PARENT SESSION
Thursday, August 10, 5:00-6:30 pm
Poster Session 23 - Arid and semi-arid ecosystems: deserts, grasslands, shrublands, and savannas
Exhibit Hall, Ballroom Level, Cook Convention Center

The effects of shrubs on ephemeral plants: soil or canopy?

Gutiérrez, Julio^{*,1, 2, 3}, Squeo, Francisco^{1, 2, 3}, Aguilera, Lorgio¹, Valdivia, Luis¹, Meserve, Peter⁴, Kelt, Douglas⁴, ¹ Universidad de La Serena, La Serena, Chile² Centro de Estudios Avanzados en Zonas Áridas, La Serena, Chile³ Instituto de Ecología y Biodiversidad, Santiago, Chile⁴ Northern Illinois University, DeKalb, IL

ABSTRACT- In arid and semiarid ecosystems shrubs may facilitate or inhibit the presence of ephemeral plant species. Microclimate and soil conditions differ underneath shrubs from those in open sites. In the Chilean coastal desert, ephemeral plant assemblages underneath and outside Porlieria chilensis shrubs differ. We hypothesized that the most probable cause was the differences in soil nutrients. We designed an experiment to assess the single effects of canopy and soil underneath and outside P. chilensis shrubs on ephemeral plant assemblages in Fray Jorge National Park in north-central Chile. We collected surface soil (5 cm topsoil) from underneath and outside P. chilensis shrubs. One plastic pot containing soil underneath and another plastic pot containing soil from outside P. chilensis canopy were laid out underneath P. chilensis canopy. The same procedure was repeated outside P. chilensis canopy. Each treatment was replicated 10 times. The experiment was performed in a rainy year, 2000. Plants emerging in each pot were recorded until no more plants emerged. Final density numbers per species were analyzed by a factorial ANOVA. Twenty- three species emerged from the pots. Twenty species responded to the soil factor confirming the previous hypothesis; however, four species responded to the location factor, and the interaction of soil x location was significant for two species. Soil seed bank only partially accounted for differences in species composition. This study was financed by FONDECYT 1030225.

Key words: arid and semiarid zones, nurse effect, annuals and geophytes