Illinois Ecological Conservation: Using Earth Observations to Identify Areas of Oak Decline in Illinois and Investigate Contributing Risk Factors

Rapid white oak mortality is an increasing concern in the Midwestern United States, including Illinois, where
oak forests are a key component in ecosystem functionality. The Morton Arboretum is conducting research
to determine the main drivers of white oak (Quercus alba) decline and in turn, create plans to conserve these woodlands across Illinois. We partnered with this organization to test the feasibility of using Earth
observation data and GIS technologies in determining areas of white oak decline and its drivers. We used
Harmonized Landsat and Sentinel-2 and data from Landsat 5 Thematic mapper, Landsat 7 Enhanced
Thematic Mapper Plus, Landsat 8 Operational Land Imager (OLI), and Landsat 9 OLI-2 to identify changes
in forest canopy greenness by calculating differences in the Normalized Difference Vegetation Index (NDVI)
between 2010 – 2024 in two regions of Southern Illinois: the Shawnee National Forest and Kaskaskia River
Basin. We examined relationships between NDVI differences and potential drivers, including topographic,
climate, and agricultural variables to compute a present-day risk map for white oak forest decline. For each
study area, we identified key years of climatic stress and detected negative NDVI change within known areas
of oak decline; however, more ground truth data is needed to conduct a comprehensive and unbiased
accuracy assessment. Through Principal Component Analysis of risk variables, we found that drought
conditions, Topographic Wetness Index, and slope emerged as the most consequential variables in both study
regions for our generated risk map. Areas exhibiting high risk in the generated risk map were clustered along
the eastern, central, and northwestern regions of the Shawnee National Forest, while high risk areas in
Kaskaskia were more widespread.