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Last modified
7/28/2009 2:42:25 PM
Creation date
4/30/2008 2:47:32 PM
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Template:
Weather Modification
Project Name
Sierra Ecology Project
Title
The Sierra Ecology Project - Volume II - Workshop IV, Workshop V
Date
7/1/1980
Weather Modification - Doc Type
Report
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<br />~ <br /> <br />Glacial soils tend to be shallow and devoid of much character, primarily because of historic <br />climatic patterns. Table 1 illustrates the very wide range of soil conditions encountered in the <br />watershed. Textures range from coarse, sandy loam to clay; permeability from as slow as 5 to <br />15 mm/h (0.2 to 0.6 in/h) to the rapid rate of 50 to 160 mm/h (2.0 to 6.3 in/h); plant available <br />water-holding capacity from a low of 0.11 mm of water for each millimeter of soil to a high of <br />0.18 mm of water for each millimeter of soil; and pH ranges from 5.1 to 7.3. <br />Soil freezing is a phenomenon of some importance in cold regions. Frozen soils do not allow <br />water to infiltrate and are subject to large damaging volume changes called "frost heaving." The <br />main periods of freezing and thawing occur during cold periods prior to snowfall at the beginning <br />and the end of the snow season. Soil freezing is not a major problem in zones where snow <br />blankets the soil prior to cold weather. <br /> <br />" <br /> <br />~ <br /> <br />Vegetation.- The American River Basin is a complex of four intergrading vegetation zones <br />along an elevational gradient. They are: valley grassland and savannah, 9 to 820 m (30 to 2700 ft); <br />lower montane, 820 to 1830 m (2700 to 6000 ft); upper montane, 1830 to 2440 m (6000 to 8000 ft); <br />and subalpine, 2440 to 3050 m (8000 to 10 000 ft)' Mosaics of herbaceous, shrub, and tree vegeta- <br />tion aggregations exist in different relative magnitudes in all four vegetation zones except in the <br />harshest environments of the subalpine zone, where trees may not exist. Few trees or shrubs are <br />present in the valley grassland and few shrubs are present in the savannah zone. Several major <br />plant communities can be identified with each of the four vegetation zones. The discussion of im- <br />portant plant communities will be limited to life forms or species that constitute a particularly <br />abundant component of the vegetal cover (relating to water use and soil protection) or those that <br />have extraordinary impacts on nutrient cycles or sediment movement. <br />Seven important plant communities are recognized from the foot of the American River Basin <br />to about 820 m (2700 ft) elevation: the California annual type (Heady [4]); the woodland savan- <br />nah (Munz and Keck [5]); four phases of foothill woodland including valley oak, blue oak, in- <br />terior live oak, and north slope phases; and the riparian forest (Griffith [6]). Except for the north <br />slope phase of the foothill woodland plant community and the riparian forest community, the <br />dominant herbaceous plants in these communities are generally annual grasses including the <br />genera Bromus, Festuca, A vena, Hordeum, Aira, Gastridium, and many others. Important her- <br />baceous forbs include the genera Erodium, Medicago, Agoseris, Hypochoeris, Trifolium, and <br />Lotus. Typically, the north slope phase of the foothill woodland plant community and the <br />riparian forest along streams are so dense that little understory herbaceous cover exists. <br />Shrubs are the most important of the seven low-elevation plant communities in the north slope <br />phase of the foothill woodland plant community. Some of the common genera are Arc- <br />tostaphylos, Ceanothus, Quercus, Heteromeles, Rhamnus, and Rhus. Locally, especially on <br />south slopes, chaparral vegetation may dominate the foothill landscape and the shrub chamise <br />(Adenostoma fasciculatum) is often one of the dominant species along with shrub species of the <br />genera listed above~ Little understory is present on chaparral-covered sites except after fire. <br />Various species df oak (Quercus spp.) are dominant in six of seven plant communities in the <br />vegetation zone below 820 m (2700 ft). Q. lobata, douglasii, and kelloggii are winter deciduous <br />while Q. wislizenii and chrysolepis are evergreen. The deciduous buckeye (Aesculus californica) <br />and evergreen California bay (Umbellularia californica) are important in the north slope phase of <br />the foothill woodland plant community. The conifer digger pine (Pinus sabiniana) is often abun- <br />dant at the higher elevations of the foothill woodland plant communities. Ponderosa pine (P. <br />ponderosa) occurs as low as 305 m (1000 ft) but is more abundant at higher elevations with in- <br />cense cedar (Libocedrus decurrens). Cottonwoods (Populus), sycamore (Platanus), and alder <br />(Alnus) are abundant along riparian zones. <br /> <br />; <br /> <br />IV-7 <br />
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