- Road Ecology - Paved highways through Mojave National Preserve create barriers for some species, conduits for others, and mortality for animals killed by cars. We are especially concerned about road mortality of desert tortoise. Highway barrier fencing may be needed along roads through desert tortoise habitat. Roads and sections of roads need to be prioritized given the expense of fencing, insufficient budgets, and the fact that there are 145 miles of paved roads through desert tortoise habitat. Locations where tortoises are more likely to cross highways need to be identified for installation of culverts. The effectiveness of culverts for tortoise habitat connectivity needs to be confirmed and the effects of habitat fragmentation investigated. The ability of tortoises to repopulate habitat behind newly constructed barrier fencing is an open research question.
Climate Change
- Desert Tortoise Habitat - Recent advances in habitat modeling have made it possible to model suitable habitat for species, and the USGS recently published a habitat suitability model for the desert tortoise covering its entire listed range. This model identified key physical and environmental factors that are thought to be influential on the distribution of desert tortoises. Initial exploratory modeling indicates that the tortoise may undergo shifts in suitable habitat within the next 50 to 100 years if temperatures continue to increase at the rates forecasted in future climate scenarios. This would result in changes in tortoise distributions within several national parks, and would likely result in changes to management of habitat that may become inhabited by tortoises as they adapt to changing climates. The southwestern United States is forecast to experience increases in both drought and flooding as rainfall events become more concentrated and separated by longer dry periods. The mountains in the region will see less precipitation falling as snow as temperatures increase, which will result in a shift in the timing of runoff from precipitation events. This region has already experienced increases in temperature of 1.5 º F and is projected to experience increases of 4 to 10 ºF. The combination of increases in temperature, and reductions of precipitation is predicted to increase the incidence of wildfires, which has recently become a source of major habitat loss and degradation in the Mojave. Research is needed to predict where desert tortoise habitat will occur, and where habitat will disappear, as a consequence of climate change through the 21st century.
- Fire Ecology - Blackbrush communities are one of the most flammable native plant assemblages in the Mojave Desert and the effects of fire appear to be long-term. The Invasive annual grasses red brome (Bromus madritensis ssp. rubens) and cheatgrass (Bromus tectorum) are among the most common species to appear post-fire, leading to increased fire-frequency and transition from native shrub to exotic grassland. Blackbrush is associated with Joshua tree, increasing the threats to this charismatic species. Restoration of burned blackbrush communities is problematic because of infrequent reproduction, low germination, and poor survival of seedlings. Climate change will likely exacerbate the loss of blackbrush communities and other native shrubs through upslope shift in environmental conditions, increasing temperatures leading to increasing fire frequency, and increasing drought conditions with more variability in annual precipitation. Research is needed to provide the Mojave Network parks with basic information to plan for managing a transition to an anthropogenically warmed climate. Habitat niche models need to be developed to predict where blackbrush may continue to persist in a time frame of 50 to 100 years under various greenhouse gas emission scenarios. Long-term monitoring plots need to be established in the Mojave Network parks to monitor demographic changes and community shifts, including invasions of exotic annual grasses. Finally, experimental techniques for blackbrush propagation and restoration need to be developed so that managers can restore burned areas where that habitat models predict that blackbrush can persist into the future.
- Fire frequency and intensity have increased dramatically in the Mojave Desert in the past few decades, converting desert shrubland to invasive grassland. Reversing this transition will be difficult to impossible. Climate-driven fire cycle dynamics may be the most important factor in future distributions of vegetation communities in arid lands. While a drying trend may moderate annual plant invasions, increasing precipitation variability could exacerbate both plant invasions and fire dynamics. Invasive annual plants respond preferentially to heavy winter precipitation, atmospheric nitrogen deposition, and elevated carbon dioxide. Wet winters followed by dry summers result in high fuel loads, easily ignited by summer lightening storms. Research is needed to develop an effective strategy in the Mojave Desert for invasive grass and fire management. How might interannual precipitation variability effect both plant invasions and fire? Given the rapidly changing dynamics, and potential harm to the desert ecosystem, it is essential that Mojave Desert parks obtain the best science to develop and implement a comprehensive invasive grass control and fire management strategy.
- Paleoclimate Proxies -The desert southwest is experiencing a transition to a drier climate as a consequence of global climate change. The Mojave Desert area of southern California and adjacent Nevada is identified as a "climate change hotspot," due mainly to a predicted increase in variability of precipitation from year to year. The most important consequence of these predictions - an increase in the frequency, intensity, and duration of droughts in an already extreme, water-limited environment - may threaten the sustainability of ecosystems and wildlife populations in National Parks and Preserves in the area, thereby compromising the few remaining intact landscape-scale ecosystems in the Mojave region. Variability imposed by climate change, especially extended drought, could undermine park planning efforts to manage desert water sources (springs and seeps) and to preserve these resources for future generations. Research is needed to assess threats to desert water sources and wildlife habitats. Reconstructing environmental conditions during prehistoric droughts using paleoclimate proxies, or analog data, in the form of wetland, lake, and playa sediments, paleospring deposits, and pack rat middens could provide data on how wetlands may respond to modern, anthropogenic climate change. Reconstructions of past precipitation variability and extremes could lead to improved forecasts of future hydrologic and vegetation change, and provide essential tools for resource managers to implement mitigation strategies in response to a changing global climate.
