Environment

Urban Forestry

History of Western Spruce Budworm in the Kamloops Area

Western spruce budworm is a naturally occurring forest health agent in the southern portion of B.C. Annual aerial overview surveys to detect and map forest health concerns such as WSB across BC have been conducted by the Canadian Forest Service (1912 to 1996) and the BC Ministry of Forests and Range (1997 to present).

A recent analysis of this data identified that stands within the Interior Douglasfir (IDF) biogeoclimatic zone were the most susceptible and suffered the greatest amount of chronic, sustained budworm activity. In the IDF, the driest, warmest subzones (IDFdk and IDFxh) were most frequently defoliated.

Douglas-fir growing in the Ponderosa Pine (PP) biogeoclimatic zone was also observed to sustain chronic budworm defoliation and damage. The range of defoliation was shown to be very extensive and it has expanded greatly during the past 100 years, especially since 1980. This increase may be related to the increased availability of host trees, increased susceptibility due to drought and past harvesting practices (Maclauchlan et. al, 2006).

In the Kamloops Forest District there appears to be two sub-regions where outbreaks are common: the central, dry Cache Creek area and the North Thompson area. Outbreak periods for the North Thompson were noted as localized and short in 1991-1992 and 1997-1998 but one outbreak was very prolonged (1984-1989), intense and extensive (Maclauchlan et. al, 2006).

Figure 3 Young Douglas-fir defoliated by western spruce budworm

Defoliation by WSB recorded in the Kamloops Forest District during the aerial overview surveys identified a peak in 1998 with 16,780 ha damaged, followed by distinct population "crash" possibly caused by a hot dry fall followed by a cold, wet spring. Populations slowly rose again with a peak of 15,544 ha in 2002 of (primarily light) defoliation followed by three years of 7,000 ha or less of mainly light defoliation. Most of this damage occurred in the Cache Creek area.

In 2006 however, mapped defoliation jumped to a dramatic 71,600 ha of damage, of which 40% was identified as moderate. This represents significant defoliation as seen from the survey height of 1500 to 3000 ft above ground (moderate is described as noticeably thin foliage, top third of many trees severely defoliated, some completely stripped, Figure 3).

The damage expanded in 2006 up the North Thompson River as far as Barriere, and east to Monte Creek (Westfall 2001-2006). Hectares of recorded damage almost doubled again to 126,162 ha in 2007. Most of this was defined as light, but over 8,000 ha were moderate defoliation.

Logo

Contact
Urban Forest
955 Concordia Way
Kamloops, BC V2C 6V3
ph (250)828-3461
fax (250) 828-3790
email scook@kamloops.ca

Note: All correspondence is entered into our system, and will be dealt with in due process. Please allow several working days for a response. Thank you.