M261D
Southern Cascades
Location map, M261D

Ecology

The Southern Cascades section extends north from the Sierra Nevada to the Oregon border and lies between the Modoc Plateau to the east and the Klamath Mountains to the west. At low elevations, the coniferous vegetation is gray pine, and as elevation increases, vegetation is a mixture of ponderosa and sugar pines, Douglas-fir, and white fir. Mid-elevation zones have white fir with some
sugar and ponderosa pines, and incense-cedar. At high elevations, red fir, lodgepole pine, and whitebark pine are found; Jeffrey pine also grows at the high elevations and on drier sites.

Forest Health Issues

The extended dry period continues to affect most conifer species in this section. Normal or above normal precipitation has been observed in only 2 of the past 11 years—1993 and 1995 (see weather discussion). Pine and fir mortality in 1994 and 1995 was above normal in many areas because of extreme moisture stress and bark beetle and engraver attacks. Insect damage that is of minor importance was more pronounced on many conifer species because the drought reduced individual tree resiliency.

Jeffrey pine. Jeffrey pines are characterized as being drought tolerant, but the number of Jeffrey pines killed by Jeffrey pine beetle increased markedly over the past two to three years in this section, despite the relief from the drought during 1993. Groups of dead trees were concentrated in Lassen Volcanic National Park and adjacent areas to the north and east on the Hat Creek and Eagle Lake Districts, Lassen National Forest (fig. 18). Several groups of attacked trees in the general vicinity of each other are commonly visible. These groups of dead trees sometimes cover several acres of a drainage. One infestation near Lost Creek, in Lassen Volcanic National Park, started about three years ago as a small group attack, and during 1994, more than 800 trees were attacked in this area.

Pine mortality caused by Jeffrey pine beetle
Figure 18 — Concentrations of pine mortality caused by the Jeffrey pine beetle, 1994 and 1995.
 

Large, individual trees have been attacked and killed over the past three years around Manzanita Lake, Manzanita Lake Campground, administrative sites, and Butte Lake at the north end of Lassen Volcanic National Park. Affected trees included some of the largest specimens (>50 inches dbh) known for this species.

Forest health concerns in young Jeffrey pine are few, although insects occasionally cause damage. An outbreak of pine needle sheathminer caused extensive damage to Jeffrey and ponderosa pines in a mixed plantation in the Pondosa Burn, east of Pondosa, Siskiyou County. The infestation in 1994 was estimated at more than 1,000 acres, and several hundred of these acres on the east side of the plantation were heavily defoliated. Although 1995 populations were significantly less than in 1994 (1.8 larvae per shoot vs. 9.4 larvae per shoot), they were high enough to cause noticeable defoliation.

Lodgepole pine. Lodgepole pine mortality from attacks by the mountain pine beetle increased over the past two to three years. A substantial proportion of the lodgepole pines around Crater Lake and Crater Lake Campground, Lassen National Forest, died during 1994. Chronic mortality from beetle attack exists between Butte and Snag Lakes in Lassen Volcanic National Park. North of the Park, groups of lodgepole pines were killed by mountain pine beetles in the Thousand Lakes Wilderness, Lassen National Forest.

Ponderosa pine. Western pine beetles, mountain pine beetles, and the effects of prolonged drought were the most common causes of ponderosa pine mortality in the southern Cascades. In some areas, the number of affected trees decreased, but mortality remained above normal. The greatest increases in mortality were on the Goosenest District, Klamath National Forest; on the drier sites near McCloud Flats, eastward to Pondosa; and in the Lake Britton-Burney basin area, Shasta-Trinity National Forests. Mortality of individual trees and groups of ponderosa pines were common on the Eagle Lake and Hat Creek Districts, Lassen National Forest. Mountain pine beetles were associated with smaller trees, and western pine beetles were found in the larger trees.

Other insects damaged trees in several areas. Snow breakage and increases in populations of California fivespined ips during 1993 resulted in top-killed groups of ponderosa pine on McCloud Flats, McCloud District, Shasta National Forest, in 1994. Pine needle sheathminer caused extensive damage to ponderosa and Jeffrey pine in a mixed plantation in the Pondosa Burn (see Jeffrey pine, this section). An infestation of western pine shoot borer reduced terminal growth in several thousand acres of ponderosa pines in the Pondosa Burn. Infestation rates in 1994 were similar to those detected in 1993, with 20 to 40% of terminals infested.

Sugar pine. Sugar pine mortality caused by drought and mountain pine beetle has continued to increase across northern California since the early 1990s. Overstory trees were killed as in previous years, but mortality was also detected in younger age classes. Killed trees were scattered throughout the Lassen National Forest.

White fir. White fir mortality continues in eastside vegetation types throughout the Southern Cascade section. Fir engravers, overstocking, overabundance of white fir, and drought have contributed to extremely high mortality in white fir. Mortality has been chronic in the Ball Mountain Late-Successional Reserve, Goosenest District, Klamath National Forest. Scattered white fir mortality is visible from almost any viewshed where the species exists on the Lassen National Forest. Mortality on the Lassen continued to be noted on PegLeg, Antelope, and Harvey Mountains, Eagle Lake District, and around the Thousand Lakes Wilderness Area, Hat Creek District. The rapid deterioration of the white fir after mortality has altered forest stand structure, added to the fuel loading, and increased the amount of sunlight reaching the ground.

Aspen. Many aspen clones have declined in extent or disappeared altogether in northeastern California. This decline is due in large part to decades of season-long grazing access by domestic livestock, and to changes in fire occurrence. Two situations are common: remnant trees in meadows with sparse or absent regeneration, and mature or old aspen stands that are being overgrown with conifers such as white fir, lodgepole, and western juniper. In contrast, a few clones appear vigorous and healthy with a full-crowned overstory and abundant regeneration in several different size classes (Sydney Smith, personal communication).

Current Forest Health Activities

Several forest-health restoration projects are underway on the Lassen National Forest; they were initiated because of increased tree mortality and include both salvage and thinning. Several analyses have determined pre-European forest conditions, which ecosystems are outside of the natural range of variability, and what efforts can restore these ecosystems to their desired state. Thinning in plantations and natural stands are in progress, with the goal of preventing future mortality related to bark beetles and engravers and reducing fuel buildup.

Studies to monitor Jeffrey pine beetle outbreaks were initiated in three areas during 1995: Lost Creek, and Manzanita Lake Campground and its administrative sites, both in Lassen Volcanic National Park; and the Pole Springs area, Eagle Lake District, Lassen National Forest. All infested trees were tagged and recorded. Monitoring will continue until the outbreaks decline.

In northeastern California, the number of male Douglas-fir tussock moths caught in monitoring traps increased from 1994 to 1995. The most pronounced increase was on the Eagle Lake District, Lassen National Forest. Larval sampling will be conducted in the summer of 1996. (See "Current Forest Health Activities," M261E).

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