In just one day, two gophers transformed a volcano

The impact lasts for decades.

On May 18, 1980, Mount St. Helens in Washington State, USA, suddenly erupted, spewing 1.5 million tons of sulfur dioxide and 540 million tons of volcanic ash, becoming one of the most destructive volcanic eruptions in U.S. history .

Mount St. Helens (Image credit: Lyn Topinka, Public domain, via Wikimedia Commons)

The high temperatures directly destroyed vegetation within 10 kilometers of the crater; and beyond that, huge shock waves swept across the land, razing large tracts of forest to the ground. Pumice and volcanic ash spread to areas hundreds of kilometers away from the crater, and more than 350 square kilometers of coniferous forests and mountain habitats in the Cascades Mountains were reduced to ruins.

The destructive power of this volcanic eruption is not limited to the surface, but also has a profound impact on the underground ecosystem. The originally active soil microorganisms were almost wiped out by the hot volcanic ash. At the same time, the volcanic ash made the soil more acidic, seriously damaged the underground ecological function, and further inhibited the growth of vegetation. Even two years after the eruption, the land is still barren and it is difficult to find traces of life . Although birds occasionally bring plant seeds, it is very difficult for seeds to grow in this barren soil, and only scattered plants can be seen.

Scientists Michael F. Allen and James A. MacMahon of Utah State University speculate that although the topsoil here has been destroyed, there may still be living bacteria and fungi in the deep soil, which may be a hope for promoting vegetation recovery. However, if the reproductive bodies of fungi are buried under thick volcanic ash for too long, they may also die. So, how to save this land before they disappear completely?

Allen and McMahon came up with a bold idea: If the bacteria and fungi remaining deep in the soil can be "dug" to the surface, can they help restart the ecological recovery process of this land? So they turned their attention to an animal known for its burrowing ability - the northern gopher (Thomomys talpoides). This small gopher is native to North America and is covered with long brown hair. It is said that each northern gopher can loosen up to 227 kilograms of soil per month.

Northern gopher (Photo credit: Henggang Cui, CC0, via Wikimedia Commons)

To test this hypothesis, they placed some northern gophers in a specific area covered by volcanic ash and let them move around for only one day. In a paper recently published in Frontiers in Microbiomes, they evaluated the long-term impact of this experiment. Unexpectedly, the one-day experiment had a profound impact on the land that lasted for decades .

The power of the northern gopher

Allen and McMahon visited Pumice Plain north of Mount St. Helens in September 1982 and August 1983. The area above Spirit Lake was covered with more than 20 meters of ash and was barren, devoid of life except for a few scattered Pacific lupines (Lupinus lepidus).

In the Pumice Plain and another area flattened by the eruption, Allen and McMahon set up a one-square-meter wire fence, each enclosing a Pacific lupine plant and placing a locally captured northern gopher in each fence. The two northern gophers stayed in the fence for only 24 hours, during which time they moved freely, and were then removed. Surprisingly, after a period of time, the Pacific lupine in the fence grew arbuscular mycorrhizae (AM), while the plants outside the fence did not show similar changes.

Mycorrhizae, symbiotic structures formed between plant roots and fungi, are essential for vegetation restoration. Because most plants cannot effectively obtain all the nutrients and water they need on their own, they need to rely on these tiny but powerful fungal partners. Mycelium, which is only a few microns in diameter, forms a vast network in the soil, using its huge surface area to draw water and nutrients from the environment and deliver them to the plant. At the same time, these symbionts can also help plants resist pathogens in the soil. In return, the plants provide the fungi with carbon-containing organic matter they need to grow.

Northern gopher in enclosure (Image source: original paper)

Six years after the experiment ended, Allen and McMahon found that the plots where the northern gophers had been placed and the plots where they had not been placed had presented completely different scenes. The plots that the northern gophers had briefly visited had grown lushly with about 40,000 plants , and even attracted and restored the native northern gopher population; while the areas where the northern gophers had not been placed were still desolate.

