LESSONS FROM THE SOCIAL LIFE OF PLANTS

Published in the Proceedings of the National Academy of Sciences (PNAS), the research examined annual plant communities in Western Australia and Spain, two regions with distinct evolutionary histories but remarkably similar Mediterranean climates. What the researchers found reinforces an idea that sits at the heart of ecological planting design - plants are not simply collections of species. They are communities.

For decades, the horticulture industry has largely focused on competition. Plants compete for light, water, nutrients and space and the strongest survive. This study is a timely reminder that competition between plants does exist but doesn’t paint the full picture. 

Researchers found that at low neighbourhood densities, positive interactions between different plant species were surprisingly common. In both Australia and Spain, facilitation (where one plant benefits another) was the dominant interaction type. More than half of all interactions observed at low densities were facilitative rather than competitive.

In practical terms, this means that neighbouring plants can improve one another's chances of success. They may provide shade, moderate temperature extremes, reduce water stress, improve pollinator activity or create favourable growing conditions that would not exist in isolation.

The findings challenge the common perception of plants as solitary competitors and instead reveal a living network of relationships that help sustain biodiversity.

One of the study's most significant findings was that these relationships change as neighbourhood density increases. As plant communities become more crowded, facilitation gradually gives way to competition. In the Australian plant communities studied, around two-thirds of interactions became competitive at higher densities. Similar patterns were observed in Spain.

The shift makes intuitive sense. When resources become scarce, plants begin competing more intensely for access to light, water and space. What this means is that the relationship between plants is fluid and a species that acts as a helpful neighbour under one set of conditions may become a competitor under another.

For planting designers like us, this highlights the importance of understanding not only species selection, but also the consideration of density and long-term community dynamics.

Across both countries, plants with conservative resource-use strategies consistently acted as stronger facilitators. These are species that use resources carefully, retain water efficiently and tend to be more resilient in challenging conditions. In other words, the most generous neighbours were often the most resource-efficient plants.