White ash increased in basal area between 1962 to 1979 on continuous forest inventory (CFI) plots in Massachusetts, but 20% of 82 ash plots ($>$10% basal area ash) were classified as decline (from growth and mortality rates). Reclassification of 18 plots on the basis of % crown dieback in 1991 validated the decline classification system and indicated little change in plot decline status in the past decade. Mortality of dominant and co-dominant trees was associated with sites characterized by a high landscape position and soils shallow to bedrock (R$\sp2$ = 0.6926, p = 0.0007). Ephemeral streams were common; these sites would be prone to fluctuations in moisture supply. Similar relationships were identified on three 2 ha intensive study sites. Distribution of decline-prone microsite types and decline of ash was highly heterogeneous on the study sites (but not on the CFI plots). Tree-ring analysis showed that trees growing on 'decline-prone' sites were sensitive to drought (measured by growing year Palmer Drought Severity Index) and indicated that the present episode of decline on these sites began in the 1960s, the most severe drought period since 1836. Ash yellows was identified on one and possibly the second of the two study sites with ash decline, and on two of the three decline CFI plots resampled in 1991. Sites with a SI $>$ 80 supported healthy trees in 1991. For sites with a SI $<$ 80, a decline index estimated from landscape position and soil moisture predicted the distribution of decline on the two intensive study sites on which ash decline was present and shows promise as a method of evaluating sites for their potential for ash decline. The relationship between decline and site factors was unique to white ash among several species tested (i.e. it was species-specific). On ash decline sites, red oak and sugar maple increased in relative importance.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8690 |
| Date | 01 January 1993 |
| Creators | Woodcock, Hilary |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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