The relationship between site factors and white ash ( Fraxinus americana L.) decline in Massachusetts

Abstract

Forest inventory records incorporating individual tree data are an important source of information about the extent and severity of past rates of forest decline, thus providing a temporal perspective for contemporary observations. We demonstrate the potential of this approach by using continuous forest inventory (CFI) data to reconstruct the extent, severity, pattern of development and site-factor associations for white ash decline in Massachusetts. White ash ( Fraxinus americana L.) increased in basal area on Massachusetts CFI plots at about 1.5% per year from 1962 to 1979. Ash decline is, however, locally severe. Plot decline status was estimated, based on vigor rating, and growth and mortality rates of white ash. Plots with a mean change in basal area per year of ⩽ −0.5% and/or with a mean vigor rating of ⩽2.0 (on a scale of 0–4) were classified as ‘decline’. Using these criteria, 20% of the 82 CFI plots with ⩽10% total basal area of white ash in 1962 were classified as ‘decline’ in both 1979 and 1991. These results suggest that statewide there has been no net loss of ash basal area since 1962. The total forest area affected by ash decline has not increased in the past decade. Analyses of the CFI data indicate that decline was most prevalent on mesic sites, high on the landscape and/or on steep slopes. Such sites are potentially subject to large fluctuations in soil moisture availability during drought periods. Relationships identified between the prevalence of ash decline and site factors were further evaluated within a 2 ha intensived study site in the center of a 13 ha white ash stand affected by ash decline in 1990. Decline was heterogeneously distributed within the stand, with declining trees most frequent on the ‘decline-prone’ site-type identified through CFI plot analyses.