Postfire response of red alder, black cottonwood, and bigleaf maple to the Whatcom Creek fire, Bellingham, Washington
The June 1999 pipeline leak and subsequent explosion in Whatcom Creek resulted in a fire that scorched ~10 ha of coniferous and riparian forest in Bellingham, Washington, USA. This fire provided an opportunity to study the postfire responses of red alder (Alnus rubra), black cottonwood (Populus trichocarpa) [P. balsamifera subsp. trichocarpa], and bigleaf maple (Acer macrophyllum) in the 3.2-ha scorched riparian zone. Bigleaf maple endures all but the most intense fires, resprouting vigorously after fire. Red alder and black cottonwood are known resprouters that may survive low intensity fires, but data about their responses to fire are sparse. The postfire status of every tree in the burn zone was evaluated immediately after the fire in June 1999, and during the first postfire growing season in May 2000. Tree response, in relation to trunk diameter, percent crown scorch, and percent bark scorch, was categorized as (1) alive with a new leafy crown; (2) topkilled and resprouted; or (3) dead. Fire intensity was higher on the left bank (left side of the creek when facing downstream), where trees experienced greater mortality. More than half the 854 trees in the burn zone survived the fire, 57% by forming new leafy crowns and 43% by resprouting. Red alder, black cottonwood and bigleaf maple demonstrated abilities to survive a disturbance to which they are not ordinarily subjected. All three species resisted low intensity fire and reformed leafy crowns on the right bank, and they endured moderate to high intensity fire by resprouting after topkill on the left bank. On the left bank, probabilities of surviving 100% crown scorch were 0.24 for red alder, 0.66 for black cottonwood, and 0.68 for bigleaf maple; probabilities of surviving 100% bark scorch were 0.09 for red alder, 0.66 for black cottonwood, and 0.60 for bigleaf maple.