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Southern Colorado Plateau Network (SCPN)

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Southern Colorado Plateau Ecosystems

Landscape at Glen Canyon NRA

Southern Colorado Plateau Network Overview

In all its vastness, the Colorado Plateau is rich in natural resources, with great natural beauty and endless diversity. Nearly 500 million years old, this distinct mass of uplifted continental crust has been sculpted by wind, water and volcanic activity, and shaped by millennia of human habitation. Considered part of the Colorado Plateau Physiographic Province, it is distinguished by the horizontal layering of sedimentary rock, a great range in elevation, from the heights of the San Francisco Peaks to depths of Grand Canyon, and hundreds of escarpments and canyons deeply dissecting high plateaus.

Figure 1. Overview of Southern Colorado Plateau Network park unit locations
Figure 1. Overview of Southern Colorado Plateau Network park unit locations. Click image for map showing Indian lands and nearby cities(840 KB).

The Southern Colorado Plateau Network (SCPN) encompasses 19 parks (fig. 1) which together cover 4,780 square miles (12,379 km2). The network is located in the culturally diverse Four Corners region: an area that overlaps portions of northern Arizona, northwestern New Mexico, southwestern Colorado, southern Utah and several Native American Reservation Lands. The parks range in size from 35 acres (14 ha) to 1.25 million acres (506,000 ha). More than half of the total park area within the network is currently designated or proposed as wilderness.

The Southern Colorado Plateau Network (SCPN) is one of 32 National Park Service inventory and monitoring networks that have developed vital signs monitoring plans to assess and track changes in resource conditions in park ecosystems. The network approach facilitates collaboration, information sharing, and economies of scale in natural resource monitoring and provides parks with a basic monitoring infrastructure that can be built upon in the future. See the The Vital Signs Monitoring Plan for the Southern Colorado Plateau Network for more information.

Figure 2. Elevation across the Southern Colorado Plateau Network
Figure 2. Elevation across the Southern Colorado Plateau Network. Click image for larger map (3 MB).

Physical and biotic variation across the SCPN

Elevation

Key physical and biotic qualities characterize the Colorado Plateau and may serve as drivers, state factors, and/or interactive controls of Colorado Plateau ecosystems.

The wide range in elevation (fig. 2) and the topographic complexity of the Colorado Plateau landscape have created environmental conditions in which temperature, humidity, soil composition and solar radiation vary. As a result, different life zones have developed which support different vegetation and faunal communities.

Climate

Figure 3. Average annual precipitation across the Southern Colorado Plateau Network
Figure 3. Average annual precipitation across the Southern Colorado Plateau Network. Click for larger map (3 MB).

The Colorado Plateau lies in a cold, semi-arid climate zone characterized by periods of drought and irregular precipitation, relatively warm to hot growing seasons, and long winters with sustained periods of freezing temperatures.

The southern Colorado Plateau experiences a bi-modal precipitation regime, with most precipitation occurring during the winter months and during the summer monsoon rains (fig. 3). Average annual precipitation ranges from 16 to 54 cm across SCPN parks. Much of this moisture is lost through evaporation from being exposed to a nearly vertical noontime solar position, clear skies, and dry, thin, high-elevation air.

Geology and Soils

The Colorado Plateau rises to elevations of approximately 5,000 feet near the western edge, and climbs to almost 11,000 feet (3,350 m) at the eastern edge. In the west and southwest, the plateau forms escarpments that loom over the more broken and divided landscape of the Basin and Range geologic province. The Rocky Mountains province adjoins the northern and eastern boundaries of the plateau.

An ancient landform, the Colorado Plateau's geologic base consists of Precambrian metamorphic rocks formed more than 600 million years ago. Periodic flooding by Paleozoic seas deposited a sequence of sedimentary limestone, sandstones, and shale over the base rock. Volcanic eruptions during the Mesozoic era covered parts of the Plateau with igneous material and volcanic ash. Miocene uplifting raised the region more than 2 kilometers. Geologic stresses associated with this period of uplift caused widespread faulting in the Basin and Range province but left the sedimentary formations of the Colorado Plateau relatively intact.

