ABSTRACT
In 1997, 30 one-ha stem mapped plots were located in randomly selected juvenile lodgepole pine (Pinus contorta Dougl. Ex Loud.) leading stands aged 15-20 years. The growth and yield model TASS was then used to predict volume losses at rotation. The average loss at rotation due to hard pine rusts in lodgepole pine dominated stands was estimated to be 7.2%. In order to model rust impacts over a rotation three basic modelling assumptions had to be made. This study reviews those three basic assumptions by re-assessing all trees within the 30 plots seven years later. The first assumption was that rust incidence would have stabilized in stands aged 15-20 years. I found that the incidence of both comandra blister rust (Cronartium comandrae Peck) (CBR) and western gall rust (Endocronartium harknessii (J.P. Moore) Y. Hiratsuka ) (WGR)
continued to increase. The greatest increase in CBR incidence occurred in stands that already had a high incidence while increases in WGR incidence were universally distributed over all 30 plots. The second assumption was that the voids created by rust killed trees would not fill with merchantable sized non-host trees by the time the lodgepole pine crop was ready to harvest. I found that the mean height of interior spruce is just over 1/3 the height of the lodgepole pine crop trees. The mean stocking of interior spruce is 243.7 + 102.0 sph while that of lodgepole pine was 968.2 + 196.2 sph. (95% CI). It is unlikely these spruce trees will be of merchantable size prior to harvest of the lodgepole pine crop. The third assumption was that CBR infected trees would die at an annual rate of 5% between the ages of 20 and 40 years. I found that after approximately 1/3 of that time period elapsing, 1/3 of the CBR infected trees were dead. Very few WGR infected trees have died. I also examined the relationship between the abundance of alternate host and the number of CBR infected trees. I conclude from the reassessment of the three main modeling assumptions used to predict rust impact that the those
assumptions were valid and that the impact of hard pine rusts in juvenile lodgepole pine dominated stands in central British Columbia is approximately 7.2%.
