Wood burning worries

 Question from a sustainability student:

In the last few years I've seen demands that using wood as a power/heat source (by burning it) should not be declared sustainable.

I understand that burning wood releases particulates. I also understand that sometimes we burn woods from forest that are not reafforested which is obviously unsustainable.

However, if we filter the particulates while burning wood and we reafforest the forests that the wood comes from, isn't burning wood sustainable? What am I overlooking?

Mick's answer: 

We burn wood for 80 of our heat (in total energy terms), about half or less our heating costs. We harvest about half of it from our own woodlots at a rate of about two cords a year. The remaining trees in our woodlots are growing, and some are growing faster as a result of "tree release", getting more sunlight. Our trees are sequestering far more carbon than the small amount we take each year. We have seven acres and take up to two cords. Using typical averages (of cords produced per acre and weight per cord) for New England hardwood forests, that means we are sequestering 8 to 10 tons/tonnes a year (very roughly), some of which forgives the logging needed for our other two cords which we buy and some proportion of the fossil fuel needed for our stove and vehicles. The trees we take are all ash, which is threatened by the invasive emerald ash borer and will very likely die anyway. The larger mass particulate pollution from wood burning, which contains far less aerosolized component than the equivalent from gas, oil or coal, typically falls out of the atmosphere after only a few miles at the most. It is a form of pollution that is predominant (and harmful) in cities, not in low density rural areas like ours, where they are only 21 people per square mile, and so what particulate there is, is diluted. The biggest sustainability problem with wood burning is when large scale power plants add wood biomass to the fossil fuels used in turbines. So, for instance, woody biomass in the southern US is clear cut from plantations and even natural forests, then shipped to Britain where is is burned in old coal fired plants like Drax in Yorkshire. This industrial use of wood is far less sustainable because a) natural forests store carbon in the soils and much of this is lost when clearcut, b) the fossil fuel used in transportation and processing, and c) the much larger density of particulate produced on-site. It is only cost effective because of "perverse" economic incentives set up by EU carbon regulation.

https://newenglandforestry.org/wp-content/uploads/2019/10/NNE-carbonstorage-100119.pdf

https://www.bbc.com/news/science-environment-63089348

BTW, what I like about this question is that it neatly illustrates the wide variety of disciplines needed to solve sustainability problems.