Ecological dynamics
In reference condition, this site is dominated by great basin wildrye (Leymus cinereus), black greasewood (Sarcobatus vermiculatus), and basin big sagebrush (Artemisia tridentata ssp. tridentata). Other bunchgrasses such as Thurber's needlegrass (Achnatherum thurberianum), bluebunch wheatgrass (Pseudoroegneria spicata), inland saltgrass (Distichlis spicata) and Sandberg bluegrass (Poa secunda), are also common. There are relatively few native forbs found on this site.
Fluctuations in species composition and relative production may change from year to year dependent upon abnormal precipitation or other climatic factors. Plant community composition may vary throughout the site based on factors such as soil sodicity and the presence of surface and subsurface supplemental moisture. Inland saltgrass increases with a higher surface pH and moist surface conditions. Great basin wildrye may decrease were saturated soil conditions are present for much of the year and where soil is highly sodic. Basin big sagebrush will also decrease where soils are saturated and/or highly sodic. Greasewood tolerates very high sodicity as well as saturated soil and will increase where these conditions are present. Western juniper (Juniperus occidentalis) may occur on this site but will be limited in areas with high sodicity and salinity levels.
Black greasewood is a phreatophytic (groundwater dependent) shrub species that is highly tolerant of sodic and saline soil conditions and typically prefers heavy soil textures. While fire often leads to topkill of greasewood, it sprouts quickly following all but the most severe fires. The ability to resprout following aboveground damage also helps greasewood to increase in dominance following plant community disturbance.
Great basin wildrye is an important bunchgrass species where it occurs. This large bunchgrass species has an extensive fibrous root system that can stabilize soils and reduce erosion in disturbed areas. Great basin wildrye is generally tolerant of fire and responds by resprouting from root crowns and rhizomes. Plants may be top killed by high intensity fire, especially where older plants have accumulated significant dead material within the crown.
Basin big sagebrush is a prominent shrub in low elevation areas within the sagebrush biome. Compared to other subspecies of big sagebrush, basin big sagebrush is not as common in Eastern Oregon and occurs in areas with greater subsurface moisture accumulation or higher water tables. As a fire intolerant species that is readily killed by most fires and does not resprout, basin big sagebrush will be reduced on a site following fire and may be eliminated with frequent fires. Periodic insect outbreaks of Aroga moth (Aroga websteri) are an important component of the natural disturbance regime for big sagebrush, resulting in complete or partial mortality of sagebrush plants and potentially impacting thousands of acres.
Historically these communities would have likely encountered infrequent stand replacing wildfire due to sparse understory conditions. Estimates of fire return intervals vary between 35 to 100 years for salt desert systems with similar plant community composition. Fires may have been more likely during years with higher production and therefore higher fuel loads. Livestock grazing has likely altered much of the extent of this site. Increases in composition of black greasewood and decreases in great basin wildrye may result from chronic improperly managed grazing.
Given an altered disturbance regime and degraded site conditions, invasions of exotic forb species and annual grass species may occur on this site. These may include pepperweed (Lepidium spp.), whitetop (Cardaria draba) and Russian thistle (Salsola tragus). Exotic annual grasses such as cheatgrass (Bromus tectorum), may also invade the site. Exotic annual grass invasion may increase the frequency of fires and extend the season when fires are likely by augmenting early season fines fuel loads and fuel continuity. In addition to exotic species, native shrub species such as broom snakeweed (Gutierrezia sarothrae) and green rabbitbrush (Chrysothamnus viscidiflorus) may also increase following disturbance and may be important members of early seral communities. Ecological resilience and restoration success of sites with sodic soils is often strained by the low nutrient levels, low organic matter levels and salt induced dispersion of soil aggregates.
Since this site occupies limited acreage in MLRA 10 in Oregon, an understanding of the site specific ecological dynamics are incomplete. The characteristics of this site resemble those of similar "Sodic" ecological sites in the Great Basin, therefore, the state and transition model below is informed by these sites, especially the Nevada disturbance response group 12AB, (Stringham et al. 2015). Restoration pathways are incomplete for this site but likelihood for success is low.
State 1
Historical Reference State
The Reference State is representative of the natural range of variability for the site under pristine conditions. The Reference State is a bunchgrass shrubland. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These are maintained by elements of ecosystem structure and function such as the presence of all structural and functional plant groups, the retention of organic matter and the maintenance of plant community cover. Plant community phase changes are primarily driven by infrequent fire and periodic drought.
Community 1.1
Reference Plant Community: Black Greasewood-Basin Big Sagebrush/Basin Wildrye
This community is dominated by great basin wildrye (Leymus cinereus), black greasewood (sarcobatus vermiculatus), and basin big sagebrush (Artemesia tridentata ssp. tridentata). Other bunchgrasses such as Thurber's needlegrass (Achnatherum thurberianum), bluebunch wheatgras (Pseudoroegneria spicata), inland saltgrass (Distichlis spicata) and Sandberg bluegrass (Poa secunda), are also common.
Table 5. Annual production by plant type
| Plant type |
Low
(kg/hectare) |
Representative value
(kg/hectare) |
High
(kg/hectare) |
| Grass/Grasslike |
1009 |
1261 |
1513 |
| Shrub/Vine |
247 |
308 |
375 |
| Forb |
78 |
101 |
118 |
| Tree |
11 |
11 |
11 |
| Total |
1345 |
1681 |
2017 |
| Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
Community 1.2
Basin Wildrye
This community represents an early seral phase following disturbance and is dominated by perennial grasses such as great basin wildrye (Leymus cinereus), Thurber's needlegrass (Achnatherum thurberianum), bluebunch wheatgras (Pseudoroegneria spicata), inland saltgrass (Distichlis spicata) and Sandberg bluegrass (Poa secunda). Sprouting shrubs will decrease following fire but will soon increase in abundance while non-sprouting shrubs will take longer to recolonize.
