Eating your greenery -- and having it too

My latest Mind and Matter column in the Wall Street Journal:

Driving home the other day it occurred to me that almost none of the greenery I could see-trees, garden shrubs, grass shoulders on the highway-was going to be used by humans for food, fuel, clothing or shelter.

That would not have been true 500 years ago. The roadside grass would have fed horses, the trees would have supplied firewood and their acorns would have fed pigs. Although the England of my day has 10 times the population of Tudor times, there's more greenery for wild nature now than there was then.

John S. Dykes

Italy has more forest cover than it did 50 years ago, and Austria has doubled its production of greenery over what it would otherwise be.

Fossil fuels have well known disadvantages, but this is one of their easily overlooked benefits. By substituting oil and coal for horses and firewood, we have relieved the pressure on greenery to supply our needs. By using gas to make fertilizer, we can feed ourselves from a smaller acreage, leaving more acres for other species.

A professor in Vienna named Helmut Haberl has been investigating this phenomenon under the acronym HANPP-or human appropriation of net primary production (a fancy phrase for greenery or biomass). He concludes that human beings currently appropriate for themselves and their domestic animals 14.2% of the world's greenery-including farms, forests, swamps, grasslands and scrub, but excluding the oceans. We destroy or prevent another 9.6% of greenery from growing, by paving or over-grazing; 76.2% remains for nature to use.

One of Haberl's papers is here. And here is an encyclopedia article summarising the argument.

So there is still some headroom for the human enterprise. But I see an even more encouraging result hidden in Mr. Haberl's numbers. He finds that the most industrialized parts of the globe do not necessarily have the largest impact on the biomass of natural ecosystems, even when you take into account their importation of primary production from other places.

The reason is that rich economies tend to boost plant growth, especially on farms, through fertilizer and irrigation. In some cases they do so to such effect that even a large human appropriation still leaves lots for other wildlife. Italy, for example, has more forest cover than it did 50 years ago, yet produces more food.

Mr. Haberl's native Austria more than doubles its land's production of greenery over what it would otherwise be. Consequently, since 1830 Austria has actually reduced the proportion of biomass it pinches for human use even while increasing its consumption. Through irrigation, other places, like the Nile delta, produce more biomass for wildlife than would grow without human intervention-even after people have appropriated much of the biomass for themselves.

Here's a homely example. Some of the birds that visit my garden feed in fields-on seeds, shoots, worms and insects. Man-made fertilizer boosts the quantity of that food, and therefore of birds, whose droppings fall in my garden, transferring that fertility to an ecosystem that will not be harvested, just admired.

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John S. Dykes

Almost none of the greenery I could see-trees, garden shrubs, grass shoulders on the highway-was going to be used by humans for food, fuel, clothing or shelter.

This means that so long as energy and water are abundant, humans might eventually aspire to make global appropriation net-negative. That is to say, our grandchildren could live wealthy consumer lifestyles consuming huge quantities of plant growth, yet actually increasing the amount of plant growth available to wildlife above what it would naturally be.

How would we get there? First, we would stop using the landscape for biofuels, a catastrophic policy mistake, and help rural Africans to switch from charcoal to kerosene or solar stoves. Second, we'd have to find abundant cheap energy with a small land footprint. That means gas, nuclear and maybe solar. Because nitrogen fertilizer is made by a reaction between natural gas and air, abundant gas means abundant fertilizer.