When the glacier ice is gone, plants get to work

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Engineer plants mountain avens (Dryas octopetala, Swiss Alps) and creeping pohue
Engineer plants mountain avens (Dryas octopetala, Swiss Alps) and creeping pohuehue (Muehlenbeckia axillaris, New Zealand) trapping and locking moving sediments in place. Both are growing in Utrecht University’s botanic gardens!
Around the world, retreating glaciers leave vast areas of unstable sediments behind. Researchers from Utrecht University, University of Bayreuth and University of Wuerzburg found that across mountain regions, plants actively aid the stabilisation of these sediments in a similar way, regardless of climate and plant species. By growing their stems and roots in a way that locks moving sediments in place, they ’eco-engineer’ unstable glacier sediments to create safe living space for other plant species - and humans. The findings were published online today in the journal Ecosphere.

Across mountain regions, completely different plant species stabilise moving sediments in a very similar way.

Jana Eichel

Engineer plants securing moving slopes

The researchers looked at colonisation of unstable glacier foreland slopes in two contrasting mountain regions, the Swiss Alps and the Southern Alps in New Zealand. Though the plant species are completely different between the mountain regions, they have adapted their way to grow and stabilise moving sediments in a very similar way, says Jana Eichel , researcher at Utrecht University and the lead author of the study.

The plants do so in a clever way: by growing in flat, dense patches, they can slow water flow and thereby decrease erosion. At the same time, their extensive root systems keep sediments in place both at the surface and in the deeper soils.

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Stabilisation speed: climate matters!

Plants stabilise moving sediments in a so-called ’biogeomorphic succession’. This means that once engineer plants manage to establish, they stabilise moving sediments the more they grow and thereby create safe space for less adapted shrubs and trees to establish.

We see this phenomenon in both climates, but the timescale in which sediments stabilised differed between the two mountain regions, Eichel explains. In New Zealand with more than 4 metres (!) precipitation per year, engineer plants still have not managed to colonise some of the frequently moving sediments deposited by the glacier more than 1000 years ago. In the Swiss Alps with precipitation similar to the Netherlands, engineer plants usually manage to colonise moving sediments within decades and stabilise them within centuries.

In a changing climate, rainfall intensities in the Alps are expected to increase, which could keep sediments moving for longer, possibly increasing natural hazards. However, for some threatened alpine species continued sediment movement could actually be good as they can best survive in unstable areas, Eichel concludes.

Publication

Eichel, Jana, Draebing, Daniel, Winkler, Stefan, and Meyer, Nele. 2023. Similar Vegetation-Geomorphic Disturbance Feedbacks Shape Unstable Glacier Forelands across Mountain Regions. Ecosphere 14( 2): e4404.  https://doi.org/10.1002­/ecs2.4404