Restoration of biogeomorphic systems by creating windows of opportunity to support natural establishment processes

Abstract

In degraded landscapes, recolonization by pioneer vegetation is often halted by the presence of persistent environmental stress. When natural expansion does occur, it is commonly due to the momentary alleviation of a key environmental variable previously limiting new growth. Thus, studying the circumstances in which expansion occurs can inspire new restoration techniques, wherein vegetation establishment is provoked by emulating natural events through artificial means. Using the salt-marsh pioneer zone on tidal flats as a biogeomorphic model system, we explore how locally raised sediment bed forms, which are the result of natural (bio)geomorphic processes, enhance seedling establishment in an observational study. We then conduct a manipulative experiment designed to emulate these facilitative conditions in order to enable establishment on an uncolonized tidal flat. Here, we attempt to generate raised growth-promoting sediment bed forms using porous artificial structures. Flume experiments demonstrate how these structures produce a sheltered hydrodynamic environment in which suspended sediment and seeds preferentially settle. The application of these structures in the field led to the formation of stable, raised sediment platforms and the spontaneous recruitment of salt-marsh pioneers in the following growing season. These recruits were composed primarily of the annual pioneering Salicornia genus, with densities of up to 140 individuals/m 2 within the structures, a 60-fold increase over ambient densities. Lower abundances of five other perennial species were found within structures that did not appear elsewhere in the pioneer zone. Furthermore, recruits grew to be on average three times greater in mass inside of the structures than in the neighboring ambient environment. The success of this restoration design may be attributed to the combination of three factors: (1) enhanced seed retention, (2) suppressed mortality, and (3) accelerated growth rates on the elevated surfaces generated by the artificial structures. We argue that restoration approaches similar to the one shown here, wherein the conditions for natural establishment are actively mimicked to promote vegetation development, may serve as promising tools in many biogeomorphic ecosystems, ranging from coastal to arid ecosystems.

Recovering wetland biogeomorphic feedbacks to restore the world’s biotic carbon hotspots

“…Moreover, the same can be achieved when individual small seagrass or marsh grass plants are transplanted within biodegradable structures that temporarily mimic facilitating effects of larger patches, such as suppression of waves and sediment mobility (46,85). Finally, depending on the system, it may also be possible to artificially create a Window of Opportunity with engineering measures to allow natural re-establishment (86).…”

Life cycle informed restoration: Engineering settlement substrate material characteristics and structural complexity for reef formation

“…Beyond bivalves, using seed/propagules in restoration reduces the need for adult transplants that are often used in restoration (Silliman et al., 2015; van Katwijk et al., 2016). Structures can be designed to first trap and protect plant seeds, as lack of seed retention is often limiting establishment on bare intertidal flats or in the riparian zone of fast flowing rivers (Fivash, Temmink, et al, 2021; Wang et al., 2019). Once seeds are trapped, the structures should help to overcome subsequent bottlenecks, by mimicking emergent traits found in patches of adult plants that facilitate juveniles.…”

Facilitating Salt Marsh Restoration: The Importance of Event-Based Bed Level Dynamics and Seasonal Trends in Bed Level Change

“…Similar bed level dynamics at the salt marsh edge suggest that disturbance-decreasing measures at the constructed Marconi salt marsh have been successful in creating sheltered areas to enhance vegetation presence (c.f. Fivash et al, 2021;Gijón Mancheño et al, 2021).…”