Plant repopulation along Mt. Pinatubo

Fifteen years after Mount Pinatubo erupted, an ecologist at the University of Guam took advantage of the changed landscape to understand how one plant community can replace another in the same area.

Thomas Marler collected plant samples from several spots on the eastern slope of the volcano in early 2006. He focused on how the presence of humans and natural events such as typhoons influence the way plant life returns and recovers after a volcanic eruption, especially one whose effects were felt around the world.

“My interest was sparked by the paradox that this volcano’s cataclysmic 1991 eruption was so powerful it changed global climate, yet after a full 15 years the biology of the recovering ecosystem had not been studied,” he said in a statement regarding the report on the sampling trip that appeared in the April issue of the journal Pacific Science.

In their paper, Marler and his colleague and coauthor Roger del Moral at the University of Washington noted that while the “Pinatubo effect” had been the subject of many papers in the past 20 years, none had thus far focused on the plant life in the region surrounding the eruption itself. The data, they said, offers “a critical baseline for future studies of ecosystem recovery.”

The effects of Mount Pinatubo’s eruption were felt around the globe, and one example the researchers cited linked the tiny volcanic particles to changes in the dynamics within a forest ecosystem. Other studies conducted over the years have also mentioned that the average global temperature dropped by less than half a degree Celsius after the eruption, easing the impact of global greenhouse gas emissions for more than a year. The number to the right of the decimal point may not seem like much, but the temperature reduction is not that far off from the figure given in a study last year that outlined the potential benefits of installing reflective white roofs in urban areas around the world to cool down the planet.

“In this light, the absence of publications on vegetation recovery without Mount Pinatubo’s own landscape is conspicuous,” Marler and del Moral wrote.

Nonnative plant species

Focusing on the slope east of the caldera, and going along the Pasig-Potrero and Sacobia rivers, the researchers identified nearly 60 plant species, 34 of which were not native to the area. The two plants that dominated the sampled landscape were talahib grass and a tree with a tolerance for nitrogen-poor soil that has been found at other post-eruption sites.

Marler and del Moral also said the location of the nonnative plants along the slope seems to have been influenced by humans, as there were twice as many of them on the lower sampling sites than higher up. Slope stability was another factor as some spots along the rivers remained barren due to unstable soils.

Based on the information, the researchers suggest that plant diversity in the area will only increase over time, and further studies would help track the influence nonnative plant species have on the developing ecosystem.

“The situation on this mountain serves to remind us that recovery from the damage inflicted by hurtful events may linger for many years,” Marler said.

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