Archbold Biological Station Venus, Florida, United States
Background/Question/Methods
Wetlands are prone to non-native species invasions, which can outcompete native vegetation and affect wetland functioning. In Florida, one such species is West Indian marsh grass (Hymenachne amplexicaulis (Rudge) Nees), hereafter, WIMG. It is a large clonal grass species capable of forming monospecific stands in seasonal wetlands and floodplains. As such, WIMG can be a particular concern in wetland restoration easements. Contrary to other non-native invasives, WIMG is highly palatable to cattle, thus cattle could be used to manage the WIMG population. Our study addressed the effectiveness of using cattle grazing vs. herbicide application in controlling WIMG. To do this, we selected 10 seasonal wetlands embedded in three different working cattle ranches and setup 4 plots in each wetland with 4 different treatments in each: i) no grazing, no herbicide, ii) no grazing + Herbicide, iii) grazing, no herbicide and iv) grazing + herbicide. We conducted baseline plant surveys in spring 2021, applied herbicide treatment between August-October, and resurveyed plant communities at least 2 months following treatment application. We also estimated seed output in each treatment and collected plant biomass.
Results/Conclusions
This project is a 3-year project, and we completed the first year of data collection. At the start of the experiment, WIMG was the dominant species in each plot with canopy cover ranging from 50 to 90 % and representing on average 85% of the plant biomass present at these sites. When no grazing and no herbicide was applied, WIMG quickly reach 100% canopy cover with few to no other species detected in the plots. Both the grazing or the herbicide treatments (applied solely) reduced WIMG cover, biomass, and seed output substantially and similarly. For example, we estimated that cattle consumed ~1t of WIMG/acre. We did not detect a strong effect of applying both grazing and herbicide treatments together. Despite the short-term decrease in WIMG cover, we still observed resprouts in both grazed and/or herbicide treatments. This suggests that additional herbicide application and better timing of grazing are needed. Our study could have important implications for managing wetland restoration easements where grazing was removed. Herbicide application is expensive, time-consuming, and may have potentially adverse environmental effects. We showed similar results can be obtained with only grazing at least in the short-term, representing a cost-efficient alternative to the herbicide.
