Create mounds or hollows: brackish/saline swamps
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) to provide suitable conditions for emergent wetland vegetation. The scale of this action falls somewhere between reprofiling/relandscaping (large-scale landscape features, tens of metres wide) and disturbing the soil/sediment 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 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). Depressions might provide sheltered and moist microclimates, in which the first colonizing plants can become established. Large woody debris will release nutrients as it decomposes.
Studies that simply compare vegetation on mounds vs hollows (e.g. Bruland & Richardson 2005) have not been summarized as evidence here, even if those mounds and hollows were deliberately created.
Bruland G.L. & Richardson C.J. (2005) Hydrologic, edaphic, and vegetative responses to microtopographic reestablishment in a restored wetland. Restoration Ecology, 13, 515–523.
Vivian-Smith G. (1997) Microtopographic heterogeneity and floristic diversity in experimental wetland communities. Journal of Ecology, 85, 71–82.
Supporting evidence from individual studies
A study in 2013–2014 in a disused aquaculture pond in South Sulawesi, Indonesia (Oh et al. 2017) reported that approximately seven months after depositing a mound of branches (and releasing mangrove propagules), the mound had been colonized by 29 mangrove tree seedlings. Methods: In November 2013, a 770-m2 pile of branches was added to a disused aquaculture pond to create a raised mound (extending above the range of elevations colonized by mangroves in other ponds). Walls within the wider pond system were breached to improve tidal exchange. In December 2013, >218,000 propagules (of >7 species) were added to the ponds at high tide. Seedlings growing in the pile of branches were counted in June 2014.Study and other actions tested