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Researcher says field verification trims GDE mapping in Tehama subbasins
Summary
A consultant presented field verification and GIS refinement of Nature Conservancy GDE maps across Corning, Antelope and Red Bluff subbasins, recommending targeted monitoring based on NDVI, repeat photography and Arundo removal in some areas to reduce groundwater stress and fire risk.
Kristen Kosinski, a botanist and applied ecology professor working with Subterra/Heritage Resource Investigations, presented a two‑tiered method of field verification and GIS analysis to refine groundwater‑dependent ecosystem (GDE) mapping in the Corning, Antelope and Red Bluff subbasins.
Kosinski said her team sampled 30 sites in 2024–2025 (10 in Antelope, 20 in Corning), conducting vegetation transects and verifying mapped polygons against aerial imagery and land‑use data. She calculated long‑term NDVI (2013–2024) for each polygon to assess relative vegetation health; she recommended prioritizing monitoring for polygons with lower NDVI averages and using repeat photography and a simplified woody‑species rapid assessment for periodic checks.
On results: Kosinski reported that a modest share of mapped polygons did not meet field criteria for GDEs after verification, and that differences across subbasins reflect local groundwater dynamics. "In Corning, we started off with 6,472 acres, and I identified about 30% of those were likely not GDEs," she said, recommending those areas be deprioritized for monitoring while flagged sites with low NDVI be retained.
Kosinski also recommended Arundo removal and native species planting where Arundo dominates: she said Arundo both depletes shallow groundwater and increases fire hazard. She urged twice‑annual photographic monitoring (spring and late summer) and periodic field sampling where possible.
Commissioners asked about access limitations that reduced Antelope samples and whether GDE monitoring would feed into corrective actions or GSP modifications; staff replied that the monitoring methodology would inform future oversight but that formal GSP changes require additional steps.
