Conclusions

Forests and rangelands throughout the United States are at risk of severe insect and disease outbreaks and catastrophic wildfires. Epidemic insect infestations have already caused extensive mortality in many of the Nation’s forests and rangelands. The severity and large extent of mortality, coupled with the lack of routine monitoring in some areas, has made it difficult to assess the damage, ecological impact, and fire hazard in a timely and cost-effective manner.

The multistage sampling method used in this study offers a statistically rigorous approach to estimate tree mortality across large geographic areas, increases sampling efficiency, and provides a confidence interval about the mean. By using a digital dot-grid to assess mortality from high-resolution aerial imagery, the need for time consuming and costly field assessments was eliminated. The use of imagery also allowed samples to be drawn from remote areas that would have been prohibitively time consuming to sample in the field. This method was tested over a 332,000-acre piñon/juniper woodland west of Flagstaff, AZ, but the technique is applicable to many other forest types impacted by insects and diseases. The multistage sample estimated that, as of spring 2004, dead-tree canopies occupied approximately 7 percent of the area within the piñon/juniper woodlands of the Williams Ranger District. Relative to the total tree cover, approximately 20-percent mortality was sustained. For the piñon/juniper study area, the cost to estimate mortality was approximately $0.04 per acre. In other areas, the cost per unit area to conduct a similar study could vary greatly depending on the location, size of the study area, and imagery requirements.