The Great Divide

Commentary on Biological (Microphytic) Soil Crusts in the Rawlins Resource Management Area

Jack S. States, PhD
Emeritus Professor of Biology, Northern Arizona University
Adjunct Professor of Botany, University of Wyoming
2 Canyon Shadows Rd.
Lander, WY 82520-9712

Introduction: The Scoping comments on biological soil crusts submitted below review their biological attributes, ecological roles and distribution within the boundaries of the Great Divide Basin and other lands of the BLM Rawlins Resource Management Area. Comments have been directed to the existing and potential adverse impacts of human related activities within the management area and their potential long-term consequences. The report concludes with management recommendations for assessment, mitigation, and monitoring.

Definition of Biological Soil Crusts.

Communities of microorganisms, predominantly cyanobacteria (blue green algae), green algae, filamentous fungi, lichens, and non-vascular plants (mosses), inhabit the surface soil layer in arid and semiarid landscapes throughout the world. These biological soil crusts (BSC), also known as cryptogamic, microbiotic, or microphytic crusts, consist of water-stable aggregations of soil particles, primarily silt and clay, held together by the vegetative bodies and adhesive properties of the colonizing organisms (1). Limited annual precipitation facilitates BSC development. Therefore BSC communities are found worldwide either within areas inhospitable to vascular plant growth or where plants are slow to establish and are marginally productive having sparse canopies and widely spaced individuals.

In the initial stage of development BSC are smooth in contour, often appearing as fragile, wafer-thin aggregations of surface soil particles. They are formed by the binding action of bluegreen algae, green algae and fungi. Soil erosion at the margins of crust colonies results in other crust forms (morphologies): rough, with markedly roughened surfaces; rolling, where they become evenly mounded; and pinnacled, pedicelate mounds that can be up to 15 cm high (1, 5). A predictable succession of algae and fungi, then lichens and finally mosses inhabit the crusts as they mature and become stabilized. Crust thickness and biological composition can often be used as indication of BSC age. Apart from human related disturbances, the rate at which crusts develop is strongly influenced by climatic factors and soil conditions. Whereas soil factors greatly influence vegetation structure and composition, the vegetation likewise influences the type and extent of crust development. As measured by observations of recovery following disturbance the time required for BSC to reach maturity ranges widely from 2 years in cool deserts to over 300 years in extreme deserts (2).

Ecological benefits: role in maintaining vegetation, watershed integrity and soils.

By virtue of numerous scientific studies, BSC are regarded as important components of healthy arid and semiarid landscapes because they perform an essential role in maintaining vegetation, soil, and watershed integrity (3,10). Healthy landscapes have been defined as those with little or no evidence of active erosion, and the ability to support a diverse BSC and vascular plant cover. Perhaps the greatest asset of BSC to the fragile habitats in which they occur is the reduction of the erosive effects of wind and water (4, 7). It should be noted however that soil stabilization is not realized in dune areas where the sand content exceeds 80% and the soils are not frost-heaved (16). Human caused desertification processes have dramatically increased dune landscapes to the detriment of BSC communities on a worldwide scale (1).

Because semi-arid soils, like those of the Rawlins RMA, are generally nitrogen limited, BSC can be important sources of nitrogen for vascular plant growth. Crust-dwelling blue-green algae are capable of binding atmospheric nitrogen in a form available to and quickly utilized by plants and plant seedlings (12). Plant growth and establishment is also benefited in stable soil crust areas by their facilitation of flow and retention of water in the underlying soil (3). Crustal organisms contribute as much as 2 kilograms of organic matter per hectare which retains water against gravitational loss and also binds significant amounts of mineral nutrients needed for vascular plant growth. BSC enhance seed entrapment and provide favorable sites for the establishment of plant seedlings. The provision of suitable growth conditions for plants indirectly contributes to the long-term stability and production of animal forage in arid and semiarid landscapes (1). Another, but less studied benefit is the role of BSC as a natural barrier to the establishment of weedy annual species, like Cheat grass (11).

Distribution and habitats of soil-crust communities

The greatest development of biological crusts in Western North America is associated with the semiarid shrublands of the Great Basin. These soil crusts, heavily dominated by lichens and mosses, occur extensively over the entire region. They have been found to cover 80% or more of the soil surface in the absence of vascular plants (9). In both shrublands and woodlands, soil crusts occupy the interspaces between plants or beneath sparse canopies where sunlight, essential for crust growth, is available. Pinnacled crusts are more common in sagebrush steppe dominated by sagebrush species, and in coniferous woodlands with juniper and pine species. Rough crusts are typical of semi-desert shrublands with greasewood and shadscale/saltbush species as principal shrubs. Smooth crusts are typical of the mostly barren playas and the initial stages of crust succession in dunes (1).

