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    Giant sequoia [Sequoiadendron giganteum (Lindl.) Buchholz] groves are found entirely within the Sierra Nevada mixed-conifer type. Several of its companion tree species, mainly ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and Jeffrey pine (P. jeffreyi Grev. & Balf.), show foliar injury after exposure to present levels of ozone in the southern Sierra Nevada. Observations at nine giant sequoia groves in Sequoia National Park from August 1983 through September 1986 showed that surviving seedlings in 1986 averaged 18 percent of the original number. These observations did not provide evidence of a causal relationship between ozone exposure and seedling mortality. Field fumigation studies with container-grown seedlings at Giant Forest during the summers of 1987 and 1988 tested morphological and physiological responses of seedlings exposed to charcoal-filtered air, I X, and 1.5X the ambient ozone concentration for the entire summer season. In both 1987 and 1988, very slight levels of visible ozone injury to cotyledonary and primary leaves were observed in fumigation chambers and at sites in natural groves at 1X ambient ozone concentrations; however, at 1.5X ambient in chambers the symptoms of foliar injury were extensive. The end-of-season harvests of seedlings exposed to 1.5X ambient ozone showed no significant reductions of root, shoot, or total plant weights in 1987 or 1988. Gas exchange measurements made during the 1988 experiment found that ozone exposure of seedlings and rooted cuttings to 1.5X ambient ozone over the duration of a growing season increased the light compensation point, lowered CO, exchange rate at light saturation, and increased dark respiration compared to controls. A 2-month branch-chamber fumigation of large giant sequoia saplings (120 years old) with charcoal-filtered air and ozone at IX, 2X, and 3X ambient ozone concentrations did not yield visible injury or any detectable changes in photosynthetic rates.

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    Miller, P.R.; Grulke, N.E.; Stolte, K.W. 1994. Air pollution effects on giant sequoia ecosystems. USDA Forest Service Gen. Tech. Rep.PSW-151: 90-98.

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