Seedling shuffle: Climate warming reshapes plant communities by changing the order of seed germination

Kirtland, OH — Our world is warming, and how exactly that will affect our ecosystems is a critical question. As the climate shifts, plants and animals are already responding in some obvious ways—like your daffodils blooming a bit earlier each spring—but the finer details are still unfolding. This timing of natural events, known as phenology, is changing across species and ecosystems as the climate warms, with potentially important consequences. 

For instance, the timing of when seeds germinate and seedlings emerge in spring can affect not only individual species but entire communities. Some species may be responsive to warmer spring temperatures, germinating earlier in the year, while other species may not be as flexible. A new study from Holden Forests & Gardens reveals that these shifts in germination timing can give the more responsive plants an advantage, ultimately altering plant communities and the ecosystems that depend on them.

Published in the journal Ecology, the new research explores how warming-induced changes in germination timing alters the order in which plant species establish themselves, and how that, in turn, affects how big they can grow (a common measure in ecology of how well plants are faring against their competitors). This shift in “assembly order” could have a lasting impact on plant community composition, with important implications for ecosystem function. Research specialist Emma Dawson-Glass, in the Stuble lab at Holden, led the work. Dawson-Glass is now at the University of Michigan studying for her doctorate. 

The team tested how different assembly orders affect plant communities in a controlled environment by simulating “ambient” (current) and “warmed” (+3°C) conditions for 15 species common in old-field ecosystems in the region. They used a growth chamber to test which species would germinate earlier, and how much earlier, under warming. Then, they replicated their newfound “arrival order” by sequentially planting seedlings into pots in the greenhouse. They found that the species more adept at advancing their germination under warming tended to dominate, significantly altering the balance among species. 

These patterns differed species by species. For instance, certain species such as curly dock (Rumex crispus), wrinkleleaf goldenrod (Solidago rugosa), and tall ironweed (Vernonia gigantea) produced significantly more biomass (grew bigger) after they established in their warmed assembly order. Conversely, other species, including spotted St. John’s wort (Hypericum punctatum), bristly buttercup (Ranunculus pensylvanicus), and Canada goldenrod (Solidago canadensis), performed better in the ambient (not warmed) assembly order. Meanwhile, a number of species showed no significant difference in biomass production at all, underscoring that responses to warming can vary widely across species.

"This work illustrates that warming can change the order of species arrivals, ultimately reshaping community composition,” explains Dawson-Glass. “The implications are especially important as we consider how to manage or restore plant communities in a warming world.”

In addition to identifying species with strong responses to warming, this study highlights the importance of understanding phenological sensitivity—the degree to which species adjust to seasonal changes. “Our results provide a new perspective on how climate change is already shaping ecosystems in ways we’re only beginning to understand,” adds Stuble. The findings also support the need for ecologists and land managers to consider germination timing when forecasting how plant communities might adapt or change in the future.

This research is part of an ongoing effort by Holden Forests & Gardens to advance ecological understanding of how climate change impacts native ecosystems.

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Citation: Dawson-Glass, E., R. Schiafo, S.E. Kuebbing, and K.L. Stuble. 2024. Warming-induced changes in seasonal priority effects drive shifts in community composition. Ecology. http://dx.doi.org/10.1002/ecy.4504

About Holden Forests & Gardens: Holden Forests & Gardens is made up of two of Northeast Ohio’s most important environmental and cultural institutions—the Holden Arboretum and Cleveland Botanical Garden—whose mission is to connect people with the wonder, beauty, and value of trees and plants, to inspire action for healthy communities. One of the largest public gardens in the country, Holden Forests & Gardens has 21,000 member households and an annual attendance of nearly 350,000 for whom we strive to provide inspirational and educational visitor experiences. For more information, visit holdenfg.org.