In mixed-jurisdiction landscapes of the Intermountain West, unprotected wildlands in private and State Trust ownership buffer protected areas, support ecosystem and watershed processes, and maintain landscape connectivity, while their subdivision and development, results in losses of habitat and biodiversity, fragmentation, and isolation of neighboring protected areas. In recent decades, conservation easements (CEs) have emerged as the primary tool for protecting private lands, but as private agreements, there is no explicit expectation that land protected provides these conservation values. With this dependence on CEs, identifying their conservation outcomes is critical to understanding their role in landscape-scale conservation efforts. Focusing on the Madrean Archipelago in Arizona and New Mexico, I conducted a mixed methods study assessing the spatial pattern of existing CEs relative to grasslands, riparian areas, and distance from protected areas, and completed stakeholder interviews to identify any process underlying these spatial patterns. Results show that more than 10% of private wildlands in the region are in CEs. They exhibited a strong affinity towards grasslands (almost 20% of private grassland area is in CEs) and protected areas (more than 80% of CEs lie within 1 km of a protected area) but tend to avoid riparian areas. Interviews revealed a moderate level of consistency between the spatial patterns identified and stakeholder objectives. These results suggest that CEs in the Madrean Archipelago do support landscape-scale conservation outcomes, in part because stakeholders engaged in establishing them are prioritizing resources and values with landscape-scale significance. They also affirm the need for more access to spatial data on CEs to better integrate them into regional conservation planning efforts.

Distributional and ecological dynamics of Neotropical migratory birds at stopover sites where they maintain critical fat reserves during migration remain poorly understood in North American aridlands. I examined spatiotemporal abundance and timing of migrants relative to 1) upland and riparian habitats, 2) post-fire landscape mosaics, and 3) phenological synchrony and overlap of migration with tree flowering in southeastern Arizona's Madrean Archipelago (2009-2011), and 4) abundance, habitat breadth, and foraging substrates relative to tree flowering along the Colorado River in southwestern Arizona and northwestern Sonora, Mexico (2000-2003). I explored these dynamics relative to local weather conditions and El Niño Southern Oscillation (ENSO) climate phenomena. In Madrean habitats, migrants showed three non-exclusive responses to high precipitation, snowfall, and low minimum temperatures associated with El Niño in 2010; migration timing adjustments, habitat shifts, and reduced abundances suggesting migration route shifts. Foliage-gleaning insectivores were most abundant in high severity burns, disproportionate to their availability, and decreased with time since fire (TSF); flycatchers were most abundant in low-moderate severity and increased with TSF. Migrant abundance increased with tree flowering. Phenological overlap declined with increasing difference in timing of these events. Overlap was lowest in 2011 in riparian habitat due to low willow (Salix goodinggii) flowering, despite high migrant abundance, but lowest in 2010 in montane conifer, despite high pollen cone production by Douglas-fir (Pseudotsuga meziesii), suggesting temperature limitation of insect abundance at high elevations, but water limitation of plant phenology at lower elevations. Along the Colorado River, migrant abundance and habitat breadth had inverse positive and negative quadratic relationships, respectively. Abundance increased with tree flowering, but only in 2003 during severe drought. Habitat breadth increased with monsoon precipitation. Foraging substrate use tracked flowering, shifting from willow to mesquite (Prosopis sp.); the overlap coincided with peak abundance and narrowest habitat breadth. Maintenance of diverse vegetation and post-fire landscape mosaics in the Madrean Archipelago should benefit migratory bird diversity. Flowering phenology likely provides large-scale cues of local-scale stopover habitat condition associated with interannual climatic variation. Management and restoration of upland habitats and large riparian woody perennials will be critical for migratory bird conservation in aridlands.

