Mesic Xeric Loamy Hills Ponderosa Pine Warm Dry Grass

Description

This state is dependent on the occurrence of frequent low intensity ground fires keeping an open grown pine stand with a dominant ground cover of bunchgrass. When fire intervals are infrequent pine regeneration can survive and a patchy pine woodland develops underneath the large old pine. Drought stress make the large old pine subject to beetle kill and the understory pine stands subject to dwarf mistletoe infestation. It is also possible to have a stand replacement fire when stand density is increased and ladder fuels can reach the larger pine crowns.

Across the overall landscape stand structure was expressed by a combination of small patch openings, clumpy (overstocked) tree groups in the younger size classes, and as well-spaced mature overstory trees encompassing larger stand groups. These mosaic patterns could occur over the landscapes in a scale of upwards of tens of thousands of acres. Disturbances from fire and other biotic and abiotic sources impacted much smaller areas within the larger landscape, on the order of thousands of acres.

The fire regime of the Historic Reference Community phase is summarized as follows:

Fire Regime Group Fire Interval (years)
I 2 – 15

Replacement Mixed Low
Fire Severity (%—probability of occurrence) 5 18 77
Mean Fire Return Interval (MFRI- years) 125 35 8

Primary Source: BpS model 910531
and FEIS Fire Regimes of N. Rocky Mountain Ponderosa pine communities.

Fire Regime Groups: I: 0-35 year frequency, surface severity; II: 0-35 year frequency, replacement severity; III: 35-100+ year frequency, mixed severity; IV: 35-100+ year frequency, replacement frequency; V: 200+ year frequency, replacement severity
Fire Severity Classes: Replacement, >75% kill or top kill of the upper canopy layer; Mixed 26-75%, and low severity, < 25%

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 of dominant and co-dominant trees, usually referenced to 50 or 100 years of age. Site index is an indicator of site quality with implications of forest productivity. Additional information on SI and CMAI are provided in the table shown immediately below.

Ponderosa pine is the only conifer, and therefore the only commercial tree species in this ESD.

The NRCS site index interpretations is summarized as follows:

Site Quality & Productivity
Plant Association Conifer Symbol Site Index-Low Site Index-High CMAI* CMAI Age of CMAI SI ADP Code** Curve Basis
Low High

Ponderosa Pine
PIPO/PSSP (12) PIPO 72 85 58 77 50/40 600 100TA

Ponderosa Pine
PIPO/FESC (3) PIPO 45 74 34 60 60/50 600 100TA

Ponderosa Pine
PIPO/CARU (1) PIPO 91 87 40 600 100TA

* CMAI (volume) is the point at which the annual growth rate is at the maximum level. The CMAI (age) is where that growth increment occurs. CMAI is expressed as cubic foot per acre per year (ft3/ac/yr.) of growth.
** The base reference is Meyer, NRCS code 600. The full citation is in the reference section.

Plant List
Overstory

Trees
Ponderosa pine (Pinus ponderosa)

Shrubs
Antelope bitterbrush (Purshia tridentate)
Currant (Ribes spp.)
Snowbrush ceanothus (Ceanothus velutinus)
Big sagebrush (Artemesia tridentata)
Rabbitbrush (Chrysothamnus spp.)

Understory

Trees
Ponderosa pine (Pinus ponderosa)
Douglas-fir (Pseudotsuga menziesii)

Shrubs
Buckwheat (Eriogonum)

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

Grasses:
Pinegrass (Calamagrostis rubescens)
Prairie junegrass (Koeleria macrantha)
Sandberg bluegrass (Poa secunda)
Bluebunch wheatgrass (Pseudoroegneria spicata)
Idaho Fescue (Festuca idahoensis)
Needle and thread grass (Stipa comata)
Rough fescue (Festuca campestris)

Submodel

Description

Fire Exclusion for 50 or more years leads to a light to medium dense pine woodland with all ages present. Canopy cover ranges from 30 to 60 percent. Canopy cover will be higher in the pine/fescue habitat. Mixed severity fires will create a mosaic of pine stands between burned areas which will seed in with pine maintaining a multi-level pine woodland.

Submodel

Description

Invasion of introduced perennial and annual cool-season grasses from adjacent pastures, homesteads, and abandoned areas. One particular annual grass of concern from past overgrazing is the invasion of cheatgrass. Once it gets established in the understory it will prevent native bunchgrasses from reestablishing and restoring site.

Submodel

Description

Lower level terrain converted to crops, pasture or urban development. Much of the Mesic Xeric Loamy hills, Ponderosa Pine Warm Dry Grass ecological site is adjacent to local towns and cities. They have been converted to housing developments, shopping malls, or urban recreation areas. In the more rural areas, these sites have been converted to pastures and dry or irrigated cropland.

Note: Significant urban conversion of this forest type has occurred, especially in the Spokane area, but the impact is not specifically addressed in this ecologic site. Urban conversion is a permanent loss of the extent of this ecologic site, and not a true state/transition ecologic process. Additionally, there are limited restoration opportunities for land converted to urban uses.

Submodel