More weeds

I re-read the article about weeds that I posted about earlier today and did a little follow-up research.

Since I've been thinking about fires today (given that so much of Northern California is ablaze, and it's fairly hazy even here in Vegas), I began to see how climate change is related to more frequent and severe fires in ways that I hadn't thought of before. That global warming means some areas will get less precipitation and be drier--and consequently more likely to burn--I understood.

But I hadn't known that higher CO2 levels actually produce more fuel for the fires. For example, the article has this to say about cheatgrass, a common invasive grass that was everywhere in Kansas even when I was growing up 30 years ago:

Cheatgrass’s combustibility is inherent in the plant’s pattern of growth. Sprouting in the fall, it resumes growth at winter’s end to mature and set seed in early summer, whereupon the plant dies, leaving a tuft of dry, highly flammable leaves through the following dry season. Ziska and his colleagues discovered, though, that the weed’s flammability seems to have been greatly augmented by the increases in atmospheric CO2 that occurred during the period of cheatgrass’s spread through the West.

The scientists grew the plant at four concentrations of CO2: at 270 p.p.m. (the ambient level at the beginning of the 19th century, before the Industrial Revolution), at 320 p.p.m. (a 1960s level), 370 p.p.m. (a 1990s level) and 420 p.p.m. (the approximate level predicted for 2020 in all the climate-change panel’s estimates). What they found was that an increase of CO2 equivalent to that occurring from 1800 until today raised the total mass of material (the biomass) each cheatgrass plant produced by almost 70 percent. In addition, the composition of the cheatgrass changed as the CO2 level increased, the tissues becoming more carbon-rich so that the plant leaves and stems are less susceptible to decay. In a natural setting, this would mean that the dead material would persist longer, adding yet more fuel for wildfire.

More fuel, with a longer life — Ziska says that the rise in greenhouse gases we have already achieved may have played a decisive role in the spread of a weed that has already transformed the ecology of the Western United States. The situation seems likely to worsen too. The cheatgrass that Ziska grew at the CO2 level equal to that projected for 2020 increased the plant’s biomass by another 18 percent above current levels. Global climate change, it seems, will further stoke the rangeland wildfires.

This year-old article in the High Country News has similar bad news with respect to other invasive grasses.

As hard as it is to believe--or as hard as it was to believe when we were all a bit younger--we are changing the environment of our planet in ways that we don't yet fully understand.