Floristic quality improves following restoration at two drained peatlands

Abstract

Peatlands are globally important ecosystems because their vegetation drives key ecosystem services such as peat formation and hydrologic regulation. As drained peatlands have lost these functions, restoration is critical but there is limited understanding on how floristic composition, a primary indicator of peatland ecosystem health, can quickly return to a reference point when a targeted restoration technique is applied. We evaluated the outcomes of vegetation restoration at two formerly drained acidic peatland sites (North Field and South Field) in northern Minnesota where the moss layer transfer Technique (MLTT) was applied to accelerate the reestablishment of peatland species and the return of peatland functions. Following drain blocking to raise water tables, site leveling, and the MLTT, plant communities at both the North and South Field sites shifted rapidly within five years from upland-dominated to wetland-dominated plant assemblages. Non-metric multidimensional scaling and PERMANOVA showed significant temporal shifts, with plant community similarity to 43 regional reference wetlands rising from <5% initially to 9 to 15% by the end of monitoring in 2022. Mean Coefficient of Conservatism values (C-values) increased from 2.0 to 4.3 at the North Field and from 3.5 to 5.5 at the South Field, indicating replacement of generalist upland plant species by higher-fidelity peatland taxa. Non-native plant cover peaked early, then declined after approximately five years, but showed minor increases after herbicide treatments ceased. These results show that rewetting coupled with the MLTT can enhance floristic quality, but compositional convergence with reference peatlands remains slow and spatially variable within each site.