Camels Hump
Long-Term
Vegetation Study

Timothy D. Perkins, Ph.D
Forest Decline Project
Department of Botany & Agricultural Biochemistry
University of Vermont

Vegetation surveys on Camels Hump mountain in the Green Mountains of Vermont were initiated by Thomas Siccama as part of his doctoral research in 1964 (Siccama 1968).  Visible mortality of trees in high elevations led to a follow-up survey in 1979, which revealed significant reductions in red spruce density and basal area (Siccama et al. 1982).  Subsequent surveys were conducted in 1983, 1986, 1990, and 1995 (Vogelmann et al. 1985, 1988, Klein and Perkins 1992, Perkins unpublished).  The next survey is tentatively scheduled to take place in the year 2000.

Sampling is conducted at 200 ft elevational intervals from 1800 to 3800 ft on the southwest slope of Camels Hump along the Burrows trail.  Ten 10' x 100' plots are used at each elevation from 1800 to 2800 ft, and five plots from 3000 to 3800 ft. 

Density (the number of trees) and basal areas (a measure of the cross-sectional area of live standing wood) of trees > 2.0 cm diameter at breast height (dbh) are shown for each sampling year in the table below. Calculations are based upon areas within the natural distribution zone for each species (Vogelmann  et al. 1988).

Figure 1. Density of red spruce and balsam fir   
by diameter size class                                         

By looking at the diameter distributions of red spruce and balsam fir (Figure 1), we can see that the majority of the increase in density of red spruce has resulted from new recruitment and growth of seedlings (< 2.0 cm dbh) into the sapling size (2-5 cm dbh).  This follows a trend which started in 1990.  Some of the red spruce saplings have grown enough to move up to the next larger size class (5-8 cm dbh) as well.  Only small changes were observed in the larger diameter size classes.

Balsam fir density increased in most size classes (except 8-10 cm) due to recruitment of seedlings into the sapling size class and also because of growth of surviving trees into larger size classes.

This leads us to the question of whether or not red spruce decline is over.   Recent evidence supports the notion of at least a temporary recovery.  Radial increment growth  has increased in surviving trees in recent years (Siccama unpublished).   Density of red spruce trees is increasing, at least in the smaller size classes.   Basal area is also increasing slightly. Vigor of red spruce has also been higher in the last two vegetation surveys (Figure 2)

Figure 2. Vigor of red spruce trees (> 2.0 cm dbh)
on Camels Hump, Vt.
In this figure, the green color indicates healthy trees, yellow represents moderate levels of defoliation, and red indicates severe defoliation. Vigor of the red spruce tree population (measured as defoliation) decreased sharply in 1986, but has increased steadily since.

All of these indicators seemingly point to a recovery of health in the high-elevation forest on Camels Hump.  It is important to note however, that winter injury has been relatively light over the past several years.  Severe, repeated winter injury to current-year red spruce foliage is believed to be mechanism which precipitates decline in red spruce.  Although the precise physiological mechanisms and mode of damage (extreme cold, thaw-induced dehardening, rapid freezing, freeze-thaw cycling) are not known, it is clear that acidic deposition in some manner renders red spruce foliage susceptible to winter conditions.

For further information about this research contact Dr. Tim Perkins at (802) 899-9926 or  tperkins@zoo.uvm.edu

References

Klein, R.M. and T.D. Perkins.  1992.  Long-Term Fates of Declining Forests. Chapter 19. pp. 360-373. In: D. Dunnette and R.J. O'Brien (Eds.). The Science of Global Change. American Chemical Society, Washington, D.C.

Acknowledgements

This research was funded in part by the A.W. Mellon and R.K. Mellon Foundations and the Conservation & Research Foundation.