Accessing Location Data in Mobile Environments - The Nimbus Location Model

Location-based applications and services are getting increasingly important for mobile users. They take into account a mobile user's current location and provide a location-dependent output. Often, location-based applications still have to deal with raw location data and specific positioning systems such as GPS, which lead to inflexible designs. To support developers of locationbased services, we designed the Nimbus framework, which hides specific details of positioning systems and provides uniform output containing physical as well as semantic information. In this paper, we focus on the location model, which takes into account the requirements of clients in mobile environments. A domain model contains logical links and allows the expression of semantic relations between locations. A decentralized and self-organizing runtime infrastructure offers operations to resolve the current location efficiently

Tree line shifts in the Swiss Alps: Climate change or land abandonment?

Questions: Did the forest area in the Swiss Alps increase between 1985 and 1997? Does the forest expansion near the tree line represent an invasion into abandoned grasslands (ingrowth) or a true upward shift of the local tree line? What land cover / land use classes did primarily regenerate to forest, and what forest structural types did primarily regenerate? And, what are possible drivers of forest regeneration in the tree line ecotone, climate and/or land use change? Location: Swiss Alps. Methods: Forest expansion was quantified using data from the repeated Swiss land use statistics GEOSTAT. A moving window algorithm was developed to distinguish between forest ingrowth and upward shift. To test a possible climate change influence, the resulting upward shifts were compared to a potential regional tree line. Results: A significant increase of forest cover was found between 1650 to and 2450 m. Above 1650 m, 10% of the new forest areas were identified as true upward shifts whereas 90% represented ingrowth, and we identified both land use and climate change as likely drivers. Most upward shift activities were found to occur within a band of 300 m below the potential regional tree line, indicating land use as the most likely driver. Only 4% of the upward shifts were identified to rise above the potential regional tree line, thus indicating climate change. Conclusions: Land abandonment was the most dominant driver for the establishment of new forest areas, even at the tree line ecotone. However, a small fraction of upwards shift can be attributed to the recent climate warming, a fraction that is likely to increase further if climate continues to warm, and with a longer time-span between warming and measurement of forest cover