Soil types on the Colorado Plateau vary due to the influences of parent material, climate, biotic communities, and geomorphic processes of the region. Soil types range from badlands composed of marine shale, small areas of colluvium collected next to cliffs, sand dunes, loess-covered tablelands, and fine textured alluvium along rivers and washes. Soils of the plateau are predominantly alkaline, except in mountainous areas where greater precipitation rates and abundance of organic material results in acidic soils.

Hydrologic and hydrogeologic regimes

More than nine-tenths of surface water on the Colorado Plateau drains to the Colorado River, which drops from the Rocky Mountains, crosses the plateau, and enters the Grand Canyon on its route to the Sea of Cortez. Portions of the Colorado River or its tributaries, the San Juan and Little Colorado Rivers, as well as the Rio Grande River, cross through or border various SCPN park units. Most of the smaller streams in SCPN parks tend to lose a great deal of water to seepage through streambeds and evaporation, when crossing drier, lower elevations of the Colorado Plateau.

Groundwater storage is limited in a variety of perched aquifers that occur in the SCPN region, but is much greater in deep and extensive sandstone and limestone aquifer systems. Fractures and secondary openings in Paleozoic and volcanic rocks, particularly faults, provide zones of large permeability allowing for lateral and vertical movement of water. Mountain snowmelt and rainfall seep into aquifers through sand and gravel near the edges of basins, under normally dry washes, and via sub-surface flow through fractures beneath mountains. Natural discharge from aquifers delivers water back to the surface via streams, springs, seeps, and other emergent wetlands for use by plants and animals.

Vegetation

Figure 4. Map of National Vegetation Classification Standard Macrogroups across the Colorado Plateau
Figure 4. Map of the distribution of National Vegetation Classification Standard Macrogroups across the Colorado Plateau and surrounding areas. Click image for larger map (4 MB).

The Colorado Plateau region supports one of the highest levels of endemism in the U.S., with an estimated 10% of the 3,000-3,500 plant species found only in this region. The evolution of flora and vegetation patterns in the SCPN region has been influenced by the uplift of the Colorado Plateau and the associated climatic changes.

Vegetation on the Colorado Plateau is predominantly open-woodlands composed of drought-adapted conifers on the high rims, with extensive areas of shrub steppe on the lower interior regions. See Figure 4 for a map of the distribution of National Vegetation Classification Standard macrogroups across the Southern Colorado Plateau and surrounding areas.

Fire regimes

Except for climate, fire has probably had the largest single impact in shaping the ecology of the southern Colorado Plateau. Natural fire regimes vary greatly by ecosystem, with pre-European fire frequencies ranging from 2 to 30 years in ponderosa pine woodlands, from 30 to 400 years in pinyon juniper woodlands, and from 150 to 400 years in spruce-fir forests.

Fire regimes changed dramatically with the coming of European and American settlers. Fire frequency and size were reduced as livestock removed grassy fuels that carried frequent, surface fires; and roads and trails fragmented the continuity of forest fuels. Fires that did break out were suppressed by settlers and fuels accumulated. By the early 1900s, fire exclusion began altering forest structure and fire regimes. In some ecosystems, such as ponderosa pine woodlands, fire exclusion resulted in a shift from frequent, surface fires to stand-replacing, high-intensity fires.

Ecosystems of the SCPN

Early in the monitoring planning process, as the most important natural resources were being identified and prioritized by park resource managers and regional scientists, network staff began working with technical experts to develop conceptual models of four key Colorado Plateau ecosystems: dryland, montane and subalpine , riparian and aquatic, and springs. Conceptual models help us understand the key drivers and processes that characterize a particular ecosystem, help us identify assumptions about how key processes and biotic components are related, and express our working hypotheses about how an ecosystem functions and how it may respond to changing conditions. Overall, conceptual models can increase the ecological understanding we gain from long-term ecological monitoring. The full conceptual model reports are included as supplements to the Vital Signs Monitoring Plan for the Southern Colorado Plateau Network.

