Draft, Remedial Measures Primer Pilot Version 1.0

SOUTHERN INTERIOR GRASSLANDS

Three major grassland types occur along a vertical gradient.

1. Lower grassland zone - Elymus spicata - Artemisia tridentata (Bluebunch wheatgrass-Big sagebrush)

This grassland is confined to the lowest and warmest elevations, with most of it being in private ownership. The climax vegetation (determined from a few relic sites) is characterized by an abundance of well-spaced bunchgrasses with bare ground between them, relatively few plant species and the presence of big sagebrush. Bluebunch wheatgrass is the characteristic species but under conditions of overuse it is replaced by Sandberg’s bluegrass, big sagebrush and pussytoes.

The climate is characterized by warm to hot, dry summers and moderately cold winters with relatively little snowfall. Typically, December and January are the wettest months, while a second precipitation peak occurs in June. Because spring is normally dry and summer precipitation evaporates before it can contribute to recharging soil moisture, plant growth depends mainly on winter moisture. Soil moisture depletion begins with the start of the growing season, the plants become increasingly stressed as the summer progresses.

Edaphic Communities

The climax and its derivative, the Artemisia tridentata - Poa sandbergii (Big sagebrush-Sandberg’s bluegrass) community, occur on fine to medium textured soils. Where there are coarser soils (loamy sands, sands, and gravely sandy loams) the vegetation is characterized by needle-and-thread, sand dropseed, and rabbitbrush.

Needle-and-thread and sand dropseed replace bluebunch wheatgrass and Sandberg’s bluegrass. Rabbitbrush replaces big sagebrush. Another shrub, Antelope bitterbrush, and the perennial grass, red three-awn, are also common.

Effects of grazing

This grassland has been highly modified by grazing. It is the most accessible type and is susceptible to grazing because of the aridity. The growing season is mostly restricted to April, May and early June, followed by a summer drought. Plants grazed closely during this period have little opportunity to recover.

A disclimax, the Artemisia tridentata - Poa sandbergii (Big sagebrush-Sandberg’s bluegrass) type, develops under continual heavy livestock grazing and now occupies much of the lower grassland area. Big sagebrush is the characteristic species with a sparse understorey covered by perennial and annual forbs. Bluebunch wheatgrass lost or greatly reduced in the community. The dominant shrub cover and low ground cover combine to give the community an appearance of the sagebrush steppe.

Areas that are grazed in the winter can retain bluebunch wheatgrass, but those heavily grazed at other times become dominated by the Artemisia tridentata - Poa sandbergii disclimax. The introduced annual, downy brome, is widespread.

2. Middle Grassland Zone- Elymus spicata - Poa sandbergii (Bluebunch wheatgrass-Sandberg’s bluegrass

Middle grasslands are characterized by the absence of big sagebrush and rabbitbrush which are found in the lower grasslands. Grass species include bluebunch wheatgrass, rough fescue, junegrass and Sandberg’s bluegrass. Forbs are a minor part of the plant community. Pasture sage is the dominant woody species. Ponderosa pine is found in localized areas (draws and canyons).

The absence of big sagebrush, closer plant spacing, and greater diversity of species, distinguish it from the lower grassland zone.

Effects of Grazing:

As a general rule, the vegetation of this type has not been as altered by historic overgrazing as the lower grassland. It is less accessible and has better growing conditions (cooler, moister). The principal plant assemblages that replace the Elymus spicata-Poa sandbergii type are the Stipa comata-Elymus spicata-Poa sandbergii and the Bromus tectorum-Poa sandbergii-Stipa comata types.

Mid seral: Stipa comata-Elymus spicata-Poa sandbergii type (Needle-and-thread-Bluebunch wheatgrass-Sandberg’s bluegrass)

This community is best developed on easily accessed sites that livestock repeatedly use. The outstanding feature is the dominance by needle-and-thread. The potential dominants, bluebunch wheatgrass and Sandberg’s bluegrass, are present but reduced in cover and vigor. The shorter growing grasses, junegrass and Sandberg’s bluegrass are less affected by heavy grazing.

Early seral: Bromus tectorum-Poa sandbergii-Stipa comata type (Downy brome-Sandberg’s bluegrass-needle-and-thread)

The principal and most common species is downy brome (cheatgrass) This community appears to develop from the Stipa comata-Elymus spicata-Poa sandbergii type with continual heavy grazing.

3. Upper grassland zone - Elymus spicata - Festuca campestris (Bluebunch wheatgrass-Rough fescue)

This type is distinguished by higher cover, greater production and richer flora (forbs) than the lower grassland types. Its climate is cooler and moister than the lower and middle grasslands. Clumps of trembling aspen are common in depressions and draws.

Bluebunch wheatgrass is a dominant throughout this type. The abundance of rough fescue varies from site to site. Rough fescue is more common on sheltered sites (east and north exposures) and bluebunch wheatgrass dominates on the harsher sites such as south and west slopes. Junegrass and dryland sedge are common.

Idaho fescue replaces rough fescue to a great extent in the Similkameen and Kettle valleys and southern part of the Rocky Mountain Trench. The shrubs, big sagebrush and rabbitbrush are absent.

Rocky Mountain fescue replaces rough fescue in the Caribou/Chilcotin grassland.

There appears to be no definite period of dormancy during the growing season. In contrast, vegetation in the lower grassland zones enters summer dormancy, but can maintain some very slow growth in the mild winter conditions.

Effects of Grazing

Under improper grazing management Stipa columbiana-Poa pratensis and Poa sandbergii-Bromus tectorum communities develop.

Mid seral: Stipa nelsonii-Poa pratensis type (Columbia needlegrass-Kentucky bluegrass)

Columbia needlegrass is widespread and expresses its dominance on exposed sites with coarse soils. Kentucky bluegrass is the only rhizomatous grass in the area and it is restricted primarily to fine textured and deep soils in sheltered areas. Bluebunch wheatgrass and rough fescue are often present but are no longer dominant.

Early seral: Poa sandbergii-Bromus tectorum type (Sandberg’s bluegrass-downy

brome)

This community is produced as the result of continued severe grazing.