Dr. Susan E. Meyer
Genetic Issues in Restoration
One of the principal practical outcomes of our many years or work on within-species variation in germination timing mechanisms and establishment ecology is a clarification of why it is important to pay attention to the geographic and habitat origin of seeds used in restoration plantings. Because populations of widely distributed species exhibit such strong ecotypic differences, it is not sufficient in a restoration planting just to get the species right and then obtain 'off the shelf' seed lots. A seeding may fail even if all the right species are included, if the seeds of those species were obtained from populations not adapted to the planting site.
On the other hand, though, it is the average adaptive response that varies measurably among populations within a species. In fact, Intermountain species are characterized by tremendous within-population genetic variation in adaptively significant traits like germination timing mechanisms. There is often more spread among individuals within a population in these traits than the spread of average differences among populations. What this means is that it may not be quite as necessary to get a perfect habitat match between the seed collection site and the planting site. Natural selection will operate at the new site to favor those individuals that are genetically adapted to that site, even if those individuals were in the minority, off on the tail of the normal curve, so to speak, in the original population. This high within-population genetic diversity is probably maintained by temporal variation in the selective regime at a particular site, in other words, by year to year variation in the weather. This is because it is the weather the year a particular seedling is establishing that determines its survival and future contribution to the gene pool, not the average weather at the site.
Our focus has been on coming up with seeding prescriptions and recommendations that result in stand establishment and persistence through time at a restoration site for particular native species. There are other genetic issues in restoration. Depending on the land ownership and jurisdiction on a particular site, specific legal mandates may apply. For example, for the National Park Service, one of the resource values to be maintained and protected is the genetic makeup of species. In this context, it would not be appropriate to bring in seeds from a distant site, even if they were adapted to prosper on the Park Service site.
A more fundamental issue with moving seeds from one place to another is that of possible negative impact on local gene pools with the addition of 'foreign' genes through outbreeding depression. It is not yet known how important this effect might be. But if we are ever going to make any progress on restoring literally millions of acres of public land, now infested by exotic weeds, to diverse, productive native vegetation, we will need to strike a balance among these various concerns. We will also need a lot more good science to really understand these issues. Fortunately, with the advent of molecular genetic techniques, we now have the tools to seriously address these questions.