In recent years, plant materials programs and policies have emphasized the development and deployment of genetically appropriate native plant materials. The foundation of genetic suitability is the concept of local adaptation with the intent of exploiting genetic variation to both preserve and capitalize on spatially diverse functional traits to improve restoration outcomes. Generalized provisional seed zones (GPSZ) are one method proposed to match seed sources to restoration sites. In this study we assess the utility of generalized provisional seed zones to assemble pooled, stock seed sources of basin wildrye (Leymus cinereus). Basin wildrye was selected as the test species because it is a common restoration species in the Intermountain region, yet genecological seed zones have not been developed.
Within the Central Basin and Range ecoregion, a substantial array of climatic and ecological variation occurs across basin wildrye’s distribution, which ranges over 1,100 meters in elevation and across nine level-four ecoregions. This variation may lead to the development of localized adaptions between spatially divergent populations. We hypothesize seed sources planted on test sites similar to their home generalized provisional seed zones will demonstrate local adaptation through higher initial establishment and better short-term persistence.
Within the Great Basin, populations of basin wildrye (n = 107) occur in nine GPSZs. Five zones are poorly represented, containing one to three populations within their boundaries, while four zones account for the remaining 91.6 percent of populations. GPSZs are most effective when nested within Omernik’s level III ecoregions. Consequently, for this study, source populations were restricted to origins within the Central Basin and Range ecoregion and the four zones with the highest frequency of basin wildrye occurrence. Basin wildrye occurs in both tetraploid and octoploid forms. When developing genetically appropriate stock seed supplies, leading recommendations suggest pooling seed from at least five populations representing more than 50 total parents. For this study, basin wildrye populations were mapped according to seed zone and cytotype to identify populations for each zone/cytotype combination.
A primary objective of this study was to compare establishment success among populations seeded in a manner similar to a restoration planting. In 2013 and 2014, basin wildrye seed was harvested from 25 wildland populations and planted at the four test sites. Basin wildrye is not known for excellent seedling vigor, so to improve the chances of seedling establishment a replicated set of plots was enclosed with row cover. Plant establishment data were collected in the fall of each year following seeding. Short-term persistence data were recorded fall of 2017, four years after the 2013 planting and three years after the 2014 planting.
The primary objective of this study was to test whether generalized provisional seed zones (GPSZ) geographically represent apposite partitions of selective gradients that basin wildrye has evolved under and thereby aptly partition populations into adaptive groups. We hypothesized local adaptation expressed by pooled local sources would perform better initially and over time, than pooled non-local sources. However:
While in this study, sources did not demonstrate local superiority, they also did not reveal maladaptation. In this sense, the lack of differences suggests, relative to initial establishment and short term persistence, that basin wildrye, functions as a habitat generalist when grouped by GPSZs.