Use herbicide to maintain or restore disturbance: freshwater marshes

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

40%
Certainty

30%
Harms

30%

Calculating overall effectiveness category

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.}

Study locations

Key messages

One study evaluated the effects, on vegetation, of using herbicide to maintain or restore disturbance in freshwater marshes. The study was in the USA.

VEGETATION COMMUNITY

Community composition (1 study): One replicated, randomized, controlled, before-and-after study aiming to restore freshwater marshes in the USA found that applying herbicide to trees (along with other interventions) significantly affected the overall plant community composition over the following five years.

VEGETATION ABUNDANCE

Characteristic plant abundance (1 study): One replicated, randomized, controlled, before-and-after study aiming to restore freshwater marshes in the USA reported that of the 26 plant taxa that became more frequent after applying herbicide to trees (along with other interventions), 16 were obligate wetland taxa.

VEGETATION STRUCTURE

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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
Referenced paper
Martin K.L. & Katherine K.L. (2009) Management of ecological thresholds to re-establish disturbance-maintained herbaceous wetlands of the south-eastern USA. Journal of Applied Ecology, 46, 906-914.

Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Remove plant litter: freshwater marshes Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Cut large trees/shrubs to maintain or restore disturbance: brackish/salt marshes Action Link	No evidence found (no assessment)	0	Synopsis Link
Use grazing to maintain or restore disturbance: freshwater swamps Action Link	No evidence found (no assessment)	0	Synopsis Link