Add below-ground organic matter before/after planting trees/shrubs: brackish/saline wetlands
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
This section involves adding organic matter (i.e. remains or waste products of living organisms) below the ground surface (i.e. by mixing it into the sediment, or placing it into holes) to areas planted with marsh or swamp vegetation.
Organic matter could increase the initial survival and/or growth rate of introduced plants, helping them to establish. Organic matter directly supplies nutrients to growing plants, supplies carbon and energy to soil organisms (which can indirectly increase nutrient availability), helps bind the soil together, retains water during dry periods, and mediates soil temperature (Donahue et al. 1983; Weil & Brady 2016). However, the soil organic matter content of wetland soils may be reduced by disturbance. For example, drainage allows oxygen into the soil, whilst reprofiling removes surface layers rich in organic matter (Bruland et al. 2006). Substances than can be used to add organic matter to wetland soils include compost, sewage sludge, wood chips and seaweed extract.
Note that many studies testing this action do not separate the effects of adding organic matter and disturbing the soil/sediment. We have included such studies, as well as those that do separate the effects of these actions with appropriate controls.
Bruland G.L., Richardson C.J. & Whalen S.C. (2006) Spatial variability of denitrification potential and related soil properties in created, restored, and paired natural wetlands. Wetlands, 26, 1042–1056.
Donahue R.L., Shickluna J.C. & Robertson L.S. (1983) Soils: An Introduction to Soils and Plant Growth, Fifth Edition. Prentice-Hall, Englewood Cliffs, NJ, USA.
Weil R.R. & Brady N.C. (2016) The Nature and Properties of Soils, Fifteenth Edition. Pearson, USA.
Supporting evidence from individual studies
A replicated, randomized, controlled study in 2002–2005 in a degraded coastal swamp in southeast Brazil (Zamith & Scarano 2010) reported that adding manure had mixed effects on survival and growth of planted tree seedlings over three years, depending on species, dose and metric. Manure increased survival for one of five planted species (manure: 77–83%; no manure: 67%) but reduced survival for two species (manure: 57–83%; no manure: 77–93%). For the other two species, manure either increased or reduced survival depending on the dose. Statistical significance of these survival results was not assessed. Manure had no significant effect on seedling growth in 20 of 30 comparisons. It did increase diameter growth in 4 of 10 comparisons, height growth in 4 of 10 comparisons, and canopy area growth in 2 of 10 comparisons (see original paper for data). However, manure did not consistently increase growth, across all metrics and doses, for any species. Methods: In May 2002, ninety seedlings of each of five tree species were planted, 1.5 m apart, into a degraded coastal swamp. Thirty seedlings/species received each manure treatment: 30 L/seedling, 15 L/seedling or none. The study does not report further details of the manure or application. Invasive trees and grasses were removed from the swamp before planting. The survival of each seedling was monitored until May 2005. The diameter, height and canopy area of each seedling were measured in August 2002 and August 2005.Study and other actions tested