Using metapopulation models to assess species conservation-ecosystem restoration trade-offs

Ecological restoration is needed to counter global-scale ecosystem degradation, but can conflict with endangered species conservation when restoration impacts habitat quality. In such cases, prioritizing long-vacant patches for restoration is an intuitively appealing strategy for minimizing the effects on endangered species. Metapopulation models grounded in empirical data potentially provide a rigorous framework for developing theoretical “patch vacancy thresholds” (i.e., duration of vacancy required before implementing restoration) and assessing the implications of such criteria for restoration objectives. We develop such a model for spotted owls (Strix occidentalis), which embody the species-ecosystem dilemma given their preference for closed-canopy forests that are also susceptible to severe fire and drought and hence the center of debates about forest restoration intended to reduce fire and drought risk. We leveraged a >20-year territory occupancy dataset to parameterize a Stochastic Patch Occupancy Model (SPOM) to assess relative risk to a metapopulation of owls in California under alternative conservation guidelines, including a range of vacancy thresholds. Territories with greater amounts of owl habitat were more likely to be recolonized and less likely to go extinct. Importantly, the probability of a vacant owl territory becoming recolonized declined as length of vacancy increased; territories vacant for 1 and 10 years had annual recolonization probabilities of 0.34 and 0.06, respectively. Based on our SPOM, projected territory occupancy rates declined as the vacancy threshold decreased and as habitat within territories was impacted by restoration. However, more liberal territory vacancy thresholds were projected to increase the proportion of territories (and thus landscape) that could be restored and that restored conditions could be maintained with repeated treatments. Reintroducing natural disturbance regimes, which eliminated the need for repeated treatments, was projected to reduce risk to owls, particularly with relaxed vacancy thresholds. We provide a simple, yet novel, metapopulation framework for quantifying how alternative conservation guidelines might impact owl occupancy and influence forest restoration guidelines. Similar analyses could facilitate restoration efforts in other systems by more explicitly quantifying tradeoffs between species-ecosystem objectives.