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Learn why it’s more beneficial to remove invasive species than to control them (a brief summary of a case study conducted in freshwater marshes and wet meadows in Michigan).
Diversity Increases
It is well known that invasive plant species are primary culprits in decreasing native species diversity. This is of concern for many reasons, including economic, aesthetic, and ecological considerations. From an ecological perspective, often a biodiversity-ecosystem function (BEF) context is used. Specifically, higher levels of species diversity are associated with a higher degree of ecosystem function. For example, ponds with more native species are better able to sequester nutrients associated with eutrophication. Different plant species “do” different things, like take up nutrients from different parts of the water column or sediment. Fewer plants mean less nutrient uptake, and less nutrient uptake means less desirable water qualities.
The authors carried out harvesting of Typha (over 3 years) and compared this with mowing and control treatments (note that the use of chemical treatment was not even considered an approach that was relevant). Their focal response was that of seed bank emergence as representing plant diversity at the sites.
Harvesting of Typha and its litter was associated with increased diversity of plants in both marsh and wet meadow sites, whereas mowing alone had little effect on diversity. Sites with litter removed created conditions that facilitated seed germination, thereby increasing the likelihood that native plants would thrive.
One novel contribution in this study was the focus on “deep” diversity—not “deep” as in water depth, but as in phylogenetic diversity. More distantly-related seeds, i.e., diversity that reflected deeper branches in the evolutionary tree (phylogenetic diversity), were found in the harvest treatments. Plants with deeper evolutionary separation represent greater levels of overall diversity. This relates to BEF—communities with diverse plants provide more ecosystem functions that we value (such as nutrient uptake).
Critically, the study highlighted removing invasive plant biomass as opposed to just controlling it. Only in this way can more natural ecosystem functioning be attained in these systems. Take away Typha plant litter for a little bit of deep diversity—sounds like a good trade off to us.
Reference: Lishawa, S. C., et al. (2019). “Invasive species removal increases species and phylogenetic diversity of wetland plant communities.” Ecology and Evolution 9(11): 6231-6244.
