TO a political strategist at the Scottish Government, there is nothing like finding a cause to use as ammunition against the Westminster coalition. Oil remains the SNP s favourite, of course. Nuclear has been a lot of fun. High-speed rail will run and run. But since London published its review of the subsidy system for renewable energy a couple of weeks ago, the Nationalists have been trying out a new weapon. This one may not have sharp edges or any high-tech gadgetry attached, but what better than trees for battering against the door to Scottish nationhood in the run-up to the referendum?  Led by Energy Secretary Fergus Ewing, the Scottish Government has been raising concerns about the future of the timber industry. The root of its gripes, if you ll pardon the pun, is biomass power: burning wood to produce heat and electricity. The Government is all in favour of both small-scale biomass generators and the domestic wood-fired boilers that will be subsidised from next October. But it has come out against big biomass of the kind that would power many thousands of buildings, which is generally defined as 50MW and upwards.  The Government s argument, which echoes what the timber industry has been saying in Scotland for some time, is that biomass will severely damage timber processing businesses. This includes sawmills, panel makers, cabinet makers and paper mills. These industries, plus customers ranging from joinery firms to furniture shops, are naturally vulnerable to changes in timber prices. The industry is afraid that heavy new wood demand from biomass generators could make the main material unaffordable. It is not talking about a little bit of extra pressure, either. as Stuart Goodall of industry association, Confor, says: Demand from these big stations is in some cases more than one million tonnes of wood a year, in a country that produces about seven million tonnes [10 million in the UK as a whole]. and that s just one plant.  across the UK, biomass plants are already burning four million tonnes of various materials   mostly wood but also things like straw and paper sludge, mostly imported. and that demand for the equivalent of nearly half the annual UK wood supply is almost entirely from small plants, with the exception of the 222MW operation at Drax in Yorkshire.  Yet this is nothing compared to the 20 new plants that have been approved by the authorities. With eight planning to produce more than 100MW of power each, and several at 750MW, which is getting on for the size of a traditional power station, these will burn 31 million tonnes of mostly wood each year. If you add on those that are either in the planning stages or being proposed   including plants in Dundee (120MW), Grangemouth (120MW), Rosyth (120MW), Leith (200MW) and Hunterston (224MW)   the total extra wood demand will be at least 50 million tonnes. With this huge wood requirement, the industry is obviously expecting to import most of the supplies. But this doesn t assuage any concerns from the industry and the Scottish Government. They argue that the combined wood demand from these and other plants in other major economies will drive up world prices of timber.  Even with long-term supply contracts, eventually, they say, there will be so many biomass plants worldwide that supply will be too tight and biomass companies will be forced to raid local markets. any timber processor still left after the initial surge in prices will find it can t get wood. Moreover, they argue, importing wood comes with its own issues: it reduces the security of our energy supply and it means we are burning large amounts of transport fuel to get the wood to the plants   thus undermining the carbon neutrality of the technology.  The answer, according to the Scottish Government, is to kill all subsidies for big biomass forthwith. It is particularly worried about plants that produce only power, since this is a huge waste of the heat that they give off at the same time. and with Scotland producing most UK trees and more than half of all sawn wood, the Nationalists are also putting pressure on Westminster to follow suit. as Ewing recently said:  Extensive use of large-scale biomass for electricity-only is likely to push up timber prices and risk hundreds of jobs in traditional wood industries.  Interestingly, there seems to be no split between the processors and the foresters on this issue, even though the latter ought to gain from higher prices. Stephen Vickers, group strategy director at the Buccleuch Group, which owns 10,000 hectares of forest and also has interests in small biomass, says that forest owners need to think beyond short-term gains.  The timber processors have always been there, helping turn our crop into what end-customers need. What if something replaces biomass a few years later? Where would that leave us if many of the processors have gone out of business?  he says.  He also rejects a common counter-argument from the biomass industry, which is that wood for burning is lower quality than wood for sawing, and that they re not competing in the same markets. He says biomass on a small scale will buy up the so-called forest residue. Demand from big biomass would make this stuff more valuable, however, and he believes it would expand further down the tree and eat into higher-quality stocks.  So do these arguments stack up? One point to note is that the UK Government is not as keen on big biomass as the Scottish Government seems to be suggesting. It is true that they are proposing to continue subsidies, but in their consultation document they cite research by engineering consultancy arup that found that big biomass was not economically viable at the subsidy levels being proposed (one-and-a-half times the standard power price, or two times if it includes heat). If this is correct, it will make no difference that 20 plants have been approved and many more are on the drawing board. They won t get built because the returns won t be there. In other words, the argument between the UK and Scottish Governments is really a debate about how best to encourage small biomass while discouraging bigger plants.  There are also arguments in favour of big biomass. Notwithstanding the imports issue, it still contributes to carbon reduction targets and is better for the planet than getting electricity from burning coal or gas, which are also often imported.  Calum Wilson, managing director of Forth Energy, the joint venture between Scottish and Southern Energy and Forth Ports that is behind the plant proposals for Leith, Dundee, Rosyth and Grangemouth, argues that his industry is simply not interested in UK wood. It is too slow-growing, has too much moisture content, and the foresters are not able to offer the suitable long-term supply contracts. So not only would his plants use more or less 100% imported wood now, they would not want to use UK wood in the future, either.  He points out that they would produce heat as well as power, and claims they are not, therefore, the main target of the Scottish Government s concerns. Yet each plant will harness at least two or three times the amount of power as heat, even though burning wood to produce electricity gives off about three times as much heat. This means most of the heat the plants give off would be wasted, which environmentalists argue is inevitable with big plants. Wilson argues though that the proposals are designed to harness as much heat as required for nearby local district heating networks or businesses.  There is still the question of whether big biomass will push up world timber prices. Wilson says:  While demand for biomass may well increase on a global scale, I would also anticipate that growers will respond to that by growing biomass crops. There is already evidence of growers and processors responding to increased demand for sustainable biomass.  This may be right, but increasing the biomass crop might be hit by the same problem that has bedevilled biofuels: if you take land away from agriculture, you might push up food prices and leave people starving.  Opponents such as Vickers of Buccleuch concede that world timber prices are a fact that we may not be able to control . If so, the bottom line is that the debate about subsidies between Scotland and London may be a side show. The real choice m