The influence of the average annual cone crop of 170 Engelmann spruce trees on the average basal area increments over a period of 23 years was tested in climatically compensated and uncompensated multiple regression models. In addition, three outstanding cone producing trees were analyzed with the climate compensating model. The cone production of the individual trees were analyzed for the effect on each basal area increment without climatic compensation. A multiple regression model with bimonthly climatic parameters for the growing season, yielded the best prediction (R2 = 98%) of annual basal area increment from the independent parameters among which was the current cone crop. The current year's cone crop showed highly significant negative influence on the increments. No significant effect was attributable to the current year's cone crop when monthly climatic parameters were used. The climatically uncompensated relationship between average cone crops and mean annual relative basal area increment proved to be significant, and the cones accounted for 13.1% of the increment variation. In contrast, the analysis of individual cone crops with individual basal area increments indicated that the cone crops accounted for only 1.4% of the increment variation. One of the reasons for this discrepancy was the use of indexed basal area increments so that the increments could be made comparable, but this process cost lost sensitivity between trees for individual cone crop and growth comparisons. The three exceptional cone producers showed a highly significant effect of cone crops on basal area increment, but the effect was positive or negative on basal area increment depending on the site and individual. In the one case of the positive effect of cones on basal area growth, the cone crops and growth fall off rapidly with time.
Hager, Herbert (1971). Influence of size of cone crop on diameter growth of Engelmann spruce (Picea Engelmannii Parry). MS. 78p.