Permanent water and vegetation have drawn humans to Ash Meadows, a springs complex on the border of the Great Basin and Mojave desert , for over 10,000 years. With the arrival of Euro-American settlers in the late 1800s, agriculture, cattle grazing, peat mining, and construction of roads, dams, ditches, and reservoirs have drastically altered the landscape. Designated as a national wildlife refuge due to its 24 endemic species, 12 of which are threatened or endangered, Ash Meadows is undergoing extensive habitat restoration that involves restoring hydrology, species composition, and disturbances to their historical conditions. To aid in this restoration, we are investigating historical and current dynamics of woody vegetation and fire.

Velvet ash (Fraxinus velutina), a riparian tree species native to the southwestern United States, has been identified by refuge staff as a species of interest and a key component to their restoration plan. Historical aerial photographs and written accounts suggest that the amount of velvet ash within the refuge has varied greatly over the last century, but the extent and source of these fluctuations is unknown. We will reconstruct the historical distribution of velvet ash from archival records, remote sensing data, and dendrochronology to determine its relative importance on the landscape prior to Euro-American settlement. Because climate, hydrology, and other factors have also changed since Euro-American settlement, we will analyze the current distribution of velvet ash to determine the ecological conditions necessary for ash establishment and survival. To complement this analysis, we will explore factors that may influence the germination, establishment, and seedling survival of velvet ash using field and greenhouse experiments. Refuge staff will be able to use this information to determine reference conditions and the most effective ash planting practices.

Because desert springs and riparian areas have greater litter accumulation than the surrounding arid regions, it is hypothesized that these areas may have historically been prone to fire. We plan to examine the historic role of fire in desert spring systems through analysis of the life history traits and distributions of plant species, focusing on endemics because they are uniquely adapted to historical conditions at Ash Meadows. Because invasive species (e.g., Tamarix, Centaurea, and Bromus) and human activities can increase fire potential relative to historical conditions, the current fire frequency may not be similar to the historic one. From 2000 to 2005, approximately 10% of the wetlands within Ash Meadows burned, with some areas burning on multiple occasions. To determine the current fire regime and its role in shaping vegetation structure and distribution in the refuge, we will reconstruct fire occurrences and lightning strikes from remote sensing data.