Ecological dynamics

This bottomland site is a grassland plant community characterized by inland saltgrass and alkali sacaton. Fourwing saltbush, the dominant shrub, comprises <5% of the vegetation. Forbs such as seepweed and iodinebush are present in small amounts. When the plant community deteriorates, inland saltgrass, seepweed, iodinebush, and saltcedar dominate amidst large bare–ground interspaces.

Inland saltgrass withstands a shallower water table, ponding, and high salt concentration better than alkali sacaton. Saltcedar likes to have its roots 5 feet or deeper to water table. Recovery from the saltcedar-dominated state requires combined, multiyear treatments--herbicide, root plow, fire, seeding, and follow-up control of resprouts. These communities can be thought of as zonal based on water depth and salt concentrations with Community Phase (CP) 1.1 being surrounded by CP 1.2, CP1.2 surrounded by CP 2.1, and CP 2.1 surrounded by CP 3.1, progressing from CP 1.1 to CP 3.1 as distance to water table increases.

Overview
This site occurs on floodplains adjacent to streams and rivers, and is occasionally flooded for brief periods during the summer. Along the outer edges, this site may intergrade with Salty Bottomland, Clayey Bottomland, or Bottomland sites. The soils are deep, salt-affected, and somewhat poorly drained with a seasonal (April through September) high water table. The reference plant community is a grassland characterized by salt tolerant species such as inland saltgrass and alkali sacaton. Saltgrass is typically the dominant grass on areas that have a high salt content, fine textured soils, and a shallow water table. Alkali sacaton may dominate on soils with lower salt concentrations or where the water table occurs at a greater depth. Overgrazing, soil sealing, soil compaction, or increases in salinity are thought to initiate the transition to the Inland Saltgrass-dominated State. Overgrazing reduces the competitive influence of the more palatable grasses, promotes soil sealing by reducing plant cover and organic matter, and increasing the amount of bare ground. Inland saltgrass possesses the ability to break through compacted soils and survive under conditions of extreme salinity. On areas with high salt concentrations, flooding may help flush salts from the system, provided the site has adequate drainage. Seeding may be necessary to reestablish the more palatable grasses. The introduction of saltcedar propagules may be all that is necessary for saltcedar to establish and dominate some areas. On those areas with a water table less than 4 feet, saltcedar typically occurs as scattered shrub-like trees. On those areas where the water table is deeper (5 to 20 feet) saltcedar may completely dominate in dense stands. Disturbance such as fire, heavy grazing, and drought may encourage saltcedar establishment by reducing the competitive influence of native vegetation. Changes in the timing, intensity, and frequency of flooding may also favor saltcedar establishment. Saltcedar control is costly and may require a combination of control methods and the return of natural flooding regimes.

Catalog of states and community pathways

Reference State
Reference Plant Community: The reference plant community is dominated by inland saltgrass with subdominant alkali sacaton. Other important grass and grasslike species include western wheatgrass, salt sedge, Nuttall’s alkaligrass, and alkali cordgrass. Fourwing saltbush and iodinebush are characteristic shrubs, with desert seepweed typically occurring as the most common forb/sub-shrub. Plant community composition on this site is regulated by water table depth, salinity, and soil texture. Inland saltgrass is favored by high salinity, a shallow water table, and fine-textured soils. Alkali sacaton may attain dominance on soils with lower salt concentrations or on areas where the water table occurs at a greater depth.

Diagnosis: Grass and litter cover is uniform with few large bare areas present. Shrubs are scattered with canopy cover averaging 5%. Evidence of erosion such as pedestalling of grasses, rills and gullies is infrequent.
Additional States:

Inland Saltgrass-dominated State: Dense sod-like areas of inland saltgrass with frequent interspaces of bare salt-crusted ground characterize this state. Iodinebush or fourwing saltbush are scattered between patches of saltgrass. In areas of heavier salt concentrations, iodinebush may be more prevalent.

Diagnosis: Inland saltgrass dominates. Alkali sacaton and western wheatgrass are sparse or absent. Physical and chemical crusts are common.

Transition to Inland Saltgrass-dominated State (T1A) Overgrazing, compaction, soil surface sealing, and increased salinity are thought to initiate this transition. Heavy grazing causes a decrease in the more palatable grasses, providing a competitive advantage for inland saltgrass. The loss of grass also increases the size and frequency of bare patches that often quickly seal over with chemical or physical crusts. Soil crusts can limit seedling establishment and increase salinity at the soil surface by decreasing infiltration and not allowing the water to flush salts from the rooting zone. Excessive trampling or vehicle traffic can cause the formation of a compaction layer in soils, restricting root growth. Inland saltgrass is equipped with a dense network of sharp pointed underground rhizomes enabling it to spread even in heavy compacted soils.3 Presumably, these rhizomes possess the ability to pierce soil crusts. Salinity may increase due to changes in water table depth, drainage, or the amount of water the site receives. Saltgrass can survive under conditions of extreme salinity, in part due to its ability to take up salty water and extrude the salt through specialized glands on the leaves.

