S&T model Desert Sand (sand sage) V1

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(notes: I developed a 4 state system only because I don't tend to beleive that sand sage is indicative of highly degraded systems like coppiced systems. I've seen a high abundance of ARFI on eolian sands on the cockscomb, supposedly ungrazed or long rested. We can simplify back to the 3 state model, but I bet there's a gradient in grass vs. sand sage dominance, and corresponding crust cover variation. I think T 3,4,5 likely obey threshold dynamics, and sites may become stuck in S3,4)

Desert sand (Sand sagebrush)

States

S1: Reference tussock grassland

Historic and extant examples suggest a reference condition and site potential of tussock grassland dominated by Heterostipa comata, Sporobolus, and a shrub component of Artemisia filifolia, Ephedra. Interspaces are dominated by cyanobacterial biological soil crusts, possibly with some degree of moss cover especially near plant canopies. Bowker et al (2006) estimates the following potential crust cover for various functional groups: light cyanobacterial crusts (35.9 ± 37.1), dark cyanobacterial crusts (32.3 ± 19.9), mosses (15 ± 9.2), lichens (2.3 ± 4.1), late successional elements (moss + lichen + dark cyanobacteria) (57.9 ± 19.5). The draft ecosite description provided by NRCS agrees reasonably well with these estimates, stating that 40-60% of the interspaces would be represented by bare ground (inclusive of cyanobacteria, exclusive of mosses and lichens). Soil surfaces tend to be stable, and threshold friction velocity and erodibiltiy are very strongly regulated by biological crust development on these siliceous sands (Bowker et al. 2008).

S2: Sand sage community, compromised crust cover

Grass elements are reduced, and Artemisia filifolia may become dominant. Late successional crust elements are sharply reduced. This may be reflected in lower overall cover or greater cover of light cyanobacteria at the expense of later successional crust elements. These states may be characterized by more sand redistribution within the site, and more deposition originating from outside the site. This type of community is sometimes thought of as a slightly or moderately degraded or mid-seral state (Tuhy and McMahon 1989, Costello 1944, Hefley and Sidwell 1945), though it could conceivably arise simply due to locally higher deposition rates of saltating sand and thus could be the current potential of some sites.

S3: Coppiced

In open areas exposed to high winds required to drive sand erosion-deposition requirements (Hodgekinson 1983), physical disturbances of the soil surface (e.g grazing, off-road vehicles) or excessive sand deposition from an off-site sand source, soil stability is further diminished, sand deposition tolerators are favored, and the landscape becomes dominated by deposition tolerant shrubs such as Ephedra spp and Quercus havardii. Coppice dunes of accumulated eolian sand, either from on-site or offsite, accumulate around shrubs. Relative abundance of bunch grasses is further diminished, crust cover decreases further or is shifted from later to earlier successional states (e.g. light cyanobacteria), and plant interspaces are deflated due to the diminished ability of BSCs to stabilize the soil surface. Characteristic of deflation is a loss in magnetic minerals, silt, Na, Mg, P and N (Neff et al. 2005). Sand deposition retards BSC succession (Bowker et al. unpublished)

S4: Invasive-dominated

In sheltered areas lacking high winds or excessive sand deposition from offsite, Due to prolonged grazing, palatable vegetation (Heterostipa and Sporobolus) decreases in favor of less palatable native species such as Guiterrizia. Associated soil disturbance allows establishment of Salsola, and perhaps to a lesser degree Bromus grasses, although the nutrient environment does not favor annualization by Bromus (Mark, do you still tend to believe this regarding Navajo soils??). The seasonal growth and senescence of Salsola leaves soils unprotectred foir part of the year, not unlike annualized communities.

Hefley, HM, Sidwell, R. 1945. Geological and some ecological observations of some high plains dunes. American Journal of Science 243: 367 – 376.

Costello, DF. 1944. Important Species of the Major Forage Types in Colorado and Wyoming. Ecological Monographs 14: 107-134.

Tuhy, J.S., MacMahon, J.A., 1988, Vegetation and relict communities of Glen Canyon National Recreation Area. Final Report to the National Park Service. The Nature Conservancy.

Neff, JC, Reynolds, RL, Belnap, J., Lamothe, P. 2005. Multi-decadal impacts of grazing on soil physical and biogeochemical properties in Southeast Utah. Ecological Applications 15: 87-95.

Bowker, MA, Belnap, J., Chaudhary, VB, Johnson, NC. 2008. Revisiting classic water erosion models in drylands: the strong impact of biological soil crusts. Soil Biology and Biochemistry 40: 2309 -2316.

Bowker, MB, Belnap, J., Miller, ME. 2006. Spatial Modeling of biological soil crusts to support rangeland assessment and monitoring. Rangeland Ecology and management 59: 519-529.

Bowker, MA, Belnap, J., Johnson, NC. 20xx. Why do biological soil crusts recover form disturbance so slowly: nutrient limitations, sand deposition, or inherent growth rate? Second revision in prep.

Johnson, N.C. 1998. Responses of Salsola kali and Panicum virgatum to mycorrhzial fungi, phosphorus and soil organic matter: implications for reclamation. J. Applied Ecology 35:86-94.

Transitions

T1 (Syndromes B1, B4). Either physical disturbance due to on-site grazing, or sand deposition from offsite compromises the cover, or successional maturity and functionality of biological crusts. Shrubs that are

T2 (Reversal of syndromes B1, B4). Cessation of grazing or sand deposition allow recovery of soil crusts and increases in the relative prevalence of tussock grasses.

T3 (Syndrome B4, A3). In the case of grazing-triggered transitions, unpalatable shrub species within the community are favored at the expense of the grasses. In the cases of both grazing triggered or off-site sand source triggered transitions, sand deposition tolerant plants are favored, most of which are large statured, laterally spreading multi-stemmed shrubs. These processes result in a coppiced sand shrub community dominated by Quercus havardii, or Ephedra spp.

T4 (Syndromes B3a, B6). By acting as soil disturbers and seed dispersers, livestock can facilitate the invasion of exotic annuals and senescent perrenials, especially Salsola, but to a lesser extent Bromus tectorum or rubens. Because there are significant portions of the year where the soil surface is unprotected due to the life cycle of these plants, deflation can continue unchecked. Also because most of these species are poor mycorrhizal hosts, the pools of mycorrhizal propagules may be compromised (Johnson 1998).

T5 (Syndromes B3a, B6). Essentially the same as T4.