Introduce fragments of non-woody plants: freshwater wetlands

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Source countries

Key messages

  • Five studies evaluated the effects, on vegetation, of introducing fragments of emergent, non-woody plants to freshwater wetlands. Three studies were in the USA. Two studies were in one marsh in Australia, but used different experimental set-ups.

VEGETATION COMMUNITY

 

VEGETATION ABUNDANCE

  • Overall abundance (2 studies): Two replicated, randomized, paired, controlled, before-and-after studies in a floodplain marsh in Australia found that plots planted with wick grass Hymenachne acutigluma had similar overall vegetation cover to unplanted plots after one year. One of the studies continued for longer, and found that planted plots had greater overall vegetation cover than unplanted plots after three years.
  • Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in a floodplain marsh in Australia found that plots planted with wick grass Hymenachne acutigluma had similar overall sedge/grass cover to unplanted plots after one year.
  • Individual species abundance (4 studies): Four studies quantified the effect of this action on the abundance of individual plant species. For example, of two replicated, randomized, paired, controlled, before-and-after studies in a floodplain marsh in Australia, one found that wick grass Hymenachne acutigluma was more frequent and had greater cover, after 1–3 years, in plots where its runners had been planted than where they had not been planted. The other study reported that wick grass cover was present, with approximately 1% cover, in 5 of 10 plots where its runners had been planted. This study monitored vegetation one year after planting.

VEGETATION STRUCTURE

 

OTHER

  • Germination/emergence (1 study): One replicated, randomized, paired, controlled study in a floodplain marsh in Australia found that planting wick grass Hymenachne acutigluma had no significant effect on the germination rate of invasive mimosa Mimosa pigra over three years.
  • Survival (5 studies): Two replicated studies planted sedge Carex fragments into freshwater wetlands in the USA. One study reported 38–79% survival of planted tubers over one growing season, whilst the other study reported 0–73% survival of planted rhizomes after 1–9 months. One replicated study in a tidal freshwater marsh in the USA reported that 6–31% of planted California bulrush Schoenoplectus californicus rhizomes had produced shoots after three months. For two other species, all planted rhizomes died within three months. Two replicated, randomized, paired, controlled, before-and-after studies in a floodplain marsh in Australia reported absence of planted wick grass Hymenachne acutigluma from 17–50% of plots after one year.

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

  1. A replicated study in 1991–1992 in an excavated freshwater wetland in Pennsylvania, USA (Stauffer & Brooks 1997) reported that 38–79% of planted lurid sedge Carex lurida tubers survived over one growing season. Survival was 79% in plots with added leaf litter, but only 38% in plots without added leaf litter (see Action: Add below-ground organic matter before/after planting). Methods: In October 1991, lurid sedge tubers (number not reported) were transplanted from one wetland into a nearby recently excavated wetland (formerly cropland). The tubers were planted 10 cm deep into eight 6 x 6 m plots, then watered. Leaf litter was mixed into the surface of four plots before planting. Survival was last recorded in August 1992.

    Study and other actions tested
  2. A replicated study in 1994–1996 in three experimental freshwater wetlands in Minnesota, USA (Yetka & Galatowitsch 1999) reported 0–73% survival of planted sedge Carex spp. rhizomes over 1–9 months, and that the abundance of one species increased over two growing seasons. Statistical significance was not assessed. Overall survival rates were 27% for lake sedge Carex lacustris and 4% for tussock sedge Carex stricta. However, for each species, survival varied with planting season, water regime and elevation. For example, 73% of lake sedge rhizomes were alive in June after planting in spring under a rising water regime. This dropped to 38% for spring-planted rhizomes under a falling water regime, and <2% for autumn-planted rhizomes under any water regime. The study also monitored the abundance of lake sedge in plots planted with that species. After one growing season, there were 14 shoots/m2 and 80 g/m2 above-ground biomass. After two growing seasons, there were 36–39 shoots/m2 and 236–497 g/m2 above-ground biomass (averaged across implementation options). Methods: Field-collected sedge rhizomes were trimmed (to 10 cm length; roots removed) and planted (2–4 cm deep) into three adjacent wetlands. There were 56 rhizomes for each combination of species, season (autumn 1994 or spring 1995), water regime (stable, low over winter/rising through growing season, high over winter/falling through growing season) and elevation (six levels). Survival (presence of living shoots) was monitored in June 1995. Shoots were counted in October 1995 and 1996. Biomass was cut, dried and weighed in August 1995 and 1996.

