Land management is increasingly focusing on sustaining ecosystem processes and services and building resistance and resilience in natural forests. While areas that are highly impacted attract the most attention, and therefore appear to be a restoration priority, they do not offer the best locations to efficiently allocate limited resources to achieve sustained conservation of threatened tree population and ecosystems. The Regeneration for Resilience (R4R) framework was developed to guide management decisions to offer the best likelihood of success in positioning a threatened tree species to support self-sustaining populations over multiple generations and avoid species extinction.
The R4R framework guides management decisions to offer the best likelihood of success in positioning threatened tree species to support self-sustaining populations over multiple generations in the presence of the nonnative invader by (1) increasing tree population size to offset invader-caused tree mortality, (2) strategically deploying pest-resistant tree seedlings in habitats that enable the expression and durability of the resistance traits to reduce future mortality and facilitate tree population sustainability and recovery, and (3) maintain tree species genetic diversity, adaptive capacity, and population connectivity. This approach will position forests for accelerated adaptation to new conditions while sustaining viable population sizes will promote resilience. Prioritizing areas of lower risk for management may lead to local extinctions of the tree species in some highly impacted areas; their loss may be unavoidable, even with intervention, and may be the cost of preventing species-wide extinction with limited time and resources.
The research demonstrates the application of the framework to the white pine blister rust pathosystem throughout North America including areas that have been invaded for decades as well as the threatened natural forests of the southern Rockies, Great Basin, Southwest, and Mexico.
The key factors that determine the outcome of the invasive pest-tree interaction may vary due to differences in invasive species’ dispersal, risk factors and preferences, and tree traits, but the R4R decision process can be applied widely. It recommends to: (1) take the long view with an evolutionary approach across multiple generations to build and sustain species and forest resilience, (2) prioritize areas for intervention that have the highest probability of success to promote self-sustaining tree populations in the presence of the invader, (3) avoid heavily impacted areas that will require large investments and offer low probability of restoration success, and (4) time interventions early in the invasion process to better utilize natural ecosystem processes to attain conservation goals.
Discussions include applications to whitebark, limber, bristlecone, and southwestern white pines threatened by the non-native pathogen Cronartium ribicola that causes the lethal disease white pine blister rust.