MONITORING THE GROWTH OF AMERICAN BEECH AFFECTED BY BEECH BARK DISEASE IN MAINE USING THE KALMAN FILTER

The effect of beech bark disease on tree growth was tracked using pair ed resistant and susceptible American beech trees in two locations in Maine. Within each site, the paired trees were chosen in close proximi ty and with similar morphological characteristics (e.g. stem diameter and crown class) to minimize environment effects in subsequent analysi s. A Kalman filter approach was employed to analyse the yearly time-de pendent mean differences between paired susceptible and resistant tree -ring widths using simple structural time series models in state space form. On one site, under the influence of a moderate maritime climate , stand dynamics is hypothesized to account for the 34 year difference in onset of decline of trees in codominant, versus those in the inter mediate crown classes. The harsher winter conditions associated with t he second, more northerly site and known to limit the insect component of the disease complex, are hypothesized to be more of a factor in th e close (six year) difference in decline onset between the two crown c lasses on this site. Some strengths and cautions in the Kalman filter approach are discussed in relation to the analysis of time-dependent t rends in tree-ring series.