Vital Signs: Biological Integrity

Vegetation Change

This vital sign combines the specific justifications for the individual vegetation communities that have been separated out as vital signs, as well as communities that are present but have not been considered of enough significance to have their own vital sign.

Monitoring Questions:

1. What vegetation "units" (communities, associations, alliances, etc.) are present in the parks and how big are they? What species, and in what relative abundances, are present in each of the vegetation units?
2. What trends in vegetation prompt changes in near surface soil properties important for nutrient cycling and hydrologic function?
3. How do faunal communities and species change in response to changes in plant community structure?
4. What are the effects of land use and management practices on the existing plant communities? How are these practices changing the vegetation communities?

Invasive/Exotic Plants

Non-native, invasive plant species are invading new areas at unprecedented rates. This is having profound consequences on ecosystems worldwide and is a great threat to wildland biodiversity. Specific concerns include threatened and endangered species sustainability, alteration of density, biomass, and diversity of native plant communities, species extirpation/extinction due to changes in fire regime, and alteration of basic soil processes. At least 66 non-native plant species have been identified in two or more park units within the Mojave Network. Invasive annual grasses are the most widespread and the greatest concern to park managers.

Monitoring Questions:

1. Is the relative abundance, percent cover, and distribution of invasive plant species, particularly invasive annual grasses, changing over time?
2. Is the rate of spread of invasive species changing over time?
3. What are the long-term changes in native plant communities after an invasive species has been eradicated?

At-Risk Populations

At-risk populations include species designated as rare, endemic, and NPS sensitive. All network parks except MANZ have “at-risk” species that are important components of the park’s biodiversity and that are the focus of park managers. Nearly 1,000 native plant species have been identified at DEVA, and approximately 12% of these native plants are considered special status species, including two federally listed plant species and 12 endemic plant species.

Monitoring Questions:

1. What are the long-term trends in abundance and distribution of at-risk populations in network parks?
2. What are the long-term trends in availability and quality of suitable habitat for at-risk species?
3. What are the long-term trends in at-risk populations in areas that have been invaded by selected non-native plant species?

Riparian Bird Communities

Riparian bird species may be particularly good indicators of change in riparian communities. Almost all birds in the MOJN depend on wetland and riparian habitats during at least some phase of their annual cycle. Riparian bird communities are also significant in terms of maintaining bird species of special concern, including the federally endangered Southwest willow flycatcher. Degradation and destruction of riparian areas are widely viewed as the most important causes of the decline of land bird populations in the MOJN.

Monitoring Questions:

1. What are the long-term trends in species composition, abundance, and distribution riparian bird communities?
2. Are urbanphyilic birds being subsidized and what are the trends in abundance and distribution of these species in response to increasing urbanization?
3. How does the abundance and distribution of riparian bird communities vary seasonally and along elevational gradients?

Reptile Communities

Reptiles, particularly lizards, tend to be long-lived and abundant in arid ecosystems and may potentially serve as a good indicator of environmental change. Research suggests that snake species richness may be a good indicator of edge effects. Reptiles also represent a vertebrate taxa with a significant number of species of special concern. For example, desert tortoise and gila monster are species that network parks already spend a significant amount of time and money monitoring. Because hunting is permitted in LAME with an Arizona hunting license the potential for a significant collecting to occur within the park exists.

Monitoring Questions:

1. Is the total harvest of reptiles in the Mojave Desert, associated with commercial pet collecting, changing over time?
2. What are the long-term trends in reptile community species composition, relative abundance, and distribution along elevational gradients?
3. What is the relationship between drought/wet years and reptile populations?

Small Mammal Communities

Contemporary populations of 16 montane mammal species across the Great Basin-Mojave Desert region are presently isolated on mountains and probably have been since the Pleistocene Epoch. Research in National Park units on the Colorado Plateau, Sierra-Cascades, and Rocky Mountains indicate that the number of mammal population extinctions has exceeded the number of colonizations since park establishment. Mammalian populations and communities may be good indicators of environmental change because environmental variables largely influence species composition and density. Small mammals are of particular interest due to their potentially significant role in soil processes, seed distribution and germination.

Monitoring Questions:

1. Is small mammal community species composition and population density, along elevational gradients, changing over time?
2. What changes in small mammal communities are occurring over time in response to ecosystem stressors?
3. Are changes in small mammal species composition correlated with changes in vegetation communities (e.g. species composition, cover of invasive species, etc.) or selected environmental variables?