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We now have yet another green battleground in this election campaign: trees.

After claim and counter claim about everything from a ban on fracking to improving flood defences to reducing carbon emissions, there's a flurry about forests.

The Conservatives say they'll plant at least 30 million more trees every year, a pledge that is roughly in line with a recommendation from the government's official climate advisers. But that would represent a massive increase compared with earlier targets set by the government and, as the other parties are keen to point out, these have not been met.

For their part, the Liberal Democrats have gone much further than the Conservatives by promising to plant 60 million trees a year - that's double the Tory number - arguing that that's needed to help fight climate change.

The Labour Party says its plan for trees, when it comes, will be guided by the science.

Experts in forestry say a huge programme of tree planting is needed if the UK is to have any chance of reducing its carbon emissions to effectively zero. They also say that the aim, though difficult, is feasible but will depend on careful planning - "to get the right trees in the right places", as one specialist put it to me.

Finding enough land may be one of the toughest challenges. Farmers will want incentives to convert their fields to forests, not just to help with the cost of planting trees but also to compensate them for the long decades before they can earn an income from them.

Prime arable fields are unlikely to be selected for this role but areas currently used for livestock may be in line, and that might force the country to make some highly sensitive choices between producing meat and growing forests.

It could also mean a profound change to the look of much of the countryside, with the familiar sights of grazing cattle and sheep replaced by woodland.

Officials in Defra are currently working on a new post-Brexit system of subsidies for farmers, the exact details and aims of which may well determine whether these vast tree schemes succeed.

Urban areas may offer scope for planting but these will be relatively small and possibly more expensive.

Another concern is tree disease. The UK could theoretically grow enough saplings for the new forests but a crash programme of planting would probably mean buying from abroad, just at a time when many species are already suffering from pests that have arrived from other countries.

The specialist I spoke to also said the effort had to be properly funded and "joined-up", by which he means coordinating many different government agencies, forestry organisations and farmers - no easy task.