Introduce tree/shrub seeds or propagules: freshwater wetlands

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Two studies evaluated the effects, on vegetation, of introducing seeds or propagules of trees/shrubs to freshwater wetlands. One study was in Australia and one study was in the USA.




  • Tree/shrub abundance (1 study): One study in a floodplain swamp clearing in the USA simply reported the number of tree seedlings present within three years of sowing tree seeds. There were no seedlings of two of the five sown species.




  • Germination/emergence (1 study): One replicated study in Australia reported 0–18% germination of tree/shrub seeds sown into a wet meadow, depending on the species and whether vegetation was cleared before sowing.
  • Survival (1 study): The same study reported 0% survival, after 8 months, of seedlings that had germinated from sown tree/shrub seeds.

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 1995 in a wet meadow in New South Wales, Australia (de Jong 2000) reported 0–18% germination of sown tree/shrub seeds after two months, depending on the species and whether vegetation was cleared before sowing, but 0% survival after eight months. In plots that had been cleared of vegetation before sowing, all five sown species germinated. The number of seedlings present after two months was 1–18% of the number of seeds sown. In plots that had not been cleared of vegetation, only two of five species germinated. For these species, the number of seedlings present after two months was ≤1% of the number of seeds sown. After eight months, after prolonged saturation or flooding, no seedlings were present in any plot. Methods: In January–February 1995, seeds of five tree/shrub species present in local wetlands were sown on to a wet meadow, with the aim of restoring a swamp. For each species, three hundred 25 x 25 cm plots were sown with approximately 50 seeds. Of the 300 plots, 200 were cleared of vegetation before sowing. Half of the plots/species were higher (and drier) than the others. Seedlings of the planted species were counted in every plot after two and eight months.

    Study and other actions tested
  2. A study in 2006–2009 in a floodplain swamp restoration site in Wisconsin, USA (Thomsen et al. 2012) reported that seedlings of only three of five sown tree species were present. Neither black ash Fraxinus nigra nor river birch Betula nigra seedlings were present in the site within three years of sowing seeds. Seedlings of the other three sown species were present (green ash Fraxinus pennsylvanica, American elm Ulmus americana and silver maple Acer saccharinum; abundance data reported graphically) but the study does not distinguish seedlings originating from sown vs naturally arriving seeds. Methods: Between November 2006 and May 2009, seeds of five tree species (numbers not clearly reported) were broadcast across 16 plots in a floodplain swamp restoration site (a clearing created by a storm). All plots had been cleared of invasive reed canarygrass Phalaris arundinacea and disked in November 2006 (before first sowing). Herbicide was then applied regularly through to November 2008). Tree seedlings were counted in August 2007–2009.

    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.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

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

What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust