Using a geographic information system (GIS) to associate forest stand characteristics with top kill due to defoliation by the jack pine budworm

The occurrence and spatial distribution of top kill 1 year following a jack pine budworm (Choristoneura pinus pinus Freeman) outbreak were examined for possible associations with forest stand characteristics derived from resource inventory maps. Associations were computed between top-kill severity and jack pine (Pinus banksiana Lamb.) maturity, stand height, crown closure, and site quality. Three different measures of association with data from a geographic information system (GIS) (Cramer's V, Spearman's nonparametric rank correlation, and Minnick's coefficient of areal determination) were used to assess the strength of these associations. There were no statistical differences among average top-kill lengths, which averaged 2 m, among the light, moderate, and severe top-kill categories. The proportion of trees that experienced top kill ranged from 55% in the light to 61% in the severe top-kill classes. Site quality and stand maturity were more highly associated with top kill than stand height and crown closure. Jack pine areas that sustained moderate and severe top kill were those on poor sites that were overmature (> 85 years), 15-20 m tall with 30-55% crown closure. The GIS approach can be a useful tool for identifying vulnerable stands, and increasingly so as forest inventory classification systems become more detailed.