Impact of Spring or Fall Repeated Prescribed Fire on Growth of Ponderosa Pine in Eastern Oregon, USA

Prescribed burning is used to reduce fuel loads and to return fire to its historic disturbance role in western forests. Managers need to know the effects of prescribed fire on tree growth. Growth of residual ponderosa pine (Pinus ponderosa Dougl. ex Laws.) was measured in an existing long-term study of the effects of season-of-prescribed burn in combination with a single or a repeated burn. Each of six previously thinned mixed-age stands in the Blue Mountains near Burns, Oregon, was subdivided into three experimental units, and one of three treatments was randomly assigned to each: fall 1997 burn, spring 1998 burn, and no burn (control). Treatments were operational-sized prescribed burns. In 2002/2003 each burned unit was split, and one-half was burned again, maintaining the original season of burn. Sample trees were evaluated for growth 5 and 10 seasons after the initial prescribed fires. We conclude that after accounting for the crown scorch proportion neither a single spring or fall prescribed fire treatment nor a repeated fire treatment 5 years later affected the growth of thinned ponderosa pine 10 years after the initial 1997/1998 fires. A linear regression is included to estimate bark thickness based on dbh.