Long-term trends in height growth of jack pine in north central Ontario

Although most investigations of long-term growth trends of trees involve description of radial growth of trees, investigation of height growth of dominant and codominant trees also warrants attention for two significant reasons-the dependent variable is largely independent of stand density and it represents an index of stand productivity. Residuals from a height growth equation for jack pine (Pinus banksiana Lamb.) were used to examine long-term trends in height growth. No consistent longterm trend was apparent; however, a period of superior growth was identified during the 1960s. Shortterm changes in climatic variables could account for a short duration of increased growth. As anthropogenic factors, such as air pollution, did not exhibit a trend coincident with the growth trend, they do not represent a reasonable explanation. An additional benefit of detailed examination of trends in residuals is the ability to uncover misidentification of models. The examination may suggest an inappropriate form for the equation was used, or may suggest that important variables are missing from the model.