Under future climate change, plant species are expected to shift their ranges in response to increasing temperatures and altered precipitation patterns. As seeds represent the single opportunity for plants to move, predicting potential range shifts requires an understanding about the relationship between the environment and reproduction. While seed production is clearly important, seed quality is equally as critical and often overlooked. Spring temperatures in particular, during flowering and seed maturation are expected to affect both seed quantity and quality. To quantify how environmental variation affects seed quality and quantity, the reproductive output of red maple (Acer rubrum) was measured along an elevation gradient in the Monongahela National Forest, WV. In spring of 2018, 44 seeding trees were identified, and another 44 non-seeding trees were randomly selected for comparison. A variety of individual-level characteristics were measured for each tree, including canopy volume, tree age, diameter at breast height, stand density, age and basal area increment. Two seed traps were placed under seed-bearing trees to collect samaras and quantify total seed production. From each tree a random subsample of the collected seeds was micro-CT scanned to determine embryo and seed cavity volume, photographed for morphology measurements, and then used for germination trials.
Results/Conclusions
Trees with larger canopy volumes were the most likely to produce seed, and trees experiencing less frost, lower growth in the past 3 years, and in areas with lower stand density produced the most seeds. The likelihood of embryo presence increased with lower growth rates in the past 5 years. And embryos from taller trees, with a lower DBH, and in areas dominated by coniferous, ectomycorrhizal species had larger seeds. Both larger embryo volume and larger overall seed size increased the likelihood of germination. Out of the 662 seeds measured 62% had an embryo present and of those with embryos only 22% germinated. Highlighting the importance of examining seed quality in conjunction with seed quantity. While a direct link with climate was there may be an indirect impact from climate as it impacts stand dynamics and individual characteristics. Understanding factors affecting seed quality as well as quantity will refine our understanding of forest regeneration and species migration, leading to better informed forest management plans and more precise predictions of future forest composition.