The Lake Tahoe Basin is an environmentally sensitive area that experiences everincreasing residential development and recreational use. Because this area is particularly valued for its winter recreation, public safety concerns demand that the Nevada Department of Transportation (NDOT) keep roadways clear of snow and ice. However, de-icing compounds such as NaCl have been linked to damage to vegetation, contamination of surface and ground waters, and corrosion damage to vehicles and highway structures (EPA 1999). NDOT is faced with the difficult task of balancing acceptable levels of risk for winter driving against the potential for environmental degradation.
Preliminary results from an ongoing field study indicate increased tree damage near roads at Lake Tahoe and suggest that road deicing salts are a potential source of tree damage near roads. However, in recent decades Tahoe forests have experienced high levels of tree damage and mortality (i.e. forest decline) across the entire Basin, which has been attributed to non-road-related factors such as increased tree density due to fire suppression, regional drought, and outbreaks of forest pathogens and insects.
For NDOT to ameliorate and monitor the potential effects of de-icing salts on forest health, it will be important to separate the effects of road-related tree damage from damage due to other causes, and to do so across basin-wide scales. Further, recent efforts by NDOT to mitigate salt effects (drainage basins and less deleterious salt compounds) need to be evaluated as to whether they have resulted in reduced rates of tree damage and mortality.
Remote sensing investigations provide a means for understanding potential road-related effects on tree crown mortality in a Basin-wide and long-term context. Note that “crown mortality” refers to loss of photosynthetic material in tree crowns, and does not imply tree death.
Archival sources of satellite imagery allow historical analysis of crown mortality due to drought, forest pathogens and anthropogenic factors. Remote sensing can also provide an inexpensive, efficient and repeatable protocol for future monitoring.
Building upon ground data from the ongoing field-based study, UNR researchers are using satellite imagery at multiple scales of spectral and spatial resolution to assess road-related effects on crown mortality across the Nevada portion of the Tahoe Basin.
This study will help to place road-related effects on forest health within a regional context including other pathogenic agents, and will result in an efficient methodology for future monitoring.