Warren’s collar weevil in lodgepole pine stands in the Kispiox Forest District

• Main Author: Byford, Geoffrey Thomas
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/5186

The distribution and abundance of Warren’s collar weevil, Hylobius warreni Wood (Coleoptera: Curculionidae), was examined in lodgepole pine, Pinus contorta var. latfolia Engelni, plantations in the Kispiox Forest District in north-central British Columbia. The effect of weevil feeding damage on height growth of dominant and co-dominant trees was also examined. The weevil was found distributed throughout the forest district. All 31 surveyed plantations, ranging in age from 5 years to 16 years, had evidence of larval feeding damage. Weevil-caused mortality ranged from 0-8.8%. The average percentage of sampled trees attacked was 29%. The percentage of trees attacked within a plantation was directly related to plantation age and average tree height. There was not a significant relationship between the thickness of the organic layer above mineral soil and the percentage of trees attacked in the first year of the study. Plantation density had no apparent effect on the percentage of trees attacked. The highest levels of weevil damage were found on circum-mesic, well drained sites in the ICHmc3 biogeoclimatic variant. Plantations established on sites which originally had a pine component appeared to be particularly susceptible to weevil damage. It appears that the collar weevil is not reducing plantations to below minimum stocking levels (<700 sph). The populations of the collar weevil found in 2 of the 3 intensively sampled plantations, ranging in age from 13-17 years old, were similar to those reported for naturally regenerated stands of similar age in Alberta. One plantation had populations considerably higher than reported elsewhere. This may have been due to a scarcity of lodgepole pine in the surrounding timber types. The percentage of stems attacked within a diameter class increased proportionally with increasing diameter class, and increasing basal area class. The percentage of the stem circumference girdled increased with increasing root collar diameter and LFH layer depth. The percentage of lodgepole pine attacked within the 3 study sites ranged from 81 % to 92 %. These attack rates were higher than rates reported for naturally regenerated stands. This may have been due to lower tree densities found in planted versus naturally regenerated stands. The high incidence of root collar weevil within the Kispiox Forest District may be related to a man-caused increase in lodgepole pine within the area. This increase has occurred because of the conversion of mature mixed species coniferous stands to lodgepole pine plantations following clearcutting. Destructively sampled trees indicated that initial weevil attacks within plantations had occurred within the previous 6 years. The time of first attack was uniform within plots indicating that weevils were not dispersing from the stand margin. Results from stem analysis indicated that height growth of weevil damaged trees was not affected in the short term. The long term impacts of sub-lethal multiple weevil attacks and larval damage on height growth are not presently known. === Forestry, Faculty of === Graduate