Taking Termites into Account

Two studies on their role in wood decomposition in southeastern forests

A pair of protected and unprotected bolts in flooded (left) and unflooded (right) plots in northeastern Mississippi. Photo by U.S. Forest Service.
A pair of protected and unprotected bolts in flooded (left) and unflooded (right) plots in northeastern Mississippi. Photo by U.S. Forest Service.

 

Every homeowner in the Southeast knows about termites and the damage they can do to a house, but most people don’t think about them as forest insects. Termites are saproxylic, meaning they depend on dead or dying wood for at least part of their life cycle, and they play a major role in recycling dead wood in the forest. Though there’s quite a bit known about termites in houses, much less is known about the role they play in forests.

U.S. Forest Service researcher Michael Ulyshen recently published the results of two multi-year studies in Mississippi that show that up to a fifth of wood loss from decomposition in forests can be attributed to termites and other insects, showing the importance of wood-eating insects to forest carbon and nutrient cycling.

“The carbon released during decomposition is important to forest carbon budgets, but it remains poorly understood how insects contribute to this process, ” says Ulyshen. “Recognizing the importance of these organisms to wood loss can benefit global decomposition and carbon modeling efforts.”

For the first study, Ulyshen, research entomologist with the Forest Service Southern Research Station Insects, Diseases, and Invasive Plants unit, and his collaborators cut 34 loblolly pines on the Noxubee National Wildlife Refuge in Mississippi into one meter bolts, using mesh cages to protect some of the bolts from insects and leaving the others completely exposed to insect attack.

The researchers compared wood losses between the bolts where insects were or were not excluded to estimate the role of insects in wood loss and to determine the relative importance of termites and other insects to the wood decay process. They found that wood-feeding insects consumed 15 to 20 percent of dead wood volume in loblolly pine forests, with termites causing most of the damage.

Insect damage after two years. Photo by U.S. Forest Service.
Insect damage after two years. Photo by U.S. Forest Service.

For the second study, which was published in the journal PLOS ONE, the activity of wood-eating insects was compared between seasonally flooded and unflooded mixed hardwood/pine forests, this time using mesh bags to exclude insects and driving stakes in the ground to measure below-ground activity. General findings echoed those of the first study, with 14 to 20 percent of wood loss attributable to termites and other insects.

“Below-ground activity of termites in the flooded forests was five to six times lower than in unflooded forests,” says Ulyshen. “But there was little difference in above-ground activity between the two forest types. The findings from this study echo the first in showing that, in southeastern forests, wood-eating insects significantly accelerate above-ground wood decomposition. They also show, however, that seasonal flooding has the potential to substantially reduce the contribution of insects to below-ground wood decomposition.”

These studies represent some of the first experimental efforts to quantify the contributions of saproxylic insects to wood decomposition. The findings show the important role termites play as decomposers in southeastern U.S. forests and provide baseline data for future studies that will address the insects’ contributions to nutrient cycling and forest productivity.

Read the full text of the insect exclusion study.

Read the full text of insects and flooding study.

For more information, email Michael Ulyshen at mulyshen@fs.fed.us.

 

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