Climate Change, Weather, and Geography Shape Seed Mass Variation and Decline Across Western North America

Area of Science:

• Ecology
• Botany
• Climate Change Biology

Background:

• Seed mass is a critical plant reproductive trait influenced by environmental factors.
• Observed climate change-driven size changes in organisms prompt investigation into seed mass responses.
• Understanding seed mass dynamics is vital for predicting plant adaptation and ecosystem stability.

Purpose of the Study:

• To investigate temporal, geographic, and environmental patterns influencing seed mass across numerous native plant species.
• To determine if climate change is affecting seed mass in native plants of the western United States.
• To explore phylogenetic signals and environmental drivers of seed mass variation.

Main Methods:

• Utilized a large dataset from the "Seeds of Success" national program, encompassing over 13,000 locations and 2092 native plant species.
• Analyzed seed mass variation in relation to climate change metrics, geographic location, and temporal trends over two decades.
• Employed phylogenetic comparative methods to assess the conservation of mean seed mass and seed mass variation.

Main Results:

• Over 42% of species showed climate change-influenced seed mass, indicating potential adaptation or maladaptation.
• Mean seed mass was phylogenetically conserved, but variation showed little phylogenetic signal.
• Seed mass generally declined over time (0.012 mg/year average) and was larger in warmer, wetter areas, with C3 and C4 species responding differently to climate variables.
• Species with higher seed mass variation occurred in areas with wider temperature ranges, northern latitudes, and longer growing seasons.

Conclusions:

• Plant seed mass is responsive to climate change, exhibiting both adaptive and potentially maladaptive shifts.
• Observed changes in seed mass, particularly the decline in some species and differential responses of C3/C4 plants, warrant further investigation.
• Continued native seed collection is essential for conservation and restoration, given the dynamic nature of plant reproductive strategies under climate change.