Source Article: Zobel, D.B., Antos, J.A. & Fischer, D.G. Community development by forest understory plants after prolonged burial by tephra. Plant Ecol 223, 381–396 (2022). https://doi.org/10.1007/s11258-021-01216-3
Featured Image Caption: After the 1980 eruption of Mount Saint Helens, ash and debris covered the landscape, affecting ecosystems miles from the volcano’s vent. Here erosion has made deposits of volcanic tephra at Mount Saint Helens visible.Image Source: Flickr by Richard Droker
When a volcano erupts, what happens to plants growing nearby? Some are buried by volcanic tephra, ash and rocks thrown into the air by the volcano. Amazingly, newly published results suggest that this might not kill the plant community underneath the debris. Recently, researchers concluded a 36-year-long study, testing the effects of erosion of debris that buried plants for different amounts of time. Then, they watched how the unearthed plant communities were affected, even decades later.
Tracking Recovery After Burial and Unburial
To do this, they took advantage of the 1980 eruption of Mount Saint Helens in Washington, USA. Their study site was about 14 miles (22 km) from the vent of Mount Saint Helens in an old growth forest which was blanketed with 5 or 6 inches (12-15 cm) of volcanic tephra. At this site, they established many small plots for each of three treatments: undisturbed tephra, tephra that had been removed 4 months after the eruption, and tephra that had been removed 28 months after the eruption.
These tephra removal treatments simulated how erosion may take different lengths of time to remove sediment from buried plants. At each plot, the researchers noted all understory plant species present, as well as the number of shoots of each species and the area of the plot that each species covered. They repeated these observations periodically from 1980 through 2016 and watched the plant communities change over time, specifically monitoring herbs, shrubs, and bryophytes, such as mosses.
The researchers found that the early and late unearthed plots returned to having similar plant communities to each other and to their pre-eruption communities, but that process took at least seven years. After tephra was removed from the 28-month delayed plots, the plant communities bounced back, with plant species diversity and cover increasing quickly. Different plant species were affected differently by delayed removal of tephra, but with time, the resulting communities were essentially the same for all unearthed plots. For example, white avalanche lilies (Erythronium montanum) reappeared quickly after the tephra was removed from each of the delayed erosion plots. Contrastingly, Trautvetteria (Trautvatteria caroliniensis) reappeared immediately in the 4-month delayed erosion plots and took years to slowly reappear in the 28-month delayed erosion plots.
The undisturbed tephra communities, on the other hand, were still different from the unearthed communities after 36 years. After 20 years, the undisturbed tephra communities possessed herb diversity similar to the unearthed communities, however the mix of species remained different. For example, the undisturbed tephra communities had much more prevalent (number of stems per plot) foamflower (Tiarella unifoliata), but they also had almost none of the white avalanche lilies (Erythronium montanum) which were the most common herb in the unearthed communities.
Bouncing Back from Burial
These findings suggest that plants can recover from being buried with sediment much faster than expected by surviving under the debris for multiple growing seasons and waiting for the debris to erode. Recovery of a plant community after burial of plants in tephra could take decades, but if that tephra erodes, the recovery process may take much less time.
Plants can be buried by lots of processes, from volcanic eruptions to floods or strong winds that move sediment. In the understory, plants can also be buried by falling leaves from trees. Plants that can survive being buried for a long time have an advantage in all these scenarios because the sediment or leaves could move again, freeing the plant. This study’s findings change how we see the effects of processes that bury plants. Of course, the buried plants suffered from being buried. The lack of sunlight probably led plants to use up what resources they had to stay alive, causing their shoots to be smaller at first after they were unearthed. However, it seems that, given some time, the consequences of plant burial can largely be reversed if there is erosion of the sediment within three growing seasons.
Understanding the Rules Governing Plant Communities
More generally, this long-term study is helping scientists to understand how and why forests and other ecosystems each have specific plant communities. By learning why certain plants live certain places, we can better understand what shapes plant communities, and, in turn, what impacts our actions as humans could have on them. Additionally, by understanding the rules that govern plant communities over time, we can better predict how they might change in the future with disturbances, like volcanic eruptions, or changes to their environment.