| Revegetation Plan continued: |
| Appendix IV. Summary of two revegetation studies in the Owens
Valley Results of four revegetation treatments on barren farmland in the Owens Valley, Calif. – 1996 progress report, May 1996, by Irene S. Yamashita and Sara J. Manning. In December 1991, 400, 3-4 year old, fourwing saltbush shrubs were transplanted onto barren abandoned farmland in Laws. The transplants were subjected to four treatments: irrigation, density, fertilizer, and weed control, and their growth and survival were monitored annually for five years. The four treatments were applied as follows. Irrigation consisted of 2 liters of water once a month April through September for the first three years. Density consisted of planting shrubs either in rows spaced 2 m apart for low density or 1 m apart for the high density treatment; plants within rows were spaced 2 m apart. The high density spacing, when combined with no irrigation, has not been maintained due to low survival. Fertilized shrubs received 10 g of a 9-month release formula (Osmocote 18-6-12) in the bottom of the planting holes prior to transplanting. No additional fertilizer has been applied since planting. Weed control consisted of removing weedy species once a year within 0.5 m of the shrubs for the first three years. Results from five years of monitoring demonstrated that irrigation was the most important treatment for increasing survival. Survival rates of at least 84% were maintained in combinations that included irrigation with one exception that also combined high density, no fertilizer, and no weed removal. For irrigated shrubs, applying fertilizer appeared to be the next most important treatment for increasing survival followed by low density planting. In unirrigated treatment combinations, weed control, followed by low density planting, enhanced survival while the presence of fertilizer generally had a negative effect. Based on survival rates, irrigation appeared beneficial for three years at the high density planting and two years at the lower density. There have been no significant within-year or overall differences in growth among the 16 treatment combinations during the five growing seasons. In 1996, 91% of the shrubs were reproductively mature. Data from this site shows that monoecious shrubs can change sex and that reproductively mature shrubs may not flower annually. In general, higher growth enhances reproductive maturity. No statistics were performed on sexual expression and treatments. This site is not yet considered permanently revegetated because after six growing seasons, during which the last four have had high seed production and precipitation, there has been only one naturally occurring seedling that has survived for more than a year. In 1994, 30 plants representing, five additional species were transplanted on the site. These species included rubber rabbitbush, greasewood, winterfat, desert needlegrass, and budsage. No treatments were applied and only 1 winterfat survived. In 1996, 88 additional plants were installed and the dead plants from 1994 were replaced. These plants are currently being irrigated with 2 liters of water. This planting included Nevada ephedra, winterfat, allscale, shadscale, and budsage. Seeding basins were tried in 1993 and 1995. In 1993, 112 hand-dug basins were seeded with 6 species with 16 basins serving as controls. In 1995, four additional species were used to replace some of the 1993 plantings and during spring some germination was observed but none of these seedlings survived the summer. It was interesting to find that an unusually wet winter and cool moist spring still resulted in 100% seedling mortality. Using plant shelters to increase plant establishment: 2nd annual report, May 1997, by Irene S. Yamashita This study began in 1995 to investigate using plant shelters on naturally occurring seedlings as a method of revegetation. Five sites were selected and 100, 7.5 in. TUBEX brand shelters were used. The study was concluded because of high mortality, loss of shelters, and the difficulty of relocating test and control seedlings. Only minimal data were collected in 1996 precluding statistical analyses. However, with the few plants remaining, shelters appeared to improve survival in both 1995 and 1996. It was apparent that shelters need to be stabilized more securely than in this study. Physical disturbances such as wind, herbivores, and possibly vandalism appeared to contribute to loss of the shelters and tags on control seedlings because the one fenced site, had a high recovery of sheltered and control seedlings. |