Ecological site group description

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

Physiography

This ESG is found on gentle slopes (

Climate

The average annual precipitation in this MLRA is typically 20 to 65 inches but can range from 13 to 123 inches (176 to 2,471 millimeters). This ESG typically averages under 25 inches. It is lowest in the lower valleys and highest on the mountain peaks. The precipitation falls mainly from fall to spring, mostly as snow. Winter precipitation is from Pacific storms that are frontal in nature. The amount of precipitation decreases from west to east. Summers are typically warm and dry, but there are occasional thunderstorms. The average annual temperature is 27 to 61 degrees F (-3 to 16 degrees C). The frost-free period for this ESG is generally less than 100 days, and the freeze-free period averages 215 days and ranges from 85 to 350 days. The lowest annual temperatures and the shortest freeze-free periods occur in the mountains.

Soil features

The soils of this ESG are mesic Mollisols and Alfisols ranging from loams, sandy loams, gravelly sandy loams and stony sandy loams that are very deep, well drained soils derived from tephra deposits with some higher available water capacities.

Representative soils include:

Fleener, an Andic Argixerolls
Gasper, a Andic Haploxeralfs
Jimmerson, a Vitrandic Palexeralfs

Vegetation dynamics

This ESG is primarily dominated by ponderosa pine forests and an understory of chaparral shrubs and perennial grasses and forbs. Across the range, successional advancement is slower in the drier areas. In many fire-excluded areas, ponderosa pine and other early-seral, shade-intolerant tree species have been replaced successionally by late-seral, shade-tolerant species. Stand structure has changed from a mostly single canopy layer to multiple canopy layers.

The ponderosa pine habitat includes pure stands of ponderosa pine as well as stands of mixed species in which at least 50% of the canopy area is ponderosa pine. Associated species vary depending on location in the state and site conditions. Typical tree associates include white fir, incense-cedar, Coulter pine, Jeffrey pine, sugar pine, Douglas-fir, canyon live oak, California black oak, Oregon white oak, Pacific madrone and tanoak.

Associated shrubs include manzanita, ceanothus, mountain-misery, Pacific dogwood, hairy yerba-santa, yellowleaf silktassel, bitter cherry, California buckthorn, poison-oak, Sierra gooseberry. Grasses and forbs include slimleaf brome, Orcutt brome, carex, smallflower melicgrass, bluegrass, bottlebrush squirreltail, bedstraw, bracken fern, bush morning-glory, rhomboid clarkia, Child's blue-eyed mary, shrubby eriastrum, splendid gilia, Sierra iris, whisker-brush, Inyo bush lupine, summer lupine, purple nightshade, streptanthus, gooseroot violet, and wild iris.

Montane chaparral species are common post-disturbance on these deeper forest soils. After disturbance (logging, fire, erosion) chaparral proliferates and may exclude conifers and other vegetation for many years. However, chaparral may facilitate the germination of red fir seedlings and other shade tolerant conifers by providing a protective cover, moderating microclimate, and improving soil conditions. Chaparral shrubs may be an essential link in forest succession by building up soil nutrient levels, especially nitrogen, to the point where trees can survive. In mature timber stands, chaparral species may senesce due to insufficient light through the canopy and are only present as a sparse understory. Thus, silvicultural practices have a strong influence on the structure of montane chaparral.

Ranges from being dominated mostly by ponderosa pine, incense cedar, greenleaf manzanita, pinemat manzanita, snowbrush ceanothus, squirreltail and scattered white fir at the driest end of the concept and dominated by Jeffrey pine, white fir, incense cedar, Douglas-fir, sugar pine, greenleaf manzanita. Ponderosa pine, California black oak, pinemat manzanita, snowbrush ceanothus, bush chinkapin, mountain whitethorn, serviceberry, pacific dogwood, snowberry, rose, needlegrass, bottlebrush, squirreltail in the cooler, wetter areas.

FEIS. Pacific Ponderosa Pine, https://www.fs.fed.us/database/feis/plants/tree/pinponp/all.html. Accessed September 28, 2020.

California Wildlife Habitat Relationships System
California Department of Fish and Game
California Interagency Wildlife Task Group
E. Lee Fitzhugh

Major Land Resource Area

MLRA 022B
Southern Cascade Mountains

Stage

Provisional