    Study and other actions tested
  3. A replicated, randomized, paired, controlled, before-and-after study in 1999–2000 in a floodplain marsh in the Northern Territory, Australia (Paynter 2004) reported that 50% of plots planted with wick grass Hymenachne acutigluma runners contained wick grass after one year, but found that planting had no significant effect on vegetation cover. After one year, wick grass was present in 5 of 10 planted plots (at approximately 1% cover). Presence in unplanted plots was not clearly reported. Planted and unplanted plots had statistically similar cover of vegetation overall (approximately 90%), sedges and grasses overall (approximately 12%) and invasive mimosa Mimosa pigra (approximately 10%). Before planting, plots destined for each treatment had statistically similar cover of vegetation (<1%), dead mimosa stumps (15%) and bare mud (85%). Methods: In November 1999 (at the end of the dry season), fifteen 5 x 5 m plots were established (in five sets of three) on a degraded floodplain marsh. Mimosa had recently been cleared from the marsh using herbicide, crushing and burning. Then, 10 plots (two random plots/set) were planted with locally-collected wick grass runners (36 or 121 runners/plot). The other five plots (one random plot/set) were not planted. Vegetation was surveyed immediately before planting and approximately one year after (October 2000). This study used the same marsh as (4), but a different experimental set-up.

    Study and other actions tested
  4. A replicated, randomized, paired, controlled, before-and-after study in 2000–2003 in a floodplain marsh in the Northern Territory, Australia (Paynter 2004) found that plots planted with wick grass Hymenachne acutigluma runners contained more wick grass than unplanted plots over three years and had greater vegetation cover after three years, but supported similar mimosa germination rates. Immediately before planting, these plots had no vegetation cover. After one year, wick grass was more frequent and had greater cover in planted plots (present in 10 of 12 plots at 6% cover) than unplanted plots (present in 2 of 12 plots at <1% cover). Overall vegetation cover was statistically similar in planted plots (60%) and unplanted plots (66%). After three years, planted plots still had greater wick grass cover (24%) than unplanted plots (<2%) and now had greater overall vegetation cover (68%) than unplanted plots (50%). Finally, germination rates of invasive mimosa Mimosa pigra did not significantly differ between planted and unplanted plots in any year (see original paper). Methods: In July–September 2000 (at the end of the wet season), twelve pairs of 7.5 x 7.5 m plots were established on a degraded floodplain marsh. Mimosa had recently been cleared from the marsh using herbicide, crushing and burning. Then, one plot in each pair was planted with 16 locally-collected wick grass runners. The other plots were not planted. Vegetation was surveyed immediately before planting and in the following three dry seasons (July–October 2001–2003). This study used the same marsh as (3), but a different experimental set-up.

    Study and other actions tested
  5. A replicated study in 2010–2012 in a tidal freshwater marsh in California, USA (Sloey et al. 2015) reported that all planted sedge and reed rhizomes died for two of three species, but that they survived and spread for the other species. Three months after planting, all rhizomes of hardstem bulrush Schoenoplectus acutus and broadleaf cattail Typha latifolia had died (i.e. none had produced shoots). In contrast, California bulrush Schoenoplectus californicus rhizomes were alive in all four areas where they were planted, with 6–31% of individual rhizomes having produced shoots. After 24 months, California bulrush was still present in all four areas and had spread to cover 4–23 m2/site. Methods: In June 2010, one hundred and ninety two rhizomes were planted into four areas within the marsh (16 rhizomes/species/area). Survival was quantified in September 2010. Cover was measured until June 2012. The study areas were flooded for 82–99% of each summer.

    Study and other actions tested
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.

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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