Abstract
Anthropogenic legacy effects often occur as a consequence of land use change or land management and can leave behind long-lasting changes to ecosystem structure and function. This legacy is described as a memory in the form of ecological structure or ecological interactions that remains at a location from a previous condition. We examined how forested floodplain restoration strategy, based on planting intensity, influenced wetland community structure and soil chemical and physical factors after 15 years. The site was divided into 15 strips, and strips were assigned to one of five restoration treatments: plantings of acorns, 2-year-old seedlings, 5-ft bareroot trees, balled and burlapped trees, and natural seed bank regeneration. Our community composition survey revealed that plots planted with bareroot or balled and burlapped trees developed closed tree canopies with little herbaceous understory, while acorn plantings and natural colonization plots developed into dense stands of the invasive species reed canary grass (RCG; Phalaris arundinacea). Restoration strategy influenced bacterial community composition but to a lesser degree compared to the plant community response, and riverine hydrology and restoration strategy influenced wetland soil conditions. Soil ammonium concentrations and pH were similar across all wetland restoration treatments, while total organic carbon was highest in forest and RCG-dominated plots compared to mixed patches of trees and open areas. The differences in restoration strategy and associated economic investment resulted in ecological tradeoffs. The upfront investment in larger, more mature trees (i.e., bareroot, balled and burlapped) led to floodplain forested communities, while cheaper, more passive planting strategies (i.e., seedlings, seedbank, or acorns) resulted in dense stands of invasive RCG, despite the similar floodplain hydrology across all sites. Therefore, recovery of multiple ecosystem services that encompass plant and microbial-derived functions will need to include additional strategies for the recovery of plants, microbes, environment, and functions.
Highlights
Anthropogenic legacy effects often occur as a consequence of land use change or land management, and these legacies can have lasting impacts on the structure and function of ecosystems undergoing restoration (Fraterrigo, Turner, et al, 2006; Kulmatiski and Beard, 2011; Hawkes and Keitt, 2015)
We addressed the following questions in this study: (1) To what degree does restoration strategy, defined by planting intensity, impact understory plant and soil bacterial community composition and the soil environment? and (2) How does restoration strategy influence wetland plant and soil bacterial community composition compared to reference floodplain wetland conditions? We used a neighboring reference site to determine the efficacy of the different approaches by determining which restoration strategies yielded understory plant and bacterial communities more similar to the reference communities and which strategies were limited by lingering restoration treatment legacy effects
Our study provided evidence that the effectiveness of wetland mitigation relies on initial management strategy, resulting in restoration treatment legacy effects
Summary
Anthropogenic legacy effects often occur as a consequence of land use change or land management, and these legacies can have lasting impacts on the structure and function of ecosystems undergoing restoration (Fraterrigo, Turner, et al, 2006; Kulmatiski and Beard, 2011; Hawkes and Keitt, 2015). We define legacy effects as the residual impacts on chemical, physical, and biological factors due to prior land uses such as agriculture or urban development, or previous land management such as restoration activity. Once residual legacy effects are identified, it is critical to consider how restoration strategies can incorporate knowledge of the prior land use in order to enhance restoration outcomes and reduce tradeoffs in ecological functions (e.g., diversity vs carbon storage) (Jessop et al, 2015; Bürgi et al, 2017).
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