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Infested trees can die with three to five years, while white fir withstand infestation with no apparent ill effects.

Conditions favored shade-tolerant trees — white fir, red fir and incense cedar — that prefer dense, closed canopies.

The official Christmas White House Tree is an 18½-foot white fir from Auburn, Pennsylvania, that features handmade renderings of the official birds from all 57 states, territories and the District of Columbia.

There are now more fire intolerant shrubs and tree species, such as white firs, at lower elevations.

“We’re not looking to take every grand fir and white fir out of the forests.”