Restoring functionally diverse communities enhances invasion resistance in a freshwater wetland

Abstract

1. Understanding how plant communities reassemble is particularly relevant when invaders are part of the species pool and can compromise restoration or conservation goals. If initial species composition has a lasting impact on community dynamics, it may be possible to enhance biotic resistance to invasion, particularly through diversity effects, by manipulating early community composition. Diversity effects have been investigated much less in wetlands than in uplands. 2. We conducted a large plant community restoration experiment in a freshwater wetland to investigate species and functional diversity effects on biotic resistance to invasion during early community assembly. The wetland was under propagule pressure mostly from Phragmites australis (common reed), but all species not sown in this experiment that established in the plots were treated as 'invaders', whether exotic or native. We used a two-step model selection approach and a diversityinteraction model framework to test hypotheses about the contribution to invasion success of abiotic conditions, species richness, as well as functional group richness, identity and pairwise interactions, providing a rare test of diversity effects against multiple invaders in wetlands. 3. In all, 20 species invaded the plots. They were grouped for analysis to evaluate the overall resistance of resident communities. The three main invaders, P. australis and two native taxa (Salix spp., Populus deltoides), were also analysed separately. Diversity-interaction models revealed invader-specific responses. Functional group identity determined resistance to P. australis, whereas pairwise interactions between functional groups explained resistance to Salix spp. Both effects were retained when grouping all invaders. Resistance to P. deltoides was determined by abiotic conditions. 4. The contribution of specific functional groups varied with invader. Annuals and clonal perennials explained resistance to P. australis, suggesting priority and limiting similarity effects. Interactions, when significant, mostly included fast-growing annuals. When considering all invaders, identity effects were detected for all functional groups.

Landscape and site factors drive invasive Phragmites management and native plant recovery across Chesapeake Bay wetlands

“…In other words, it is not just proximity to intact native stands that drives recovery (as found by Rohal, Cranney, & Kettenring, 2019), but also the quality and diversity of the surrounding areas that are important. Given the importance of restoring diverse native vegetation for future invasion resistance to Phragmites (Byun et al, 2013; Byun, de Blois, et al, 2020), it is essential to restore wetlands in watersheds where the vegetation in the larger landscape is of sufficient quality and diversity to facilitate rapid recovery. Where this approach is infeasible, it is important to recognize that landscape conditions will constrain what is possible in a restoration site (Matthews, Peralta, et al, 2009) and that greater financial investment is required including to augment recovery by reintroducing appropriate native species.…”

The invasion paradox dissolves when using phylogenetic and temporal perspectives

“…Previous observational studies have found that uninvaded native communities have higher functional diversity than invaded communities, which was interpreted as evidence of invasive species decreasing functional diversity through competitive displacement (Jucker et al, 2013;Michelan et al, 2010). Of the few invasion studies to manipulate functional diversity experimentally, two found that invader performance decreased in more functionally diverse native communities, providing support for the biotic resistance hypothesis (Byun et al, 2020;Feng et al, 2019). However, another experiment found that colonizers were more successful in more functionally diverse plots and attributed this to unoccupied niche space increasing with functional diversity (Galland et al, 2019).…”

Reduced Invasiveness of Common Ragweed (Ambrosia artemisiifolia) Using Low-Dose Herbicide Treatments for High-Efficiency and Eco-Friendly Control

“…The richness of native species was negatively correlated with A. artemisiifolia seed yield, regardless of herbicide treatment. It is likely that plant species in more diverse communities occupy a wider range of ecological niches and are more apt to compete with A. artemisiifolia ( Byun et al, 2013 , 2020 ). Diversified interspecific competition largely reduces the fitness of A. artemisiifolia , thereby providing a solid basis for effective weed control using herbicides at low doses prior to A. artemisiifolia outbreaks.…”