Experimental evidence of positive association between exotic woody species: Facilitation by Pyracantha angustifolia on Ligustrum lucidum sapling survival.

TECCO, PA; DÍAZ, S; GURVICH, DE; PÉREZ-HARGUINDEGUY; CABIDO, M; BERTONE, GA

APPLIED VEGETATION SCIENCE

Opulus Press

Lugar: Uppsala, Sverige; Año: 2006

1402-2001

Question: (1) Is there any post-dispersal positive effect of the exotic shrub Pyracantha angustifolia on the success of Ligustrum lucidum seedlings, as compared to the effect of the native Condalia montana or the open herbaceous patches between shrubs?; (2) Is the possible facilitation by Pyracantha and/or Condalia related to differential emergence, growth, or survival of Ligustrum seedlings under their canopies? Location: Córdoba, central Argentina Methods: We designed three treatments, represented by ten mature individuals of Pyracantha, ten of the dominant native shrub Condalia montana, and ten patches without shrub cover. Under each treatment we planted seeds and saplings of Ligustrum collected from nearby natural populations. Seedlings emerging from the planted seeds were harvested after one year to measure growth. Survival of the transplanted saplings was recorded every two month during a year. Half of the planted seeds and transplanted saplings were cage-protected from rodents. Results: Ligustrum´s seedling emergence did not differ among treatments while growth was significantly higher in the absence of shrub cover. Sapling survival was significantly higher under the canopy of Pyracantha, intermediate under Condalia, and lowest in the absence of shrub cover. Caging did not affect growth but enhanced seedling emergence and sapling survival. Conclusion: The differential sapling survival observed under the shrub canopy treatments is consistent with natural sapling distribution in the study site. We found evidence of a nurse-plant effect of Pyracantha, and to a lesser degree of Condalia, on Ligustrum. This facilitative association appeared to be the result of the balance of contrasting effects of the shrubs on different stages of Ligustrum’s life cycle: nil effect on seedling emergence, negative effect on seedling growth, and positive effect on sapling survival. We suggest that the spread of Ligustrum is more favoured by its enhanced recruitment and survival under Pyracantha canopies than diminished by their negative effect on growth. The synergistic links between these two invaders suggests that efforts to control the expansion of Ligustrum over the landscape should tackle Pyracantha as well.