The Complexities of Longleaf Pine Cone Production

It can take more than 2 years for longleaf pine to produce mature seeds. The green cones pictured here are about 6 months from maturity. Photo by Erich Vallery, U.S. Forest Service, courtesy of Bugwood.org.
It can take more than 2 years for longleaf pine to produce mature seeds. The green cones pictured here are about 6 months from maturity. Photo by Erich Vallery, U.S. Forest Service, courtesy of Bugwood.org.

“Longleaf pine forests are among the most important ecosystems in the southeastern United States,” says U.S. Forest Service research ecologist Qinfeng Guo. “However, they have declined dramatically since European settlement and are considered endangered.”

Longleaf pine ecosystems once covered an estimated 80 to 90 million acres across the southeastern U.S. – from Virginia to Texas – but by 1995, only about 2.4 million acres remained. Timber harvesting, land use change, and fire suppression contributed to longleaf pine’s decline.

However, longleaf pine trees also produce seeds sporadically. This makes natural regeneration a challenge. “Sporadic seed production is a significant factor in longleaf pine’s decline,” says Guo. “The species’ irregular seed production impairs restoration efforts and complicates management.”

It can take almost 3 years for a mature longleaf pine to produce viable seeds, and during this time, many factors can adversely impact cone and seed development. The leisurely pace of seed development could be part of the reason why longleaf pine produces good seed crops so infrequently.

The U.S. Forest Service has monitored longleaf pine cone production in stands on the Escambia Experimental Forest since 1958, and in more recently established study sites that span the southern coastal plain from Louisiana to North Carolina.  Several scientists have analyzed these data and found evidence of a highly complex relationship between seed production and climate.

Guo and his colleagues used a method called multiscale entropy to explore cone production across different sites, as well as the relationships between cone production and local climate. The study was led by Xiongwen Chen, a researcher at Alabama A&M University, and published in the Journal of Sustainable Forestry. Dale Brockway, a research ecologist at U.S. Forest Service, was also a coauthor. “Previous studies of cone production for longleaf pine focused on detailed biological or ecological factors,” says Guo. “Our study discovers the pattern of complexity in the dynamics of cone production at different sites.”

Six study sites from across the Southeast – representing Alabama, Florida, Georgia, Louisiana, and South Carolina – were included. The scientists discovered that part of the reason cone production has been so difficult to characterize is because of abrupt changes in cone production. Shifts to a new pattern of cone production were detected at 5 of the 6 sites. The new time scales varied depending on the site. In some sites, the regime shifted to a 9-year time span, indicating that most seed production will happen very infrequently in these stands. However, knowing when this shift will occur allows managers to create the conditions that will favor longleaf pine seedlings.

Guo and his colleagues found that the complexity patterns of cone production were highly correlated to air temperature and precipitation. “Our results indicate that in general, past climate fluctuations have not affected the relationship between climate and cone production,” says Guo. “Whether this relationship will persist under the increasingly rapid rates of climate change is unknown.”

Read the full text of the article.

For more information, email Qinfeng Guo at qguo@fs.fed.us.

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