Ecologists spend a whole lot of time studying which qualities—or traits—of which plants make them better or worse at surviving and thriving in a restoration project. The short version usually ends up being that the invasive and/or exotic species (that we're trying to get rid of) have traits a, b, and c; which allow them “win” against the natives’ measly traits x, y, and z.
Plant traits are not a new discovery-- humans have known how to breed species for desired traits for millennia. Many Americans today have long forgotten that the corn we eat isn’t a "natural" species—it comes from early Americans re-planting the teosinte plant with the biggest seeds, over and over again, until we ended up with what we now call corn. Dogs were once wolves. Pigs were once wild boars. If we know which traits make plants perform better in different environments, why don't we breed the species in our natural environment to keep up? If given the time, natural selection would work this out on its own, but unfortunately humans are changing the environment quite a bit faster than evolution is used to.
There’s a little evidence that this happens on accident already, but mostly for species that are already relatively good competitors. Many seeds used in restoration projects are collected from a wild source, but many more are grown in bulk and purchased by seed suppliers. The latter have created a positive feedback loop for themselves—the plants that were already best at growing are grown the most and are sold for cheapest (and therefore sold the most… and therefore grown the most… and so on). Land managers with tight budgets want to sow as many seeds as possible, so the majority of what they buy is whatever’s cheapest. So, because what is cheapest is both the best at growing, and gets sown the most, those species can take over completely! Some prairie restoration practitioners don’t even plant Big Bluestem (Andropogon gerardii) anymore, for this very reason.
A field of Big Bluestem, which presumably
was supposed to be a prairie that contained
other species, too. You can see Big Blue is good at
keeping out weeds, but it's also good at
keeping out the other native prairie plants.
Photo from Big Bluestem Prairie.
In other cases, the species that are the most receptive to being grown in an agricultural field and harvested in bulk are not actually suited for their target environments at all. Chivers et al. call this “the elephant in the room, that is the often inadequate performance of available plant materials under increasingly challenging restoration conditions.” In some arid grasslands, for instance, the establishment rate of sown species is embarrassingly low because the seeds that are available from cultivation grew in an irrigated field, and can't grow at all in dry conditions (which they're sold for)! Sure, extensive breeding and cultivation programs would be expensive, but surely this would be more efficient in the long run than the current status quo of throwing money away on seeds that don’t grow. (Beth Leger from U. Nevada-Reno studies this. Check out her research!)
So what are we waiting for?
One potential hold-up is that there are often trade-offs between traits. We can’t always pick all the characteristics we want without losing some others along the way. For example, plants that get better at making roots are forced to do so at the expense of above-ground mass, due to an eventual limit in resources. Additionally, there is worry that breeding could cause a loss of overall genetic variation—differences in genes of individuals within a species—which would decrease those plants’ ability to adapt to changes up the road (so far, evidence says this won’t be an issue). Scientists are hard at work studying these possible barriers in order to assess the feasibility of breeding programs.
Perhaps the biggest, and most potentially compelling, argument against breeding plants for restoration deals with what, exactly, we are trying to restore. If we are trying to save species and systems, selecting for plants with the best traits makes perfect sense. However, purists will say that native plants that have been bred have lost something special-- and worse, will “pollute” the remnant gene pool with their different genes when they interbreed with the natural, unaltered, populations.
This final issue changes the debate from a scientific to a philosophical one, and forces us to ask hard questions about why we want to restore native ecosystems and what we’re trying to preserve in the process. As more and more native species are displaced by invaders, and more and more of our remaining natural land is cleared, I hope we can make up our minds about it soon.
Citation: Chivers, I. H., T. A. Jones, L. M. Broadhurst, I. W. Mott, and S. R. Larson. 2016. The merits of artificial selection for the development of restoration-ready plant materials of native perennial grasses. Restoration Ecology.
About the authors:
Ian Chivers is at Native Seeds Pty. Ltd. In Australia
Tom Jones, Ivan Mott, and Steve Larson are with USDA in Logan, UT
Linda Broadhurst is at CSIRO National Research Collections, Australia