Optimization of restoration techniques: In-situ transplantation experiment of an endangered clonal plant species (Typha minima Hoppe)

In the current context of biodiversity erosion, ecological restoration is sometimes the only way to reinforce plant population and preserve them from the deterioration of their natural habitat. Dwarf bulrush (Typha minima Hoppe) is an endangered pioneer clonal plant, which grows in frequently disturbed habitats along Eurasian temperate piedmont rivers. In the Alps, its population has decreased by 85% over the last century and numerous pressures (e.g. river works) continue to threaten its remnants. The main objective of this study is to identify an adapted ecological engineering protocol for field transplantation of T. minima in order to maximize restoration success. Several transplantation experiments were implemented between 2013 and 2016 along a French alpine river, the Isere. Five distinct transplantation protocols were tested by individually varying the following parameters: bank type (redesigned bank and embankment protection), transplantation height above water level (5 levels between +0.45 m and + 1.55 m above the average water level), initial biomass transplanted (high, medium and low), initial plot shape (linear strip or square plots) and species association (without or with Salicaceae or Poaceae). During the first two or three years, several clonal traits relative to the spatial monopolization and colonization abilities of T. minima were monitored and analyzed. Our analysis showed that T. minima's ability to colonize was optimal on natural banks, at medium transplantation heights and in linear strip plots. In addition, spatial monopolization and colonization speed, through both sexual and vegetative reproduction, were maximized with a higher initial biomass. Lastly, species association did not affect the colonization ability of T. minima. Our study provides valuable information for future conservation plans and restoration projects for T. minima.