Working closely with forest managers, PNW Research Station scientists designed an experiment tailored to the problem. Prescribed fires were set in the fall and spring. The stands were then monitored for several years to determine the response of understory plants, black stain root disease development, and ponderosa pine tree mortality. Although more trees died in fires set in the fall, the season of burn did not really matter. What did matter was the severity of fire and the amount of damage to the trees. There was also no evidence that burn season influenced the understory native perennial (longlived) grasses and forbs. However, exotic and native short-lived species were more abundant in the areas burned in the fall. As with tree mortality patterns, fire severity is probably driving this pattern. Short-lived native plants showed postfire invasion and spread patterns similar to exotics, but exotics were more abundant than natives.

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