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Study shows modest recovery at Griffey Lake after deer culls; board approves continued monitoring
Summary
EcoLogic and city staff reported small improvements in plant growth metrics at Griffey Lake in 2024 but said heavy browse persists on preferred species; the Parks Board approved a 2025 monitoring agreement to continue tracking impacts.
The Bloomington Parks and Recreation Department on Tuesday heard results of a multi-year study showing modest vegetation recovery at Griffey Lake after the city began controlled deer harvests in 2018, and the board approved continuing monitoring in 2025.
Heidi Shoemaker, natural resources coordinator, introduced Kevin Tungusvick of EcoLogic, which has monitored transects at Griffey Lake since 2020. EcoLogic presented year‑to‑year measurements showing that several indicators — woody sapling height and diameter, and the height of spring wildflowers such as jack‑in‑the‑pulpit and Solomon’s seal — rose in 2024 after a period of stagnation. “There were small improvements in all metrics in 2024,” Kevin said.
Why it matters: staff and the consultant said the improvements suggest the site is recovering from intense deer browse but is not yet returned to a balanced condition. EcoLogic cautioned that weather and other environmental factors (for example, flash droughts) also affect growth rates, so the vegetation trends do not reflect deer browse alone. Kevin noted that while overall browse has moderated since the culls began, “browse remains locally heavy on favored species,” meaning certain shrubs and herbaceous plants still suffer heavy damage.
Key findings and context - Sapling growth: Average sapling height and root‑collar diameter showed renewed gains in 2024 after leveling off in 2022–2023; EcoLogic cautioned these metrics also respond to drought and other climatic factors. - Herbaceous plants: Jack‑in‑the‑pulpit reached its highest average height since monitoring began; Solomon’s seal — a species deer favor — increased but remains below its 2022 peak. - Spatial pattern: Browse and invasive pressure are concentrated in the Griffey Creek floodplain upstream from the reservoir, where dense privet thickets provide deer winter shelter and food. The report says invasive shrubs help sustain higher local deer densities and also facilitate spread of other invasives (for example, Japanese stiltgrass and garlic mustard) as seeds are transported on deer hooves.
During board discussion members asked whether current cull levels are reducing the herd or merely maintaining it. Kevin observed that recent cull numbers may be near replacement rates because fawn recruitment appears to offset removals, and the overall deer population may be holding steady rather than declining. He said improving the efficacy of harvests would require coordination with wildlife practitioners; he did not offer specific operational changes.
Board action and next steps A board member moved to approve a 2025 contract with EcoLogic to continue deer browse monitoring and vegetation surveys; the motion was seconded and approved unanimously. Staff said ongoing data will inform management decisions at Griffey Lake, including whether adjustments to deer management, invasive‑plant control, or habitat restoration are needed.
What the consultants recommended EcoLogic recommended continuing the transect monitoring and noted two complementary needs: (1) continued deer management that reduces browse pressure on heavily preferred species, and (2) active invasive‑plant control in the floodplain to reduce winter forage and the seed sources that spread invasives upslope.
Ending The board approved the 2025 monitoring agreement so staff and EcoLogic can return next year with updated metrics to assess whether the modest upward trends continue and whether deer‑management efforts are producing longer‑term recovery.
