It was election day, and the subject of debate was climate change. After a political campaign in which environmental issues were generally so neglected it was refreshing to find Coillte, the State-owned commercial forestry company, bringing together forest managers, businesspeople, civil servants, scientists and NGOs for an open-minded conference on climate and Irish forestry at Farmleigh House, in Phoenix Park.

Refreshing but also perplexing, because forestry’s relationship to climate and the environment in general is not straightforward. As Oisín Coughlan of Friends of the Earth put it, we can’t simply adopt, as some vested interests in agriculture are doing, a simplistic attitude that he summed up as “Plant, baby, plant”.

Many speakers stressed that, in terms of climate benefits, there are still big question marks over what trees should be planted in what places, and over how best to manage them to meet diverse and sometimes conflicting economic, environmental and social needs.

A recent article in Science, cited at the conference by the climatologist John Sweeney, suggests that increased afforestation in Europe has actually been slightly negative in climate terms, because of excessive harvesting and misguided policies about species selection. This indicates how tricky designing the right future for Irish forestry is – and that's before we even start considering the social and political factors.

The broad climate benefits of forestry are clear enough. Young growing trees are carbon sinks, sequestering carbon dioxide rapidly from the atmosphere through photosynthesis and transferring some of the carbon to the soil. Mature forests are carbon stores. As Coillte Forest’s managing director, Gerard Murphy, pointed out, 85 per cent of that store resides in the soil.

Trees also supply bioenergy, substituting for fossil fuels. Burning wood does release carbon back into the atmosphere, but because wood is renewable, unlike peat, oil and coal, bioenergy is arguably carbon neutral.

Murphy and Eugene Hendrick, of the Department of Agriculture, made the case for further climate benefits from timber. It can also substitute for high-energy materials such as concrete and steel, which have much bigger carbon footprints, in construction, for example. Hendrick showed a remarkable image of a new high-rise building made entirely of timber in the UK.

So far, so good, but we are not starting with a blank sheet in Irish forestry. Deforestation used to be the problem. Ireland had only 1 per cent forest cover – the lowest in Europe – in 1900. Although State agencies and, increasingly, private landowners have increased that cover to 11 per cent, much of the forestry created is environmentally problematic.

Vast blankets of alien conifers were planted on our peatlands, often releasing much more greenhouse gas than they sequestered, through disturbance of this carbon-rich soil. And, according to the Science article, conifers offer much fewer carbon benefits than native broadleaf trees. But no one knew about these problems at the time, and in any case the great "social forestry" schemes of the last century gave desperately needed livelihoods to many in remote areas.

But how should we manage this legacy now? Gerard Murphy says that Coillte will never plant forests on virgin peatlands again, but he freely admits to being uncertain about the best strategy for existing peatland forests.

“In some cases they can be cleared and restored to bogland, and we have done that very well where we could,” he says. But he argues that clearance on other sites might only release more carbon from the soil, and flush damaging sediments into streams important for salmon, trout and pearl mussel.

He believes that we are only beginning to understand the complexity of forest carbon budgets.

He questions the view, held by most environmentalists and endorsed by the Science article, that native broad-leaf forest is nearly always preferable in climate terms to alien conifers in temperate zones like ours.

Murphy points out that fast-growing trees such as Sitka spruce sequester a lot of carbon quickly over a 30-year cycle. A broadleaf woodland sequesters carbon more slowly, although it may store more carbon long term. He is deeply sceptical of those who express complete certainty on either side of this debate.

He argues that much more research is necessary, meanwhile pursuing a “no regrets” strategy, combining multiple approaches known to do the least climate damage. “Of course, there may be greater biodiversity and recreational benefits from broadleaf plantations,” he says, and agrees that more species diversification is desirable. He is obviously proud that Coillte has a wide mandate, which obliges it to manage 15 per cent of its estate for biodiversity.

“We produce a whole suite of ecosystem services,” he says, “from timber through carbon benefits to recreation and protecting endangered species.” He agrees that the role of the forester has morphed into that of “ecosystem manager”.

The great difficulty for a commercial company, however, is how to prioritise different ecosystem services in our market economy, where only timber has a well-defined cash value.

“My job as manager is to make a profit,” says Murphy. “At the moment I can only make a profit from timber. If the market gave me a different signal – if someone offered me €60 for a tonne of carbon [as against about €48 today] – then that would create very different management options.”

Several speakers suggested that we need to apply a “social value” to carbon, accounting much more accurately for the climate benefits of sequestering and storing it.

Meanwhile, as new threats are triggered, the climate scenarios keep getting more complicated. John Sweeney demonstrated in a vivid presentation that higher temperatures are favouring the expansion on forestry of native pests; in the case of the pine weevil it literally gives it wings – which developed only rarely in previous climate conditions.

Warming is also assisting the arrival of new pests, such as the horse-chestnut leaf miner, threatening our capacity to sustain productive forests.

“We are constantly layering in new sets of uncertainties as to how climate will affect our work,” says Murphy.

The way ahead for forestry in climate terms is far from clear. But at least foresters are thinking about it, and thinking about it hard.

Forest carbon: Who should benefit?

Government contributions to the discussions at Paris COP21, last year’s UN climate change conference, put an extraordinary onus on our forestry sector to rapidly increase its capacity as a carbon sink.

Oisín Coughlan of Friends of the Earth claims that this pressure comes from the agribusiness lobby and its political supporters, who currently see a big growth opportunity for the beef and diary sectors – which will significantly increase the already very high carbon emissions from agriculture.

“They simply don’t want climate policy to get in the way of this opportunity,” he says, “and they will happily put all marginal land into trees, regardless of the consequences for biodiversity, to protect it.”

But he says that the numbers will not add up. Agriculture already emits 19 million tonnes of greenhouse gases a year, and that figure will rise under current policy. Forestry accounts for less than four million tonnes a year of carbon sequestration, and it cannot realistically make up the difference in the future. Coughlan says that we must require agriculture to reduce emissions, not increase them.

The climatologist John Sweeney puts it this way: “Is it ethical that carbon credits from forestry should automatically go to cover the agriculture sector? Farmers pay no tax on agricultural emissions. Drivers and householders pay taxes on theirs. We need a national conversation about this.”