What the bramble lacks in hectarage, it makes up for in variety
Intriguing ecological answer emerges for the origin and manuring of new and dense thickets
Mammals such as foxes and pine martens make an autumn feast of all the blackberries they can reach.
Among the many indelible images of BBC’s natural history television, one could just as well have been filmed on our acre: a time-lapse study of plant growth that captured the headlong thrust of a bramble, arching out of a hedgerow to touch down and root a metre or more away.
There was a time when summer patrols with the secateurs kept these seasonal grapnel irons at bay. That was before the rewilding, so to speak, that has come with the burgeoning of hedges and trees and my own late retreat to the polytunnel.
The brambles now defy me from new, unassailable strongholds at the dark heart of shrubs and a couple of prostrate conifers. The froth of their white flowers could almost be wild roses and their nectar is just as appealing to such flying insects as favour us. There will be blackberries, too, if the birds don’t get there first.
Away from the colonising spread of brambles, in a leap from one root to the next, the birds get most immediate credit for sowing their seeds in fresh ground. The odd purple splash on a sheet pegged out on the clothesline has offered evidence.
Badgers, it seems, have an even more enthusiastic appetite, perhaps fulfilling a selective purpose in their genes
However, research in the Co Cork countryside suggests an intriguing ecological explanation for the origin and manuring of new and dense bramble thickets. Mammals such as foxes and pine martens make an autumn feast of all the blackberries they can reach. But badgers, it seems, have an even more enthusiastic appetite, perhaps fulfilling a selective purpose in their genes.
The UCC mammalogist Dr Paddy Sleeman has spent much time studying badgers in the field as part of long research into their role in bovine TB. His work has since brought unexpected insights into the animals’ impact on their immediate environment and its biodiversity.
Important evidence in the study, carried out with his students, comes from the badgers’ distinctive behaviour in digging a number of holes around their multi-tunnelled sett to serve as latrines.
In autumn, these loos can take on a positively purple appearance, as digested blackberries accumulate. Collected at setts in pasture and woodland at Warrenscourt, Co Cork, tests on samples packed with seeds have now prompted a paper in the journal Mammal Communications: “Are badgers Meles Meles effective dispersal agents for bramble Rubus fruticosus agg in Ireland?”
There’s more to this than an obvious affirmative. The study found that badgers eat blackberries even where elderberries are more common. Their digestion leaves the seeds quite skinless and scarified, which makes them germinate faster and at a higher rate when sown in the ground than those of the bramble’s “unprocessed” fruits.
(I think, tangentially, of kopi luwak, the coffee berries eaten by Indonesian palm civets – stoat-like animals in the badger’s mustelid family – then gathered from their droppings and sold to connoisseurs of coffee flavour for more than €500 per kilo. The civets are now farmed for the purpose.)
By passing the seeds through their gut, they distribute and maintain a plant on which they rely
In more serious, ecological, speculation, Dr Sleeman also reaches for the tropics, where fruiting seasons tend to be short and the vital role of animals in dispersing the seeds is most obvious. A much-cited example is the African acacia bush, with leaves and fruit the elephants like to eat. By passing the seeds through their gut, they distribute and maintain a plant on which they rely. “We suggest,” writes Dr Sleeman, “something similar for badgers”.
In Ireland, the animals can cover several home ranges, travelling up to 22km to gather blackberries – unusually far compared with badgers elsewhere in Europe. The harvest results in the bramble thickets that cover most big badger setts.
Left to spread on open ground, the plants launch a long progression to hawthorn scrub, seeded by birds from the hedgerows. I have seen neglected pasture covered with briars from fence to fence, but slowly restored to rough grasses once sheep were reintroduced.
What the island’s brambles may so far lack in hectarage, they make up for in variety. Differences in leaf-shape, blackberries and thorns add up to at least 80 microspecies of Rubus fruticosus (the “agg” in the title of the Sleeman paper). Identifying them along country roads has been a particular passion of visiting British botanists.
One bramble specialist, Alan Newton, made two circuits of the country some years ago, stopping five times a day to examine the hedgerows at hand. He ended up with 57 micro-species.
Specimens preserved in the herbarium of the National Botanic Gardens have recently let Irish botanists test a new kind of plant evidence for assessing climate warming. Brambles have, indeed, been flowering and fruiting earlier with higher temperatures. Although, as I write, the first ripe blackberry still seems a long way off.