Nature slowly begins to change if meadows and grasslands are allowed to grow wild without human interference or grazing animals.

Weeds do well with disturbance from cows and sheep that graze and tramp on the soil, for example. However, weeds have a harder time if there is no disturbance, and other plants then begin to take their place. The competition for sunlight and good soil increases.

Theoretically, when competition between plants increases, the 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 baffling to Christian Frølund Damgaard, professor at the Department of Ecoscience, who is behind the new results.
 
“Heavy seeds give a competitive advantage in environments where plants struggle for resources. Heavy seeds are loaded with a large ‘lunchbox’ 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 a better position to absorb sunlight.”

However, when Christian Frølund Damgaard looks at the data from nature, they tell 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 simply can't see why,” he says.

Although Christian Frølund Damgaard is a biologist, he mostly works with statistics and large data sets. And that is exactly what he did when he discovered that nature is not behaving as the textbooks predict.

After combining data from 8,859 samples collected from 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.

Weed species are declining. This might be because there is less grazing in the areas. But this also means that plants that disperse heavy seeds should increase. But they’re not. And neither are plants with thin leaves, even though that should be a natural development.

“It's a mystery. There's something going on here that we just don't understand.” 

It may sound strange that a researcher has difficulty explaining what is going on. But it confirms just how complex nature really is, explains Christian Frølund Damgaard.

“There are so many things we don’t understand about ecosystems. They’re incredibly complex. Nature seems to change quite slowly, and there can be many reasons for this.”

Christian Frølund Damgaard does not think there is only one explanation for why nature is changing and acting completely opposite to the way predicted by theory.

“There can be many different reasons. The climate is changing. We’re getting more rainfall. The number of ecological niches is increasing. The areas may be experiencing less grazing and receiving less nitrogen than before. All of this contributes to a change in the composition of species.

But we may well be able to find an explanation for why plants are behaving the way they are. It’ll just require carrying out some manipulated experiments to test different possible explanations for nature's behaviour,” he concludes.