The biodiversity of plants and animals under our cultivated forests is better than expected, writes Claire O'Connell
Next time you walk along a forest road, take a closer look at what thrives in the ditches beside you. Researchers at Trinity College Dublin (TCD) and University College Cork (UCC) have discovered that open spaces such as roadsides and glades provide a welcome boost for biodiversity in managed forests in Ireland, and their new report recommends a range of options for ensuring that more grows in forest plantations than just trees.
The five-year "Bioforest" project, funded by Coford and the Environmental Protection Agency, was a first look at biodiversity in managed plantations, which make up the bulk of Irish forest and cover around 10 per cent of Ireland's land area, explains Dr Daniel Kelly, a senior lecturer at Trinity's botany department.
"Plantations are expanding fast and they were biologically unknown territory," he says. "The general feeling was that they are dismal places with not much going for them. We started from the premise that we don't know what's there, and we went in with an open mind to see what we would find."
Twenty scientists worked at around 60 sites across Ireland, mainly ash or Sitka spruce forests, which were selected with the help of Coillte. They monitored biodiversity at every stage of afforestation, from the green-field site through the thicket phase to young and mature plantations.
And what they found wasn't so dismal after all: a range of plant and animal species live in and around the different forest types. "We found that plantations of forests are not an oasis of biodiversity but neither are they a desert," says Dr Kelly.
Researchers physically scaled the trees and found over 100 types of mosses, liverworts and lichens - including some rare and endangered species - which grew quite well in the evergreen Sitka plantations, says Dr Kelly. Meanwhile, flowering plants tended to flourish better under the open canopy of leafless ash trees in spring. This diversity is one reason to include patchworks of multiple tree types in a single plantation, the scientists argue.
The report also makes a series of other recommendations to help Ireland comply with international agreements on biodiversity in sustainable forest management, explains Dr Fraser Mitchell, also a senior lecturer at Trinity's botany department. Many of the suggestions aim to work around the factors that limit plant growth, such as light.
"Most forests start out with high biodiversity and then when the tree canopy closes over there's a reduction in certain plant and animal species because of the shade, and then it can open up again, partly because of thinning but also because the trees get bigger so there's more space," explains Dr Mitchell.
This is why the scientists recommend leaving some trees to mature to over 40-50 years rather than chopping everything down at once. "If you leave some over-mature Sitka spruce when you are coming into the next planting cycle, it will act as a nice little honeypot of biodiversity which can then spread out," says Dr Mitchell.
Light-filled open spaces such as forest access roads and glades are also key hives of biodiversity, and should be maintained, according to the scientists. "When you think about it, even just taking a casual walk through a forest plantation, what you see along the roadside is generally more diverse than when you leave the roadside, and also a glade is quite a diversity of habitats," says Dr Kelly.
The research team at UCC, led by Prof John O'Halloran, focused on animals. They found that spiders and hoverflies can do well in glades over a certain size, and that the presence of shrubby, broadleaf plants is good for bird nesting and feeding.
However the researchers admit the study has its limitations. There are little comparable data on forest biodiversity from Europe, where forests tend to be better established. And much of the current study focused on only ash and spruce. "We got a lot of information just about two species," says Dr Kelly. "We would love to have done oak and a comparable study on oak needs to be done."
Another project is planned to start this year which will continue to monitor plantation biodiversity and also widen the focus to reforestation cycles.