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USGS2008

Change in the forested and developed landscape of the Lake Tahoe basin, California and Nevada, USA, 1940-2002

The current ecological state of the Lake Tahoe basin has been shaped by significant landscape-altering human activity and management practices since the mid-1850s; first through widespread timber harvesting from the 1850s to 1920s followed by urban development from the 1950s to the present. Consequences of landscape change, both from development and forest management practices including fire suppression, have prompted rising levels of concern for the ecological integrity of the region. The impacts from these activities include decreased water quality, degraded biotic communities, and increased fire hazard. To establish an understanding of the Lake Tahoe basin's landscape change in the context of forest management and development we mapped, quantified, and described the spatial and temporal distribution and variability of historical changes in land use and land cover in the southern Lake Tahoe basin (279 km2) from 1940 to 2002. Our assessment relied on post-classification change detection of multi-temporal land-use/cover and impervious-surface-area data that were derived through manual interpretation, image processing, and GIS data integration for four dates of imagery: 1940, 1969, 1987, and 2002. The most significant land conversion during the 62-year study period was an increase in developed lands with a corresponding decrease in forests, wetlands, and shrublands. Forest stand densities increased throughout the 62-year study period, and modern thinning efforts resulted in localized stand density decreases in the latter part of the study period. Additionally forests were gained from succession, and towards the end of the study period extensive tree mortality occurred. The highest rates of change occurred between 1940 and 1969, corresponding with dramatic development, then rates declined through 2002 for all observed landscape changes except forest density decrease and tree mortality. Causes of landscape change included regional population growth, tourism demands, timber harvest for local use, fire suppression, bark beetle attack, and fuels reduction activities. Results from this study offer land managers within the Lake Tahoe basin and in similar regions a basis for making better informed land-use and management decisions to potentially minimize detrimental ecological impacts of landscape change. The perspective to be gained is based on quantitative retrospection of the effects of human-driven changes and the impacts of management action or inaction to the forested landscape. ?? 2008 Elsevier B.V. All rights reserved.

Forest Ecology and Management↗

USGS2008

Comparison of effects of humans versus wildlife-detector dogs

The use of dogs ( Canis lupus familiaris ) trained to locate wildlife under natural conditions may increase the risk of attracting potential predators or alter behavior of target species. These potentially negative effects become even more problematic when dealing with threatened or endangered species, such as the Mojave Desert tortoise ( Gopherus agassizii ). We addressed three concerns regarding use of dogs trained to locate desert tortoises in the wild. First, we looked at the potential for dogs to attract native and non-native predators to sites at a greater rate than with human visitation alone by comparing presence of predator sign before and after visitation by dogs and by humans. We found no significant difference in predator sign based upon type of surveyor. Second, we looked at the difference in risk of predation to desert tortoises that were located in the wild by humans versus humans with wildlife-detector dogs. Over a 5-week period, during which tortoises were extensively monitored and a subsequent period of 1 year during which tortoises were monitored monthly, there was no predation on, nor sign of predator-inflicted trauma to tortoises initially encountered either by humans or wildlife-detector dogs. Third, we looked at movement patterns of tortoises after encounter by either humans or wildlife-detector dogs. Movement of desert tortoises was not significantly different after being found by a human versus being found by a wildlife-detector dog. Based upon these initial results we conclude that use of trained wildlife-detector dogs to survey for desert tortoises in the wild does not appear to increase attraction of predators, increase risk of predation, or alter movement patterns of desert tortoises more than surveys conducted by humans alone.

Southwestern Naturalist↗