Ultrasound Sensors Reveal Secrets of Drought-Resistant Trees

Researchers at the University of Innsbruck in Austria have discovered a new way to study the effects of drought on mature trees. By outfitting stands of mature spruce and beech trees with waterproof ultrasound sensors in the Kranzberg Forest outside Munich, they were able to monitor the trees for five years and gain new insights into the underlying mechanisms that make some trees more drought-resilient than others.

 

Scientists are intently observing trees in a forest near Munich to comprehend the reasons behind some trees' ability to recover from droughts while others cannot, with the aim of improving forest resilience as droughts become more frequent and intense.

Beeches (Fagus sylvatica) were found to be more drought-resilient than spruces (Picea abies), according to the team's report in the December Plant Biology. The researchers discovered that drought-stressed trees produced more ultrasound signals than those exposed to summer rains. The faint acoustic waves were found to be bouncing off air bubbles called embolisms deep within the trees’ vasculature.

 

Spruces had far more embolisms than beeches, despite the fact that beeches appear to be less conservative with their water management. Beeches suffered fewer embolisms than spruces, even though they kept their pores open longer than the conifers did. This may be because beeches have roots that extend into deeper, wetter soil as well as more robust water reserves.

 

To explore how mature spruce and beech trees manage prolonged droughts, researchers equipped them with ultrasound sensors and electrical probes.

The team’s findings have important implications for the future of temperate forests. As climate change causes droughts to become more frequent and intense, species that can withstand drought conditions and recover more quickly may become more populous in future forests. This could result in changes to the composition of trees in temperate forests, with uncertain consequences for other plants and animals in these ecosystems.

 

The researchers plan to test whether a more diverse forest could help drought-sensitive species like the spruce survive by planting deep-rooted beeches alongside spruces to increase moisture in the soil's upper levels by wicking water up to where spruce roots are.

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