Transplantation of the subshrub Lotus scoparius: Testing the home-site advantage hypothesis

The long-term success of restored populations may be jeopardized by the col lection locality of transplants if they are ill matched to their new enviro nment. The home-site advantage hypothesis predicts that the relative succes s of introduced populations will decrease as their genetic and environmenta l distance to the local native population increases. We evaluated this hypo thesis for a geographically variable shrub, Lotus scoparius, in southern Ca lifornian coastal sage scrub by planting two common-garden experiments with seedlings from 12 source populations. The common-garden sites differed in environment and were each home to different source populations of the two t axonomic varieties, L. s. var. scoparius or L. s. var. brevialatus. We used allozyme data from each source population to calculate genetic distances b etween populations, and a combination of climatic data and soil traits to c alculate environmental distances. At the more mesic, coastal common garden, cumulative fitness of transplants (survival x flower production) was inver sely related to genetic distance between source and resident populations. A t the more xeric, inland common garden, cumulative fitness (survival x size ) decreased significantly with both genetic and environmental distance afte r one taxonomic variety was excluded from analyses. Geographic distance was only weakly correlated with genetic distance and had little value in predi cting cumulative fitness of transplants. Our data support the home-site adv antage hypothesis and the idea that mis-matching source populations of thes e genetically differentiated seed sources may result in lowered success of restored or constructed populations. The genetic and environmental similari ties of source populations should be considered when source materials are c hosen for transplantation.