PARENT SESSION
Contributed Oral Session 33: Grassland and Shrubland Communities
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal
Multi-trophic dynamics of an assembling grassland community.
Hamilton, E. William*,1, Knox, John1, Oakley, Clinton1, Hurd, L1, 1 Washington and Lee University, Lexington, VA
ABSTRACT- The impact of plant species richness on community processes has been most often studied in pre-established natural or synthetic communities. In contrast, we present early data (2003 and 2004 growing seasons) from an ongoing study of grassland succession in which a native plant species mix was experimentally established by seeding into a denuded site. Initial plant diversity was established at three richness levels (3, 12 and 24 native Virginia grassland species) in 22, 3x3m replicated plots per treatment. We measured soil organic matter, soil nitrogen, canopy light absorbance (environmental variables), microbial biomass, soil micro-arthropods (decomposers), plants species cover (producers), and arthropod abundance and diversity at two trophic levels (herbivores and carnivores). All of the environmental variables were significantly higher in the 12 and 24 species plots than the 3 species plots. Soil microbial biomass and micro-arthropod numbers and richness were greater in 12 and 24 species plots. The dominant plant species in all plots was Elymus virginicus (C3-grass) but, cover was significantly reduced by 4% and 8% in 12 and 24 species plots, respectively from 2003 to 2004. This grass was replaced between years by initially planted species, but not by non-planted colonizers, resulting in higher richness in the plots from 2003 to 2004 (3, 6, and 10 species in 2003 and 4, 10, and 15 species in 2004 in 3, 12 and 24 plots respectively). The observed increased richness among treatments was associated with higher above-ground arthropod richness and abundance in the 12 and 24 plots compared to the 3 plots. Diversity and abundance within the cursorial spider guild of the carnivore trophic level did not vary among treatments in either year, but the relatively greater structural diversity afforded by the two higher plant diversity treatments enhanced orb-weaver diversity in 2004. These data suggest that a trophic linkage mediated by the producer level exerts bottom-up control when plant species richness is high. The presence of native species and not non-planted colonizers potentially provides a broader variety of substrates for decomposers, herbivores, and orb-weaving spiders, increasing the productivity of all trophic levels.
Key words: richness, plant communities, trophic interactions