Analysis of Wyoming soil crusts, distribution, condition, and trends

To date, assessment and monitoring of biological soil crusts in Wyoming has been largely neglected by both the scientific community and land resource managers. A recent survey of soil crusts in Wyoming showed them to be similar in morphology to those found in the sagebrush steppes of Utah, but not in composition. Well-developed crust cover was documented only in areas free from local grazing disturbances. Comparison of the prevalent crust species by presence and commonness in undisturbed and disturbed sites revealed both quantitative and qualitative decrease in diversity and abundance in the disturbed site (13, 14).

I conducted a cursory survey of biological soil crusts within the Great Divide Resource Area (GDRA), and verified the widespread presence of biological soil crusts. Crust composition and cover was inventoried in numerous sites in the following areas: a 50 mile transect through the Great Divide basin parallel to WY Highway 789; a 36 mile transect through BLM checkerboard lands parallel to Interstate 80; a 34 mile transect along US Highway 287 between Lamont and Rawlins; and various transect segments in the Ferris, Laramie, Seminoe, and Shirley mountains, Shirley basin, and the upper north Platte River valley (States 2002. See APPENDIX for survey documentation).

As is typical of all grasslands bordering the eastern slopes of the Rocky Mountain front ranges, crust presence and cover in the eastern half of the GDRA (in Converse, Albany, Laramie and parts of Natrona counties) was sparse and often absent in areas of high cover vegetation. The greatest density and diversity was confined mostly to exposed ridges and escarpments. Bryophyte crusts were the most common indicating historical stability but limited tolerance to recent disturbances. Extensive soil crust destruction was observed in disturbed sites, highlighting the need for assessment disturbance factors.

In the western half of GDRA (Carbon, Sweetwater, Fremont and parts of Natrona counties) shrublands and woodland vegetation replace grasslands. Wyoming big sagebrush is the most abundant shrub and occurs in a vast mosaic intermixed with other species of sagebrush, greasewood, shadscale and juniper. Although soil crusts are widely distributed throughout these rangelands, they are only locally abundant and are often discontinuous as small fragmented patches harbored beneath shrub canopies. Crusts were also fairly abundant in a few management exclosures that had not been breached by livestock in recent years. Again a preponderance of bryophyte crusts was indicative of past crust stability and maturity but their current condition reflects a long history of disturbance continuing up to the present. On the basis of BSC survey results from analogous sagebrush steppe and desert shrubland areas in Idaho and Utah (9), the relative abundance and diversity of soil crusts were found to be considerably lower than expected. Of the 60 sites selected for soil crust inventory, few were free from disturbance impacts (see Appendix for photographic illustrations of crust disturbance).

Disturbance factors and soil crust recovery potential.

Likely causes for soil crust disturbance observed in the GDRA survey:

Trampling by domestic livestock and ungulate wildlife species (e.g. antelope, wild horses)

Mineral Resource Industry activities (seismic exploration, oil & gas development, coalbed methane development)

Recreation activities (ORV/vehicle trampling, hiker trampling)

Invasive weeds and agricultural crops (decades of encroachment)

Rodents and other soil dwelling/digging animals (minimal area affected)

Fire (appears to be particularly damaging in shrub communities; less in grasslands)

Climatological events (e.g. Extreme drought, soil erosion and burial of crusts esp. in dunes)

Chemical spills and other biogeochemical changes (potential impacts by airborne pollutants)

The highly degraded condition of soil crusts in the GDRA is indicative of the dire need for additional investigation, mapping and assessment. Human activities, particularly land-use by the mineral resource industry, livestock grazing and agriculture with associated introduction of crop and invasive plants, and recreation have been and will undoubtedly be major contributors to (1) decrease in BSC density/abundance, (2) alteration of crust species composition and (3) diminution of their ecological role. Collectively, this will have a direct effect on the stability, biodiversity, and biogeochemistry of the landscapes where they are found (4, 2). Recovery from long-term disturbance has been documented, but it may require protection for many years, depending on climate, soil type, and severity of disturbance (2). Additionally, timing and intensity of disturbance impacts will, to a large degree, dictate the success of restoration efforts.

Management of biological soil crusts.

There is good evidence that BSC will recover if given the opportunity (2). Recommendations and guidelines for the management of landscapes containing BSC have been documented in a recent BLM publication (18). Of great significance is the fact that many of the same factors that threaten crust survival and ecosystem functioning are also common to the shrubs, particularly sagebrush, in shared habitats. For the most part management strategies developed for shrublands, including assessment, monitoring, and mitigation protocols, are also applicable to biological soil crusts. BLM studies in sagebrush steppe in Idaho indicate a strong correlation between the Biological Soil Crust Stability Index (BSCSI) and the health of sagebrush steppe (10). Unfortunately there has been only minimal testing of this model but its further refinement and application is urgently needed (see recommendations). The urgent need for improved management of Wyoming's 50,000 square miles of sagebrush was succinctly expressed in a editorial by Tom Reed in Wyoming Wildlife, the official publication of the Wyoming Game and Fish Commission: "Many sagebrush stands are imperiled. Drought, oil and gas development; overgrazing by livestock, feral horses, and wildlife; conversion of sagebrush grasslands to monocultures of grass and weeds; and ORV use are all having significant impacts on the State's sagebrush communities." (17).

