Use herbicide to maintain or restore disturbance: freshwater marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Disturbance can clear dominant plants, maintain light availability and control nutrient levels – and may maintain vegetation in a desirable and/or species-rich state (Hall et al. 2008; Middleton 2013). Therefore, conservationists sometimes want to actively restore disturbance where it has ceased, or maintain disturbance at a site where it would otherwise be lost. Applying herbicide might be one way to do this.
Bear in mind that the effects of herbicide might be highly dependent on the chemical used, how it is applied and local site conditions (e.g. nutrient availability, water levels, presence/density of wild herbivores) (Tobias et al. 2016).
Caution: In many herbicides, the active chemicals are not specific to the problematic species so can cause collateral damage to desirable species. Relying on herbicides as the only tool to manage problematic plants can lead to the development of herbicide resistance in future generations (Powles et al. 1997). Herbicides can have severe negative side effects on biodiversity, the environment and human health (Pimentel et al. 1992). Accordingly, herbicide use – particularly in or near wetlands or water bodies – is limited in many countries.
Related actions: Use herbicide to control problematic plants, whose success is not linked to a change in disturbance regime.
Hall S.J., Lindig-Cisneros R. & Zedler J.B. (2008) Does harvesting sustain plant diversity in Central Mexican wetlands? Wetlands, 28, 776–792.
Middleton B.A. (2013) Rediscovering traditional vegetation management in preserves: trading experiences between cultures and continents. Biological Conservation, 158, 750–760.
Pimentel D., Acquay H., Biltonen M., Rice P., Silva M., Nelson J., Lipner V., Giordano S., Horowitz A. & D’Amore M. (1992) Environmental and economic costs of pesticide use. BioScience, 42, 750–760.
Powles S.B., Preston C., Bryan I.B. & Jutsum A.R. (1997) Herbicide resistance: impact and management. Advances in Agronomy, 58, 57–93.
Tobias V.D., Block G. & Laca E.A. (2016) Controlling perennial pepperweed (Lepidium latifolium) in a brackish tidal marsh. Wetlands Ecology and Management, 24, 411–418.
Supporting evidence from individual studies
A replicated, randomized, controlled, before-and-after study in 2000–2005 aiming to restore ephemeral freshwater marshes within pine forest in Georgia, USA (Martin & Kirkman 2009) found that applying herbicide to trees (along with cutting and prescribed burning) altered the overall plant community composition, favouring herbaceous and wetland-characteristic species. Over five years, the community composition of managed wetlands diverged significantly from that of unmanaged wetlands (data reported as a graphical analysis). This effect was stronger in the core of the wetlands than on the wetland-upland boundary. Of 26 plant taxa whose frequency increased in managed wetlands (statistical significance not assessed), 25 were herbs and 15 were obligate wetland taxa. Methods: In summer 2000, mature stands of oak Quercus spp. trees – that had developed following fire suppression – were removed from five depressional wetlands by cutting and/or applying herbicide (Pathway® and/or Imazapyr). Then, the wetlands were then burned three times (once every two years). The study does not distinguish between the effects of cutting, applying herbicide and prescribed burning. Five additional wetlands were not managed (trees not removed and no burning). Plant species presence/absence was recorded before (2000) and after (2005) intervention, in three to seven 100-m2 plots/wetland.Study and other actions tested