80 years ago, America was going through The Dust Bowl and farmers got a lot of the blame. They didn't let land lay fallow, or used monocultures. Now we know it was the worst drought of the last 1,000 years, 7X larger than other comparable intensity droughts that struck North America since 1000 A.D. 75 percent of the country was affected, 27 states severely, and farming had very little to do with it.

But farmers have gotten a lot more scientific since then anyway. They know monocultures can be cultivated efficiently but they are not sustainable so crops are often rotated. Monocultures remain the principal crop form in some regions because it is believed that is the only way to get higher yields in plant production.

That's not really true but not every farmer can afford the best methods. Bernhard Schmid, an ecology professor at the University of Zurich, says a novel form of agriculture and forestry and that by using plant communities, yields can be larger than those of monocultures. 

Their study is in grassland plants so poor farmers in India are not just going to risk their food sources just yet, but it is a data point.

Diverse plant communities of grassland plants used resources more effectively

In a 10-year study, a team of researchers from Switzerland, Germany and the Netherlands examined the yields from grassland plants which they had cultivated in monocultures or mixed plant communities. The latter proved to be more productive than the monocultures. "Due to their diversity, plant species in communities occupy all the niches available in an ecosystem. This enables them to use soil nutrients, light and water far more effectively than monocultures, which ultimately leads to greater yields," explains Dan Flynn, a postdoc in Schmid's group.

Another advantage: There is less pressure from parasites on plants in diverse communities than on those in monocultures. In other words, a parasite can spread less effectively as it is unable to find its special host plant as easily in a biodiverse plant world. The different plant species thus act as protective shields for each other.

This mutual protection within the group enables individual plants to invest the resources available into growth and the production of offspring instead of pest control.

"Diversity offers protection against pests and is a prerequisite for higher yields in plant communities," says Schmid.

Plant species evolve with each other

Moreover, the researchers discovered that species adapt to their plant communities in the time of a few generations. This so-called short-term evolution leads to a continued increase of crop yield in mixtures – a possibility that, according to Schmid, was unexpected in both basic research and plant cultivation.

In this adaptation process, the various species specialize in their strengths and thus improve the complementary utilization of resources throughout the plant community by a process called character displacement.

Grasses, for instance, develop thicker leaves, which are able to utilize the direct sunlight in the upper layer of a meadow while clover species sprout larger but thinner leaves to absorb the weaker light close to the ground more effectively.

Paving the way for sustainable agriculture and forestry

Today, biodiversity is primarily associated with pure conservation, the preservation of species and genetic diversity. "The research results reveal that diversity enables the functionality of the ecosystems to be stabilized at a high level in the course of time and in different environments," concludes Schmid.

He is convinced that the results can trigger a paradigm shift in agriculture in the long run. After all, the positive effects of mixed crops are not just evident in plant communities like meadows and forests, but also in the mixed cultivation of different varieties or genotypes of a single crop such as wheat. 

"Plant breeding and cultivation methods should therefore be geared towards mixtures instead of improving the output of monocultures," says the ecologist from UZH. The fact that more sustainable farming will also be promoted in the process because mixtures require less pest control and utilize fertilizers more effectively is a welcome bonus.