Community 1.3
Black Greasewood-Basin Big Sagebrush
Following a lack of fire for an extended period, black greasewood (sarcobatus vermiculatus), and basin big sagebrush (Artemesia tridentata ssp. tridentata) will increase in abundance while perennial grasses will decrease.
Pathway P1.1a
Community 1.1 to 1.2
Wildfire occurs reducing aboveground biomass and favoring an increase in grasses followed by fire adapted sprouting shrubs.
Pathway P1.1b
Community 1.1 to 1.3
Long intervals without fire, significant herbivory of herbaceous species, or extended drought will increase shrub composition and decrease perennial grass composition. Perennial grasses will decrease yet inland saltgrass may increase depending on herbivory dynamics.
Pathway P1.2a
Community 1.2 to 1.1
Time without fire will allow shrub species to increase
Pathway P1.3a
Community 1.3 to 1.2
Wildfire occurs reducing aboveground biomass and favoring an increase in grasses followed by fire adapted sprouting shrubs.
State 2
Current Potential State
This state is similar to the Reference State. Ecological function has not changed, however the resiliency of the state has been reduced by the presence of invasive weeds. Non-native plant species may increase in abundance but will not become dominant or control ecological processes within this state. These species can be highly flammable and can promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These are maintained by elements of ecosystem structure and function such as the presence of all structural and functional groups, and retention of organic matter and nutrients. Positive feedbacks driven by plant community invasion decrease ecosystem resilience and stability of the state. These include exotic plant species' high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate, and adaptations for seed dispersal. Plant community phase changes are primarily driven by infrequent fire, periodic drought and ungulate herbivory.
Community 2.1
Current Potential Community
Current potential plant communities mirror those of the above Reference State 1 with the addition of a low level of invasive exotic plants.
State 3
Shrub State
Plant community dynamics within this state are primarily driven by shrub species. Native perennial grass composition has been reduced considerably. Sprouting species such as black greasewood, green rabbitbrush and broom snakeweed as well as non-sprouting species such as big sagebrush are dominant on the site. Western juniper may also be present. Exotic herbaceous species are often present..
Community 3.1
Black Greasewood/Basin Wildrye-Sandberg Blue
Black greasewood dominates the shrub layer, basin big sagebrush may be codominant. Deep-rooted perennial grasses have been reduced yet are still present. Shallow-rooted perennial grasses are increasing.
Table 6. Annual production by plant type
| Plant type |
Low
(kg/hectare) |
Representative value
(kg/hectare) |
High
(kg/hectare) |
| Shrub/Vine |
504 |
622 |
740 |
| Grass/Grasslike |
269 |
336 |
404 |
| Forb |
90 |
112 |
135 |
| Tree |
34 |
50 |
67 |
| Total |
897 |
1120 |
1346 |
| Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
Community 3.2
Black Greasewood-Broom Snakeweed/Sandberg Bluegrass
Black greasewood and broom-snakeweed dominate the shrub layer. Other sprouting shrubs such as green rabbitbrush may also be present. Non-sprouting shrubs such as basin big sagebrush are largely absent. Deep rooted perennial grasses have been greatly reduced. Shallow rooted perennial grasses are increasing.
Pathway P3.1a
Community 3.1 to 3.2
Fire or soil disturbing treatments will reduce the sagebrush overstory and allow for an increase in sprouting shrubs.
Pathway P3.2a
Community 3.2 to 3.1
Sufficient time may allow sagebrush and great basin wildrye to recolonize the site if sufficient seed source is available and other disturbances are mitigated, yet data is lacking to fully support this pathway.
State 4
Invaded State
Plant community dynamics within this state are primarily driven by exotic annual and perennial herbaceous species. Native perennial grass composition has been greatly diminished. Shrub species and western juniper may also be present. Rehabilitation of this state is uncertain given the difficulty of establishing plant material in the sodic soils and under the influence of an aridic soil moisture regime.
Community 4.1
Invaded Community
Common exotic species may include cheatgrass (Bromus tectorum), pepperweed (Lepidium spp.), whitetop (Cardaria draba) and Russian thistle (Salsola tragus).
Transition T1A
State 1 to 2
Introduction of non-native annual plants leading to a decrease in site resilience relative to reference conditions.
Transition T2A
State 2 to 3
Improperly managed livestock grazing may dramatically reduce native perennial grasses and increase shrub cover. When heavy herbivory is combined with fire or mechanical removal of shrub species, basin big sagebrush may be reduced or eliminated.
Transition T2B
State 2 to 4
High severity fire, or multiple fires at short intervals, in the presence of sufficient seed source or invasive plant species may lead to a loss much of the native plant community composition and a dramatic increase in invasive annual plants.
Restoration pathway R3A
State 3 to 2
Treatments to remove shrubs and seeding of native species. This may require the use of herbicide.
Context dependence. Chance of success is limited by the droughty, sodic soils.
Transition T3A
State 3 to 4
High severity fire, or multiple fires at short intervals, in the presence of sufficient seed source or invasive plant species may lead to a loss much of the native plant community composition and a dramatic increase in invasive annual plants.
