Trends in Snag Populations in Drought-Stressed Mixed-Conifer and Ponderosa Pine Forests (1997–2007)

Snags provide important biological legacies, resources for numerous species of native wildlife, and contribute to decay dynamics and ecological processes in forested ecosystems. We monitored trends in snag populations from 1997 to 2007 in drought-stressed mixed-conifer and ponderosa pine (Pinus ponderosa Dougl. ex Laws) forests, northern Arizona. Median snag density increased by 75 and 90% in mixed-conifer and ponderosa pine forests, respectively, over this time period. Increased snag density was driven primarily by a large pulse in drought-mediated tree mortality from 2002 to 2007, following a smaller pulse from 1997 to 2002. Decay-class composition and size-class composition of snag populations changed in both forest types, and species composition changed in mixed-conifer forest. Increases in snag abundance may benefit some species of native wildlife in the short-term by providing increased foraging and nesting resources, but these increases may be unsustainable in the long term. Observed changes in snag recruitment and fall rates during the study illustrate the difficulty involved in modeling dynamics of those populations in an era of climate change and changing land management practices

Recent and Projected Future Wildfire Trends Across the Ranges of Three Spotted Owl Subspecies Under Climate Change

A major task for researchers in the twenty-first century is to predict how climate-mediated stressors such as wildfires may affect biodiversity under climate change. Previous model predictions typically did not address non-stationarity in climate-fire relationships across time and space. In this study, we applied spatially-explicit non-stationary area burned projection models to evaluate recent and future climate-driven trends in area burned across the ranges of three spotted owl subspecies in the western United States. We also used high-severity fire probability models to evaluate the risk of high-severity fire in recent times. Results suggest that the proportion of area burned will increase within the range of all three subspecies under climate change, but the extent of that increase will vary both among subspecies and among ecoregions within subspecies. Similarly, the current risk of high-severity wildfire varies both among subspecies and among regions within subspecies. The Mexican spotted owl is expected to have a 13-fold increase in area burned within its range by the 2080s. The combination of increased climate-driven fire extent and risk of high-severity fire suggests a potential for large-scale future loss or modification of spotted owl habitat. We recommend conducting further studies to understand the interaction and synergistic effects of climate change and wildfire on the spotted owl, especially in regions that are understudied such as Mexico

Forest and woodland replacement patterns following drought-related mortality

Forest vulnerability to drought is expected to increase under anthropogenic climate change, and drought-induced mortality and community dynamics following drought have major ecological and societal impacts. Here, we show that tree mortality concomitant with drought has led to short-term (mean 5 y, range 1 to 23 y after mortality) vegetation-type conversion in multiple biomes across the world (131 sites). Self-replacement of the dominant tree species was only prevalent in 21% of the examined cases and forests and woodlands shifted to nonwoody vegetation in 10% of them. The ultimate temporal persistence of such changes remains unknown but, given the key role of biological legacies in long-term ecological succession, this emerging picture of postdrought ecological trajectories highlights the potential for major ecosystem reorganization in the coming decades. Community changes were less pronounced under wetter postmortality conditions. Replacement was also influenced by management intensity, and postdrought shrub dominance was higher when pathogens acted as codrivers of tree mortality. Early change in community composition indicates that forests dominated by mesic species generally shifted toward more xeric communities, with replacing tree and shrub species exhibiting drier bioclimatic optima and distribution ranges. However, shifts toward more mesic communities also occurred and multiple pathways of forest replacement were observed for some species. Drought characteristics, species-specific environmental preferences, plant traits, and ecosystem legacies govern post drought species turnover and subsequent ecological trajectories, with potential far-reaching implications for forest biodiversity and ecosystem services.Peer reviewe

Winter Movements and Range Use of Radio-marked Mexican Spotted Owls: An Evaluation of Current Management Recommendations

We summarized existing knowledge on winter movements and range and habitat use of radio-marked Mexican spotted owls. In light of that information, we evaluated the adequacy of current management guidelines

Modeling snag dynamics in Northern Arizona mixed-conifer and ponderosa pine forests

17 pages (PDF version). File size: 1303.143 KB

Dietary Overlap Between Sympatric Mexican Spotted and Great Horned Owls in Arizona

The Mexican spotted owl (Strix occidentalis lucida) occurs in forested mountains and canyonlands through-out the southwestern United States and the mountains of Mexico (Gutiérrez and others 1995; Ward and others 1995). This owl was listed as threatened in the United States under the Endangered Species Act of 1973 (USDI 1993). The recovery plan for the Mexican spotted owl (USDI 1995) listed competition with other species as one biological factor in need of further investigation in evaluating the status of this owl