Warm Dry Ridges Hills and Canyons Ponderosa Pine Dry Shrub and Grass

Description

This state can have highly variable plant cover depending on fire disturbance. With frequent ground fire every 7 to 10 years the Reference Plant Community will be an open pine/grass woodland with bunchgrasses dominating and scattered pine. In variable mixed severity fires a patchy mosaic of pine stands with open areas of bitterbrush or grass will be the common appearance. With fire exclusion, a medium to dense multi-story Ponderosa pine forest will develop, creating an alternative state. Past human disturbance has allowed introduced annual and perennial grasses to establish and mix into the natural cover, sometimes out competing the native vegetation causing an alternative state.

Ponderosa pine is the only tree species. Antelope bitterbrush is the major shrub species with kinnikinnick, snowbrush ceanothus, spirea, snowberry, and sagebrush in minor amounts depending on location and moisture. Idaho fescue and bluebunch wheatgrass dominate the grass component with varying amount of geyer’s sedge, needle and thread, blue wildrye, and rough fescue.

Site Quality/Productivity:

Site index (SI) and the resulting derivation of the Culmination of Mean Annual Increment (CMAI) are different indicators of site quality, as well as an indicator of potential yield and of the general economic rotation age of a site.

Site index is a common unit of measure for forest trees and stands. It is a simple measure of the age and height relationship of dominant and co-dominant trees, usually referenced to 50 or 100 years of age (the base age). The Culmination of Mean Annual Increment (CMAI) is an expression of maximum productivity for unmanaged, even-aged stands. It is expressed as a volume measure and is given at the age of CMAI.

Ponderosa pine is the only commercially viable tree species in the MLRA in this ecological site (Douglas-fir occurs minimally). Only two site indexes values are projected for this site: 99 and 105, and they are relatively even in terms of the acreage extent that they represent. The site index value is derived from the Meyers 100-year total age table. The corresponding CMAI ranges is 99 and 105 cubic feet/acre/year at 40 years of age in a “fully stocked stand”. It is probable that the CMAI value(s) should be lower due to the low stocking (density) as compared to fully stocked stands. Most stands are less than 40 percent stocked, but it’s uncertain that this adjustment was made to the CMAI value.

Forage production estimates from NRCS Range 5 from Columbia and Walla-Walla for this particular ESD….) in Ponderosa pine / antelope bitterbrush sites are as follows, based on overstory tree canopy. Forage production figures are in pounds per acre for all vegetation below 4.5 feet (grass, sedges, forbs, shrubs, tree regeneration):
Overstory tree canopy – Forage production
0 – 20% - 800 to 1400 lbs/ac
20 – 40% - 300 to 650 lbs/ac

The bulk of the grass production is bluebunch wheatgrass and Idaho fescue. Other grass species include needle and thread grass, prairie Junegrass, rough fescue, pine grass and big bluegrass. The most prominent forbs are lupine, balsamroot, pussytoes, hawkweed, and yarrow. The most prominent shrub is bitterbrush. Other shrubs include currant, snowbrush ceanothus, big sagebrush, rabbitbrush, and buckwheat. Tree regeneration included mostly ponderosa pine with an occasional Douglas-fir.

This ecological site is in Fire Regime Group I. For more information regarding the historic wildfire characteristics of the GF-CMF ecologic site refer to the LANDFIRE Biophysical Setting Model (BpS) which cover this ecological site (Biophysical Setting model 0910531 -- Northern Rocky Mountain Ponderosa Pine Woodland and Savanna-Mesic).

BpS model 0910531 will provide a more detailed overview of the various plant communities and the associated disturbance(s) and growth over time expressions of the individual plant communities.

The BpS summary of the historic fire regime of the reference community of State 1:

Fire Regime Group Typical Fire Interval Overall Mean Fire Return Interval
MFRI, (in years)
I 8-125 years 6


Replacement Mixed Low
% of all fires 5 18 77
Average Fire Return Interval (AFRI-in years) 125 35 8
Range of Fire Return Intervals 100+ 28-75 2-8

Source: BpS Model 0910531

The historic fire event “average size(s)” is not provided in this BpS model.

Fire Severity Classes: Replacement, greater than 75 percent kill or top kill of the upper canopy layer; Mixed, 25 to 75 percent, and low severity, less than 25 percent.

Plant List
Overstory
Trees
Ponderosa pine (Pinus ponderosa)
Shrubs
Antelope bitterbrush (Purshia tridentate)
Currant (Ribes spp.)
Snowbrush ceanothus (Ceanothus velutinus)
Serviceberry (Amelachier alnifolia)
Big sagebrush (Artemesia tridentata)
Rabbitbrush (Chrysothamnus spp.)

Plant List (continued)
Understory
Trees
Ponderosa pine (Pinus ponderosa)
Douglas-fir (Pseudotsuga menziesii)— (minor occurrence)

Shrubs
Buckwheat (Eriogonum)
Bearberry (Arctostaphylos uva-ursi)
Common snowberry (Symphoricarpos albus)
Shiny-leaf spirea (Spirea betulifolia)
Snowbrush ceanothus (Ceanothus velutinus)

Grasses:
Bluebunch wheatgrass (Pseudoroegneria spicata)
Idaho Fescue (Festuca idahoensis)
Needle and thread grass (Stipa comata)
Pinegrass (Calamogrostis rubescens)
Beardless bluebunch wheatgrass (Agropyron inerme)
Elk sedge (Carex geyeri)
Pinegrass (Calamagrostis rubescens)
Prairie junegrass (Koeleria macrantha)
Bluegrass (Poa spp.)

Forbs:
Lupine (Lupinus spp.)
Arrowleaf balsamroot (Balsamorhiza sagittata)
Western yarrow (Achillea millefolium)
White hawkweed (Hieracium albiflorum)
Pussytoes (Antennaria spp.)

Submodel

Description

Fire exclusion for over 50 years allows Ponderosa pine stands to dominate cover, and form multi-aged medium to dense woodlands. In most cases mixed severity to stand replacing fires will not revert site back to a pine/savanna condition in State 1.

Submodel

Description

The plant composition in this state is variable with cool-season introduced grasses encroaching from adjacent homesteads and pastures. One annual species of special note that can cause a drastic shift in grass species is cheatgrass (Bromus tectorum). It invades from overgrazed or heavily disturbed pastures and can out compete the native bunchgrasses changing to a shrub/cheatgrass site.

Submodel

Description

This ecological site over time has had human settlement encroachment, and some of the site extent was converted to homesteads, pastures and cropland.

Submodel