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NMSU research proving ‘tough love’ helps tree seedlings survive harsh environments

Giving forest tree seedlings a fighting chance to survive when planted on wildfire-scarred mountains in New Mexico and the Southwest is the goal of New Mexico State University researchers.


Man kneeling looking at plants
Owen Burney, New Mexico State University associate professor and superintendent at the John T. Harrington Forest Research Center at Mora inspects ponderosa pine seedlings being watered by the sub-irrigation greenhouse system. (NMSU photo by Jane Moorman)
Two green circles
The blacken dyed tissue indicates the impact of high and low irrigation practices on the xylem of ponderosa pine seedlings. Research that is being conducted at New Mexico State University’s John T. Harrington Forest Research Center at Mora. (NMSU photo)

Researchers and land managers have had poor success in getting planted seedlings to thrive, with an average survival rate of 25 percent.

Many things play into the survival rate of the seedlings, including growing and planting techniques, climate and precipitation, temperature and animal activity in the area.

Research in nursery protocols at NMSU’s John T. Harrington Forest Research Center at Mora is proving that “tough love” impacts the seedlings survival rate.

“It comes down to producing seedlings that are going to be successful on a given specific site,” said Owen Burney, NMSU associate professor and superintendent of the facility. “In forest restoration the goal is long-term. In 30-40 years you want the area to be a forest again. But there are critical front end concerns, details that go into improving seedling survivability.”

In the first-of-its-kind research in the U.S, the team hypothesized that drought-conditioned seedlings would develop structures and processes that make the plant hydraulics and water-use more efficient within the seedling.

“In short, can we train plants to function with less water so they are better adapted to the harsh planting site?” Burney asked.

Pondarosa pine and aspen seedlings are the tree species being used in the study.

“Normally, nurseries water at a rate that does not happen in nature,” Burney said. “We wanted to see how plants adapt to reductions in the amount of watering. We developed a scientific procedure that stresses plants to just above wilting point.”

Burney and his research team discovered physiological changes in the plants’ xylem, the vascular tissue in plants that conducts water and dissolved nutrients upward from the root and also helps to form the woody element in the stem.

“Through microscopic analysis of the xylem elements, we discovered that there was a greater abundance of the xylem in plants that were stressed,” Burney said. “This translates to building a buffer against drought environments.”

He explained the results this way. If there were 10 drinking straws in the control plants, and 100 in the drought-tolerant plants, when the harsh conditions took away four of the straws from both groups, the ones with more straws are more likely to survive.

The true test came when 800 ponderosa pines were planted north of Flagstaff, Ariz. Of those plants, 400 were normal nursery protocol and 400 were drought-conditioned.

“The field test was on a really harsh, dry site,” Burney said. “This study was designed for all the plants to die, but they didn’t. Out of the original 800 seedlings, 109 survived. Of the survivors, 92 were the drought-conditioned trees.”

During the research, Burney and his team made another discovery. They found a better way of watering the seedlings in the greenhouse.

“Using the overhead sprinkler system worked fine as the seeds germinate, but once there is foliage on the plants the water does not reach the root systems evenly,” Burney said. “We needed a more consistent irrigation system.”

The team developed a system that watered the plants from the roots up.

“We created a sub-irrigation system where the seedling-racks are placed in a water-tight platform that we fill with water,” he said. “This allows the potting medium to absorb the water evenly.”

Measuring the amount of water in the soil and plants was part of the scientific procedures to determine when to water the drought-conditioned seedlings.

“We accomplished creating a scientific sub-irrigation system for our entire greenhouse, which is actually the largest such system in use,” he said.