Responses of Pioneer and Later-Successional Plant Assemblages to Created Microtopographic Variation and Soil Treatments in Riparian Forest Restoration

Riparian forest restoration generally involves introduction of later-successional tree species, but poor species suitability to severely altered or degraded site conditions results in high mortality and poor community development. Additionally, while microtopographic heterogeneity plays a crucial role in the development of natural riparian forests, little is known regarding effects of restored or created microtopography on the development of introduced plant communities. The objective of this study was to determine the influence of created microtopography and soil treatments on early development of introduced pioneer and later-successional plant communities in riparian forest restoration. Ridges, flats, and a mound-and-pool complex were created, and pioneer and later-successional tree assemblages were planted within plots in each of these three microtopographic positions. Straw-based erosion control mats were placed on half the plots as a source of mulch. After two growing seasons, growth and survival of the pioneer assemblage were equal among microtopographic positions, but survival of the later-successional assemblage was significantly higher on ridges (59%) than on mounds and pools (22%) and flats (26%). A suitability index indicated that performance of the later-successional assemblage on ridges was higher than that of the pioneer assemblage for all microtopographic positions. Flood duration explained much of the variation in plant assemblage survival, and erosion control mats had little influence on seedling survival. Restoring microtopographic features has the potential to enhance species survival and promote community development. Microtopographic restoration may be as important in riparian forest restoration as proper species selection and hydrologic reestablishment, especially at severely disturbed sites.