Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2003
Publication Date: 7/29/2003
Citation: Liston, A., Wilson, B.L., Robinson, W.A., Doescher, P.S., Harris, N.R., Svejcar, A.J. The relative importance of sexual reproduction versus clonal spread in an aridland bunchgrass. Oecologia 2003. 137:216-225. Interpretive Summary: Native bunchgrasses are important for the stability and forage production potential of Great Basin rangelands. Our understanding of the manner in which these plants reproduce and spread is rather limited. ARS scientists in Burns, Oregon, in cooperation with faculty from Oregon State University used plant maps from 1937 and modern genetic techniques to determine whether Idaho fescue plants established from seed or if the plant bunches fragment and slowly migrate over time. Most of the individual plants not present in 1937 appear to have established from seed. When increasing bunchgrass density is an objective, it will be important to apply management strategies which encourage seed production and seedling establishment.
Technical Abstract: Festuca idahoensis (Idaho fescue) is a perennial caespitose grass, common in semi-arid rangelands of the Intermountain West. To determine how individuals are recruited into a population, we studied two long-term monitoring plots that were established in 1937 at the Northern Great Basin Experimental Range in southeastern Oregon. The plots measured 3.05x3.05 m, and were located approximately 30 m apart. One plot was ungrazed, the other was subject to moderate levels of cattle grazing. The number of F. Idahoensis plants in both plots increased ten-fold between 1937 and 1996, but whether this was due primarily to reproduction by seed or clonal fragmentation was unknown. In 1996, we mapped and sampled 160 plants of F. Idahoensis. We used dominant inter-simple sequent repeat (ISSR) markers and codominant allozyme markers in order to identify genetic individuals and measure genetic diversity. Both plots were characterized by high levels of genetic and clonal diversity. When information from ISSRs, allozymes and sample location were combined, 126 genets were recognized, each consisting of one to four samples (ramets). By measuring the diameter of clones surrounding plants that were present in 1937, we estimated that clonal spread occurred at a rate of approximately 3.7 cm per decade, and thus was of secondary importance in the maintenance and increase of F. Idahoensis stands. Sexual reproduction, rather than clonal fragmentation, accounted for most of the recruitment of new plants into these plots. The grazed plot had fewer ramets, genotypes, and clones than the ungrazed plot, but the ramets were significantly larger. Levels of genetic diversity did not differ in the grazed and ungrazed plots, but there was some evidence for a small, but significant level of genetic differentiation between the two. The results also indicate that F. Idahoensis has the potential to be a long-lived species with some individuals persisting in excess of 60 years. This study demonstrates how long-term monitoring can be supplemented by genetic analysis to obtain detailed information on the population dynamics of plants. In the case of this information for understanding succession and developing management and restoration strategies.