PARENT SESSION
Poster Session #44: Plant Ecology II.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
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Mechanisms of facilitation between a perennial tussock grass and a shrub in a semiarid degraded steppe.
Maestre, Fernando1, Bautista, Susana1,2, Cortina, Jordi1, 1 2
ABSTRACT- Facilitation between plants is a widespread phenomenon that is especially important in harsh environments. In degraded steppes of SE Spain we have observed the presence of facilitation between a tussock grass (Stipa tenacissima) and a late-successional shrub (Pistacia lentiscus), and we are currently investigating the mechanisms involved in this process. We performed a factorial experiment in which 1-year-old seedlings of P. lentiscus were randomly planted under and outside the canopy of S. tenacissima (tussock and open microsites, respectively), with control treatments (both microsites), runoff exclusion treatments (both microsites), and elimination of shade and competition (by bending or herbiciding the tussocks). In addition, we carried out a greenhouse experiment to test the effect of tussock soil on the growth and nutrient status of shrubs. We are currently evaluating seedling performance of introduced seedlings by measuring survival, photosynthesis rate, and chlorophyll fluorescence. Spring and autumn soil moisture curves showed higher water availability after a rainfall in tussock than in open microsites. Stipa tenacissima individuals consumed significant amounts of water, but they increased moisture content by shading. We observed no differences in seedling growth in the greenhouse, suggesting that soil fertility plays a secondary role in facilitation.
KEY WORDS: facilitation, plant interactions, steppe, Stipa tenacissima