SANTA FE ― The defoliation of Douglas-fir and White fir on several thousand acres on the Pecos/Las Vegas Ranger District of the Santa Fe National Forest appears to be coming to a natural end.
In August, specialists from Forest Health Protection out of the Forest Service’s Southwestern Regional Office in Albuquerque documented an outbreak of the Douglas-fir tussock moth (DFTM), a native defoliating insect that feeds on the trees’ needles, in the Cañada de los Alamos area near Shaggy Peak.
In the most heavily affected areas, defoliation ranged from 90 to 100 percent, which could cause some tree mortality. But there was also evidence that the tussock moth population in the area was crashing.
Forest Health Protection and New Mexico State Forestry recently conducted a survey of DFTM egg masses on trees throughout the area as a follow-up to the defoliation observed in August. Based on the proportion of the egg mass count to the number of trees surveyed, they predict “light or no defoliation around Shaggy Peak during the summer of 2017.”
Based on earlier observations, the Forest Health Protection team believes the DFTM infestation in this dense stand of Douglas-fir and white fir is at the end of a four-year cycle due to several conditions, including predators that eat the larvae, the loss of host trees to feed upon, and viral and fungal diseases that spread as the moth population increases. Additional surveys will be conducted in spring 2017 to assess the moth population.
Although there is visible tree mortality in the defoliated stands, the specialists said they do not anticipate “additional defoliation leading to tree mortality throughout most of the outbreak area.” The Douglas-fir and white fir are interspersed with ponderosa and piñon pines, which are unaffected by the tussock moth.
The Forest Service decision last summer not to treat the area for the insect still stands. Future assessments will look at the tussock moth and other threats to trees in the area, including bark beetles.