Mesic Xeric Loamy Hills and Canyons Ponderosa Pine Moderately Warm Dry Shrub

Description

The Reference State has a variable but predictable plant expression across the landscape. In the larger context, these forests tended to be heterogeneous and spatially complex. A wide array of wildlife species benefited from the edge effects created by the spatial intersections within the larger landscape, and by naturally occurring snags and large woody debris.

The Ponderosa pine forest is comprised of pure, self-replacing stands that function under the ecological parameters that were described in the section entitled “Ecological Dynamics of the Site.”

Fire is the most important disturbance agent in the Reference State.

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

Fire Regime Group Fire Interval (years)
I 6 – 15

Replacement Mixed Low
Fire Severity (%—probability of occurrence) 15 18 77
Mean Fire Return Interval (MFRI- years) 125 35 15

Primary Source: BpS model 910531
Also referenced by FEIS “Fire Regime/Blue Mountains” publication, Fire Ecology of N. Idaho Habitat types, 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%

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.

Following a disturbance event that eliminated or significantly reduced the number of established Ponderosa pine within a given forest stand, the key to re-establishing and sustaining the reference state was dependent on the successful recruitment of Ponderosa pine seedlings from adjacent sources, or from remnant surviving seed trees. Larger sized patches, isolated from seed sources and devoid of remnant Ponderosa pine of any size class, may tend to revert to long-term grass/shrub with very sparse pine occupancy.

The Reference Plant Community was a relatively low-density mature Ponderosa pine stand. The various common successional stages are shown on the state and transition diagram. Those conditions occur in shifting locations across the overall larger landscape over long periods of time.

Characteristics and indicators

Production Interpretations of the Ponderosa pine/snowberry and Ponderosa pine/ninebark Reference State ESD:

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 codominant 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. Site index value ranges depend on local soil-site characteristics. The combination of these soil-site characteristics is recognized within the defined attributes of established NRCS forested soil series and phases.
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/SYAL PIPO 60 122** 53 134 50/40 600 100TA

Ponderosa Pine
PIPO/PHMA PIPO 85 90 54 89 100/78 600 100TA

* cubic foot per acre per year (ft3/ac/yr.)
** a wide span of values in the SYAL phase: the lower values were on Gibbs, Stutler, Speigle, Northstar and Formound soils,and the higher values are represented by Larkin, Driscoll and Jacket soils.

Submodel

Description

Since the arrival of Euro-American settlers to the region in the late 1880’s, the character and function of these forests have changed. Logging, grazing, conversion to other uses, and fire exclusion have impacted the natural processes of this fire-dependent ecosystem. Depending on the severity and degree of impact, alternative states (which function outside of the parameters of the Reference State), have developed.

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 (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