Chronosequences show soil changes lag behind plant community recovery in restored wetlands
Wetland restorations aim to regain ecosystem services lost during wetland destruction. Yet, ecosystem service provision requires recovering basic wetland functions, like carbon (C) storage. The accumulation and storage of C (and other important ecosystem functions) is an especially speculative assumption of Wetlands Reserve Program (WRP) projects in western New York (WNY) because those involve reestablishing isolated wetlands on sites directly degraded by agricultural conversion. To assess ecosystem recovery, we analyzed soil and vegetation data from 17 WRP sites in WNY restored from tillage or non-tillage agriculture (aged 0-15 years since restoration when sampled in August-October 2010) over chronosequences to detect divergence from pre-restoration baselines (estimated using data from active agricultural fields paired to each WRP site) and convergence towards “natural” benchmarks (estimated using data from four naturally-occurring wetlands in WNY).
With few exceptions, restored WRP soils remained similar to agricultural soils in terms of organic matter, bulk density, moisture, and root biomass across the chronosequences, indicating negligible C storage and soil development during the first 15 years following restoration. Additionally, development is limited in sites restored following both tillage and non-tillage agriculture and throughout the disparate habitat zones that characterize these sites (upland meadows, emergent-dominated shorelines, and open-water areas). Many plant metrics like aboveground biomass matched natural wetlands within 15 years. Yet, some metrics did not recover consistently among previously tilled and previously untilled sites, or across all habitat zones, suggesting that some plant community metrics are influenced by land-use history and/or the zone in which they are measured. So, while plant communities can recover rapidly following wetland restoration, the underlying soils can lag behind in terms of recovery and remain in an impaired condition for the first 15 years.