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<br />~ <br /> <br />The lower montane vegetation zone occurs from 820 to 1830 m (2700 to 6000 ft). It includes <br />two major plant communities, and a complex ponderosa pine plant community at the lower <br />elevation that grades into a white fir (Abies concolor) mixed conifer plant community at higher <br />elevations. <br />Little herbaceous cover is present except in open meadows and stringer meadows along riparian <br />zones. Shrubs are particularly important at the lower elevations in the lower montane vegetation <br />zone, but occur on shallower soils throughout. Large tree life forms are the dominant vegetation <br />in most of this zone. <br />The ponderosa pine community is complex because it occurs over a very wide elevational range <br />and integrates with both lower elevation and higher elevation communities. Douglas fir (Pseudot- <br />suga menziesil) is commonly found on north slopes with ponderosa pine and at lower elevations <br />with black oak (Q. kelloggil) and chaparral types. Dogwood (Cornus spp.) and big leaf maple <br />(Acer macrophyllum) are abundant on moist sites. <br />The white fir-mixed conifer plant community typically contains five important conifers: white <br />fir, incense cedar, ponderosa or Jeffrey pine (P. jeffreYl), sugar pine (P. lambertiana) and <br />Douglas fir. Black oak is an associated species at lower elevations. At higher elevations, white fir <br />mixes with red fir (A. magnifica). Three species of Ceanothus, Ceanothus integerriums, C. cor- <br />dulatus, and C. parvifolius, are common on poorer sites and are favored by fire. Along riparian <br />zones, alder species are abundant. Herbaceous cover is sparse in the white fir type and heavy ac- <br />cumulations of branches, twigs, litter, and duff occur as a result of the practice of suppressing <br />natural fire. <br />The upper montane vegetation zone occurs from 1830 to 2440 m (6000 to 8000 ft) and includes <br />three somewhat overlapping types: the Jeffrey pine forest, the red fir forest, and the lodgepole <br />pine forest (P. contorta). Typically, Jeffrey pine forests have a mosaic of shrub and herbaceous <br />plant understory including manzanita (Arctostaphylos spp.) and bear clover (Chamaebatia <br />foliolosa). Ceanothus spp. are also common understory shrubs in Jeffrey pine stands. <br />Lodgepole pine normally occurs above the red fir zone, but often occurs with red fir in a transi- <br />tion zone. The lodgePole forest is characterized by smaller trees and rather open stands with little <br />forest floor litter. Manzanita and gooseberry (Ribes spp.) shrubs are sometimes present, but on <br />the whole herbaceous and shrub understory is sparse. <br />The subalpine vegetation zone occurs from 2440 to 3050 m (8000 to 10 000 ft) and has four <br />characteristic species: western white pine (P. monticola), mountain hemlock (Tsuga <br />mertensiana), and juniper (Juniperus occidentalis) (Griffith and Critchfield [7]). Shrubby vegeta- <br />tion is sparse and litter accumulation is low at this elevation. Trees are often short and exhibit the <br />krummholz growth form. Few herbaceous plants are present except for those in occasional small <br />meadows. <br /> <br />.., <br /> <br />ti <br /> <br />Snowpacks.-Snowfall occurs throughout the American River Basin from below the 1220-m <br />(4000-ft) elevation zone to the Sierra crest. <br />There are no definitive data on snowpack duration from the 1220- to 1680-m (4000- to 55oo-ft) <br />elevation zone. It is known that snowfall occurs as low as 610 m (2000 ft) almost every year. <br />Ephemeral snowpack at lower elevations generally melts in a few days or is dissipated by rainfall. <br />No uniform snowpack line has been observed, other than immediately following snowstorms. <br />Thus, the snowpack line on any given date varies considerably from year to year. <br />When melt begins, rapid upward movement of the snowline occurs. It moves upward faster on <br />south and west slopes than on the colder north and east slopes. <br />Available snow course data at lower elevations begins on February 1. However, at the CSSL, <br />an average of 25 percent of the precipitation has fallen by December 18. This amount has fallen as <br /> <br />IV-9 <br />