Disturb soil/sediment surface before planting non-woody plants: brackish/saline wetlands

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

33%
Certainty

28%
Harms

10%

Calculating overall effectiveness category

Background information and definitions

This action involves shallow disturbance of the top few centimetres of soil/sediment (and any vegetation on it), without permanently removing any soil/sediment. Mechanical disturbance could be carried out by tilling, ploughing, disking or scarifying. It may improve survival or growth of planted vegetation. It can clear potentially competing vegetation, and loosen up the soil to allow roots to penetrate more easily.

Related actions: Remove surface soil/sediment before planting; Bury surface soil/sediment before planting, including by deep ploughing.

Study locations

Key messages

Two studies evaluated the effects, on vegetation, of disturbing the surface of brackish/saline wetlands before planting emergent, non-woody plants. Both studies were in the USA.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Individual plant abundance (1 study): One study quantified the effect of this action on the abundance of individual plant species. The replicated, randomized, paired, controlled study in a salt marsh in the USA found that tilling sediment before planting California cordgrass Spartina foliosa had no significant effect on its biomass or density after two growing seasons, but did reduce its biomass after one growing season.

VEGETATION STRUCTURE

Height (1 study): One replicated, randomized, paired, controlled study in a salt marsh in the USA found that tilling sediment before planting California cordgrass Spartina foliosa had no significant effect on its height after 1–2 growing seasons.
Individual plant size (1 study): One replicated, randomized, paired, controlled study on estuarine sediment in the USA found that the average size of planted salt marsh plants was similar, after 1–2 years, in tilled and untilled plots. Size was reported as an index incorporating plant height and lateral extent.

OTHER

Survival (1 study): One replicated, randomized, paired, controlled study on estuarine sediment in the USA found that survival rates of planted salt marsh plants were similar, over 1–2 years, in tilled and untilled plots.

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, paired, controlled study in 1990–1991 in a recently excavated estuarine salt marsh in California, USA (Gibson et al. 1994) found that tilling plots before planting California cordgrass Spartina foliosa had no significant effect on cordgrass biomass, stem density or plant height after two growing seasons. At this time, there was no significant difference between treatments in above-ground cordgrass biomass (tilled: 100 g/m²; untilled: 220 g/m²), cordgrass density (tilled: 30 stems/m²; untilled: 50 stems/m²) or average cordgrass height (data not reported). The same was true for density and height after one growing season, whilst cordgrass biomass was significantly lower in tilled plots (30 g/m²) than untilled plots (60 g/m²). Methods: In February 1990, four pairs of 5-m² plots were prepared alongside a tidal creek in a recently excavated salt marsh. In each pair, one random plot was tilled to 15 cm depth. The other plots were left undisturbed. In March 1990, each plot was planted with cordgrass plants from ten 4-L pots. California cordgrass stems were counted and measured until October 1991. Dry biomass was estimated from heights.
Study and other actions tested
Referenced paper
Gibson K.D., Zedler J.B. & Langis R. (1994) Limited response of cordgrass (Spartina foliosa) to soil amendments in a constructed marsh. Ecological Applications, 4, 757-767.
A replicated, randomized, paired, controlled study in 2000–2002 in an estuary in California, USA (O’Brien & Zedler 2006) found that tilling plots before planting salt marsh plants typically had no significant effect on their survival or size. Over the first year after initial planting, dead plants were replaced by stock plants of a similar age. The number of replacements needed was statistically similar in tilled plots (9.1 replacements/plot) and undisturbed plots (9.7 replacements/plot). Over the second year of the study, the treatments supported a similar average number of surviving plants (tilled: 2.9; undisturbed: 2.8 survivors/plot) and a similar survival rate under each treatment for five of five planted species (tilled: 31–72%; undisturbed: 19–86%). Across both years, surviving plants were typically a similar size in tilled and undisturbed plots (data reported as an index combining height and lateral extent). This was true in four of four comparisons of the average size of plants per plot, and 9 of 10 comparisons of the average size of individual species. Methods: In January 2000, seventy-two 2.24-m² plots were established (in 6 sets of 12) on intertidal sediment excavated earlier that winter. Half of the plots (six random plots/set) were rototilled to 30 cm depth. The other plots were left undisturbed. In December 2000, five greenhouse-reared plants (each a different species) were planted into each plot. Colonizing vegetation was removed until October 2001. Dead planted vegetation was replaced until December 2001 to maintain 36 plants/species/soil treatment. Survival, height and lateral spread of planted vegetation were recorded in August 2002.
Study and other actions tested
Referenced paper
O’Brien E.L., & Zedler J.B. (2006) Accelerating the restoration of vegetation in a southern California salt marsh. Wetlands Ecology and Management, 14, 269-286.

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
Add lime or similar chemicals before/after planting trees/shrubs: brackish/saline wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link
Add below-ground organic matter before/after planting trees/shrubs: brackish/saline wetlands Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Disturb soil/sediment surface before planting non-woody plants: freshwater wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link