Ecological dynamics

The Clayey Flats ecological site contains a mix of grasses, forbs, shrubs, and succulents. Late-seral communities are grasslands with sparsely scattered shrubs, while certain early-seral communities harbor codominant shrub communities. While warm-season plants dominate this site, cool-season grasses are quite abundant in the reference community. Within a given plant community phase, the relative abundance of cool-season plants increases in response to moisture in the spring and late fall. High temporal variation in the amount and timing of precipitation across this site strongly influences the relative cover of cool- and warm-season herbaceous species.

There are numerous variables such as elevation, latitude, hydrology, soil depth, fire frequency, grazing dynamics, and anthropogenic effects that influence plant communities. Elevation generally increases as the plateaus gently climb to the west, and proximity to greater warm-season moisture from the Gulf of Mexico increases toward the east. Thus, both factors result in an increase in the relative amount of warm-season moisture to the east. As elevation increases toward its upper extreme (about 7,500 feet) near the foot of the Rocky Mountains, cool-season plants within this site become most abundant. Therefore, blue grama and broom snakeweed are particularly abundant in the east; while western wheatgrass, fringed sage, and common sagewort increase their presence to the west.

Since the Clayey Flats ecological site occurs on alluvial landforms that are bounded by other Canadian Plateaus landforms, this site does not transition into ecological sites of other LRUs at its upper and lower elevations. Rather, it is typically bounded by the Ephemeral Drainageways and Low Terraces sites at the bottom of the landform; and by the Limy, Limy Escarpments, and Clayey Uplands at the upper end of the landform.

While the Clayey Flats site occupies rather subdued geomorphic positions, even gentle undulations cause certain landform positions to receive run-on moisture from adjacent positions. While major run-on-landforms such as drainageways and playas are covered by unique ecological sites, small concavities are included within the concept of the Clayey Flats site. In these positions, we find patches with higher total production, and a greater relative abundance of western wheatgrass.

Within this site, the dominant species of short grasses are inherently drought- and grazing-tolerant (Lauenroth et al., 1994). Across the western parts of the U.S., blue grama is one of the most extensively distributed grasses and occurs in a wide variety of different ecosites ranging from grasslands to shrubland and woodland sites. This grass evolved with grazing by large herbivores and, when grazed continuously, tends to form a short sod. When allowed to grow under lower grazing pressures, the plants develop the upright physiognomy of a bunchgrass. If blue grama is eliminated from an area by extended drought (3-4 years) or disturbance such as plowing, regeneration is slow because of very slow tillering rates (Samuel, 1985), low and variable seed production, minimal seed storage in the soil (Coffin and Lauenroth, 1989) and limited seedling germination and establishment due to particular temperature and extended soil moisture requirements for successful seedling establishment (Briske and Wilson, 1978). Buffalograss, which is more abundant at warmer, lower elevations of this site, is often found occupying swale or depression positions across the landscape. Buffalograss is less drought-tolerant than blue grama but re-establishes more quickly following disturbance due to higher seed abundance and viability and more effective above-ground tillering (Peters, 2008).

Large-scale processes such as climate, fire, and grazing influence this site. During years with favorable growing seasons, the effects of grazing may be mitigated. During years of low precipitation, grazing can magnify degradation of the site (Milchunas et al., 1989). Fire is a natural disturbance regime that suppresses succulents and shrubs while stimulating grasses and forbs, however, in contrast to mid and tall grass prairie sites, fire is less important (Wright and Bailey, 1982). This is because the drier conditions produce less vegetation/fuel load, lowering the relative fire frequency. However, historically, fires that did occur were often very expansive, especially after a series of years where above average precipitation built enough litter/fine fuels. Currently, fire suppression and more extensive grazing in the region have decreased the fire frequency, and it is unlikely that these processes could occur at a natural scale (USNVC, 2017)-G144. According to (Gebow, 2001), fire effects in the same location will vary, especially with fire timing, where seasonality can either hinder or benefit plants depending on their growing stage. Precipitation events occurring before and after fire will also influence the recovery of plants. Fire promotes rhizomatous plant species, such as western wheatgrass, that can take advantage of below-ground rhizomes from which tillering is rapidly initiated.

Correlation to Current Ecological Sites:
The Clayey Flats ecological site fits many components that are currently correlated to the Clayey Upland (R070AY002NM) sites. The latter concept is too broad and does not account for the character of deeper alluvial soils which have a more specific hydrology, soil properties, and landscape character than soils on upland plateau landforms.

Clayey Upland Legacy Tables (R070AY002NM)
Annual production by plant type
Plant Type------------------Low (Lb/Acre)------RV (Lb/Acre)------High(Lb/Acre)
Grass/Grasslike---------330---------------------660---------------------1000
Shrub/Vine-----------------30-----------------------60----------------------100
Forb---------------------------10-----------------------20-----------------------40
Total---------------------------370--------------------740---------------------1140

Community 1.1 plant community composition
Common Name-------------Symbol--------Scientific Name-------Annual Production (Lb/Acre)
GRASS/GRASSLIKE
1 blue grama-----------------BOGR2---------Bouteloua gracilis--------------200–240
2 western wheatgrass---PASM-----------Pascopyrum smithii----------160–200
3 alkali sacaton-------------SPAI-------------Sporobolus airoides----------160–200
4 James' galleta------------PLJA------------Pleuraphis jamesii-------------80–120
5 vine mesquite-------------PAOB-----------Panicum obtusum-------------40–80
6 sideoats grama----------BOCU-----------Bouteloua curtipendula------8–40
7 buffalograss--------------BODA2----------Bouteloua dactyloides-------8–40
8 New Jersey muhly-----MUTO-----------Muhlenbergia torreyana-----8–40
FORB
9 ragweed--------------------AMBRO---------Ambrosia--------------------------8–24
10 Forb, perennial----------2FP---------------Forb, perennial-------------------8–24
11 Forb, annual--------------2FA---------------Forb, annual-----------------------8–24
SHRUB/VINE
12 fourwing saltbush------ATCA2----------Atriplex canescens------------16–48
13 pale desert-thorn-------LYPA-------------Lycium pallidum-----------------16–48
14 winterfat-------------------KRLA2-----------Krascheninnikovia lanata----8–24