Estimates from radiocarbon-dated packrat middens indicate that the high elevation woodland communities of the Madrean Sky Islands were continuous as recently as 8,000 to 12,000 years ago. A number of population studies on a diverse collection of taxa have investigated the extent to which the Madrean Sky Island system has limited gene flow among mountain ranges. The results of several of these studies indicate that population divergences may be more ancient than the Holocene. Yarrow’s spiny lizards, Sceloporus jarrovii, were sampled from eight sites representing seven mountain ranges. The populations of S. jarrovii are host to the malarial parasite, Plasmodium chiricahuae. DNA sequences from the lizards and their malarial parasites were used to reconstruct the evolutionary relationships and estimate the ages of the populations for both host and parasite. The findings of these analyses indicate that the sky island populations of S. jarrovii have been isolated for hundreds of thousands of years and did not experience gene flow during the last woodland expansion. In contrast, the results indicate that the malarial infection occurred more recently, possibly during the Holocene woodland expansion. In addition, the prevalence of the malarial infection was compared to multiple attributes of the lizards. This analysis revealed a negative relationship between the genetic diversity of the lizard populations and the prevalence of infection. Furthermore, lizard populations with lower prevalence of infection have a lower frequency of multiclonal infections.

The Sierra Madre Occidental and neighboring Madrean Sky Islands span a large and biologically diverse region of northwest Mexico and portions of the southwestern United States. Little is known about the abundance and habitat use of breeding birds in this region of Mexico, but such information is important for guiding conservation and management. We assessed densities and habitat relationships of breeding birds across Sky Island mountain ranges in Mexico and adjacent portions of the Sierra Madre from 2009 to 2012. We estimated densities at multiple spatial scales, assessed variation in densities among all major montane vegetation communities, and identified and estimated the effects of important habitat attributes on local densities. Regional density estimates of 65% of 72 focal species varied significantly among eight montane vegetation communities that ranged from oak savannah and woodland at low elevations to pine and mixed-conifer forest at high elevations. Greater proportions of species occurred at peak densities or were relatively restricted to mixed-conifer forest and montane riparian vegetation likely because of higher levels of structural or floristic diversity in those communities, but those species were typically rare or uncommon in the Sky Islands. Fewer species had peak densities in oak and pine-oak woodland, and species associated with those communities were often more abundant across the region. Habitat models often included the effects of broadleaf deciduous vegetation cover (30% of species), which, together with tree density and fire severity, had positive effects on densities and suggest ways for managers to augment and conserve populations. Such patterns combined with greater threats to high-elevation conifer forest and riparian areas underscore their value for conservation. Significant populations of many breeding bird species, including some that are of concern or were not known to occur regionally or in mountain ranges we surveyed, highlight the importance of conservation efforts in this area of Mexico.

Climate change is increasing the frequency and extent of high-severity disturbance, with potential to alter vegetation community composition and structure in environments sensitive to tipping points between alternative states. Shrub species display a range of characteristics that promote resistance and resilience to disturbance, and which yield differential post-disturbance outcomes. We investigated differences in shrub patch size and stem density in response to variations in fire severity, vegetation community, and post-disturbance reproductive strategies in Sky Island forested ecosystems in the southwestern United States. Patterns in shrub structure reflect the effects of fire severity as well as differences among species with alternate post-fire reproductive strategies. Increased fire severity correlates with larger patch sizes and greater stem densities; these patterns are observed across multiple fire events, indicating that disturbance legacies can persist for decades. High severity fire produces the largest shrub patches, and variance in shrub patch size increases with severity. High severity fire is likely to promote expansion of shrub species on the landscape, with implications for future community structure. Resprouting species have the greatest variability in patch structure, while seeding species show a strong response to disturbance: resprouting species dominateatlowdisturbanceseverities,andobligateseedersdominatehighseverityareas. Differential post-fire reproductive strategies are likely to generate distinct patterns of vegetation distribution following disturbance, with implications for community composition at various scales. Shrub species demonstrate flexible responses to wildfire disturbance severity that are reflected in shrub patch dynamics at small and intermediate scales.