Dissent Of The Day

A reader writes:

Andrew, love you, babe, but ...

If one quarter of the world's forests were replanted with carbon-eating varieties of the same species, the forests would be preserved as ecological resources and as habitats for wildlife, and the carbon dioxide in the atmosphere would be reduced by half in about fifty years.

Yeah, I get a subscription to the NYRB, too, and I when I read this back in May, I nearly jumped out of my chair. Just think about it for a second. ONE QUARTER of the world's forests. Really? REALLY? Do you have any idea what that would mean?

OK, enough high dudgeon. Here are the problems with Dyson's fantastical suggestion:

  1. Turnover -- in the long term his plan might work (see RealClimate), but in the short term you would have to replace all the old trees with genetically modified trees. By removing the old ones, you are precipitating the loss of ONE QUARTER (or so) of the world's terrestrial biomass into the atmosphere as carbon dioxide (Dyson provides no concrete suggestion for what to do with the "old" biomass). And it takes decades for forests and forest soils to mature. As such, forest replacement would at no time provide the short term carbon sequestration that Dyson predicts.
  2. Disturbance -- removing the old trees will disturb the soil. In temperate forest ecosystems, most of the carbon is stored in the soil (tropical forest are different -- scant carbon is stored due to poor soil quality). Thus, removing the old trees would lead to MASSIVE atmospheric carbon dioxide release. (Never mind massive erosion.)
  3. Monoculture -- genetically modified trees of the kind prescribed by Dyson would take a long time to engineer, and would come on line in a trickle. Most of the "new" forests would therefore be of a single or a few genetically modified species, and even if they were of the same species as the previous forest (which is technical challenge that we plant biologists find laughably optimistic), in the short run the new forests would be subject to serious disease problems as well as vulnerability to climate change because of their lack of diversity.
  4. Wildlife diversity -- if you replace all the trees in a forest, you don't "preserve" habitats for wildlife; you fundamentally alter them. As far as current wildlife is concerned, this spells destruction. That's not to say that at some point these new forests couldn't support a revised version of the previous biodiversity, but that would happen in the long run, not the short run.
  5. Cost -- do you know how many trees Dyson wants to replace? About one third of the Earth's land area is forest. One quarter of that, per Dyson's suggestion, is about 1.25 billion hectares (or about 12.5 million square kilometers). Typical forest density is between 100 and 800 stems per hectare. Thus, Dyson proposes to replace between 125 billion and 1 trillion trees. To replant at high density (say about 700 trees per hectare) would cost about $500 per hectare, or $600 billion globally for a monoculture. Now that's just to pay for the (genetically UNmodified) trees. And don't forget that we won't be planting a monoculture, according to Dyson, but mixed stands, which adds much more to the cost. And don't forget all the roads we'll have to build to remove 1/4 of the world's forests and replace them with new ones. Or the laboratory costs of generating that many genetically modified tree clones. Silly stuff.

Totally unpractical.

Look, I'm all for technological solutions. I'm a plant biologist -- I work on trying to engineer to plants to reallocate their resources better for biofuels production. But Dyson is WAY out of his element here. In fact, whenever he talks about biology (except in regard to the origin of life problem), he's completely off the reservation.

I suggest RealClimate for another take.