Sagebrush steppe, a dominant feature of the Wyoming landscape for thousands of years, has been shown to be sensitive to disturbance by animal and vehicular trampling, the effects of which are still visible on the landscape from decades past. Historic trampling by grazing animals may be responsible for the observed decline in the associated biological crusts today (8). Careful study is needed in this area since some range managers refute the scientific evidence given for the beneficial role of soil crusts (19). They assert with counterarguments that intensive cattle grazing and associated trampling serves to destroy crusts which have been retarding the advance of the whole community for thousands of years. However, this is not likely to be the case since the ecological benefits of BSC and the detrimental impacts of livestock trampling to those benefits has been documented and validated in many scientifically reliable laboratory and field studies around the world (7).

Need for GDRA management objectives to address the deterioration in quality of rangelands containing biological soil crusts.

In a careful review of the GDRA RMP (15) no evidence was found to indicate the recognition of, or concern for, the extent and degree to which activities of the mineral extraction industry might have on BSC and associated soils and vegetation. Although concerns and management recommendations are available in BLM publications (18), there were no management objectives or mitigation guidelines pertaining to soil crust disturbance set forth in either the RMP or any recent POD (e.g. Cow Creek, Blue Sky, Sun Dog) issued for the GDRA. To the contrary, general management objectives of the GRDA- RMP (15) focus on providing habitat quality for wildlife species in specially designated high priority habitats at the expense of the vegetative condition and ecological quality in habitats of lower priority. The rationale given for this approach is simply stated as follows: "because lower priority habitats have less wildlife and vegetative diversity, they can be subjected to the disturbances of multiple, conflicting uses more readily without sustaining significant adverse impacts to wildlife." This may well be the case for immediate or short-term responses to most land-use impacts. However, considering the present condition of habitats in moderate and low priority categories, cumulative long-term effects have led to potentially serious degradation of soil and vegetation resources throughout the GDRA. All habitat types containing biological crusts are presently classified as either moderate priority (sagebrush steppe, and woodlands) or low priority (saltbush steppe, greasewood, badlands, and sand dunes). Given the current state of degradation, it appears that resource managers have not been able to achieve the stated general management objectives for these habitats under the existing management guidelines (15).

Identification of assessment, mitigation and monitoring needs for BSC habitat improvement and management to be included as requirements in the RMP revision.

Assessment of the cumulative long-term effects of extractive industry impacts on BSC should be prescribed in the RMP revision. Long term monitoring is required to assess rangeland health relative to the ecological roles fulfilled by BSC communities. Monitoring has been used to assess impacts of specific land uses, to measure recovery, and to determine "normal" background variation and "functional potential" of BSC in the absence of disturbance (11). BSC, particularly the lichen component, have been successfully used to monitor biodiversity and ecosystem function and health in grasslands and sagebrush steppes similar to those found in the GDRA (10). Monitoring with morphological crust groups has been shown to be an effective approach in measuring both biological crust condition and that of associated vegetation (3). Soil crusts can be evaluated using standard or slightly modified rangeland assessment techniques, including line-intercept, line-point, and quadrat based methods (11).

Conduct detailed surveys and mapping of critical resource areas. Remote sensing technologies used to map soil crust distribution have been developed but additional research is needed to refine the methodology (6). Both ground based and aerial photography was useful in this paper to identify areas of disturbance attributable to gas and coalbed methane seismic exploration (See Appendix). Ground validation of aerial photography will be necessary for accurate analysis of the visual impacts.

Analyses of the environmental impacts on biological soil crusts should be required of all development projects including but not limited to right-of-ways, coal, oil, gas and seismic exploration permits, and permits to drill and test.

BSC should be used to monitor biodiversity and ecosystem function and health in grasslands and sagebrush steppes of the GDRA The potential for the BSCSI to serve as an area-wide management indicator should be explored with the objective of establishing response benchmarks on which to base mitigation actions

Recommended mitigation actions (based on literature sources and personal observation)

