Increasing plant biodiversity – by doing nothing!

Biology. Researchers at Utrecht University call for big efforts to connect natural habitats in order to conserve and restore plant biodiversity.

Tjitske Zeekant | 27 October 2023

Plants cannot move, but their seeds can. Because plants are solely dependent on their seeds for dispersal they have developed many different strategies to spread their offspring to different areas. We witness these seed dispersal strategies everyday: a dandelion seedling getting carried by the wind, a bird eating some berries and pooping out the seeds elsewhere, or sticky seeds in the fur of our pets. Many of these strategies have been adapted to fit the environment a plant is in and have been greatly successful. However, researchers at Utrecht University (UU) predict that with the further urbanization and disruption of natural habitats some spreading tactics will soon no longer be effective.

Monique de Jager, researcher at unit Quantitative Biodiversity Dynamics of the Ecology & Biodiversity group at UU, investigates the effects of habitat fragmentation on the distribution and characteristics of seeds. Roads, deforestation and the expansion of cities divide natural habitats such as forests and rivers, into smaller disconnected patches. „Seeds need to overcome these barriers to get to new habitats but plant dispersal strategies are often not designed to do so. ”  

De Jager explains that plants adapt to their surroundings with small changes to their seed characteristics over time. Seeds may for example become smaller or lighter, when distances between natural habitats become bigger. This enables the seeds to travel further away and reach a new area to settle in. However, there is a limit to the plants’ ability to adapt. De Jager: „The travel distances can become too large. If this is the case, the plant is unable to produce seeds that can overcome the distance and get to new habitats. Plants then need to change their strategy, for example by keeping their seeds close by.”

Turning point

In her recently published paper, in science journal Evolution and Ecology, de Jager uses mathematical models to predict the dynamics of seed dispersal strategies. The evolution of seed characteristics is a slow process that gradually happens. However, the models predict an abrupt turning point when it comes to the dispersal strategy.

If seeds cannot make it to the neighbouring habitat they end up on non-natural terrain where they will not survive.  Instead of seeds that spread over long distances, seeds that stay close to the plant will now be successful. The plant thus changes its long-distance strategy to a short-distance strategy. When this happens, the local diversity of plants will rapidly decrease as there will be less mixing of species between different habitats.

De Jager explains that this is a concerning prospect: „Once we reach this turning point it will be very difficult to turn things back around.” She continues „When plant seeds evolve to short-distance dispersal strategies, it is very difficult to change back to long-distances. This is only possible with restoration of natural habitats very close by.”

Restoration efforts

With her research, de Jager hopes to reach policymakers, raising awareness that current conservation strategies might not be enough to prevent species loss. De Jager: „Restoring original habitats might not be enough anymore. Because seeds become adapted to short-distance dispersal,, they will no longer be able to reach the original habitats. In restoration efforts we thus need to implement connecting habitats as well as conserving original habitats.”

Especially in urban environments, everyone can be part of restoration and conservation. Imagine a plant you see regularly in your neighbourhood. When trying to spread this plant would likely try to get to another patch of soil in the street, a garden or maybe even a balcony with some pots. Small natural habitats throughout the cities are thus of great importance for the connection of habitats.

De Jager stresses that there are many ways in which connection can be achieved.

Simply let nature be!

„Leave some space for ‘weeds’ in your garden, create green strips near the road, or remove some tiles and just see what happens. These small actions all create green patches throughout the city, and can be of great help to keep the diversity of plants in cities.”

Further reading

Published paper:

de Jager, M., & Soons, M. (2023). Critical transitions and evolutionary hysteresis in movement: Habitat fragmentation can cause abrupt shifts in dispersal that are difficult to revert. Ecology and Evolution, 13(5), [e10147]. https://doi.org/10.1002/ece3.10147