Objective: reduce the abundance of Spartina species already present in intertidal habitats
Definitions
● Herbicide = a chemical that kills or inhibits the growth of plants.
● Intertidal = the area between high and low tide.
● Neap tide = a period of moderate tides due to the position of the sun and the
moon, with a high tide height substantially lower than that during spring tide period
while a low tide height substantially higher.
1. Description
The use of chemicals to control Spartina involves applying herbicides to areas where Spartina has become invasive to manage and/or eradicate the species. The use of herbicides is a well- established method for controlling invasive plant species and can be effective in making habitat available for feeding and roosting of shorebirds on tidal flats and salt marshes but the effect on native wildlife itself must also be taken into consideration.
2. Evidence for effects on biodiversity
Birds: Using herbicide to remove invasive plants can benefit birds by increasing the availability of habitat. Studies on tidal flats in Willipa Bay, USA, found that following the control of Spartina, using glyphosate and imazapyr, more shorebirds used the sites, including sandpipers Calidris spp., with overall shorebird usage increasing from almost zero to around 800 birds/ha following herbicide application (Patten & O’Casey, 2007; Patten et al. , 2017). At a site in the UK, more individual shorebirds, particularly Redshank Tringa totanus , foraged in areas where Spartina had been recently cleared than in areas where it has been cleared three to four years before (Evans, 1986) – it is thought that the wetter, open habitat in the more recently cleared areas made invertebrates more visible. The long-term effect of herbicide on birds in the wild is uncertain (as far as we are aware). Experimental studies on Japanese Quail Coturnix japonica suggest there may be a cumulative effect of glyphosate exposure (Ruuskanen et al. , 2020a,b). Those fed with glyphosate-contaminated seeds from 10 to 52 weeks of age had a different gut microbiome, decreased levels of male testosterone and slightly lower embryonic development compared to a control group, but there was no clear effect on reproduction, in terms of testis size and egg production. Eggs collected from these species contained glyphosate residues but there was no effect on the egg quality. Invertebrates: A study in Australia found no detrimental effects on molluscs, annelids and crustaceans of using Fusilade Forte® (Fluazifop-p-butyl) to remove Spartina. In fact, they found higher species diversity and more crustaceans (mainly the amphipod Allorchestes compressa ) in areas treated with herbicide after six months (Kleinhenz et al. , 2016). Another
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