Pondberry Seeks Sunlight

Endangered Species Highly Tolerant of Soil Flooding

Although rare and endangered, pondberry is quite hardy – for example, it blooms even when the soil is flooded. Photo by USFWS, courtesy of Wikimedia Commons.

Pondberry is rare and endangered, but don’t underestimate the species.

“Pondberry tolerates flooded soil,” says U.S. Forest Service research forester Brian Roy Lockhart. “It also tolerates living in heavy shade. It has a plasticity to light that gives managers a lot of options for improving its growth and vigor.”

Pondberry occurs in several southeastern states, including Mississippi. Lockhart and his colleagues used plants from the lower Mississippi Alluvial Valley.

In some parts of the Valley, dense forest canopies intercept most of the sunlight before it reaches the forest floor. Pondberry in these forests may receive as little as 5 percent sunlight.

“Our study suggests that 5 percent sunlight is not enough,” says Lockhart. “Heavy shade, where we recorded very low photosynthesis rates, is not conducive to long-term pondberry survival.”

Lockhart has studied pondberry for 14 years. Lockhart and Emile Gardiner, along with several other SRS scientists, recently investigated pondberry’s physiological response to light availability and soil flooding. Their results were published in the journal Photosynthetica.

The scientists grew 3,456 pondberry shrubs in the Flooding Research Facility at the Sharkey Restoration Research and Demonstration Site in Mississippi. The facility contains a dozen impoundments that can be flooded for set periods of time, and to specific depths.

Pondberry occurs in several southeastern states, but the scientists focused on the lower Mississippi Alluvial Valley. Image courtesy of NASA Earth Observatory.

The scientists flooded pondberry for 0, 45, or 90 days. They also built shade houses in the impoundments that provided 5, 37, or 70 percent of full sunlight.

“Our goal was to determine how pondberry responds to some of the stressors it experiences in floodplain forests,” explains Lockhart.

“Shrubs that received 37 or 70 percent sunlight show a photosynthesis rate 147 percent greater than shrubs that received 5 percent light,” says Lockhart. Shrubs growing in 5 percent sunlight had low rates of photosynthesis, even without any soil flooding.

Flooding displaces oxygen from the soil. The lack of oxygen is stressful and potentially deadly for plants. “We understand some of the physiological mechanisms that enable baldcypress and other tree species to tolerate soil flooding,” says Lockhart. “However, we’re not sure how pondberry tolerates soil flooding.”

Whatever the mechanism, pondberry survived multiple years with 90 days of soil flooding. However, these plants photosynthesized at low rates, no matter how much light they received.

Pondberry that endured 45 days of flooding bounced back quickly. The shrubs in this flooding regime had up to 39 days to recover from flooding before measurements, and they had similar rates of photosynthesis as plants that hadn’t experienced any flooding.

Despite the soil flooding, pondberry flowered in March, as it usually does. How can a plant this hardy be endangered? The answer is probably tied to pondberry’s inability to compete with other species.

“Pondberry may not be able to tolerate competition from other plants growing in its colonies,” says Lockhart. “We controlled all competing vegetation in our experiment so it would not interfere with the soil flooding and sunlight treatments that we studied.”

Pondberry has been listed under the Endangered Species Act since 1986. Photo by US Army Corps of Engineers, courtesy of Wikimedia Commons.

Nevertheless, the study suggests that pondberry’s ability to quickly recover after soil flooding gives it an advantage over other species.

“Our study illustrates the complexity of interacting environmental factors affecting pondberry,” says Lockhart. “We hope this research can help managers develop conservation and recovery plans for pondberry.”

Read the full text of the article.

For more information, email Brian Roy Lockhart at blockhart@fs.fed.us.

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