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

Abstract

In the Mississippi River Alluvial Valley (MAV), complete alteration of river-floodplain hydrology allowed for widespread conversion of forested bottomlands to intensive agriculture, resulting in nearly 80% forest loss. Governmental programs have attempted to restore forest habitat and functions within this altered landscape by the methods of tree planting (afforestation) and local hydrologic enhancement on reclaimed croplands. Early assessments identified factors that influenced whether planting plus tree colonization could establish an overstory community similar to natural bottomland forests. The extent to which afforested sites develop typical understory vegetation has not been evaluated, yet understory composition may be indicative of restored site conditions. As part of a broad study quantifying the ecosystem services gained from restoration efforts, understory vegetation was compared between 37 afforested sites and 26 mature forest sites. Differences in vegetation attributes for species growth forms, wetland indicator classes, and native status were tested with univariate analyses; floristic composition data were analyzed by multivariate techniques. Understory vegetation of restoration sites was generally hydrophytic, but species composition differed from that of mature bottomland forest because of young successional age and differing responses of plant growth forms. Attribute and floristic variation among restoration sites was related to variation in canopy development and local wetness conditions, which in turn reflected both intrinsic site features and outcomes of restoration practices. Thus, understory vegetation is a useful indicator of functional progress in floodplain forest restoration.• On former agricultural floodplains, some floristic differences between afforested sites and mature bottomland forests are a natural result of differing successional age. However, species-composition attributes of understory vegetation offer useful indicators of restoration progress. • Relative growth form composition (herbaceous vs. woody) reflects the role of tree-planting practices in establishing a forest overstory. Functional-group composition (based on wetland-fidelity rankings) can be an important indicator of hydrologic conditions and practices. • Active afforestation can restore forest habitat structure, but restoring local hydrology is key to enhancing functional ecosystem services such as nutrient retention and carbon sequestration.

Strategies to restore floodplain vegetation after abandonment of human activities

“…In floodplains impacted by human activities, natural riparian habitats are frequently limited to remnant forests in narrow corridors, where regeneration of disturbance‐dependent riparian vegetation, including keystone riparian trees, only takes place in encroached river channels (Cordes et al ; González et al ; Cooper & Andersen ; Dixon et al ). Fully restoring natural riparian corridors in such intensively transformed floodplains is unrealistic, but local‐scale recovery of riparian plant communities can be targeted in lands whose economic productivity is marginal and where landowners are open to yielding their properties for restoration purposes (Gumiero et al ; De Steven et al ).…”

“…For example, the decision to clear‐cut, leave trees in place, or allowing them to resprout after clear‐cutting can substantially influence the dominant tree species and floristic composition of abandoned lands (Spencer et al ; González et al ). When facing limited inflow of propagules, planting native trees could accelerate plant succession and preserve local biodiversity (McLane et al ; De Steven et al ; Bourgeois et al ). Despite the panoply of approaches to renaturalizing former floodplain lands occupied by humans, no study has directly compared the vegetation response to multiple strategies for managing these types of sites along a gradient of interventionism (and cost) and within the same river system.…”

Effects of riparian zone buffer widths on vegetation diversity in southern Appalachian headwater catchments

“…In contrast, small perennial streams in montane headwater catchments often lack alluvial benches, have steeper sideslopes, and have a closed canopy cover relative to larger or low gradient streams; features that may diminish the distinction between riparian zones and the surrounding forest (Goebel et al, 2003;Dieterich et al, 2006;Hagan et al, 2006;Clinton et al, 2010). In addition, small southern Appalachian streams may not have riparian obligate vegetation communities, or riparian indicator plant species, such as seen in other regions, particularly obligate wetland species or those associated with larger tributaries De Steven et al, 2015). With the increasing emphasis on managing headwater riparian zones (Sanders and McBroom, 2013;MacDonald et al, 2014) and the differences among headwater catchments (Meyer et al, 2007;Hill et al, 2014), setting a standard sized buffer width across geo-physiographic regions becomes problematic.…”

Poplar plantations along regulated rivers may resemble riparian forests after abandonment: a comparison of passive restoration approaches

“…Payments for ecosystems services (PES) to farmers, e.g. have been implemented in China for the conversion of croplands in steep slopes to forest or pastures and avoid soil erosion and river-bed sedimentation (Kolinjivadi & Sunderland 2012) and in the Mississippi floodplain to restore unproductive croplands to wetlands (De Steven et al 2015).…”