Monitoring Conifer Mortality in Lake Tahoe, Nevada

Project Title: Monitoring Conifer Mortality Region 5, U. S. Forest Service

Principal Investigator: Curtis E. Woodcock

Co-Investigator: John B. Collins

Duration: August 1994 – July 1995

Project Summary:

The U.S. Forest Service provides for the conservation and economic development of millions of acres of land in the United States. Remote sensing is the only practical way to obtain the data necessary to monitor the conditions of vegetation over such large areas on a regular basis. Of particular concern in the Western United States is high levels of tree mortality caused by several years of drought. The Center for Remote Sensing was asked to develop methods for monitioring forest conditions in general, and for detecting forest canopy change due to drought-induced mortality in particular.

Detecting canopy change was accomplished by comparison of two satellite images of the area around Lake Tahoe on the California / Nevada border in the Sierra Nevada Mountains. In the summer of 1994, field crews spent two weeks collecting data in the area. Data collection involved measurement of live and dead timber volume for a number of forest stands. These data allowed apparent changes between the two satellite images to be associated with precise levels of forest mortality. The conclusion was reached that roughly twenty percent of the timber in the area had been lost to drought in the three years prior to 1994 — a rather serious problem.

The results of this study had a direct effect on forest management practices over a large portion of the state of California. Furthermore, the Forest Service continues to use the satellite image analysis methods developed by the Center for Remote Sensing to monitor the conditions of other forests in the Western United States.

The following map shows levels of conifer mortality within the boundaries of the Lake Tahoe Basin Management Unit. Areas shown in grey tones are taken from a satellite image, and represent places which are either not within the management unit or are not conifer stands. Colored areas represent conifer stands, with the colors indicating mortality levels (see legend, below).

The map indicates quite effectively the variation in the severity of the problem within the study area. The information shown here has helped the Forest Service identify locations for concentration of management efforts.

lake tahoe conifer mortality Loss in basal area,
square meters per hectare:

color indicator < 2
color indicator > 2, < 5
color indicator > 5, < 10
color indicator > 10, < 15
color indicator > 15, < 20
color indicator > 20