Decisions . . . Decisions . . . How to Source Plant Material for Native Plant Restoration Projects

How far away should the genetic origin of plant material be from the restoration site? This is a primary question for restoration practitioners, but there are no simple answers. Issues involving cost, availability, adaptability, population genetics, and community resilience complicate practitioners’ abilities to determine precise locations and distances from the restoration site. The majority of formalized guidelines for sourcing plant material are determined on a project-by-project basis. This important decision can affect the longterm sustainability of the restored community and potentially negatively impact levels of adaptive variation in local populations of native species.

“Local is best” is a commonly held tenet among restoration professionals. Unfortunately, “local” means different things to different people and, depending on the long term goal of your project, local may not be best. Local or local ecotype is an extension of the concept of plant ecotypes that has been used to describe and identify populations that originated and are adapted to local conditions (e.g., climate, soils, pathogens, etc.). Using local seed sources is an effort to identify populations that have experienced similar evolutionary selective forces (abiotic and biotic interactions), which should result in higher fitness of plants introduced at restoration sites. However, our ability to predict the spatial and temporal scale of variation in adaptive traits differs among populations and species (Linhart and Grant 1996). Significant differences in fitness may occur between individuals a meter apart and another set of differences between individuals located 100s of kilometers away (Waser and Price 1985, Galloway and Fenster 2000). Defining and identifying local populations is difficult, typically occurs with imperfect knowledge of underlying genetic differences, and results in an inconsistent set of assumptions among practitioners, such as policies that state anywhere from 40 kilometers to over 320 kilometers from the site of concern (Saari and Glisson 2012).

The reason for intense scrutiny of this issue is the possibility of short-term or longterm failure of introduced plants, potential inbreeding resulting from low genetic diversity and/or increased invasive characteristics within restored populations, and introduction of novel genes into adjacent local populations (Hufford and Mazer 2003). Failure to thrive can result from maladaptation of introduced plants to local conditions that can cause poor germination, establishment, or disruption of plant-animal interactions, such as pollination (Keller et al. 2000). Local native populations experience outbreeding depression (reduced survival, seed set, and seed viability) as a result of the introduction of alien genes (Hufford et al. 2012).

Potential negative impacts to local populations and long-term success of the restored community have motivated the selection of plant material for native plant restoration. However, longterm success also depends on the restored community’s ability to adapt to changing environments and adaptation is more likely to occur in genetically diverse populations (Fant et al. 2008). In regions that need restoration, nearby remnant populations may have reduced genetic diversity because of their small size and isolation. If local sources are constrained to these remnant populations, the amount of genetic variation may not be sufficient for population persistence over time.

In order to explore this complex issue, the U.S. Army Corps of Engineers’ restoration ecologist, Brook Herman, Chicago District, organized and hosted the Plant Material Sources for Ecological Restoration Conference, focused on the restoration of native plant communities using plant material sourced from outside the project site. More than a dozen restoration practitioners, researchers, and nursery professionals gathered in Chicago, IL on July 25, 2012 to present their study results, real world examples, and expert opinions. Approximately 50 people attended. Participants ranged from local forest preserve ecologists to endangered species specialists to biologists working on mine reclamation projects. The workshop consisted of 14 presentations with intermittent open discussion among the presenters and participants. Discussion focused on the pros and cons of options for sourcing seed based on the conservation goals, type of project...