Effect of shrubs on recruitment of Quercus douglasii and Quercus lobata in California

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Examined associations between seedlings of these oaks and several species of shrubs and conducted field experiments that tested for facilitative effects of Salvia leucophylla and Artemisia californica, on seedling survival. Naturally occurring Q. douglasii seedlings were relatively common (280 seedlings/ha) and were strongly associated with shrub canopies. In two experimental plantings, 30% and 55% of Q. douglasii seedlings that emerged under shrubs survived for >1 yr; no seedling in the open survived in either experiment. Survival of Q. douglasii where shrubs were removed was similar to survival in the open grassland, indicating that association between shrubs and oak seedlings was not due to shared microsite requirements. Q. douglasii seedling survival was not different between the two shrub species. Only three Q. lobata seedlings were found in 26 study plots, although reproductive adults were present. The seedlings were under shrub canopies. However, the survival of Q. lobata was not facilitated by shrub cover or shrub simulation and no other evidence was found for nurse-shrub interactions with this oak species. Artificial shade was critical to the survival of Q. douglasii seedlings in simulated shrub environments. When grown in artificial shade, photosynthetic capacities and root elongation rates of Q. douglasii seedlings were significantly higher than those of Q. lobata. These differences may partially explain why nurse-plant interactions exist between shrubs and Q. douglasii seedlings but not between the same shrubs and Q. lobata seedlings. Causes of acorn and seedling mortality differed between the shrub and open grassland habitats. Under shrubs, acorn predation was the primary cause of mortality, whereas mortality due to shoot herbivory was much more frequent in the open grassland. Thus, propagules under shrubs that avoided predation until shoot emergence benefited from canopy shade and protection from herbivores. -from Author

Original languageEnglish
Pages (from-to)2118-2128
Number of pages11
Issue number6
StatePublished - 1992


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