Foliar consumption across a sudden oak death chronosequence in laboratory fires

Abstract

The recent introduction and spread of sudden oak death (SOD; caused by Phytopthora ramorum) has caused heavy mortality in native tanoak (Notholithocarpus densiflorus [Hook. & Arn.] Manos et al. = Lithocarpus densiflorus [Hook. & Arn.] Rehder) forests in California and Oregon, USA. Following tree death, killed tanoaks retain their dead foliage, resulting in a 1 to 3 year period of extremely low foliar moisture and increased probability of crown ignition. We compared foliage ignition and consumption in a laboratory experiment at simulated crown heights from 0.5 m to 1.5 m across a range of representative foliar moistures (80 %, 70 %, 9 %, and 5 %) found in affected regional forests. Results revealed differences in live and dead foliage consumption. All foliage categories were consumed at the lowest crown base heights; consumption of live foliage declined quickly with increasing height, with minimal consumption occurring above 1 m. Consumption of dead foliage also declined with increasing heights, but some consumption (~25 %) still occurred up to 1.25 m. These data inform the mechanism for patterns of individual tree torching and firebrand generation reported in wildfires in SOD-infected forests and woodlands.