Weeds: are they troublesome invaders, ecological opportunists or key to tackling a potential global food crisis? According to research done by weed ecologists, our ambiguous relationship to these resilient plants could soon change in a world where carbon dioxide levels are rising — and where weeds could grow to oversized proportions (think 12-foot tall lambs-quarters, a common weed).
Of course, "weed" can be a rather subjective label, depending on your context — farmers worldwide spend $10 billion annually to keep weeds in check; yet, for others, the same plants could be a beautiful part of a natural garden. But be it friend or foe, a study by scientists at the Agriculture Research Service of the U.S. Department of Agriculture shows that warming temperatures and elevated levels of CO2 resulted not only in increased weed growth rates, size and pollen production, but also a change in the plants' chemical composition.
Could climate change produce superweeds?
Using soil from an organic farm that already contained seeds of 35 common weeds, ecologist Lewis Ziska and his USDA team compared weed growth on three uniform sites in and around Baltimore, Maryland: one rural, one urban and one suburban.
In the space of five growing seasons, Ziska observed that the combined "heat island" effect of the city and higher concentrations of CO2 resulted in towering weeds (10 to 12 feet high lambs-quarters or Chenopodium album, compared to the rural site's 6 to 8 feet), increased pollen output and where a rate of species succession — which normally takes decades — was accelerated close to completion in only five years.
Using a CO2-enriched chamber, Ziska also grew ragweed with an atmospheric concentration of CO2 at 600 ppm (the same level projected for the end of this century by the IPCC's "B2 scenario"). He found that the plants produced twice as much pollen — which in addition, also contained more of an allergy-provoking protein.
Essentially, in our warming climate, weeds win over crop plants, and the consequences for agriculture, public health and food security could be serious.
Weeds as ecological and climate change opportunists
The resilience of weeds is due to their genetic diversity, something that is deliberately bred out of our industrialized crop plants in the interest of increased yields with large-scale genetic uniformity. However, this difference is what allows weeds to flourish, as Ziska reminds us that "[w]hen you change a resource in the environment, you are going to, in effect, favor the weed over the crop. There is always going to be a weed poised genetically to benefit from almost any change."
But despite the study's ominous predictions, weeds could also hold the key to offering a solution, due to their characteristic genetic diversity. Plant breeders in the past have turned to combining the genetic resistance of wild, weedy plants with their domesticated relatives in order to decrease crops' vulnerability to disease and pests. With this in mind, climate change could be just another unique opportunity for weeds and other hardy plants to fulfill other roles: as potential biofuel candidates (kudzu, swtichgrass and jatropha for example), as a source of natural materials for furniture, or even as food — because weeds are evolving, just as we are.
::International Herald Tribune
Related Links on Weeds, Lawn Care and Climate Change
Dave Pollard's Lawn Care Tips
Edible Yards (TH Forums)
Climbing Trees: Plants Move Uphill as World Warms (Scientific American)