Planting time for forest trees branches out to new seasons

Texas research shows mid-September success with containerized trees

Most foresters hold to the straight and narrow when it comes to planting pine trees: nursery seedlings go in the ground between Dec. 1 and March 1. Period.

But a Texas Agricultural Experiment Station study is branching out to show that early planting — even as early as mid-September – can give slash pine trees a growing head start towards better survivability, thus faster regrowth on harvested or burnt areas.

The key is containers. Rather than plunge the bare roots of tiny trees into the soil, research is showing that seedlings grown in containers until the moment of planting, then planted with the potting medium intact around the roots isn’t as shocking to the transplants, according to Dr. Mike Messina, Experiment Station forest scientist.

“Planting earlier is proving to be a good idea, because they do get a better start,” Messina said. “The containerized plants are having more than 90 percent survival after that critical first year in the ground.”

Bare-root trees planted in September have as little as 60 percent survival, he said.

Messina said the reason bare-root trees are planted in far greater numbers than container-grown trees is cost and efficiency. “Some nurseries annually grow 25 million seedlings on relatively few acres,” he explained. “After lifting, they pack about 1,000 of them cardboard boxes or paper bags that one person can easily lift.”

Those boxes are easy to transport, light to carry to the field and quickly planted in a matter of seconds, he added. Container-grown trees take up more space, have to be watered more often and are more difficult to transport. But the study may find that the increased survivability offsets the additional effort and cost.

The study is being funded by Boise Cascade Corp. with the research plots located on industrial tree farms in Louisiana. But, Messina said, the findings there are readily adaptable to eastern Texas and other southern forests.

The study is beginning its third of three years. By April 2003, about 18,000 slash pine trees will have been planted and measured for growth, survival and physiological performance. More conclusive data and planting recommendations are expected by the spring 2004, but Messina said some results are already obvious.

“The beauty of the containerized plants is uniformity,” Messina added. “Bareroot study plots will have rows where three or four trees died, one is doing well and one is a runt. The containterized trees are almost all alive and have about the same height.”

Uniformity is important for timber companies that seek trees of similar size for ease of processing, he explained.

“When the forest products industry finds a good performing tree, they want its offspring to be just like it,” Messina said. “So, they use vegetative propagation – taking cuttings continuously from the mother plant – so the offspring will be genetically identical.” Those cuttings, rooted in containers, become the new trees that have been performing well. The test was to see how well they would fair in the field. For each row of bare-root seedlings, a row of rooted cuttings was planted alongside. Since the containerized tree roots are not exposed, better survival might result thereby expanding the planting window of time.

“We’re trying before, during and after typical planting months of December-March,” he said. “We’re planting in September, which is considered really early, and again in November, January, early March and late April.”

If a tree survives a September planting so that its roots begin to grow in the fall, that tree will be further along in growing the following spring when new trees are just being planted. Also, if the window of planting time can be expanded, that will ease the time crunch for planting crews that are in demand during the usual December-March planting season.

Fall planting has been largely rejected by foresters, mainly because it’s “terribly, terribly hot” and often dry in much of the southern forest region, making it hard for even the most adapted plants to survive.

“We pray for autumn rains,” Messina said. “A tropical storm can be a blessing to us.”

Weather, soil moisture, air temperature and other atmospheric conditions are being recorded at each planting site so that researchers can consider those factors in analyzing tree growth and making more long-term recommendations.