Click on panels below for more information about SCPN ecosystems, including conceptual model diagrams. Expand All / Collapse All

Dryland Ecosystems

Picture of a dryland ecosystem

Dryland systems occur where mean annual precipitation is less than 450 mm, which includes about 85-90% of SCPN parkland area (see Supplement I). These systems are characterized by mixtures of pygmy conifers (Juniperus and Pinus spp.), shrub and desert grasslands, and biological soil crusts. Landforms of the dryland systems include deep and sparsely vegetated canyons, extensive mesas, lava beds, and slickrock. Limited precipitation and, in many cases, limited vegetative cover make dryland systems highly vulnerable to changes in natural disturbance and climatic regimes and to human impacts. The summary conceptual model for dryland ecosystems is shown in Figure 5.

Dryland ecosystem drivers

Regional climate and atmospheric conditions. Precipitation is the most important climatic factor defining the characteristics of dryland ecosystems, regulating key water-limited ecological processes, such as primary production, nutrient cycling, and plant reproduction. Strong winds, which are common in dryland systems, modify energy and water balances of plants and soils by affecting evapotranspiration rates, redistributing soil resources, and interacting with topography to influence wildfire behavior.

Natural disturbance. Extreme climatic events typify dryland ecosystems and contribute to their natural spatiotemporal variability. Extreme weather events, especially droughts, can cause widespread mortality, hamper the establishment of long-lived plants, and cause the redistribution of soil resources. The role of fire varies among dryland ecosystems, but low-intensity surface fires thin or eliminate fire-intolerant woody vegetation and favor the dominance of fire tolerant graminoids. Insect and disease outbreaks are linked with climatic conditions that diminish the vigor and insect resistance of host plants and generate long-term changes in vegetation structure.

Stressors and Degradation Processes

Figure 5. Summary conceptual model for dryland ecosystems. Figure 5. Summary conceptual model for dryland ecosystems. Click image for more information.

Climate change. Increasing levels of atmospheric CO2, increasing soil and air temperatures, and altered precipitation patterns are likely to affect physiological processes and competitive relations of vascular plants, nutrient cycles, hydrologic processes, and natural disturbance regimes.

Air pollution. Nitrogen in our air comes from combustion—from fire, from automobiles, from industry. Nitrogen deposition may affect numerous ecological patterns and processes, for example, ecosystem susceptibility to exotic species invasions.

Fire exclusion. Fuel removal and fire suppression cause changes in vegetation structure and functioning of associated ecosystem processes. Altered fire regimes can reduce hydrologic function and increase susceptibility to drought and various other stressors.

Visitors. Visitors affect park ecosystems by trampling soils and vegetation, disturbing wildlife, and contributing to water and air pollution.

Invasive non-native plants. Invasion by nonnative plants can lead to the displacement of native species and alterations of ecosystem-level properties, such as disturbance regimes and soil resource regimes.

Livestock grazing. Grazing modifies vegetative communities and reduces native plant populations, leading to the wide-spread colonization of nonnative plants.

Adjacent land use. Livestock grazing, forest management, urban/exurban development, and industrial and agricultural pollutants all have the potential to degrade park lands.

Montane and Subalpine Ecosystems

Picture of a montane ecosystem

Montane and subalpine ecosystems occur in nine SCPN parks and include subalpine spruce-fir forests, mixed conifer forests, ponderosa pine woodlands and forest, Gambel oak shubland, and montane-subalpine grasslands (See Supplement II). Figure 6 presents the summary conceptual model for montane and subalpine ecosystems.

Montane and Subalpine Ecosystem Drivers

Figure 6. Summary conceptual model for montane and subalpine ecosystems. Figure 6. Summary conceptual model for montane and subalpine ecosystems. Click image for more information.

Regional climatic and atmospheric conditions. The occurrence of forested systems on the Colorado Plateau is directly related to mountainous terrain and elevation-mediated precipitation gradients. A winter snowpack is common in mixed conifer and subalpine systems and contributes to summer water for plants. Lightning occurs with high frequency in these systems and is a source of forest fire ignitions.