Establish management objectives and mitigation guidelines to reduce the cumulative effects and disturbance footprints of energy development on BSC:
- require lighter impact alternatives to seismic exploration and eliminate thumper-trucks in the fragile BSC areas.
- close and restore the unused energy exploration corridors to pre-disturbance conditions and limit grazing disturbance to wildlife use until recovery is achieved.
- reduce the amount of land that will be trampled, scraped and impacted with roads and drill pads (i.e. employ directional drilling technology)
Develop and implement long-term monitoring protocols for the restoration of soil crust communities
- adapt/refine monitoring protocols, in particular the Biological Soil Crust Stability Index, for evaluation of existing BSC condition. When used in conjunction with corresponding measures of landscape stability, biotic integrity, and watershed function, the BSCSI can be used to help determine the relative health of grassland and sagebrush communities.
Implement livestock management strategies to reduce disturbance in areas where BSC represent 15% or more of the ground cover. :
- locate livestock watering and salt supplements on sites with low crust potential
- disperse livestock supplements throughout the grazing area
- limit livestock numbers, the site specific levels to be determined under the following range conditions: (1) areas of coarse grained or sandy soils with low water holding capacity (2) periods of low water availability (low annual precipitation and drought prone areas. Winter grazing reduces impacts to soil crusts when snow covered and has also been shown to be beneficial to vascular plant communities), (3) steep slopes, ridges and escarpments, (4) areas recovering from natural disturbance such as drought and fire.
Confine recreational vehicles and uses to designated roads, trails and campsites. Encourage low-density use in sensitive areas. Promote late fall or winter use by hikers, backpackers and animal packers. Provide educational opportunities and information on the importance and value of biological crusts.
Identify, map and protect from human related disturbances any remaining areas (refugia) where BSC represent 50% or more of the total ground cover (These are unlikely to represent more than 0.1% of the GRDA). This action provides for the conservation and recovery of naturally occurring BSC that can then serve as ecological reference sites for evaluation of responses to mitigation and monitoring activities. Although it is feasible to restore crusts by inoculating disturbed areas with crust layers salvaged and stored prior to disturbance projects, it is much easier and cheaper to conserve existing BSC.

Acknowledgements:

Photo documentation credits: Terri Watson, Lighthawk, Inc. Lander WY contributed the aerial photograph of sagebrush steppe disturbance by coalbed methane and gas exploration and development. Erik Molvar, Biodiversity Conservation Alliance, provided biological crust documentation in the Great Divide Resource Area. Meredith Taylor, Wyoming Outdoor Council, contributed photographs of damage to Sagebrush steppe by Seismic Thumper-Trucks.

LITERATURE CITED

1. Belnap J., Budel B, Lange OL (2001) Biological Soil Crusts: Characteristics and Distribution. In: Belnap J., Lange OL (eds) Biological Soil Crusts: Structure, Function, and Management, Springer, Berlin Heidelberg New York, pp 3-30.

2. Belnap J, Eldridge D (2001) Disturbance and Recovery of Biological Soil Crusts. In: Belnap J., Lange OL (eds) Biological Soil Crusts: Structure, Function, and Management, Springer, Berlin Heidelberg New York, pp 363-383.

3. Eldridge DJ, Rosentreter R (1999). Morphological groups: a framework for monitoring microphytic crusts in arid landscapes. J. Arid Environments 41: 11-25.

4. Evans RD, Lange OL (200l). Biological Soil Crusts and Ecosystem Nitrogen and Carbon Dynamics. In: Belnap J., Lange OL (eds) Biological Soil Crusts: Structure, Function, and Management, Springer, Berlin Heidelberg New York, pp 263-2 79.

5. Johansen JR (1993) Cryptogamic Crusts of Semiarid and Arid Lands of North America. J. Phycol. 29: 140-147.

6. Karnieli A, Kokaly RF, West NE, Clark RN (2001) Remote Sensing of Biological Soil Crusts. In: Belnap J., Lange OL (eds) Biological Soil Crusts: Structure, Function, and Management, Springer, Berlin Heidelberg New York, pp 431-455.

7. Kinter CL, Olson RA (in edit). Long-term Ecological Implications of Cryptogamic Crust Destruction on Rangelands. Department of Botany, University of Wyoming, Laramie. Pp 1-18.

8. Knight DH (1994) Mountains and Plains: The Ecology of Wyoming Landscapes. Yale Univ. Press, pp 90-130.

9. Rosentreter R, Belnap J (2001) Biological Soil Crusts of North America. In: Belnap J., Lange OL (eds) Biological Soil Crusts: Structure, Function, and Management, Springer, Berlin Heidelberg New York, pp 31-50.

10. Rosentreter R, Eldridge DJ (2002) Monitoring Biodiversity and Ecosystem Function: Grasslands, Deserts, and Steppe. In: Nimis PL, Scheidegger C, Wolseley PA (eds) Monitoring with Lichens, Kluwer Academic Publishers, Netherlands, pp 223-237.

11. Rosentreter R, Eldridge DJ, Kaltenecker (2001) Monitoring and Management of Biological Soil Crusts. In: Belnap J., Lange OL (eds) Biological Soil Crusts: Structure, Function, and Management, Springer, Berlin Heidelberg New York, pp 457-468