Introducing desirable patches to initiate ecosystem transitions and accelerate ecosystem restoration

Abstract

Meeting restoration targets may require active strategies to accelerate natural regeneration rates or overcome the resilience associated with degraded ecosystem states. Introducing desired ecosystem patches in degraded landscapes constitutes a promising active restoration strategy, with various mechanisms potentially causing these patches to become foci from which desired species can re‐establish throughout the landscape. This study considers three mechanisms previously identified as potential drivers of introduced patch dynamics: autocatalytic nucleation, directed dispersal, and resource concentration. These mechanisms reflect qualitatively different positive feedbacks. We developed an ecological model framework that compared how the occurrence of each mechanism was reflected in spatio‐temporal patch dynamics. We then analyzed the implications of these relationships for optimal restoration design. We found that patch expansion accelerated over time when driven by the autocatalytic nucleation mechanism, while patch expansion driven by the directed dispersal or resource concentration mechanisms decelerated over time. Additionally, when driven by autocatalytic nucleation, patch expansion was independent of patch position in the landscape. However, the proximity of other patches affected patch expansion either positively or negatively when driven by directed dispersal or resource concentration. For autocatalytic nucleation, introducing many small patches was a favorable strategy, provided that each individual patch exceeded a critical patch size. Introducing a single patch or a few large patches was the most effective restoration strategy to initiate the directed dispersal mechanism. Introducing many small patches was the most effective strategy for reaching restored ecosystem states driven by a resource concentration mechanism. Our model results suggest that introducing desirable patches can substantially accelerate ecosystem restoration, or even induce a critical transition from an otherwise stable degraded state toward a desired ecosystem state. However, the potential of this type of restoration strategy for a particular ecosystem may strongly depend on the mechanism driving patch dynamics. In turn, which mechanism drives patch dynamics may affect the optimal spatial design of an active restoration strategy. Each of the three mechanisms considered reflects distinct spatio‐temporal patch dynamics, providing novel opportunities for empirically identifying key mechanisms, and restoration designs that introduce desired patches in degraded landscapes according to these patch dynamics.

Jump‐starting podocarp forest establishment in a wetland dominated by invasive willow

“…However, because these wetlands have made a critical transition to an alternative stable willow-dominated state, jumpstarting successful establishment over larger areas is likely to require on-going adaptive management to reduce seed predation, increase dispersal, and seedling establishment success, as well as reduce initial shading and competition from willows. Thus, the process we propose differs from applied nucleation or directed dispersal approaches (Holl et al 2020;Michaels et al 2020;Eppinga et al 2023) in requiring an extended period of on-going management intervention before fully autogenic processes can take-over. However, once set in motion this process is likely to be able to sustain itself for many centuries given the longevity of established podocarp trees (average 560-980 years; Ogden & Stewart 1995).…”

“…"Jump-starting" has previously been proposed in relation to reestablishing active peat formation in degraded peatlands (Kareksela et al 2015), initiating forest succession in persistent exotic grasslands (Yelenik 2017), and restoring coastal mangrove and salt marsh wetlands (Yando et al 2019). Our approach to "jump-start" swamp forest restoration, involving establishment of "islands" of emergent podocarps, has similarities with applied nucleation and directed dispersal approaches (Holl et al 2020;Michaels et al 2020;Eppinga et al 2023). However, our approach differs in that we assume, due to the rapid establishment and regrowth capabilities of willow, that autogenic regeneration processes will need to be augmented by active management interventions to enable survival and growth of light-demanding Kahikatea saplings to sufficient height to emerge above the willow canopy ($8 m).…”