The key to the northern gophers' great impact on ecological restoration is their burrowing and soil-turning behavior. Through these activities, they thoroughly mix the deep soil with the surface volcanic ash, bringing fungi, seeds and insects that are essential to soil ecology to the surface . In addition, the feces of the northern gophers also contain fungi, fungal spores and plant seeds, and their excretion behavior brings vitality to the land.

Moreover, the volcanic ash particles are relatively large, and when mixed with the deep soil, the soil mixture formed has good air permeability, which is very suitable for plant growth. For this reason, plants grown in such soils tend to be healthier and more lush. This is also confirmed by the observations of Allen and others: in contrast, plants grown in soils not visited by northern gophers often turn withered and yellow.

But what was most shocking to Allen's team was that the impact of just 24 hours of activity by the northern gophers was not limited to the first few years. These changes actually lasted for a long time and even continue to this day.

Lasting Impact

In July 2014, Allen and McMahon once again set foot on this familiar land and sampled the soil in the experimental area and non-experimental area of ​​the Pumice Plain. For comparison, they also went to an area not far from the Pumice Plain, the "Bear Meadow". This area was also covered with thick volcanic ash in 1980, but due to historical reasons, it presents two completely different landscapes: one part has long been turned into a meadow due to logging, and the other part retains the ancient forest. The researchers collected soil samples from these two landscapes and sent them back to the laboratory together with the samples from the Pumice Plain to analyze their chemical and microbial composition.

In the chemical composition analysis, they focused on the carbon and nitrogen content in the soil. These indicators are related to the microbial content in the soil, because microorganisms can convert ammonia into organic nitrogen and fix it in the soil. The results showed that the soil carbon and nitrogen content in the Pumice Plain area was generally lower than that in the forest area of ​​the Bear Meadow. However, within the Pumice Plain, the carbon and nitrogen content in the soil of the experimental area where the northern gophers had been placed was significantly higher than that in the ordinary area where the gophers had not been placed . This means that the northern gopher, which stayed for only 24 hours 40 years ago, injected more lasting vitality into this land.

A map of Mount St. Helens and the surrounding area, showing the locations of Pumice Plain, Spirit Lake, and Bear Meadow (Image source: original paper)

The results of the analysis of the microbial DNA in the soil showed that there was a significant difference in the composition of the microbial community in the experimental area where the northern gophers were placed and the ordinary area where the gophers were not placed. The diversity of bacteria and fungi in the experimental area even exceeded that of the forest area of ​​the bear meadow . In particular, the diversity of arbuscular mycorrhiza increased significantly in the experimental area. This result shows that the northern gophers not only changed the chemical composition of the soil, but also played a key role in the long-term succession of the microbial community.

This study also once again confirms the importance of microorganisms to ecological restoration. Before the volcanic eruption in 1980, the forest area of ​​Bear Meadow was mainly covered with coniferous forests such as pine, spruce and fir. The coverage of volcanic ash caused a large number of needles to fall off here, and scientists once worried that the forest would disappear completely. But unexpectedly, the forest area recovered very quickly. Trees in some areas began to grow almost immediately after the disaster, while the logging areas remained barren. Researchers believe that this difference is closely related to the fallen needles, which nourish fungi in the soil, thereby helping trees to regenerate quickly.

This research reminds us that everything in nature is closely connected. From plants and animals visible to microorganisms too small to be directly perceived, they may be key forces in ecological restoration.

References

[1]https://www.frontiersin.org/journals/microbiomes/articles/10.3389/frmbi.2024.1399416/full

[2]https://www.tandfonline.com/doi/epdf/10.1080/00275514.1988.12025615

[3]https://www.universityofcalifornia.edu/news/how-gophers-brought-mount-st-helens-back-life-one-day

[4]https://link.springer.com/chapter/10.1007/0-387-28150-9_15

Planning and production

Source: Global Science (ID: huanqiukexue)

Author: Huang Yujia

Editor: Yinuo

Proofread by Xu Lai and Lin Lin