January arrived quietly this year, bringing with it a mix of winter weather. It’s been consistently pretty cold, with even the mildest days barely rising above 4° C, but we’ve had ethereally misty days, drizzly-rainy days, bright sunny frosty days and even some snow. In between, more than a few days have been dull, sunless and still, the kind of winter days that feel like time’s been suspended and the day somehow never really got started before it was over. But little by little the days are getting longer, and on my restricted Covid-lockdown-exercising-only-from-and-to home-route around my local woods, there are definite signs that spring is not so far away.
The shed leaves of the deciduous trees, mostly oaks, ash and sycamores lie in a thick carpet on the woodland floor and are still covering the less-trodden tracks. Their absence allows through the bright winter sunlight and also highlights the extent of the permanent greenery here; indeed, there’s so much of it you might feel you were in a tropical forest if it wasn’t so cold. There are several species of evergreens contributing to the winter verdure; dark brooding yews, tall twisted Scots pines and masses of shiny holly, all of which are native plants. Then there’s Holm oak (also known as Holly oak or Evergreen oak) and cherry laurel, both non-natives and classed as invasive. But most responsible for creating the jungley ambience and linking everything together, is just one species of plant; ivy. It is quite literally everywhere, covering the ground, clothing tree trunks and forming leafy frames to woodland views.
How ivy affects trees
Although prolific amounts of ivy may look unkempt and alter the appearance of trees, there are some common misconceptions regarding the effect this climbing plant has on them. The first is that ivy kills trees: be assured it doesn’t, and neither is it parasitic. Strong, healthy trees are not adversely affected by ivy; its roots take no nourishment from or through a tree’s bark, and the tree’s leaves don’t allow enough light through for the ivy to grow too vigorously.
It is only when a tree is naturally weakened and begins to die back that ivy will reach into the thinner crown, so ivy doing particularly well in a tree might indicate a tree that is already struggling, but it will not have been the cause of the tree’s sickness. In this instance though, the ivy may make a tree more vulnerable to wind damage; the added bulk of the ivy increases its resistance during high winds and may make it more likely to be blown over, so hastening the tree’s demise.
There are two subspecies of ivy that grow in these woods, both of which are native to Britain: these are the climbing Hedera helix ssp. helix and Hedera helix ssp. hibernica, which doesn’t climb, but spreads across the ground.
Ivy is an evergreen, woody climber which can grow to a height of 100ft (30m). The stems have many fibrous, clinging, adhesive-covered roots which help it to climb. Mature older plants develop thick woody stems that can allow them to become self-supporting.
The leaves are dark green and glossy with pale veins. The leaves on non-flowering young plants have 3-5 lobes and a pale underside. On mature plants leaves are oval or heart shaped without lobes, although leaf edges may sometimes be wavy.
Ivy is an essential part of the habitat, providing food and shelter for a diverse range of different organisms.
Being evergreen, ivy provides year-round dense cover for a wide variety of wildlife. During the winter it offers hibernation sites for many insects, which in turn attracts birds that come to forage for them. Butterfly species which survive the winter in their adult form often hibernate in ivy, including the lovely Brimstone, usually amongst the first species on the wing in the spring. Ivy is also the foodplant of the second, or summer generation of the caterpillars of the beautiful little Holly blue butterfly. In late July/August female Holly blues lay their eggs on swelling buds of ivy flowers, which caterpillars burrow into and eat from the inside. Once fully grown they leave the buds and pupate on the underside of Ivy stems where they will overwinter and emerge as an adult butterfly in March/April the following year.
In some instances very dense ivy may provide winter hibernation sites for bats.
One of my favourite woodland birds is the handsome Nuthatch. Although they are colourful, these beautiful birds can be hard to spot when they are foraging around tree trunks and branches, but when they choose to be heard, particularly when singing or crying out in alarm, they have a very loud voice. On a recent walk I traced the whistling sound one was making to an ivy-clad tree a few metres away. Believing itself to be well-concealed I was able to watch it carry an acorn from somewhere around the bottom of the trunk right up to near the top. I momentarily lost sight of it several times as it wove in and out of the ivy, travelling in an erratic kind of spiral up the main trunk, but I managed to follow it disjointedly until it got so high it was making my neck ache to watch it. I couldn’t see if it still had the acorn when it got to the top, it’s quite likely it may have cached it for later consumption somewhere along the way and was foraging for hibernating grubs or caterpillars to eat now.
Perhaps the greatest gifts that ivy gives to wildlife are firstly that it flowers late in the summer or early autumn, providing a bounty of late nectar to a wide range of insects from hoverflies to bees to butterflies. Then following the flowers come generous crops of berries, some of which begin to ripen in the early winter and others slightly later, providing a bountiful progression of nutritious food, lasting through to the spring, which feeds a great many birds, both residents and winter migrants.
The amount of ivy and the resultant bounty of berries it produces are a great draw to two species of birds in particular, Blackbirds and Wood Pigeons. Winter walks are practically guaranteed to be accompanied by a soundtrack of rustlings, flappings and often crashings as birds of both species fly from one ivy vine to another. From the blackbirds there are frequent alarm calls too; there’s a lot of competition for the best berries and they’re worth squabbling over. Neither bird is really purpose-built for the acrobatics required to reach the berries dangling temptingly out of range, but that doesn’t stop them trying. Blackbirds often launch themselves upwards to grab a dangling berry, a rather ungainly method, but who cares if it works?
Wood Pigeons are more ponderous and considered in their approach, eying up the best-looking berries before stepping cautiously towards them, craning their chicken-like necks forward as far as they can and making a grab for them, sometimes losing their balance and flapping madly to restore it.
Ivy berries are loved by other species of birds too, including the song thrush, mistle thrush, redwing, blackbird and blackcap. Although the berries appear in October-November, birds don’t tend to start eating them until later into the winter, shorter-lived berries such as rowan and hawthorn are eaten first, leaving the longer-lasting ivy berries until last. The berries are a great source of protein and, according to the RSPB, gram for gram contain nearly as many calories as a Mars bar! No wonder our local Wood pigeons are looking so plump!