Monitoring Forest Change Over Time

For this assignment, I was tasked with using the LandTrendr toolset in ArcGIS Pro to better understand spatial and temporal patterns of timber harvest and decection of other disturbances in the West Cascades region of Oregon. Using the Normalized Burn Ratio (NBR) index, I generated a forest recovery map showing the estimated length of the recovery process needed for replanted trees to grow to maturity. I also created a forest disturbance map to illustrate disturbances that happened in recent and earlier years.

Disturbance Events Over Time

Using my change analysis raster, I used the Detect Change Using Change Analysis Raster tool to generate a forest disturbance map. I ran this tool with specific time parameters to extract occurrences of abrupt decreases in the fitted NBR values, signifying a sudden change from a healthy forest of trees to an absence of trees due to logging activity or fires. As you can see in the map figure above (bottom) , the dark purple areas represent disturbances that happened in recent years, and the light blue areas represent disturbances that happened in earlier years. The parameters designated events that lasted not longer than four years (to show abrupt change), and showed a decrease from high NBR values (.7 - 1) to low NBR values (-1 - .35), chosen based on typical values for healthy forest and logged/burnt areas for the Fitted Value raster band.

Forest Recovery Map

Again using the Detect Change Using Change Analysis Raster tool, I generated a forest recovery map (top). This time, I extracted the start and end dates of the change periods where NBR values increased, and calculated the number of years between the start and end dates. For this calculation, I used Calculate Recovery Duration tool provided by Esri. As illustrated in the map above, areas with recent disturbances (shown on the recovery time map as white or lilac) are still in the early stages of recovery, while areas with older disturbances have had enough time to recover fully.