New Mexico State University researchers are working to give forest tree seedlings a fighting chance to survive when planted on wildfire-scarred mountains in New Mexico and the Southwest, according to an article in the Las Cruces Sun News.
Historically, researchers and land managers have had poor success in getting planted seedlings to thrive, with an average survival rate of 25%. Growing and planting techniques, climate and precipitation, temperature and animal activity all play into the survival rate of the seedlings.
“It comes down to producing seedlings that are going to be successful on a given specific site,” Owen Burney, NMSU associate professor and superintendent of NMSU’s John T. Harrington Forest Research Center, said in the article. “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.”
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. Ponderosa pine and aspen seedlings are the tree species being used in the study.
Burney said that nurseries normally water at a rate that does not happen in nature. The team wanted to see how plants adapt to reductions in the amount of watering, so it 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. There was a greater abundance of the xylem in plants that were stressed, which means they build a buffer against drought environments.
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.
Burney explained that the field test was on a really harsh, dry site. The 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 also 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. They needed a more consistent irrigation system.
The team developed a system that watered the plants from the roots up. They created a sub-irrigation system where the seedling racks are placed in a water-tight platform that is filled with water, allowing the potting medium to absorb the water evenly.