Natural disturbance. Fire regimes and effects vary with elevation. High frequency, low intensity surface fires at lower elevations consume surface fuels and small stems and rarely result in overstory mortality. Low frequency, high intensity, stand-replacing fires occur at higher elevations, creating a patch mosaic of post-fire successional forests. Wind events can result in gap formation, windthrow patches and coarse woody debris, which provides habitat and nutrients. Large-scale tree mortality occurs when climate and pathogen-induced stress weakens tree defenses against bark beetles.

Stressors and Degradation Processes

Climate change. Increases in temperature due to climate change can increase physiological stress in trees, making them more susceptible to insect infestation and pathogens. Increased temperatures can also alter the elevation domain of species, leading to the migration of forest communities farther upslope.

Air pollution. Air pollutants potentially can affect patterns of tree mortality and regeneration and thereby affect species composition and vegetation dynamics.

Fire exclusion. In general, fire exclusion increases tree densities and decreases herb and shrub cover. It also leads to increased buildup of fuels, providing conditions for high-intensity fires.

Invasive non-native plants. Nonnative plants compete with and displace native species, resulting in lower biodiversity and altered soil nutrient cycling.

Historic livestock grazing. Grazing in high-elevation forests and meadows has greatly reduced the amount of herbaceous cover and caused woody-plant encroachment in meadows and higher understory stem densities in forests.

Adjacent land use. Adjacent lands can be sources of disturbance, such as fire and forest harvest, which can lead to large-scale habitat loss, decrease regional habitat connectivity, and overall, increase insularization of park lands.

Riparian and Aquatic Ecosystems

Picture of a riparian ecosystem

Riparian and aquatic ecosystems provide water and unique habitat for numerous plant and animal species in the predominantly dry landscape of the SCPN. Aquatic systems include surface water and channel characteristics of streams. Riparian zones occupy landscape positions transitional between upland and aquatic systems and are physically dynamic and more biologically diverse than surrounding uplands. A summary conceptual model was developed for the two systems combined, given their high degree of overlap, and is presented in Figure 7.

Riparian and Aquatic Ecosystem Drivers

Figure 7. Summary conceptual model for riparian and aquatic ecosystems. Figure 7. Summary conceptual model for riparian and aquatic ecosystems. Click image for more information.

Regional climatic and atmospheric conditions. Precipitation is a key factor shaping aquatic and riparian ecosystems, driving fluvial geomorphic processes and water-limited ecological processes. Precipitation intensity is especially relevant in terms of runoff and the potential for debris flows and flash floods, and decadal-scale variations in precipitation patterns are especially important in shaping riparian areas.

Natural disturbance. Heavy flooding can cause widespread geomorphic change and plant mortality, as well as the establishment of relatively long-lived riparian species. More frequent, low-magnitude floods create hydrologic gradients that control patterns of vegetation establishment and succession. Regional drought reduces surface flows and depletes alluvial groundwater aquifers.

Upland Watershed Characteristics. The form of channels, floodplains, and many attributes of ripairian ecosystems are determined by the flux of water and sediment from upland watersheds. Soils, vegetative pattern and composition, geology and topographic relief, watershed age, and climate ultimately determine water and sediment inputs to rivers.

Streamflow regime. The streamflow regime determines the mechanical forces that erode, transport, and deposit sediment, which influences channel dimensions of aquatic systems. Streamflow variation influences the occurrence of suitable habitat patches and species abundance. Riparian ecosystems are structured by geomorphic processes and hydrologic conditions found in channels and on associated flood plains. Diminished streamflow reduces the riparian zone area. Both channel morphology and streamflow are vital signs that SCPN monitors in riparian ecosystems.

Stressors and Degradation Processes

Climate change. Increasing levels of atmospheric CO2, rising soil and air temperatures, and altered precipitation patterns are likely to affect vegetation dynamics, nutrient cycles, hydrologic and geomorphic processes, and disturbance regimes. Effects on water availability and flow variability have the potential to greatly alter the structure and functioning of riparian ecosystems.

