Ecological dynamics
Major factors affecting this ecological site are its hydrology and climate. The dominant species are adapted to hyperthermic conditions. The large width of the drainageway allows for areas of differing flooding intensities. The most frequently flooded areas are dominated by and blue paloverde (Parkinsonia florida). Small amounts of other species tolerant of water disturbance are desert lavender (Hyptis emoryi) and smoketree (Psorothamnus spinosus), ironwood (Olneya tesota), catclaw acacia (Acacia greggii). Areas of less frequent disturbance include species such as brittlebush (Encelia farinosa), burrobrush (Hymenoclea salsola), and creosote bush (Larrea tridentata).
State 1
Reference State
The reference state is representative of the natural range of variability under pristine conditions. It is maintained by periodic flooding in response to heavy rainfall events and has increased available moisture and nutrients. Fire is rare in this system. This ecological site experiences seasonal flooding and is important for redistributing moisture and nutrients throughout the landscape. Timing of disturbances combined with weather events determines plant community dynamics.
Community 1.1
Reference Plant Community
The reference plant community is diverse. The dominant species is blue paloverde (Parkinsonia florida). Other species include ironwood (Olneya tesota), desert lavender (Hyptis emoryi), smoketree (Psorothamnus arborescens), catclaw acacia (Acacia greggii), burrobrush (Hymenoclea salsola), creosote bush (Larrea tridentata), and brittlebush (Encelia farinosa).
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Shrub/Vine |
130 |
228 |
325 |
| Grass/Grasslike |
50 |
88 |
125 |
| Forb |
20 |
34 |
50 |
| Total |
200 |
350 |
500 |
Community 1.2
Plant Community 1.2
This plant community is characteristic of a post-disturbance plant community phase. Initially, it is heavily dominated by herbaceous vegetation and short-lived perennials. Sprouting shrubs quickly recover and provide a favorable environment for establishment of shrub seedlings. This plant community is ‘at-risk’ of invasion by non-natives. Non-native species are able to take advantage of increased availability of critical resources following disturbances.
Pathway 1.1a
Community 1.1 to 1.2
Pathway 1.2a
Community 1.2 to 1.1
Absence from disturbance and natural regeneration over time.
State 2
Representative State
The Representative State is characterized by the presence of non-native species in the understory. A biotic threshold is crossed with the introduction of non-natives that are difficult to remove from the system and have they potential to significantly alter disturbance regimes from their historic range of variation. Non-native annuals will persist once introduced into the plant community, due to their annual growth form, abundant seed production and long term seed viability. Non-native annuals such as red brome and cheatgrass are potential invaders on this ecological site. These non-native annuals are highly flammable and promote wildfires where fires historically have been infrequent.
Community 2.1
Plant Community Phase 2.1
Species composition is similar to the reference plant community. Ecological processes have not been compromised at this time, however, ecological resilience is reduced by the presence of non-natives. This plant community phase will respond differently following disturbance, when compared to the reference plant community. Management focused on decreasing the amount of anthropogenic disturbance is important for maintaining the health of perennial native species that protect the site against erosion.
Community 2.2
Plant Community Phase 2.2
This plant community is characteristic of a post-disturbance plant community. It is dominated by herbaceous vegetation, which may or may not be non-native, woody perennials are increasing. Nevada ephedra, desert almond and desert willow commonly sprout from rhizomes following disturbance. Sprouting species provide favorable sites for germination of species such as brittlebush, ratany, and bursage which reproduce sexually and are prolific seed producers. This plant community is ‘at-risk’ of increased erosion due to reduction of deep rooted perennials and increased non-native annuals.
Pathway 2.1a
Community 2.1 to 2.2
Seasonal flooding, wildfire, disease or insect attack.
Pathway 2.2a
Community 2.2 to 2.1
Absence of disturbance and natural regeneration over time.
State 3
Eroded State
This state is characterized by reduced cover of woody perennials. Bare ground is increasing, leading to increased erosion, decreased infiltration and loosening of the soil surface causing channeling. An abiotic threshold has been crossed preventing the natural repair of this plant community. Feedbacks keeping this state stable include reduced perennial vegetative cover causing increased runoff and decreased infiltration preventing the establishment of desirable perennial vegetation.
Community 3.1
Plant Community Phase 3.1
This plant community is characteristic of a short disturbance return interval. Long-lived woody perennials are decreasing. The ability of this site to dissipate energy during large flow events is severely reduced contributing to ecological damage downstream.
Community 3.2
Plant Community Phase 3.2
This plant community is characterized by the loss of long-lived woody perennials. Ecological processes have been altered including connectivity within the watershed, ground water recharge and habitat quality. Soil and soil nutrients are being redistributed down stream, leading to down cutting and channel widening.
Pathway 3.1a
Community 3.1 to 3.2
Seasonal flooding, wildfire, disease or insect attack.
Pathway 3.2a
Community 3.2 to 3.1
Absence from disturbance and natural regeneration over time, allow some perennials to return to the system increasing stability.
Transition T1
State 1 to 2
Introduction of non-native species due to a combination of factors including: 1) surface disturbance, 2) changes in the kinds of animals and their grazing patterns, 3) drought and/or 4) changes in fire history.
Transition T2
State 2 to 3
Large scale reoccurring disturbance, natural or anthropogenic.
Restoration pathway R3
State 3 to 2
Ecological processes can be restored to the site, but non-natives remain. Possible restoration techniques include stabilizing the site by reestablishing native perennials and the use of artificial rip-rap to dissipate energy and reestablish the flood plain.
