Canopy vs. soil effects of shrubs facilitating tree seedlings in Mediterranean montane ecosystems
2005
Góómez-Aparicio, Lorena | Góómez, Jose M. | Zamora, Regino | Boettinger, Janis L.
Question: Is the facilitative effect of nurse shrubs on early recruitment of trees mediated by a ‘‘canopy effect’’ (microclimate amelioration and protection from herbivores), a ‘‘soil effect’’ (modification of soil properties), or both?Location: Two successional montane shrublands at the Sierra Nevada Protected Area, SE Spain.Method: Seedlings of Quercus and Pinus species were planted in four experimental treatments: (1) under shrubs; (2) in open interspaces without vegetation; (3) under shrubs where the canopies were removed; (4) in open interspaces but covering seedlings with branches, mimicking a shrub canopy.Results: Both effects benefited seedling performance. However, microclimatic amelioration due to canopy shading had the strongest effect, which was particularly pronounced in the drier site. Below-ground, shrubs did not modify soil physical characteristics, organic matter, total N and P, or water content, but significantly increased available K, which has been shown to improve seedling water-use efficiency under drought conditions.Conclusions: We propose that in Mediterranean montane ecosystems, characterised by a severe summer drought, pioneer shrubs represent a major safe site for tree early recruitment during secondary succession, improving seedling survival during summer by the modification of both the above- and below-ground environment.Nomenclature: Castroviejo et al. (1986––2001) for Quercus and Pinus species, and Molero-Mesa et al. (1992) for shrub species.
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