G. Segura et al., VARIATIONS IN RADIAL GROWTH OF DECLINING OLD-GROWTH STANDS OF ABIES AMABILIS AFTER TEPHRA DEPOSITION FROM MOUNT ST-HELENS, Canadian journal of forest research, 25(9), 1995, pp. 1484-1492
Radial growth trends of old-growth mixed conifer forests were evaluate
d in areas impacted by tephra deposition from the 1980 eruption of Mou
nt St. Helens, Washington. These areas were characterized by a crown d
ecline in Abies amabilis (Dougl.)Forbes (Pacific silver fir), associat
ed with the long-term tephra retention by foliage. Post-1980 growth ch
anges of A. amabilis were quantified using standard dendrochronologica
l techniques in stands covering a range of crown decline conditions, a
mount of tephra deposited, elevation, and species composition. Time-se
ries models revealed autocorrelations in the growth trend of all speci
es at all sites. intervention analysis quantified posteruption radial
growth changes and significantly improved the description of the origi
nal time series models. Growth reductions of A. amabilis were generall
y consistent with the mean crown decline conditions of individual site
s. However, the magnitude of growth reductions did not correspond clos
ely to the decline condition of the stand. Abies amabilis experienced
significant post-1980 growth reductions in sites with high crown decli
ne, but no growth changes were detected in sites with low decline. Tsu
ga heterophylla (Raf.)Sarg.(western hemlock) and Pseudotsuga menziesii
(Mirb.) France (Douglas-fir), which consistently occurred with A. ama
bilis in the study area, did either not experience growth reductions o
r had significant positive growth after 1981. This positive post-distu
rbance growth could be explained as a compensatory response to the app
reciable growth decline of A. amabilis.