How far to build it before they come? Analyzing the impact of the Field of Dreams hypothesis in bull kelp restoration

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Jorge Arroyo-Esquivel, Department of Mathematics, University of California Davis, Davis, CA; School of Mathematics, University of Costa Rica, San José, Costa Rica, Marissa L. Baskett, Environmental Science and Policy, University of California, Davis, Davis, CA, Meredith McPherson, Department of Ocean Sciences, University of California, Santa Cruz, Santa Cruz, CA and Alan Hastings, Dept. of Environmental Science and Policy, University of California, Davis, Davis, CA

Background/Question/Methods
In restoration ecology, the Field of Dreams Hypothesis states that restoration efforts that create a suitable environment could lead to eventual recovery of the remaining aspects of the ecosystem through natural processes. Natural processes following partial restoration can lead to ecosystem recovery in both terrestrial and aquatic systems. However, understanding the efficacy of a “field of dreams” approach requires comparison of different approaches to partial restoration in terms of spatial, temporal, and ecological scale to what would happen with more comprehensive restoration efforts.
We explore the relative effect of partial restoration and ongoing recovery on restoration efficacy with a dynamical model based on temperate rocky reefs in Northern California. Through the last decade in Northern California, the coverage of bull kelp forests has declined by over 90%, with a shift to urchin-dominated barrens. Bull kelp forests are highly productive and biodiverse ecosystems that support an array of fisheries, which motivates ongoing restoration efforts focused on urchin removal. We analyze our model for both the ability and rate of bull kelp forest recovery under different restoration strategies. We compare the efficacy of a partial restoration approach with a more comprehensive restoration effort by exploring how does the kelp recovery rate changes with varying intensities of urchin removal and kelp outplanting over different time periods and spatial scales.

Results/Conclusions
Our results suggest that, for the case of bull kelp forests, setting more favorable initial conditions for kelp recovery through an enhanced urchin harvesting and kelp outplanting at the start of the restoration project has a bigger impact on the kelp recovery rate than applying restoration efforts through a longer period of time. With respect to the spatial scale of restoration, we found that only kelp reseeding is enhanced by applying efforts at a wider region of the coastline, while the other strategies are not affected. We also found that kelp outplanting is the strategy of those explored that enhances kelp recovery the most in all of the scenarios. These insights will be useful to managers, as we have identified that partial restoration efforts can be significantly more effective when applied across multiple ecological scales in terms of both the ability to and the rate at which the target outcome is achieved.