Seeing right through it: X-ray analyses of L. spikelets reveal seed production patterns across a wide spatial distribution.

Coastal dunes represent globally important ecosystems heavily impacted by human activities and requiring nature-based restoration solutions. Plants with dune building and stabilizing traits typically represent the dominant vegetation. Such species can have ranges extending >1000 km albeit in fragmented populations. Seeds of dominant species are in high demand for establishing dune restoration planting material, but supply may be limited given variable seed production across their range. The broad geographic occurrence of such species presents opportunities to question the influence of various abiotic and biotic gradients on seed production while providing answers that can inform seed-based restoration efforts. We modelled seed production of over a 2-year period from 17 populations spread over 12° of latitude (ca. 1357 km). Panicle density and dune type were strong predictors of normal seed production and number of seeds per spikelet. Interactions between eco-spatial zonation or haplotype and collection year were evident regarding the number of seeds per spikelets, but the effects were mostly negligible. Likewise, latitude and drought intensity yielded small-to-medium effects on the number of seeds per spikelet. The proportion of abnormal seeds was not unusual for wild species, and panicle density was not a strong predictor of this response. We hypothesize that a threshold panicle density exists below which seed production decreases substantially. Practitioners should assess relative panicle density at donor sites when creating seed collection plans and may consider sites with low panicle density as priority augmentation targets.