Use covers/barriers to control problematic plants: freshwater marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Covers such as plastic sheeting, fabric sheeting, wood chips or straw mulch could be used to control problematic plants. These may act as direct physical barriers, temporarily covering the ground or water surface to prevent seeds from settling and establishing. Barriers could also be used to modify environmental conditions to the detriment of problematic species. Shading or opaque screens can limit photosynthesis. In areas where the sun is strong, black plastic placed on the soil/sediment surface can increase temperatures to kill problematic plants and their seeds (a technique known as solarization; Katan & DeVay 1991). Covers can be anchored underwater, if necessary.
Caution: Covers will also affect, and may kill, desirable plant species. Temporary application, when a site is most vulnerable to invasion by problematic plants, could solve this problem. Covers may need to be punctured to allow gas to escape.
For this action, “vegetation” refers to overall or non-target vegetation. Studies that only report responses of target problematic plants have not been summarized.
Related actions: Add surface mulch or Add cover other than mulch, primarily to benefit desirable plants rather than harm problematic plants; Add surface mulch to complement planting; Add cover other than mulch to complement planting.
Katan J. & DeVay J.E. (1991) Soil solarization: historical perspectives, principles, and uses. Pages 23–37 in: J. Katan and J.E. DeVay (eds.) Soil Solarization. Boca Raton, Florida.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled, before-and-after study in 2014–2015 in two lakeshore marshes cleared of yellow flag iris Iris pseudacorus in British Columbia, Canada (Tarasoff et al. 2016) reported that the effect of covering plots on recolonizing vegetation depended on the water level. Statistical significance was not assessed. Initially, all study plots were completely covered by invasive yellow flag iris. This was clipped to ground level. One year later, in the intermittently flooded marsh, covered plots had approximately 7% vegetation cover (yellow flag iris seedlings and broadleaf cattail Typha latifolia; species cover not quantified). In contrast, open plots had 100% cover of yellow flag iris. Meanwhile, in the permanently flooded marsh, both covered and open plots had approximately 5% vegetation cover (yellow flag iris seedlings and broadleaf cattail; species cover not quantified). Methods: Nine pairs of plots (approximately 1 m2) were established in iris-dominated marshes on the shores of two lakes. In June 2014, yellow flag iris was cut to 0–4 cm above the sediment in all plots. Cuttings were removed. Then, one random plot/pair was covered with an impermeable rubber sheet for 150 days. Vegetation cover was surveyed in July 2015.Study and other actions tested