Interannual variation in provenance performance under drought in a Great Basin rangeland

Authors: AOYAMA, LINA - University Of Oregon; SILVA, LUCAS - University Of Oregon; Copeland, Stella; O'Connor, Rory; HALLETT, LAUREN - University Of Oregon

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2024
Publication Date: 6/19/2024
Citation: Aoyama, L., Silva, L., Copeland, S.M., O'Connor, R.C., Hallett, L.M. 2024. Interannual variation in provenance performance under drought in a Great Basin rangeland. Restoration Ecology. 33(2). Article e14210. https://doi.org/10.1111/rec.14210.
DOI: https://doi.org/10.1111/rec.14210

Interpretive Summary: Rapid climate change challenges the idea of using local seed sources because these sources may not be able to survive under future climate conditions, particularly climate extremes like drought. We tested the potential for seed sources adapted to warmer climates to increase restoration success under drought conditions in the northern Great Basin with a common native grass, bottlebrush squirreltail. We used a drought experiment with various rainfall exclusion rates and six seed sources of different climate origins. Some seeds from warmer and drier climates had higher survival, however, this pattern was associated with different strategies to overcome drought and freezing. Seed sources had higher emergence rates because they germinated later and avoided early season freezing events. Survival was higher for sources with drought tolerance mechanisms like high water use efficiency. These results suggest that selecting seed sources adapted to warmer and drier climates can lead to higher restoration success under drought conditions, and likely into the future with climate change. Because seed sources varied in their strategies to cope with drought and other weather stressors, mixes with multiple seed sources might lead to the most successful outcomes.

Technical Abstract: Rapid climate change poses a fundamental challenge to seed sourcing in restoration. While local provenancing is a common practice in restoration, local seeds may not survive or persist under future climate conditions. Alternative provenancing strategies, such as climate-adjusted provenancing, that mix local seeds with non-local seeds aim to increase the buffering capacity of restored populations. We hypothesized that seeds sourced from warmer and drier sites have higher seedling performance under drought than seeds sourced from cooler and wetter sites. We conducted a common garden experiment in a Great Basin rangeland where more frequent, severe drought events are expected to increase in the future. We sourced Bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey) seeds from six locations along an aridity gradient and sowed them under three rainfall scenarios: ambient, moderate drought, and severe drought. We found strong interannual variation in seedling recruitment. In 1'year, some provenances from warmer/drier sites had high emergence and subsequent seedling survival under moderate drought. In another, emergence was low across provenances and rainfall treatments. Two provenances that survived 2'years of moderate drought had divergent seedling traits. Specifically, one had a high germination temperature optimum and high water-use efficiency, such that it likely avoided freezing and resisted drought, while another had a low germination temperature optimum and low water-use efficiency, such that it likely tolerated freezing and escaped drought. We highlight that understanding these differences in recruitment and stress coping strategies across provenances is important for creating climate-adaptive seed mixes in anticipation of future climate conditions.