Estimating time since forest harvest using segmented Landsat ETM+ imagery

Modeling of forest carbon (C) dynamics requires precise information regarding when a disturbance occurred and the age of regeneration present. Generally, this information is obtained in the age class attribute of forest inventories; however forest inventories can become quickly outdated when disturbance events are not continuously integrated into the database. In this study, Landsat ETM+ image data and Tasseled Cap index values were used to estimate the age of lodgepole pine (Pinus contorta) stands from the approximate time of disturbance to 20 years of regeneration. An image segmentation procedure aided the removal of pixels representative of residual forest and other non-characteristic stand conditions within forest inventory polygons, in order to isolate the pixels representative of regenerating harvested forest. A stepwise multivariate regression procedure was used to estimate stand age for harvested areas, and an R2 of 0.68 (with a standard error of less than 2.4 years) was computed. This transferable approach provides useful information for forest C accounting when the year of disturbance, or the age of subsequent regeneration, is required for estimating C stocks.