- Impact of Megadrought -Megadroughts are characterized by exceptionally dry conditions that last for decades to centuries. These extreme events are thought have occurred in the American Southwest during both the Medieval Warm Period ('900-1300 AD) and the Altithermal Period ('7000-4500 years BP), and may be viewed as potential analogs of future conditions. Little is known about what impact these extended droughts had on springs and desert wetlands, which act as important water sources and provide critical habitats for wildlife in arid environments. Previous research has been successful in reconstructing the timing and magnitude of changes in water-table levels in desert wetlands during the late Pleistocene. Sediment cores from active wetlands may preserve evidence of drought events in more recent times. Sedimentologic analyses combined with stable isotopes, pollen, microfauna identification, and geochemistry together could provide information on past climate conditions, hydrologic environments, and vegetation regimes that will inform land managers on how wetlands and nearby vegetation responded to droughts in the past.
- Seeps and Springs -In the desert parks of the Mojave Network, small, mountain-slope seeps and springs play an important role in desert ecosystems, supporting populations of desert bighorn sheep, migratory birds, predators, and riparian vegetation to name just a few. These features appear to be primarily fed by small, perched aquifer systems in desert mountain ranges. The desert parks have developed inventories of these water features over the past few years and are developing protocols for long-term monitoring but the published literature on these springs is surprisingly sparse. Resource managers at the desert parks have pressing research needs related to the ecology of ephemeral spring systems and their role in supporting wildlife populations, maintaining habitat connectivity, and threats due to climate change. Recent projections of climate change in the southwest suggest a drying climate with changing variability in precipitation and increasing likelihood of extended drought conditions. Mojave National Preserve has initiated a water management planning process to develop potential management actions related to springs, groundwater, and artificial wildlife watering devices. Research is needed in this under-studied area of ecohydrology to support resource management planning in the face of a changing, drying climate.
Weed Management
- Sahara mustard (Brassica tournefortii) has become a major threat to the Mojave and Sonoran Desert ecosystems. Sahara mustard exploded into previously undocumented areas in the region following record winter precipitation in 2005. Sahara mustard is native to semi-arid and arid deserts of North Africa and the Middle East, as well as Mediterranean lands of southern Europe. It was apparently relatively uncommon in the deserts of southern California until a series of wet years between 1977 and 1983 when it experienced a population explosion and became abundant in southeastern California. It is most common in wind-blown sand deposits and disturbed sites. Because of its early phenology germination (it is a winter annual forb that responds to fall/winter cool season rains) it appears to monopolize available soil moisture as it builds canopy and sets matures seed long before many native species have begun to flower. One robust Sahara mustard plant can produce tens of thousands of seeds that are viable for decades. This dependence on the timing and magnitude of winter rain means that its presence is highly variable and difficult to predict from year to year. Research is needed on methods of control and on the consequences of full invasion of Sahara mustard.
Groundwater
- Groundwater resources in the Mojave Desert are becoming increasingly utilized for consumptive uses, given the scarcity of surface water and the growing population in the region.Pumping a relatively small fraction of ground water out of arid desert basins can lower the water table, potentially changing the source and quality of ground water discharged by springs and wells in the Mojave Network of Parks.Existing ground-water quality data need to be compiled to assess ambient conditions and determine if water-quality is changing in the aquifer systems underlying the parks. Groundwater levels need to be summarized and interpreted to provide information on groundwater flow directions, depth to groundwater, and a baseline for assessing aquifer depletion as it affects spring discharge. Susceptibility of springs and associated aquatic biota to water quality and quantity impacts resulting from climate change and ground-water development need to be determined.
Habitat Connectivity
- The Mojave Desert ecosystem is fragmented on a landscape scale by transportation and utility corridors that create barriers against migration of animals such as the desert bighorn sheep. Direct loss of habitat is a problem threatening numerous species including the threatened desert tortoise. Habitat loss and fragmentation will likely increase over the coming decade as a consequence of development plans for mass transit and renewable energy projects. For example, a high speed train, the DesertXpress, is proposed to connect southern California with southern Nevada, which will increase the fragmentation of wildlife habitats on either side of the transportation corridor. Applications for solar and wind energy developments have been filed for much of the Mojave Desert managed by the Bureau of Land Management and are beginning to be constructed. Land used for energy development is permanently lost for wildlife habitat and connectivity. Research is needed to mitigate the adverse consequences of these planned developments. How do different species respond to disturbance and loss of connectivity? What species might be good indicators of overall ecosystem integrity? Is connectivity an optimal way to address conservation associated with developments in the desert? What have we learned from studying desert bighorn sheep that might assist in maintaining ecosystem integrity? Where are the likely migration corridors? How do wildlife overpasses work? What are the performance measures? How can overpasses be made effective for enabling movement of large mammals?
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