Why don’t you tidy that mess up?
- Tuesday, 05 July 2016
If you have ever visited a woodland not long after harvesting machinery has been on site, you’ve probably wondered about the mess that is left behind and why we don’t clean it up. Choosing to leave the 'mess' is actually a deliberate decision as it benefits the forest ecosystem and biodiversity.
Neil McInnes, Environment Manager in North Highland Forest District for Forest Enterprise Scotland, explains why: “Why on earth don’t you foresters tidy that mess up" is a question we’re often asked. It’s a fair question too, when you compare the neatly mown grass parks of spring silage or the closely cropped golden stubble fields of autumn to the seemingly impenetrable mountain of snapped and bent stems that are a bit unsightly.
"Take a wander through a pristine ancient woodland (you’ll have to travel abroad for this – at least to central Europe), where centuries of fallen trees have accumulated on the forest floor, building thick rough mats of jumbled rotting logs and rich forest soils punctuated by the tall stumps or ‘snags’ of dead trees and you’ll start to understand just how lacking in structure a twentieth century plantation forest can be. The dead and dying timber of the ancient wood is an essential part of the ecological cycle: globally, an estimated ten million species of fungi and assorted bugs and beasties are munching their way through this build-up of litter, creating the forest soils of the future, recycling the carbon and taking their place in rich food webs.
“Those principles are the same here. In Sutherland, just south of Lairg, the remnants of our own ancient woodland are home to the most northern known colonies of aspen hoverfly. Hammerschmidtia ferruginea is one of the saproxylic species (meaning that at some stage in its short life cycle it needs dead or dying wood). As its common name suggests, what this unassuming little brown fly needs is aspen wood but not just any old lump. It has very specific tastes. Only recently dead fallen limbs or trunks will do and the wood must be damp with enough sticky goo decaying under the bark. A log around 30 centimetres diameter and hopefully about four years old is where the fussy fly will favour for a home. To keep the aspen hoverfly in deadwood requires a lot of dying aspen.
“The crested tit that lives in our northern pinewoods also needs deadwood. It chooses to build its nest in the snags left after lightning, wind or snow has taken the top off the tree and a winter or two has softened the headless trunk enough that it can excavate a cavity to call home. By way of repaying the forester for leaving it a high rise home, the bird diets on hundreds of pine looper moth larvae, hoovering up a forest pest that if left unchecked can cause a lot of economic damage. But every year the crested tit needs a new nest site to avoid an intolerable accumulation of the parasitic fleas that call the tit home!
“The plant kingdom benefits from mother nature’s destructive powers, too. As great root plates lift and tip, the bare earth below is exposed, leaving a natural seed bed. The fruiting bodies – toadstools – of some mycorrhizal fungi emerge from deadwood lying on the forest floor. Mycorrhiza form massive underground networks of thread that latch onto tree roots and absorb the nutrients from decaying wood and leaf litter as it washes through the soil from above. It’s a productive cycle adapted over thousands of years that the survival of the forest and woods depend on.
“In the thousand nooks and crannies of a patch of windblow, many dozens of species can find a home or a meal or a place to rest up.
“So once the roads, trails and fences are cleared, looking at what’s left can be a big step in how foresters reshape the structure of modern plantations. It’s so important that before a tree is felled these days, a ranger will walk through a coupe identifying patches of windblow to keep, broadleaved trees to leave after felling and even small patches of trees that will be left to hopefully blow over in some future winter storm, ensuring a succession of deadwood provides all the stages of decay that species depend on and a myriad of niches for plants and animals.
“Imagine the energy that’s released from a single log on the fire in its warming flames. Now instead, imagine all that energy slowly being released into the forest ecosystem by decay and digestion and you’ll understand that the unsightly mess you see is a furnace, firing hundreds of ecological processes that much of our native biodiversity relies on.
“So I’ll settle for the mess (once the log shed is full)! It’ll green up faster than you might think and day and night it’s doing one of the most important jobs in the forest.”