Key indicators of approach to transition:
--Decrease in alkali sacaton and western wheatgrass
--Increase in size and frequency of bare patches
--Increased salinity

Restoration Pathway to the Reference State (R2A) Where salinity is the limiting factor, decreasing salt concentrations by flooding may be necessary to reestablish alkali sacaton and western wheatgrass. Compacted soil layers, argillic horizons, or poor drainage may limit this alternative. Seeding, in conjunction with breaking up compaction layers or heavy soil crusts, may be necessary to reestablish grasses. Herbicidal control of dense patches of inland saltgrass prior to seeding may facilitate the establishment of more palatable grasses. Prescribed grazing will help to ensure proper forage use following grass establishment and reduce compaction.

Saltcedar-invaded State: This state is characterized by the presence of saltcedar. On areas where the water table is shallow (<4 feet) saltcedar typically occurs as scattered multi-stemmed trees (7), with an understory dominated by alkali sacaton or inland saltgrass. On areas where the water table is deeper (5-20 feet) saltcedar may eventually dominate forming a dense monoculture (4, 7) with little or no herbaceous vegetation beneath the tree canopy.

Diagnosis: Saltcedar is present on the site. Grass cover is variable ranging from patchy to very sparse. Soil sealing and crusts are present in most bare areas.

Transition to Saltcedar-invaded State (T2A) Disturbance such as fire, grazing, or drought may encourage the establishment of saltcedar by decreasing the vigor of native vegetation and providing competition-free areas. Changes in seasonal timing and rate and volume of run-on water may facilitate the establishment of saltcedar (2). Dams have reduced river volume and caused shifts in the timing of peak flow from spring to summer. The reduced flows may lower the water table, creating ideal conditions for saltcedar establishment. Summer water discharges provide water at times consistent with saltcedar seed production. Increases in salinity due to return of irrigation water to streams and ditches may also promote saltcedar dominance.

Key indicators of approach to transition:
--Increase in size and frequency of bare patches
--Changes in timing and volume of peak discharge
--Increased depth of water table
--Increased soil salinity

Restoration Pathway to the Reference State (R3A) Saltcedar control is costly and often labor intensive. Control programs utilizing herbicide, or herbicide in conjunction with mechanical control or prescribed fire, have proven effective in some instances (1, 5). Seeding may be necessary if adequate seed sources are not present. Rest from grazing, followed by prescribed grazing, will help to ensure grass establishment and proper forage use thereafter. Without restoring historical flow regimes, extensive follow-up management may be necessary to maintain the Reference State (6).

References
1. Duncan, K. W. 1994. Saltcedar: establishment, effects, and management. Wetland Journal 6: 10-13.

2. Everitt. B. L. 1980. Ecology of saltcedar – a plea for research. Environmental Geology 3: 77-84.

3. Hansen, D. J., P. Dayanandan, P.B. Kaufman, and J.D. Brotherson. 1976. Ecological adaptations of salt marsh grass, Distichlis spicata (Gramineae), and environmental factors affecting its growth and distribution. American Journal of Botany 63: 635-650.

4. Horton, J. S., F. C. Mounts, and J. M. Kraft. 1960. Seed germination and seedling establishment of phreatophytic species. Research Paper RM-48. USDA-Forest Service, Rocky Mountain Forest and Range Experiment Station, Ft. Collins, CO.

5. Neill, W. M. 1990. Pp. 91-98, In: M. R. Kunzmann, R. R. Johnson and P. S. Bennett (eds.) Tamarisk control in southwestern United States. Proceedings of Tamarisk Conference, University of Arizona, Tucson, AZ, September 23-3, 1987. Special Report No. 9. National Park Service, Cooperative National Park Resources Studies Unit, School of Renewable Natural Resources, University of Arizona, Tucson, AZ.

6. Smith S. D. and D. A. Devitt. 1996. Physiological ecology of saltcedar: why is it a successful invader? In The Fire Effects Information System [Data base]. U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Intermountain Fire Sciences Laboratory (2003, January), Missoula, MT. Available: http://www.fs.fed.us/database/feis/.

7. Tesky, J.L. 1992 Tamarix ramosissima. In The Fire Effects Information System [Data base]. U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Intermountain Fire Sciences Laboratory (2003, January), Missoula, MT. Available: http://www.fs.fed.us/database/feis/.