Is Restoration Beating a Dead Horse In the Face of Climate Change? Using Genetics and Other Methods to Beat the Odds
Tom Whitham
Center for Adaptable Western Landscapes and Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011 USA
An important issue in restoration is knowing when to give up and avoid beating a dead horse. Climate change involving an ongoing 22-year megadrought in the American Southwest that is predicted to continue indefinitely is severely testing the adaptation limits of local stock used in restoration. This is especially important when plantings are at the lower edge of a species’ distribution where extremes in temperature and declining water levels challenge the physiological tolerances of species to survive. Survival is difficult enough for established plants and becomes even more critical for attempting new plantings that are particularly susceptible to extreme conditions of temperature and moisture that can kill 1000s of trees in a single day. Many riparian trees such as cottonwoods naturally establish after flood events where their roots grow down as the water table declines. Establishing such trees where the water table is already 15 or more feet down (the apparent lower limit for cottonwoods), generally requires frequent watering to reach this level. The problem is exacerbated if the water level continues to decline such that tree watering may become a forever requirement. In short, as the effects of climate change increase, the difficulties of restoration increase many fold and we must become much smarter about site selection, using the best genetic stocks and mycorrhizal mutualists to prevent project failure. For example, trees in ephemeral washes are genetically adapted to intermittent stream flows, while those in permanent streams have different root architectures. As permanent streams are predicted to shift to become more ephemeral, source stocks should also shift to reflect these hydrology changes. Furthermore, tree genotypes from low elevation edge sites are critical to save as they are likely to become the optimal source populations for restoration at higher elevations sites that will become future edge populations with continued climate change. We recommend the use of small field trials to establish site quality and identify optimal stocks that can survive changing conditions before committing to large plantings that could fail if satisfactory conditions are not met. I discuss these and other solutions that can help mitigate the challenges of a changing climate.