Plant Community Recovery following Restoration in Temporally Variable Riparian Wetlands

Abstract

Abstract Wetlands historically provided many ecosystem servicesbut most have been lost or degraded through land conver-sion. Recent appreciation for wetland values and increas-ing ecotourism in the Central Platte River Valley (U.S.A.)has promoted restoration of wet meadow systems, al-though recovery patterns are not well known. We quanti-fied plant community structure in sloughs (deeper habitats)and adjacent margins (slightly higher elevation) of six wet-land sites, restored for 1–7 years at the onset of a 3-yearstudy, and three natural wetlands to assess recovery dy-namics. Plant community metrics recovered differentiallybetween habitats. Within restored margins, richness anddiversity showed aweak quadraticresponsewith time sincerestoration, indicating that both indexes overshoot naturallevels shortly following restoration. Within sloughs, rich-ness and diversity showed no change with time, suggestingthat recovery occurs more quickly in these deeper, moisterhabitats. Percent similarity of plant communities in resto-rations and natural wetlands increased linearly over time.However, ordinations of plant community compositionshowed that recovery was strongly influenced by site-spe-cific hydrology and that recovery may not be a linear tra-jectory toward natural systems. The analysis andinterpretation of plant community dynamics revealed sev-eral challenges to restoration assessment, including therole of interannual variability in precipitation, limitationsto hydrologic recovery, and temporal variability in plantcommunity structure in natural systems that resulted in‘‘moving targets’’ for recovery comparisons. Temporal var-iability in climate must be considered when assessing res-toration success in systems where plant communitystructure is responsive to variable moisture regimes.Key words: assessment, Platte River, slough, temporalvariability, vegetation, wet meadow.IntroductionWorldwide, 53% of wetlands have been lost (Mitsch G U.S. Fish and Wildlife Service 1997). The severedegradation of wetlands in the PRV is of particular con-cern because this region is extensively used by migratorybirds on the central flyway to acquire energy and nutrientsessential for migration and reproduction (U.S. Fish andWildlife Service 1997). Seven to nine million individuals of300 bird species, including the federally endangered Inte-rior Least Tern (Sterna antillarum) and Whooping Crane(Grus americana),migrate annually alongthis route(Krapuet al. 1984; Currier et al. 1985; Austin & Richert 2001).Heightened awareness of the wetland services and theextent of loss and degradation of wetland habitats hasresulted in increased efforts to protect remaining systemsand spawned widespread restoration efforts. Followingthe removal of anthropogenic disturbance (e.g., ceasingcrop production), recovery of some ecosystem aspectsoccurs through natural succession (Dormaar & Smoliak1985; Burke et al. 1995; Ihori et al. 1995). However, natu-ral recovery often requires extensive time. Therefore,restoration aims to catalyze natural recovery processesthrough habitat manipulations (e.g., returning hydrology)(Wilcox et al. 2006), reintroduction of historic plant spe-cies (e.g., seeding) (Reinartz & Warne 1993), and/or man-agement (e.g., prescribed fire) (Clark & Wilson 2001).Plants are often the focus of wetland restorations (e.g.,Willard et al. 1990; Reinartz & Warne 1993; Galatowitsch& van der Valk 1996a) because vegetation is tightly cou-pled to wetland function (Mitsch & Gosselink 2000).Although restoration is a labor-intensive process in thePRV, evaluations of these restorations have been limitedin frequency, duration, and scope (but see Currier 1994;Whitney 1997; Currier 1998).