Reintroduction of California oatgrass Danthonia californica via sowing and transplanting, and effect of seed source, topsoil removal and plant removal on establishment in coastal prairies near Santa Cruz, California, USA

  • Published source details Buisson E., Holl K.D., Anderson S., Corcket E., Hayes G.F., Torre F., Peteers A. & Dutoit T. (2006) Effect of seed source, topsoil removal, and plant neighbor removal on restoring California coastal prairies. Restoration Ecology, 14, 569-577


Two experiments were undertaken to deduce appropriate technique to reintroduce California oatgrassDanthonia californica (a formerly dominant perennial bunchgrass) into two degraded coastal prairies near the town of Santa Cruz, central California (southwest USA).

The study prairies were at Elkhorn and University of California Santa Cruz campus (UCSC). Vegetation was dominated by annual European grasses (63-69% cover) and annual European forbs (15-26%). At each site, a 52 x 52 m cattle exclosure was installed in autumn 1998 (mown once in spring and autumn until commencement of the study).Outside the exclosure, grazing continued. In January 2003, four 4-month old D. californica plants were sown per 1.5 x 1.5 m plot (12 replicate plots) of each treatment (total 1,536 transplants):
1) local versus non-local (Oregon) seed sources;
2) topsoil removal (top 0-10 cm layer) in August 2002;
3) plant neighbour removal (hand-pulling seedlings and clipping larger plants to ground level around the transplants).
Transplanted D. californica survival and growth was monitored over 1.5 years (a complete growing season and two grazing cycles). Biomass of transplants was sampled.
In October 2002, D. californica seed was sown in plots at UCSC.Seedling emergence was recorded in mid-December 2002, early January 2003 and late February 2003 (i.e. 6, 10 and 17 weeks after the first rains).

Transplants derived from non-local seeds survived better initially but those of local origin had higher survival after 1.5 year at one site. Topsoil removal greatly enhanced transplant survival, after 1.5 years at both sites under grazing or ungrazed regimes (topsoil removed 39%; topsoil intact 12%).

Neighbour removal primarily increased transplant growth, greatly increasing biomass at both sites, grazed or ungrazed (e.g. Elkhorn grazed neighbour removal: 1.18 g vs. neighbour intact 0.11 g), and significantly increased survival only at Elkhorn (neighbour removal 43% vs. neighbour intact 23%).
These results overall suggest that removing topsoil and transplanting seedlings grown from local seed represents a promising method of D. californica reintroduction at these sites. Seed emergence was very low (<1%), suggesting that transplanting is probably a better option.
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