Emerging Hotspots and Growth Trend of Vegetation Re-establishment at Mount St. Helens Between 1984 and 2024

The Mount St. Helens eruption of 1980 resulted in a catastrophic loss of vegetated land within the Pacific Northwest. This study focused on monitoring the re-establishment of vegetation throughout the blast zone with particular interest in comparing vegetation growth patterns on different management areas and it is the first to incorporate Emerging Hot Spot Analysis (EHSA) at Mount St. Helens. Using the Normalized Difference Vegetation Index (NDVI) for the years 1984–2024 and EHSA, results showed that vegetation growth was initially greater on properties where there were more remediation efforts such as Weyerhaeuser (WEYCO), Gifford Pinchot National Forest (GPNF), and Washington State Department of Natural Resources (WDNR) following the eruption. The National Volcanic Monument (NVM), where human activity is limited by law, continues to have consistent vegetation growth each year in areas where vegetation was naturally re-established. Emerging Hot Spot Analysis (EHSA) was applied to an NDVI space-time cube, combining the Getis-Ord Gi* statistic for spatial clustering with the Mann-Kendall trend test for temporal trends. Results show average NDVI increased across all areas, peaking around 2006. WEYCO and WDNR reached the highest NDVI values due to extensive replanting, but timber harvesting between 2010–2020 created oscillating and new cold spots, indicating recent declines. In contrast, the NVM and GPNF, which were largely left to natural regeneration displayed more consistent recovery. Over 93% of all diminishing cold spots occurred in the NVM, reflecting areas of historically low NDVI that have steadily increased. Overall, human-assisted reforestation produced greater cover earlier, whereas natural regeneration yielded a steadier, uninterrupted trajectory of vegetation recovery over the past 40 years.