Acid Deposition Long-Term Trends (1986) / Chapter Skim
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6. The Nature and Timing of the Deterioration of Red Spruce in the Northern Appalachian Mountains
6. The Nature and Timing of the Deterioration of Red Spruce in the Northern Appalachian Mountains
Pages 200-230
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From page 200... ...
Because of the lack of documented mechanisms, only circumstantial evidence supports claims that acid rain has caused damage to spruce in eastern North America. The suspicion that atmospheric deposition may play a role in the decline of red spruce is supported mainly by the facts that large-scale changes in the forest have taken place in high-elevation areas receiving airborne heavy metals and acidic substances at rates that appear to be greater than those experienced by almost all other forested areas in North America and that no obvious natural cause has been documented.
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From page 201... ...
HIGH-ELEVATION CONIFEROUS FORESTS OF THE APPALACHIANS Researchers have long studied the zones of vegetation types that exist on the mountains of the eastern United States where forest composition varies along an attitudinal gradient. Subalpine stands dominated by fir and/or spruce occur from tree line down to 750 m in the White Mountains (New Hampshire)
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From page 202... ...
(d) Growing season throughfall collected by three to five rain gauges under the canopy at seven elevations.
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From page 203... ...
Logging, fire, landslides, and windthrow have affected the composition and structure of the coniferous forests that have been studied in relation to red spruce decline. There is evidence that red spruce was a much more important component of the coniferous and hardwood forests of the northern Appalachians prior to the period of extensive timber harvesting in the late 1800s and early l900s (Siccama 1971)
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From page 204... ...
in the subalpine balsam fir forest is estimated to be three to six times greater than in the lower lying hardwood forest TABLE 6.1 Annual Deposition in Bulk Precipitation to a Northern Hardwood Forest at Hubbard Brook, New Hampshire, Compared with Estimated Annual Deposition by Bulk Precipitation and Cloud Droplet Capture in a Subalpine Balsam Fir Stand on Mt. Moosilauke, New Hampshire Hubbard Brook (Northern Hardwood Forest)
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From page 205... ...
. Values for major ion deposition at high elevation in the northern Green Mountains estimated from rime ice chemistry, cloud chemistry, and droplet capture by artificial collectors (Scherbatskoy and Bliss 1984)
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From page 206... ...
. Between 1966 and 1981, lead concentrations in the forest floor at Camels Hump increased by 57 percent in the northern hardwood (548 to 731 m)
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From page 208... ...
To date, the estimates of atmospheric inputs are imprecise because there are few data from short periods of record that show large variations in chemical compost tion. Largely because of the effect of cloud-droplet interception, the subalpine coniferous forests apparently receive acidic substances and heavy metals at rates that appear to be greater than the rates in neighboring lowelevation forests.
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From page 209... ...
(1984) have offered an important perspective on the current status of red spruce in the northern Appalachians.
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From page 210... ...
, but the understanding of biotic agents associated with deteriorating red spruce is incomplete because no systematic studies of the occurrence of pathogens have been reported. Changes in Red Spruce Populations Johnson and Siccama (1983)
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From page 211... ...
and dead red spruce at systematically sampled sites in the northern Appalachian Mountains. Only trees of >10-cm dbh (diameter at breast height)
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From page 212... ...
in six diameter classes is shown in Figure 6.5. These data indicate that the canopy of the northern stands is multiaged and that dead red spruce composed a similar proportion of all diameter classes with some increase in the larger size classes.
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From page 213... ...
30 40 50+ FIGURE 6.5 Percent dead red spruce in six diameter classes (DBH; diameter at breast height) at northern Appalachian sites.
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From page 214... ...
Initiation of Red Spruce Deterioration The current period of rapid deterioration of red spruce in the northern Appalachians appears to have begun sometime between the late 1950s and mid-1960s. This conclusion is based on documentation of patches of dying spruce in Vermont and New Hampshire by the early 1960s and by examination of tree rings from several sites in the Northeast.
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From page 215... ...
Qualitative examination of annual rings of red spruce in the northern Appalachians showed a series of very narrow rings beginning during the early 1960s and often continuing to 1982, when the trees were cored (Johnson and Siccama 1983)
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From page 216... ...
The start of the change in ring width appears to have begun in the period 1960-1965. The same pattern was found for ring width indices for red spruce in lower-elevation hardwood-spruce stands in the central Adirondacks (Roman and Raynal 1980)
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From page 219... ...
219 C , _ ~o _ o er (Ww)
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From page 220... ...
. 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 YEARS FIGURE 6.11 Actual and estimated red spruce tree ring indices at Lake Arnold in the Adirondack Mountains (elevation 1150 m)
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From page 221... ...
Another is that continual or increasing stress to which red spruce is particularly susceptible has caused widespread injury, mortality, and collapse of the canopy in high-elevation stands. We are unaware of any clear evidence that balsam fir are deteriorating except as a secondary consequence of gap formation and the attendant increase in microclimatic stress (i.ee, increased susceptibility to wind and winter damage)
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From page 222... ...
is an important determinant of vegetative patterns, the synchronized spruce mortality across a broad region, and mortality in all size classes, are different from the disturbance phenomena currently recognized as contributing to present-day vegetative patterns is subalpine spurce-fir forests (Foster and Reiners 1982)
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From page 223... ...
but show the same share rina widen decrease over the past 20 years. _ _ ~ _ _ , _ _ The subalpine forest on the west side of Mount Washington is a virgin forest, and it shows dieback, mortality, and decreased ring width in the same way as the rest of the high-elevation sites.
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From page 224... ...
suggest an adverse effect of cold winter temperatures and cool spring temperatures on annual ring width, although no physiological connection has been established. Numerous reports of severe winter damage, particularly during the past 20 years, suggest that red spruce is susceptible to damage from winter conditions, particularly after mid-winter thaw (Curry and Church 1952, Pomerleau 1962, Friedland et al.
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From page 225... ...
The effects of cool springs and cold winters may be of particular importance to spruce growing near the top of its elevational range where the growing season length may be marginal under average conditions. Acidic substances, heavy metals, and gaseous pollutants alone or in combination could alter life-maintaining processes in forests.
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From page 226... ...
and in higher elevation studies where deposition is higher, and where trees are in contact with acidic cloud water for a substantial part of the year. The abrupt and synchronous changes in ring width and wood density patterns across such a wide area seem more likely to be related to climate than to air pollution.
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From page 227... ...
1984a. Trace metal content of the forest floor in the Green Mountains of Vermont: spatial and temporal patterns.
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From page 228... ...
1982. Cloud droplet deposition in a subalpine balsam fir forest: hydrological and chemical inputs.
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From page 229... ...
Note 59. Upper Darby, Pa.: USDA Forest Service, Northeastern Forest Experiment Station.
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From page 230... ...
1981. The Hubbard Brook ecosystem study: biogeochemistry of lead in the northern hardwood forest.
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