Vital Signs: Landscapes

Fire and Fuel Dynamics

The annual area burned in wildfires has generally increased in the Western United States, an increase attributable partly to build-up of woody fuels, drought, and the invasion of non-native plant species. An understanding of fire and fuel dynamics is critical to science-based management of shrubland, woodland, and forested ecosystems. Change in fire regime (size, frequency, intensity) is a significant threat to parks in the MOJN. Fire is considered a critical element in maintenance of natural ecosystems, particularly patch mosaic dynamics, at GRBA. In recent years, GRBA has experienced a greater number of large, high intensity, stand-replacing fires that have threatened significant park resources such as ancient bristlecone pine stands.

Fire in the Mojave Desert is considered historically infrequent, and desert shrublands were once considered 'fire-proof'. The invasion of alien annual grasses such as red brome and cheatgrass has increased fire frequencies and intensities, and fire has become a resource management problem throughout low elevations in the Sonoran, Mojave, and Great Basin deserts. In the Mojave Desert, recurrent fire may have devastating impacts on native plants that are poorly adapted to fire, leading to loss of native species, transitional shifts in communities, and potentially permanent replacement of native plant communities by alien annual grasslands. Fuels modeling can provide information useful in predicting fire behavior, monitoring fuel condition changes, providing a means for fuel assessments, and developing fuels management plans.

Monitoring Questions:

1. Is fire size, frequency, and intensity changing over time?
2. What are the long-term trends in fire return interval and effects in predominant native plant communities?
3. What are the long-term trends in cause of wildland fire in network parks?

Landscape Dynamics

Land Use: Over three quarters of the Mojave Desert is in federal jurisdiction. Private lands, comprising 21% of the Mojave, are held primarily by ranchers, farmers, utility companies, mining interests, and urban development. Human population in the Great Basin-Mojave Desert region is predicted to experience to continue to growth. Land-use practices at the local and regional scale can dramatically affect soil quality, water quality and quantity, air pollution, level of habitat fragmentation, habitat loss, and contribute to the spread and introduction of invasive species. Understanding changes in land use lends interpretive power to other vital signs and may contribute to early detection and prediction of future resource issues.

Land Cover: Three vegetation types contribute to 75% of the land cover in the Mojave region, Creosote Bush Scrub, Mojave Mixed Woody Scrub, and Desert Saltbush Scrub. Land cover at GRBA and PARA are dominated by woodland and forest cover. Land cover is affected by natural events, including climate variation, flooding, vegetation succession, and fire, all of which can be changed in character or magnitude by human activities. Today, human-induced change in land cover is a primary factor in habitat loss, the most significant contributor in the listing of plant and animal species. Understanding of change in land cover provides critical insights into current or future changes in ecosystem services (habitat, recreation, stabilizing soils, etc.).

Landscape Pattern: Spatial heterogeneity in desert ecosystems has significant effects on basic ecological processes. The character of a landscape's pattern (patch size and structure, distribution, shape, dispersion, connection, etc.) directly influences the distribution, abundance, and movement of animals, and distribution, abundance, germination, and dispersal of plants. In deserts, where many of the organisms are living at or near the threshold for surviving the climatic extremes, the availability of resources in patches is a critical variable. Changes in climate, fragmentation, change in fire regime, and grazing have had the greatest past and current impacts on landscape pattern in the Great Basin-Mojave Desert region.

Monitoring Questions:

1. Where is land use changing in and around network parks, over what time scale?
2. Is the number of grazing allotments, allotment stocking rates, and patterns of livestock use within allotments changing over time?
3. How is the type/distribution/intensity/frequency of land use changing over time?
4. Is the extent and rate of change in land cover in and around network parks changing over time?
5. Is patch size (e. g. mean, minimum) in woodland and forested habitat at DEVA, GRBA, and LAME changing over time?