John Hekman has posted up a couple of comments on the possible effect of Owens Lake desiccation (due to diversion of Los Angeles water supply) on bristlecones. His notes and link are extremely interesting. The very unusual 20th century growth rate of the bristlecones was attributed by Graybill and Idso  to CO2 fertilization. In our E&E article, we surveyed other possible non-climatic factors which had not been eliminated, ranging from nitrate and phosphate fertilization to 19th century sheep grazing – all of which had been connected in one way or another to specific bristlecone sites. John Hekman posted up comments #1 here and recently here on the desiccation of Owens Lake near the White Mountains, after the water supply was diverted to Los Angeles in 1913 (wasn’t this the context of the movie Chinatown?). The url states:
During the late 1800’s and early 1900’s the lake fluctuated between about 7-15 m deep and had an area of about 280 km2, depending on drought conditions and irrigation diversions; the irrigation withdrawals were large enough to desiccate the lake eventually (St. Amand et al., 1986). Steamboats hauled ore across the lake from mines in the Inyo Range (fig. 1). Water was first diverted from the Owens River to the City of Los Angeles in 1913, and by 1926 Owens Lake was dry. The dry bed of Owens Lake has produced enormous amounts of windblown dust since the desiccation of the lake (fig. 2). The term "Keeler fog" (for the town on the east side of the lake, figs. 1 and 2b) was coined locally decades ago for the pervasive, unusually fine-grained, alkaline dust that infiltrates the smallest cracks and contaminates residences. The lake bed is probably the largest single source of PM10 dust (aerosol particles smaller than 10 microns in aerodynamic diameter) in the United States; by one estimate, 900,000-8,000,000 metric tons per year (Gill and Gillette, 1991). …. Marchand (1970) showed that as much as 50 % of the silt fraction of soils at high elevations in the White Mountains consisted of eolian dust, probably derived from Owens Valley and exposed sediment of Pleistocene Lake Owens over thousands of years, and modern storms originating on the Owens Lake playa have deposited measurable amounts of dust on the Ancient Bristlecone Pine Forest in the White Mountains (Gill, 1996).
One of the unique features of bristlecones, which we mentioned but did elaborate on, is that the White Mountain bristlecones accounting for the extra growth tend to be located on dolomite substrate, which is very low in nutrients. It doesn’t take a lot of imagination to suppose that the aeolian dust would have more nutrients than the dolomite soil and could easily affect growth rates on marginal bristlecone sites in the White Mountains and marginal (cousin) foxtail sites in the Sierra Nevadas.