Barriers to ecosystem restoration presented by soil legacy effects of invasive alien N₂‐fixing woody species: implications for ecological restoration

Abstract

Impacts of invasive alien N 2 -fixing woody species and how they can persist as soil legacy effects after invasive species control are well appreciated, but how soil legacy effects can present barriers to restoration is poorly understood. Finding better ways to deal with these barriers to restoration is essential to improving restoration outcomes. In this study, we review 440 studies to identify barriers to restoration and potential management actions for the barriers to restoration, and provide practical application examples of the management actions. Our findings suggest that altered soil microbial communities, depleted native soil seed banks, elevated N status, secondary invasion and weedy native species dominance, and reinvasion are potential barriers to restoration. Furthermore, carbon addition, litter removal, soil microbial treatments, establishing species adapted to low N levels, prescribed burning, classical biological control, grazing, mowing, herbicide or graminicide application, manual weeding, soil N management, soil solarization, weed mats, native species reintroduction, and nurse plants are potential management actions for these barriers to restoration. However, there is little evidence suggesting that several of these barriers to restoration hinder improved restoration outcomes and this could be due to little research on them. More research is needed to assess their relative importance in hindering improved restoration outcomes. Management actions are rarely applied in combination, despite that they often address distinct barriers to restoration. Management actions should be combined into an integrated management effort to improve restoration outcomes.

Cycas micronesica Trees Alter Local Soil Traits

“…The direction of the feedback can be negative, where nutrients are immobilized or depleted or pathogens accumulate; or, can be positive, where nutrients or mutualists accumulate [27]. "Soil legacy effects" are commonly studied in the context of invasive plant species that possess the power to engineer changes in ecosystem of the invaded habitats [28]. This subset of the plant-soil feedback agenda is often invoked for discussing allelopathic properties that remain in soils following invasive plant species growth.…”

Biological Invasions and Ecological Restoration in South Africa

“…Feedbacks likely to result in regime shifts were related to processes associated with seed banks, fire and nutrient cycling (Gaertner et al 2014). A recent review of soil legacy effects resulting from invasion by alien N 2 -fixing woody species identified several potential barriers to restoration following alien control (Nsikani et al 2018). Biotic barriers included altered soil microbial communities, depleted native seed banks, secondary invasions of alien species, and weedy native species dominance.…”

“…It is controlled by abiotic limitations that result from amplified biotic interactions and restoration requires manipulation of the physical environment in addition to the biotic components. Where alien species incur legacy effects such as N enrichment (Nsikani et al 2018), this may be a barrier to restoration and may require the physical removal of nutrient-rich biomass (Marchante et al 2009), the manipulation of soil nutrients (Zink and Allen 1998; Török et al 2000), or the use of fire to volatilise excess nutrients. In many cases, biotic and abiotic threshold effects are closely linked and may occur simultaneously.…”

Re-establishment of Protea repens after clearing invasive Acacia saligna: Consequences of soil legacy effects and a native nitrophilic weedy species

“…Furthermore, to our knowledge there is no restoration strategy that can be successfully used to restore overall native soil chemistry, although methods to immobilize elevated nitrogen are available. If elevated nitrogen availability, legacy of altered soil microbial communities and nitrophilic weedy species prove to be barriers to native species re-establishment during restoration; we urge practicing restoration ecologists to incorporate management actions such as soil carbon addition, soil microbial treatments and prescribed burning into their restoration programs (reviewed in Nsikani et al, 2018).…”