CONTEXT
Rapidly changing environments combined with increasing global restoration initiatives require improved seed sourcing strategies for native revegetation. Sourcing seed from local populations (local provenancing) has been the long-standing default for native revegetation for numerous eco-evolutionary reasons including local adaptation and species co-evolution. However, the evidence-base has shifted, revealing risks for both non-local and local provenancing in changing environments. As alternative strategies gain interest, we argue for effective decision-making that weighs the risks of changing and not changing seed sourcing strategies in a changing environment that transcends a default position and the polarising local vs. non-local debate.
Revegetation aims to restore ecosystems by reintroducing biodiverse plant communities that support key services and functions that humans rely upon (e.g., water filtration, carbon sequestration). How to best source seed to achieve resilient, long-term, self-sustaining plant populations has received substantial attention (Jones 2013; Proberet al. 2015; Bucharova 2017). Local provenancing targets adaptations that have evolved to maintain a fitness advantage to the local environment (Leimu & Fischer 2008; Hereford 2009), enhancing the establishment and long-term success of the revegetation plantings. Local provenancing also maintains important co-evolved biotic interactions such as plant-fungi and plant-pollinator relationships (Grady et al. 2017; Bucharova et al. 2021) whilst avoiding negative genetic effects of introducing non-local genotypes, such as outbreeding depression and swamping of local genotypes (Byrne et al. 2011; Bucharova et al. 2021). For these reasons, and others, local provenancing has been the long-standing default strategy for ecosystem restoration.
However, environmental change and associated impacts on plant fitness have raised concerns for the long-term viability of the default use of local provenancing. Changes to local environmental conditions (e.g., direct and indirect effects anthropogenic change, such as climate change and land-use) may decouple adaptation and fitness, resulting in greater risk of local seed being maladapted (Etterson & Shaw 2001; Anderson 2016). For example, seed sourced from small, fragmented local remnants can result in genetically depauperate, inbred progeny (Breed et al. 2015; Aguilar et al. 2019) that are less fit and more vulnerable to climate change (Nickolas et al. 2019). Thus, the perception that local provenancing is a ‘safe’ option may be misleading in a rapidly changing world (Frankham et al. 2011; Ralls et al. 2018).
Proposed alternative provenancing strategies that mix seed from local and non-local provenances aim to address these environmental change-induced issues by increasing genetic diversity or introducing putatively pre-adapted genotypes that enhance resilience and long-term adaptability to environmental change. Though there is a shift in perceptions toward these alternative strategies (e.g Australia, Hancocket al. 2023), concerns remain about the risk of using non-local provenances, with some sectors continuing to recommend only local provenancing (Hancock & Encinas-Viso 2021). Such hesitance possibly reflects a paucity of evidence on outcomes of using non-local provenances (Twardek et al. 2023). While risks associated with introducing non-local provenances in a revegetation context are valid, equally valid are the risks of using local provenances under current and future conditions.
Here, we argue that the risks of changing and not changing the local provenancing default in a changing environment needs to be weighed when determining the most appropriate provenancing strategy. We focus on the eco-evolutionary risks associated with provenance choice, including the short- and long-term fitness of plantings and their resilience and future adaptability, rather than whether provenances are local or non-local per se . We aim to help move the discussion away from a polarised local vs. non-local debate, and towards a risk-based, context-dependent rethinking of how to source seed for revegetation.