Variation in seed mass and seed fill in Western US plants, traits important for habitat restoration

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Leah Prescott, Biology, University of Nevada, Reno, Reno, NV, Fred Edwards, Bureau of Land Management, Peggy Olwell, Bureau of Land Management and Plant Conservation Alliance and Elizabeth A. Leger, Department of Biology, University of Nevada - Reno, Reno, NV

Background/Question/Methods
Native plant communities across the western United States have experienced serious degradation, invasion, and population decline. Land managers’ ability to successfully restore these communities depends on the availability of appropriate, locally adapted seed. Therefore, identifying and targeting natural populations for seed collection is critical for developing and maintaining a steady seed supply. Seed mass is highly relevant to restoration, because it has been found to be an important characteristic for predicting seedling establishment (Leger, Atwater, and James 2019), yet the relationship between seed mass, embryo development, and maternal environment is still unresolved.
This research uses data collected by the Seeds of Success program (blm.gov/sos) to address the following questions for 13,334 populations of 2,665 species collected across western states from 2000-2019: 1) How do environmental and climatic variables influence seed mass and fill? 2) How has mean seed mass changed over time? 3) How do life history characteristics influence the amount of variation in seed size?
Results/Conclusions
We found that across species, there is a strong relationship between annual available water capacity and seed fill, as well as 30-year normal precipitation and seed mass. While there is much variation in seed mass among collections and over time, in general, seed mass appears unchanged over the last two decades, and within a calendar year, follows a normal curve, possibly due to resource availability. These results indicate that both genetic factors and environmental variables contribute to the development of these important plant traits.
These results have implications for applied science and conservation. Seed collecting teams may need to consider soil variables more closely when estimating how many seeds to collect each year. If teams are collecting in areas with lower available water capacity, increasing the number of seeds collected may yield a higher filled seed lot. Although mean seed size does not appear to have changed over time, anthropogenic climate change may still be influencing plant reproductive output. Additional research is necessary to determine if the total number of seeds produced is declining among native plant communities.