Multiscale Patterns of Riparian Plant Diversity and Implications for Restoration

Abstract

Planning riparian restoration to resemble historic reference conditions requires an understanding of both local and regional patterns of plant species diversity. Thus, understanding species distributions at multiple spatial scales is essential to improve restoration planting success, to enhance long-term ecosystem functioning, and to match restoration planting designs with historic biogeographic distributions. To inform restoration planning, we examined the biogeographic patterns of riparian plant diversity at local and regional scales within a major western U.S.A. drainage, California's Sacramento-San Joaquin Valley. We analyzed patterns of species richness and complementarity (β-diversity) across two scales: the watershed scale and the floodplain scale. At the watershed scale, spatial patterns of native riparian richness were driven by herbaceous species, whereas woody species were largely cosmopolitan across the nearly 38,000 km 2 study area. At the floodplain scale, riparian floras reflected species richness and dissimilarity patterns related to hydrological and disturbance-driven successional sequences. These findings reinforce the importance of concurrently evaluating both local and regional processes that promote species diversity and distribution of native riparian flora. Furthermore, as restoration activities become more prevalent across the landscape, strategies for restoration outcomes should emulate the patterns of species diversity and biogeographic distributions found at regional scales.

Understory vegetation as an indicator for floodplain forest restoration in the Mississippi River Alluvial Valley, U.S.A.

“…Tree and shrub plantings are used to restore forest overstory on reclaimed riparian areas, whereas passive processes are expected to recover understory vegetation. Similar to our findings, understory diversity in these riparian systems is attributable to a richer and more varied herb flora compared with the woody component (Viers et al ). McClain et al () found that understory composition of tree‐planted sites differed from that of mature riparian forests; however, relative cover of native species increased with greater canopy closure over time, accompanied by floristic shifts to more shade‐adapted species.…”

Riparian plant guilds become simpler and most likely fewer following flow regulation

“…These results should encourage researchers to make further investigations of guild responses to water‐level regulation by including other stressors and other riparian guilds. An inclusion of herbs would increase the resolution since they are more diverse, more sensitive and responsive to flow changes than woody plants (Stromberg & Boudell ; Viers et al., ).…”

Maintaining channel abandonment processes increases riparian plant diversity within fluvial corridors

“…We compared the understory vegetation sampled in abandoned channels (described above) with understory data from an existing 2003 study within the Sacramento River active channel floodplain (hereafter 'floodplain' data) that comprised 91 plots located within the same range of elevation relative to water surface and landform age as our abandoned channel plots (for details, see Vaghti et al, 2009 andViers et al, 2011). The previously surveyed floodplain plots were 200 m 2 .…”