Disturb soil/sediment surface before planting non-woody plants: brackish/saline wetlands
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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.
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
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