Fungi help reduce transplant failures at the roots

It is estimated that transplant failures of trees and other plantings in grounds and roadside projects cost city and county governments millions of dollars annually.

To reduce transplant failures and preserve replanting budgets, government agencies are increasingly concentrating on plant health at the root level, adapting lessons learned in mined-land reclamation and reforestation projects.

Federal agencies, like local governments, once maintained large replanting budgets out of necessity. Reforestation projects, especially those on distressed soils, yielded large losses of first-planted trees that were unable to make the transition from the nursery. In the ’70s, the U.S. Forest Service (USFS) began researching ways to reduce those losses, and eventually found answers below the soil with mycorrhizal fungi.

Millions of years ago, forest trees and plants faced many natural stresses, such as low soil fertility, drought and temperature extremes. To survive, these plants established a symhiotic partnership with unique soil organisms called mycorrhizal fungi.

The fungi colonize the roots of about 99 percent of the earth’s plants and serve as a secondary root system, extending themselves far out into the soil. Mycorrhizae extract nutrients and water from the soil and provide them to their hosts, while the plants provide the fungi with energy-sustaining sugars. Trees and plants with thriving mycorrhizal “root” systems are better prepared for the stresses they encounter in their natural and man-made environments.

The USFS found that mycorrhizal fungi are an integral factor in the success or failure of transplanted plants, since transplant success is directly related to the speed with which a plant can rebuild its root system and become established. Unfortunately, bareroot, boxed or burlapped trees may have only 10 percent of their original root systems intact: the rest was left behind at the nursery. Additionally, natural populations of mycorrhizal fungi in the transplanting soil may be inadequate for fast colonization of the remaining plant roots or of new roots.

Inoculating trees with mycorrhizal fungi prior to or at planting has revolutionized the reforestation of mined lands and similar projects. For example, the Ohio Abandoned Mineland Reforestation Program was struggling with a survival rate of less than 50 percent for newly planted tree seedlings, and was forced each year to replant more than 75 percent of the sites included in the program.

But in 1981, the agency began planting special mycorrhizal-inoculated pine and hardwood seedlings to stabilize 3,000 acres of unreclaimed land. The survival rates for those seedlings shot up to more than 85 percent, and only 5 percent of the sites overall needed replanting.

To date, Ohio has successfully planted more than 5 million tree seedlings with specific mycorrhizae on more than 3,000 acres of abandoned mined lands. The success in Ohio, on some of the nation’s worst soils, is being duplicated daily in urban landscapes, where mycorrhizae is helping reduce losses of transplanted trees and plants.

Mycorrhizal fungi are commercially available today for the inoculation of planting material. Costs are generally less than $1.50 per tree of one-inch caliper or for three plants in one-gallon containers, and plants usually require only a single inoculation throughout their lives. Mature trees that exhibit signs of disease or damage have also shown some benefits from inoculation with mycorrhizae.

Mycorrhizal fungi spurred, in part, the USFS’s interest in returning to a more holistic, biologically based approach to plant management. The guiding principle is simple Use natural systems and processes in managing plants in order to boost their ability to use their own natural defenses against stresses in their environment.

The total plant health care concept is a preventive, rather than curative, approach to plant care management. The emphasis for transplanted plants is placed on proper planting and placement, replenishment of the mycorrhizal population and proper nutrient and water management, all elements that ensure that the plant can establish and begin fending for itself quickly.

If transplantation is a true success, the need for pesticides and other curative measures throughout the life of the plant are greatly reduced.