Streamflow alteration. Surface and groundwater extractions on lands upstream from some park units can lead to dewatering of the channel and floodplain, resulting in the mortality of riparian vegetation and encroachment of upland vegetation. These effects can cascade and lead to the degradation of site conditions. Dams disrupt the natural hydrologic regime, fragment riparian corridors, and create impoundments that modify water temperatures and interrupts sediment transport.

Visitor use. Trails in and adjacent to riparian zones, and hikers in slot canyons can increase erosion and stream channel instability, aid in the dispersal of invasive non-native species, increase levels of water and air pollutants, and alter water quality.

Invasive non-native plants. Riparian corridors are prone to invasion by non-native plant species, which typically comprise 25–30% of these areas.

Altered fire regime. An increase in catastrophic fire has resulted in the removal or reduction of the forest canopy and surface vegetation, contributing to accelerated erosion, increased suspended and bed-load sediment, and greater peak flows following floods.

Livestock grazing. Long-term grazing alters vegetation composition and structure, which can reduce the abundance and diversity of riparian-dependent species. Furthermore, trailing, trampling, and widespread reductions in vegetation cover by cattle can increase upland runoff, reduce channel stability, and initiate arroyo cutting.

Alteration of upland watersheds. Livestock grazing and exurban development on adjacent lands, emissions of industrial and agricultural pollutants and metal contaminants from upstream mines can alter watersheds, negatively affecting riparian ecosystems.

Spring Ecosystems

Picture of a spring ecosystem

Aridland springs are important sources of biodiversity and productivity in otherwise low productivity landscapes. They often function as keystone ecosystems, providing the only available water and habitat in the landscape for many plant and animal species. Springs commonly support high levels of endemism. Springs occur in 14 of the 19 SCPN parks and are viewed as a significant resource by park managers. A spring ecosystem includes the aquifer providing groundwater, the spring orifice and associated biota, and the biota supported by surface flow. These features were integrated into the summary conceptual model presented in Figure 8. (For more information see Supplement IV.)

Springs Ecosystem Drivers

Figure 8. Summary conceptual model for spring ecosystems. Figure 8. Summary conceptual model for spring ecosystems. Click image for more information.

Regional climatic and atmospheric conditions. Precipitation is critical to the existence of springs. Size, frequency, and duration of precipitation events are key factors influencing spring water availability.

Natural disturbance. Flooding, sheetwash, rockfall, seismic disturbance, and other erosional factors influence aquifer dynamics, lead to changes in groundwater flow rates, and influence the position, shape, and size of spring orifices. Drought results in seasonal or erratic desiccation of spring ecosystems and reduces biotic diversity. Fire in surrounding areas can modify flow rates and sediment loads, alter soil structures and ultimately change population dynamics.

Stressors and Degradation Processes

Climate change. Changes in precipitation regime can dramatically alter spring systems. Increased loading or drought can alter aquifers and thus flow levels, variability, and microhabitat structures, leading to substantive changes in biota.

Invasive non-native plants. Invasion by non-native species can greatly compromise ecological functioning at springs.

Ungulate grazing and foraging. Ungulates can alter spring ecosystems by removing vegetation cover, altering plant and invertebrate assemblages, increasing erosion, and contaminating surface water.

Groundwater depletion. Groundwater extraction, urbanization and changes in land use can alter spring flows and can fragment habitat, increase isolation of spring ecosystems, and interrupt biologic processes at micro, site, and regional spatial scales.

Local flow regulation and diversion. Flow diversion or regulation interrupts natural disturbance events, such as flooding, and alters structural, functional, and trophic attributes of springs.

Pollution. Groundwater and surface water pollution strongly affect springs ecosystems, shifting ecosystem nutrient dynamics to entirely novel trajectories, creating conditions to which few native species may be able to adapt.

Visitor use and park management. Recreational use at springs leads to trampling around the outflow, degrading native plant communities and potentially introducing invasive non-native plants. Management actions, such as fencing out visitors and livestock, may have unintended negative consequences, such as restricting movement of spring-associated invertebrates.

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Last Updated: December 30, 2016 Contact Webmaster