Create mounds or hollows before planting non-woody plants: freshwater wetlands

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

Study locations

Key messages

  • Two studies evaluated the effects, on vegetation, of creating mounds or hollows in freshwater wetlands before planting emergent, non-woody plants. Both studies were in the same wetland in the USA, but used different experimental set-ups.

VEGETATION COMMUNITY

 

VEGETATION ABUNDANCE

  • Individual species abundance (2 studies): Two replicated, randomized, paired, controlled studies in a wetland in the USA found that tussock sedge Carex stricta cover was typically similar across plots, after two growing seasons, whether sedges were planted into created mounds or hollows, or planted into flat ground.

VEGETATION STRUCTURE

  • Individual plant size (2 studies): Two replicated, randomized, paired, controlled studies in a wetland in the USA found that planting tussock sedges Carex stricta into created mounds or hollows had no significant effect on their individual biomass, after 1–2 growing seasons, when compared to planting into flat ground.

OTHER

  • Survival (2 studies): Two replicated, randomized, paired, controlled studies in a wetland in the USA found that planting tussock sedge Carex stricta into created mounds or hollows did not improve, and typically reduced, its survival rate compared to planting into flat ground. Survival was monitored after 1–2 growing seasons.
  • Growth (2 studies): The same studies found that planting tussock sedge Carex stricta into created mounds or hollows typically had no significant effect on its growth rate, over 1–2 growing seasons, compared to planting into flat ground.

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, randomized, paired, controlled study in 2012–2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) found that creating mounds before planting tussock sedge Carex stricta did not improve survival rates, and typically had no significant effect on sedge growth, biomass or cover. After two growing seasons, survival rates were lower for sedges planted in mounds than on flat ground in seven of eight comparisons (for which mounds: 27–93%; flat: 100%). There was typically no significant difference between treatments in sedge growth rate (11 of 16 comparisons; see original paper for data). In three of the other five growth rate comparisons, all in the second growing season after planting, sedges grew faster in mounds (0.021–0.028 mm/mm/day) than on flat ground (0.013 mm/mm/day). In most cases, there was also no significant difference between treatments for final above-ground sedge biomass (four of four comparisons, for which mounds: 5–34 g/plant; flat: 7–39 g/plant) and final sedge cover (three of four comparisons, for which mounds: 11–46%; flat: 38–62%). Methods: In spring 2012, thirty 1-m2 plots were established, in six sets of five, in a wetland undergoing restoration. Soil mounds were built in 24 of the plots (five random plots/set). Mounds were either 8 cm tall, 16 cm tall, 16 cm tall with 50% woodchip, or 32 cm tall. The other six plots were left as flat ground. Five nursery-reared tussock sedges were planted into each plot (one plant/mound in plots with mounds) then regularly watered and weeded. Survival and above-ground biomass of planted sedges, and total tussock sedge cover, were surveyed in June–August 2013. Biomass was dried before weighing. Growth rates were calculated from leaf lengths measured in 2012 and 2013. This study used the same site as (2), but a different experimental set-up.

    Study and other actions tested
  2. A replicated, randomized, paired, controlled study in 2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) found that creating mounds or hollows before planting tussock sedge Carex stricta typically had no significant effect on sedge growth, biomass or cover, and reported that creating hollows reduced survival rates. After one growing season, sedges planted in hollows had a lower survival rate (63%) than sedges planted on flat ground (≥90%; data for mounds not reported; statistical significance not assessed). The treatments had no significant effect, compared to planting in flat ground, on sedge growth rate (mounds: 0.026–0.028 mm/mm/day; hollows: 0.032–0.035 mm/mm/day; flat: 0.027–0.035 mm/mm/day), final above-ground sedge biomass (g/plant; data not reported), or final sedge cover (six of six comparisons, for which mounds: 11–38%; hollows: 3–11%; flat: 15%). Methods: In spring 2013, twenty-four 1-m2 plots were established, in six sets of four, in a wetland undergoing restoration. Soil mounds (8 cm tall or 16 cm tall) were built in 12 of the plots (two random plots/set). Square hollows (10 cm deep; 15 cm across) were dug in six of the plots (one random plot/set). The final six plots were left as flat ground. Five nursery-reared tussock sedges were planted into each plot (one plant/mound or hollow where relevant). Survival and above-ground biomass of planted sedges, and total tussock sedge cover, were surveyed in June–August 2013. Biomass was dried before weighing. Growth rates were calculated from leaf lengths measured in 2013. This study used the same site as (1), but a different experimental set-up.

    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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