San Bernardino National Forest

Extent and Intensity of Iq niy to Oveistoiy Trees in the San Bernardino National Forest... 

Data for the longest observation period of tree decline extend from 1952 to 1972 in two 5-acre (2-ha) control plots in the vicinity of Barton Flats in the San Bernardino National Forest. These plots are m the Jeffry pine-white fir subtype and are now considered to be in an area of... 

TABLE 12-4 Changes of Timber Volume and Percentage of Total Jeffrey Pines in Four Insect Risk Qasses at Two Control Plots Excluded from Sanitation Salvage Logging between 1952 and 1972 at Barton Flats, San Bernardino National Forest... 

Aocumulatkm daring IO yr period. Data obtained from the Superviaor OfAoe. San Bernardino National Forest. 

Ada]>ted from Miller/ Trees ftom 575[Pg.624]

California black oak and white fir and less often on incense cedar in the San Bernardino Mountains. No direct effects of oxidants have been noted on the mistletoe plant itself under field conditions. The true mistletoe obtains mainly water from its host and would be indirectly affected by debilitation of die host tree. The dwarf mistletoes Arceuthobium spp.) are common on ponderosa, Jeffry, and sugar pines in the San Bernardino National Forest. They depend on their host for both water and carbohydrates. Heavily infected or broomed" branches on ponderosa or Jeffrey pines severely injured by ozone often have more annual needle whorls retained than do uninfected branches on the remainder of the tree. The needles are also greener. It can be hypothesized that the infected branch is a carbohydrate sink where a pooling of carbohydrates occurs higher carbohydrate concentrations may be instrumental in either preventing or helping to repair ozone injury to needles on the broomed branches. In the long term, stresses from mistletoe and ozone are probably additive and hasten tree death. 

Photochemical injury to ponderosa pine in the San Bernardino National Forest of California is a serious problem there. Screening for resistance to ozone is being carried on in preparation for conducting a formal breeding program (16). 

In 1969 an aerial photo survey by the U. S. Forest Service of the San Bernardino National Forest showed that 1.3 million ponderosa or Jeffrey pines (12 inches or larger, diameter at breast height) on more than 100,000 acres were affected to some degree (4). 

How have ozone and insects interacted to damage trees in the San Bernardino Mountain National Forest of California ... 

Infection by dwarf mistletoe and true mistletoe of conifer hosts is commonplace in the San Bernardino and Angeles National Forests. There is no experimental evidence to define the ozone sensitivity of the aerial shoots of the mistletoes relative to the foliage of their conifer hosts. Cursory observations of dwarf mistletoe on pines suggest no injury to dwarf mistletoe shoots. The dwarf mistletoes derive their elaborated carbohydrates entirely from their host (31), and ozone probably depletes the stored carbohydrates of needle tissue (26) which may have been translocated to the parasite. The combined effect of these agents probably means greater stress on the host. On the other hand, true mistletoes manufacture their own carbohydrates (31) and may benefit the host if they are less sensitive to oxidant than the host tree. 

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