Assisted gene flow in the context of large‐scale forest management in California,USA

Abstract

As climate changes, locally adapted tree populations may become maladapted to the sites in which they presently occur. When natural adaptive processes are insufficient for populations to keep pace with changing climate, human-assisted relocation of genotypes (assisted gene flow) may be a useful tool for maintaining forest resilience. While existing empirical evidence provides insight into the potential outcomes and consequences of assisted gene flow, its applicability to large-scale plantings needs to be evaluated. We conducted a test of assisted gene flow in the context of operational postfire restoration plantings in three U.S. Department of Agriculture National Forests in California. Our experimental restoration plantings included seedling provenances representing both the local planting site and lower-elevation provenances that may be adapted to hotter and drier conditions. For the duration of the experiment, the planting sites experienced anomalously hot, dry conditions, offering a window into the potential outcomes of assisted gene flow in a future climate characterized by warmer temperatures and more frequent drought. In most cases, there was no significant difference in seedling growth or survival among provenances. However, in a few cases, lowerelevation provenances performed better than local provenances, suggesting a potential benefit of assisted gene flow as a management response to climate change. Our analyses accounted for spatial variation in shrub cover and detected a consistent and substantial negative association between shrub cover and seedling growth. In addition, our study revealed that the use of operational seed collections that are not geographically precise (and therefore also not climatically precise) can complicate selection of appropriate provenances and lead to unpredictable outcomes. Numerous other risks and uncertainties-including the fact that tree populations are often adapted to local site factors other than climate and that long-term outcomes may differ from short-term observations-complicate evaluations of the potential utility of assisted gene flow.

Can long‐lived species keep pace with climate change? Evidence of local persistence potential in a widespread conifer

“…However, geographically‐based genetic substructure in some portions of the species’ range as well as complete mortality of non‐local populations in our most water‐limited garden also indicate that some populations may be vulnerable to local maladaptation and extirpation with rapid climate change. Management of conifers is already incorporating assisted migration as part of a conservation strategy for maintaining viable populations of these long‐lived species (e.g., O’Neill et al., 2008; Young et al., 2020), and our results suggest that such efforts may be warranted for vulnerable populations, complementing the natural processes of high gene flow and local adaptation within widespread conifers.…”

Quantifying the capacity for assisted migration to achieve conservation and forestry goals under climate change

“…The poorer conservation performance of the least-fire strategy is likely because grid cells with the least fire usually developed dense canopies (i.e., generally have higher biomass, see Figure S7), which limits light availability for AM target species under the least-fire AM strategies (LFGA and LFDA). The relatively stronger conservation performance of the minimum-distance AM strategies (MDGA and MDDA) is likely because these strategies were more likely to target grid cells that have similar climatic conditions and community composition to the donor location of target species, which are likely to fit their growth requirement better (Young et al, 2020). Another advantage of the minimum-distance AM strategies, which is not captured in our modeling framework, is their potential to reduce risks of introducing invasive pests or pathogens to the recipient community, because relocation is more likely to occur on scales of natural dispersal, hence the relocated species is more likely to have common evolutionary histories with the targeted community (Wallingford et al, 2020; Williams & Dumroese, 2013).…”

“…On longer (across-generation) time scales, tree species might be able to adapt to the changing climate via evolution (Alberto et al, 2013). Part of this evolution depends on locally-adapted genes moving in space, which raises the consideration of assisted gene flow (movement of locally-adapted genes within species ranges) in addition to assisted migration as a management strategy for dispersal-limited species (Aitken & Bemmels, 2016; Young et al, 2020). To explore assisted gene flow using our framework, future studies could include evolutionary dynamics (dynamics of genotypes and corresponding phenotypes for each species) analogous to Kelly & Phillips (2019).…”

Global climate change, diet, and the complex relationship between human host and microbiome: Towards an integrated picture

“…Similar dynamics have been associated with "assisted gene flow," a practice by which suitable genotypes are relocated to help local populations to keep pace with climate change. [131] This relocation of nonlocal genotypes may result in outbreeding depression, which reduces a population's mean fitness relative to the parental population. [132,133] However, this reduction in fitness is most often temporary.…”