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

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.