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In Danish meadows and pastures, despite expectations that competition would favor plants that disperse heavy seeds and have thin leaves, the opposite is observed, puzzling researchers. An extensive new data analysis contradicts established theories and shows fewer weeds and plants with heavy seeds or thin leaves, highlighting the complexity and unpredictability of natural ecosystems.
Ecological theory and experience tell us that plants in meadows and pastures throughout Denmark should disperse heavier seeds. But they are doing exactly the opposite.
Nature slowly begins to change if meadows and grasslands are allowed to grow wild without human interference or grazing animals.
Weeds do well with the nuisance of cows and sheep grazing and trampling the soil, for example. However, weeds have a harder time if there is no disturbance, and then other plants begin to take their place. Competition for sunlight and good soil increases.
In theory, when plant competition increases, plants that disperse heavy seeds and produce large, thin leaves usually have the advantage. But reality does not follow theory. At least not in Danish nature, and that is puzzling to Christian Frølund Damgaard, a professor in the Department of Ecoscience, who is behind the new results.
“Heavy seeds offer a competitive advantage in environments where plants fight for resources. The heavy seeds are carried in a large ‘lunch box’ and can survive in the shade for a period. Light seeds, on the other hand, will perish more quickly.
Thin leaves will have a competitive advantage because plants can replace old leaves with new ones without expending a large amount of energy. And the new leaves will be in better condition to absorb sunlight.”
However, when Christian Frølund Damgaard analyzes data from nature, he tells a different story.
“As competition increases in these areas, seed size should also increase and leaves should become thinner. But the opposite is happening and I just don’t see why,” she states.
236 Danish natural areas studied
Although Christian Frølund Damgaard is a biologist, he mainly works with statistics and large data sets. And that’s exactly what he did when he discovered that nature does not behave as the textbooks predict.
After combining data from 8,859 samples collected in 236 different meadows and pastures in Denmark, he began to see some clear trends: There are fewer weeds, but also fewer plants with large seeds and thin leaves.
Grass species Are decreasing. This could be because there is less grazing in the areas. But this also means that plants that disperse heavy seeds should increase. But they are not. And neither are plants with thin leaves, although that should be a natural development.
“It’s a mystery. There’s something going on here that we just don’t understand.”
Learn more by sticking a stick in the ground
The large amount of data used in the study comes from NOVANA reports. NOVANA is an abbreviation of its Danish title Det Nationale Programme for Overvågning af VAndmiljøet og NAturenthe Nation (the national program for monitoring the environment and nature of water). Every year, the Danish Environmental Protection Agency publishes a NOVANA report on the state of nature in Denmark.
The report is based on more than 250,000 data collections at more than 35,000 stations throughout Denmark. Some of the sites are sampled 24 times a year, while others are only visited once every five years.
The data that Christian Frølund Damgaard used from the reports is coverage data collected using the pinpoint method. The pinpointing method involves a researcher pushing a stick into vegetation and recording the number of times the stick touches different plants. This is repeated at various points in the area to obtain a representative sample of the plants that grow there.
Ecosystems are very difficult to understand.
It may seem strange that a researcher has difficulty explaining what is happening. But this confirms how complex nature really is, explains Christian Frølund Damgaard.
“There are so many things we don’t understand about ecosystems. They are incredibly complex. “Nature seems to change quite slowly and there can be many reasons for this.”
Christian Frølund Damgaard does not believe that there is a single explanation for why nature changes and acts in a way completely opposite to what theory predicts.
“There can be many different reasons. The climate is changing. We are getting more rain. The number of ecological niches is increasing. Areas may be experiencing less grazing and receiving less nitrogen than before. All this contributes to a change in the composition of the species.
But we may be able to find an explanation for why plants behave the way they do. It will only be necessary to carry out some manipulated experiments to test different possible explanations of nature’s behavior,” he concludes.
References: “Decline of large-seeded species in Danish grasslands over an eight-year period” by Christian Damgaard, December 26, 2023, Flora.
DOI: 10.1016/j.flora.2023.152446
“Selection against ruderals in Danish grasslands over an eight-year period” by Christian Damgaard, October 13, 2022, Green Computing.
DOI: 10.1016/j.ecoinf.2022.101864
“Indication of a reduction in cover of thin-leaved plants in Danish grasslands over an eight-year period” by Christian Damgaard, January 4, 2021, Vegetation Science Magazine.
DOI: 10.1111/jvs.12982