Create mounds or hollows before planting trees/shrubs: brackish/saline wetlands
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
This action involves creating discrete mounds (e.g. by adding blocks of soil, bundles of sticks, other coarse woody debris) or hollows (e.g. by excavation) before planting marsh or swamp vegetation. The scale of this action falls somewhere between reprofiling/relandscaping (large-scale landscape features, tens of metres wide) and disturbing the ground surface (which may create small scale mounds or hollows, millimetres or a few centimetres wide/deep).
Often, this action aims to mimic the natural microtopography of marshes or swamps, which can be created by sediment accumulation, erosion, tree fall, root growth or animal activity (Vivian-Smith 1997, Bruland & Richardson 2005). Microtopography can increase plant diversity, because the different microclimates or microelevations may support different species (Vivian-Smith 1997). Planting into mounds can be useful if seedlings would otherwise be flooded too deeply or for too long (Zamith & Scarano 2010). Large woody debris will also add nutrients and organic matter to a site as it decomposes.
Studies that examine the effects of planting into existing microtopographic features (e.g. mounds), even if they compare effects between different kinds of features, are not summarized as evidence here (e.g. Raulings et al. 2007; Sleeper & Ficklin 2016).
Related actions: Create mounds or hollows, other than to complement planting; Reprofile/relandscape before planting; Disturb soil/sediment surface before planting without creating discrete mounds and/or hollows.
Bruland G.L. & Richardson C.J. (2005) Hydrologic, edaphic, and vegetative responses to microtopographic reestablishment in a restored wetland. Restoration Ecology, 13, 515–523.
Raulings E.J., Boon P.I., Bailey P.C., Roache M.C., Morris K. & Robinson R. (2007) Rehabilitation of swamp paperbark (Melaleuca ericifolia) wetlands in south-eastern Australia: effects of hydrology, microtopography, plant age and planting technique on the success of community-based revegetation trials. Wetlands Ecology and Management, 15, 175–188.
Sleeper B.E. & Ficklin R.L. (2016) Edaphic and vegetative responses to forested wetland restoration with created microtopography in Arkansas. Ecological Restoration, 34, 117–123.
Vivian-Smith G. (1997) Microtopographic heterogeneity and floristic diversity in experimental wetland communities. Journal of Ecology, 85, 71–82.
Zamith L.R. & Scarano F.R. (2010) Restoration of a coastal swamp forest in southeastern Brazil. Wetlands Ecology and Management, 18, 435–448.
Supporting evidence from individual studies
A replicated, controlled study in 2002–2005 in a degraded coastal swamp in southeast Brazil (Zamith & Scarano 2010) reported that creating mounds before planting tree seedlings had mixed effects on their survival over three years, but typically had no significant effect on growth. Planting into mounds rather than at ground level increased survival for two of five species (mounds: 70–77%; ground level: 57–67%), reduced survival for two species (mounds: 57–67%; ground level: 63–73%) and had no effect on survival of one species (100% in mounds or at ground level). Statistical significance of these survival results was not assessed. In 11 of 15 comparisons, growth rates were statistically similar for seedlings planted in mounds and at ground level. In the other four comparisons, seedlings planted in mounds grew more, or shrunk less, than seedlings planted at ground level (see original paper for data). Methods: In May 2002, sixty seedlings of each of five tree species were planted, 1.5 m apart, into a degraded coastal swamp. Thirty seedlings/species were planted into created mounds (10 cm high). Thirty seedlings/species were planted at ground level. All seedlings received 30 L of manure. Invasive trees and grasses were removed from the swamp before planting. Seedling survival was monitored until May 2005. Seedling diameter, height and canopy area were measured in August 2002 and August 2005.Study and other actions tested