Restoration seed reserves for assisted gene flow within seed orchardsThis article is part of a larger document. View the larger document here.
Changing climate and declining forest populations imperil the future of certain forest tree species. To complement forest management and genetic conservation plans, we propose a new paradigm for seedling seed orchards: foster genetic mixing among a variety of seed sources to increase genetic diversity and adaptive potential of seed supplies used for forest restoration. This new type of seed orchard, a restoration seed reserve (RSR) targeting imperiled species, would incorporate into seed production the seed transfer concepts of assisted gene flow and composite provenancing (Aitken and Bemmels 2016, Broadhurst et al. 2008). The RSRs can be considered a secondary restoration gene pool under the restoration gene pool concept (Jones 2003). They are a hedge against future climate uncertainty by providing seed that minimizes adaptive constraints by maximizing genotypic diversity within restored stands (Lefèvre et al. 2014). While this approach may appear risky, we view it as a responsible strategy to augment, not replace, ongoing National Forest seed programs. The goal of RSRs is to provide range-wide, restoration-ready, seed that has increased adaptive diversity beyond what is available from native local seed sources.
Operationally, RSRs differ from standard seed orchards because no attempt would be made to select for production forestry traits, surmise which adaptive traits are needed, or adhere to strict seed zones, although options remain flexible with respect to policy arising from newly drawn seed zones. At production age, a properly designed RSR would contain about 200 trees grown from seed collected from 20 or more distinct populations across the species’ range. RSRs avoid inbreeding by retaining no related individuals (no clones or family structure) and containing accessions selected only for seed production traits (by rouging an initial planting of 2000 to 2400 seedlings). Such a design assures gene flow among genotypes sampled from dispersed populations. For most tree species, especially those in the southern United States, outbreeding depression from intercrossing among diverse provenances would not be an issue (Frankham et al. 2011).