Comparing provisional seed transfer zone strategies for a commonly seeded grass, pseudoroegneria spicata

Restoration practitioners balance the desire to use locally adapted plant materials with the uncertainty of what constitutes "local." Provisional seed transfer zones are intended to guide managers on how far plant materials can be moved during revegetation with the assumption that all populations within a zone will show similarly adapted traits. There are multiple approaches to developing provisional transfer zones, including limiting transfer to specific populations, within ecoregions, within climatic zones, or within climatic zones within ecoregion; there is little information about which of these approaches is best or whether the best approach could vary by region. We used Pseudoroegneria spicata as a test species to assess (1) whether EPA Level III Ecoregion or population explained more variation in traits, and (2) which of four common provisional seed transfer zones (Ecoregion-only, Climate-only, USFS seed transfer zone, and Climate in Ecoregion) best explains trait variation. Plants from 14 populations and three ecoregions were grown in a common garden for two years; growth traits, final biomass, seed set, and mortality were measured. Ecoregion explained more variation than population for most growth traits and mortality; population explained more variation only for seed set. Only one of the three ecoregions showed strong trait differentiation. Out of the four provisional seed transfer zone models compared, we found the most support for models containing climate (Climate-only and Climate in Ecoregion). Findings suggest that Level III Ecoregions may be too broad for seed transfer and that managers should consider climate within ecoregion when making seed transfer decisions.