Plants that have adapted to exploit human activity now depend on disturbance

European mesic meadows are neither too wet nor too dry for many plants and are often biodiversity hotspots. The most productive meadows should be a great source of seeds for restoration projects, providing wildflower seeds for projects. But making these seeds commercially viable relies on understanding how they germinate. To find out, Eduardo Fernández-Pascual and colleagues added their own data to information stored in databases to examine what it takes for one of these seeds to germinate. They found the seeds germinate easily. Oddly, that might be a problem if you want to grow them reliably.

European mesic meadows are fields in clearings made by humans in wooded landscapes. The mesic description refers to the supply of water, neither too dry to cause problems with drought nor too wet to cause waterlogging. It’s the kind of place you’d use for growing hay or grazing. The plants that thrive here can tolerate disturbance by humans and could even take advantage of it. 

Fernández-Pascual and colleagues examined over two thousand germination records of ninety plant species to see what factors affected germination. They found broadly two strategies, divided between the two most common families, Poaceae – the grasses and Fabaceae – often called the bean family but also includes peas and clover.

The authors write: “The dominant family Poaceae shows a lack of response to seasonal cues (average temperature and cold stratification). Instead, Poaceae rely on large amounts of propagules and on detecting micro-niche cues (alternating temperatures, light) that can be associated with the yearly perturbation of mowing. (2) The second most-dominant family, Fabaceae, does not respond to micro-niche cues, and regulates germination timing through scarification and cooler germination temperatures, possibly because their larger size and reserves allow their seeds to decouple their emergence timing from the mowing disturbance.”

In both cases, the plants taken from the human-disturbed meadows germinated more readily than their counterparts from undisturbed land. Rapid germination indicates selection is happening so the plants can take advantage of predictable human actions. However, seeds that germinate so readily are also a problem, as it prevents the plants from building up a seed bank.

Typically when gardeners plant something, they want it to grow. So rapid germination sounds like a good thing. For plants, more reluctant germination can improve the survival chances of a species. When a plant germinates, the seed is gone, and the only way to get more is to grow and reproduce successfully to deposit more seeds in the soil. If a local catastrophe happens before the plants reproduce, the next generation of seeds is lost. In that situation, a store of ungerminated seeds in the soil ready to sprout helps protect against that kind of risk. By germinating so easily, mesic meadow plants can struggle to develop a substantial seed bank which has consequences for ecological restoration.

Fernández-Pascual and colleagues conclude: “The high germinability of meadow seeds makes them relatively easy to use in restoration projects. But it also creates a fascinating dilemma to the restoration practitioner: instead of sourcing seed from existing – and seemingly domesticated – meadows, it could be advisable to also source seeds from related wild populations of meadow species, which may hold the genetic variability and phenotypic plasticity to cope with the threats posed by new environmental challenges.”

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Fernández-Pascual, E., Vaz, M., Morais, B., Reiné, R., Ascaso, J., Afif Khouri, E. and Carta, A. (2021) “Seed ecology of European mesic meadows,” Annals of Botany. https://doi.org/10.1093/aob/mcab135