PS 30-169 - Prescribed fire increased resin duct defense against bark beetles in Pinus ponderosa.

Abstract: Bark beetles are a substantial ecological force and a potential danger to many forests stands across the US. Bark beetles will penetrate a tree’s bark and eat the phloem of the tree. Resin, produced by a resin duct, is the main defense for pine trees against bark beetles. The larger the resin ducts or the higher the density of resin ducts, the more the tree is defended against potential bark beetle attacks. There is evidence that suggests that low-intensity fire can encourage the development of resin ducts. The purpose of my research is to study potential temporal variation following a fire. Two sites were identified on the Harold Osborne Experimental Forest near Viola, Idaho. Both sites contained Pinus ponderosa in moderate to high density (Site 1: 130 ft^2/acre, Site 2: 110 ft^2/acre). Site 1 had been exposed to 2 previous prescribed burns with no physical damage evident. Site 2 had never been burned, but was logged 1 year prior to sampling. Fixed area plots were conducted and 10 Pinus ponderosa from both sites had core samples taken. Following sampling, cores were processed and the following metrics were calculated: mean duct size per ring, the total number of ducts per ring, duct area per ring, total number of ducts per ring divided by ring area, total duct area divided by total ring area (expressed as a percent). Preliminary results show a statistically significant increase in the total resin duct area and average duct size. The total duct area for the first 5 years following a burn shows an increase in total size by 41% and an increase in the average duct size by 26%. The increase in the total duct area slowly returns to a comparable level to the control site. The number of ducts was shown to not be statistically significant. This suggests that recurrent fire is required in order to keep a high level of production of total resin duct area, average duct size, and total duct area. Further analysis is required to show a potential difference in the total number of ducts per ring divided by ring area, and total duct area divided by total ring area.