of the Bovey Valley woodlands since early February it continues to bloom amongst the primrose Primula vulgaris and daffodil heads. Lesser celandine spreads in disturbed soil as their tubers break off easily – a sub species R.bulbilifers spreads even more readily as tiny bulbils between the leaf stalk and main stem are dispersed by walkers and livestock. I am not aware whether this sub species is present on the NNR.
Amongst the yellow heads on the Rudge Wood track edges, the locally common violet oil beetle Meloe violaceus adults were seen on 16 March, having emerged from nearby solitary bee nests where they overwintered as larvae to mate and lay their eggs in the soil. In the next few weeks triungulin larvae from last year’s eggs, appear briefly, like small pencil markings on the yellow flowerheads of celandine and dandelion waiting to hitch a lift on a solitary bee to start the cycle over again.
The primrose Primula vulgaris is the more well-known competitor for ‘spring flower of the year’ prize. Whilst the seeds are not very mobile individual plants can have a life span of 15-25 years, and ant activity is thought to help seed dispersal. In drier areas of the country, primroses are confined to damp conditions within woodland, but our high rainfall means they are part of the spring Devon hedgebank display beyond the woodland edge. Amongst the primroses the shining crane’s -bill Geranium lucidum is biding it’s time till May when the pink flower heads appear but its distinctive shiny, red- tinged leaves are currently blanketing many local hedge-banks.
Pine beauty moth feeding on sallow
The early blossom of the willow trees scattered along the edges of Trendlebere Down are already providing a valuable early source of sustenance for both bumblebees and moths. Some spring flying moths synchronise their emergence with sallow blossom and the pine beauty moth, Panolis flammea, seen here nectaring on sallow, is, as its name suggests found close to pine woodland, the food plant of the larvae. The buff-tailed bumblebee Bombus terrestris, the first bumblebee queen to emerge from hibernation, was first seen on 22 February exploring for nesting sites and subsequently taking advantage of this early pollen source.
Buff-tailed bumblebee queen on willow at Lower Trendlebere riding out a strong wind earlier this month
Deeper into the woodland dog’s mercury Mercurialis perennis carpets the old farm boundaries, their small flowers indistinct unless inspected up close. So named as not a true member of the mercury family they can be an indicator of ancient woodland though they colonise in younger woodland with suitable soil conditions. The common ivy has not been in flower, but as a late autumn flowering plant their fruit provides a much needed source of spring food for mammals that break their hibernation during early spring and our resident birds.
The green shoots of many of our mainstream spring flowers are already present and waiting their turn, patches of bluebells will carpet small areas of the woodland and the wood anemones and violet flower heads are starting to open. Many insects and plants synchronise their life cycles and hidden within the sheltered southern slopes of bracken litter the caterpillars and chrysalis of the pearl-bordered fritillary are developing, inextricably linked to the dog violets, in readiness for their transformation later this month.
The bracken litter layer provides a micro habitat for the development of the pearl-bordered fritillaries that is much warmer than the surrounding air temperature. A woodland resident which can actively influence the temperature of its own micro habitat is the wood ant. Ant activity was first seen by Albert Knott, Reserves Manager, as early as February 6th as overwintering workers emerged to bask on the nest surfaces in warm sunshine. Their return deep within the structure promotes an increase in the core temperature of the nest, generating further ant activity. It is still early for honeydew foraging, though, a few slow-moving ants have recently been seen foraging on trees.
Basking wood ants first seen in early February on the move
The Woodland Trust’s Nature’s Calendar is an extensive biological record, with almost 3 million flora and fauna records of the first signs of spring. You can both refer to the data or contribute to records. The data generated is used to show long-term phenological changes, which when linked to weather data contributes to our understanding of climate change impacts. Amongst current record requests is for wood anemone flowering dates, so if you are exercising in your local woodland and want to find out more visit: Nature’s Calendar
When out and about enjoying the NNR, or elsewhere, remember that much of our wildlife, including nesting birds in the coming months, feed, breed or live at ground level, hence ‘every footstep makes a difference so please keep to the paths’.