Dark Diversity in Restorations: What's missing?

摘要

Low or declining plant diversity is a persistent problem in tallgrass prairie restoration. Most efforts to increase diversity involve seed additions and ecosystem manipulation to increase establishment. However, the species added often decline and are lost after the initial planting. An alternative would be to alter composition using species commonly found in remnants. Regeneration traits (clonal and non-clonal) may affect the ability of species to reproduce in established vegetation, affecting persistence and diversity. This study compares the composition and trait dominance of tallgrass remnants to restorations in the Midwestern U.S. The relative frequency of species found in nine high-quality remnants was compared to eight degraded remnants and 18 restorations at both site and regional scales by regeneration traits. Recommended species lists from three tallgrass restoration handbooks were compared using clustering analysis. At a regional scale, ten (71%) species greater than 25% relative frequency were clonal. At an individual site scale, sixty-two (52%) species greater than 25% relative frequency were clonal. Recommended seed mix composition is, on average, 68% different from remnant composition, with guerrilla species underrepresented and non-clonal species over-represented. At the 0.25m(2) quadrat scale, richness was positively correlated with all growth forms. Where properties of natural or remnant ecosystems is a goal, a knowledge of common species or traits in a reference ecosystem should be represented in the seed mix. The regeneration niche of clonal species appears to be more advantageous than reproduction by seed in established vegetation, resulting in a majority of common species being clonal.