PARENT SESSION
Oral Session #57: Plant Competition I.
Presiding: T. Seastedt
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Prunus mahaleb regeneration: does the balance between interference and facilitation depend on the environment?

Schupp, Eugene^*,1,3, Boettinger, Janis^2,3, Jordano, Pedro³, ¹ Department of Rangeland Resources, and, Logan, Utah³ Estación Biológica de Doñana, Sevilla, Spain² Department of Plants, Soils and Biometeorology, and, Logan, Utah

ABSTRACT- Established shrubs may simultaneously interfere with seedling recruitment (e.g., competition) and facilitate seedling recruitment (e.g., amelioration of the physical environment). The outcome we see, the net effect of the interaction, is determined by the relative strengths of interference and facilitation. It is expected that the relative strengths of these forces vary across environmental gradients, and thus patterns of plant recruitment may vary from year-to-year and place-to-place. We addressed the complex interactions involved in interference/facilitation in the Sierra de Cazorla, southern Spain, with a factorial experiment with seeds of the tree Prunus mahaleb. Treatments were: (1) microhabitat (beneath the shrub Berberis hispanica, on the north side of rocks placed flat on the soil, or in open interspaces), (2) ground-level competition (with and without herbaceous and subshrub species removed), and (3) landscape position (rocky slope with very shallow clayey soils or adjacent valley bottom with moderately deep sandy soils). We replicated all except the ground-level competition portion at a second nearby site. Shrubs, rocks, and ground-level vegetation substantially reduced soil temperatures at 5 cm depth, and slope positions had considerably higher soil temperatures than valley bottom positions. Results for seedling emergence and for seedling survival differed, as did results for the two sites, although some general patterns appear to emerge. For example, rocks appeared to facilitate seedling recruitment as well as shrubs, and recruitment was greater in valley bottoms than on slopes. Main effects must be interpreted with caution, however, because the major result is large numbers of significant interactions. For example, effects of ground-level vegetation depended on the microhabitat (2-way interaction) and the interaction between ground-level vegetation and microhabitat differed across landscape positions (3-way interaction). We will discuss the implications of these interactions.

KEY WORDS: facilitation, seedling recruitment, competition