diff --git a/engine/src/modules/ecology/flora.gd b/engine/src/modules/ecology/flora.gd
index 11ad50ff..6232b57a 100644
--- a/engine/src/modules/ecology/flora.gd
+++ b/engine/src/modules/ecology/flora.gd
@@ -63,7 +63,7 @@ func process_turn(game_map: RefCounted) -> void:
 	var tiles: Array = game_map.tiles.values()
 
 	var o2: float = game_map.o2_fraction if "o2_fraction" in game_map else 0.21
-	tick_pioneer(tiles, _biome_flora, _veg)
+	tick_pioneer(tiles, _biome_flora, _veg, o2)
 	tick_canopy(tiles, _biome_flora, _veg, o2)
 	tick_undergrowth(tiles, _biome_flora, _veg, o2)
 	tick_fungi(tiles, _biome_flora, _veg)
@@ -81,12 +81,16 @@ func process_turn(game_map: RefCounted) -> void:
 # =========================================================================
 
 
-static func tick_pioneer(tiles: Array, biome_flora: Dictionary, veg: Dictionary) -> void:
+static func tick_pioneer(tiles: Array, biome_flora: Dictionary, veg: Dictionary, o2_fraction: float = 0.21) -> void:
 	## Pioneer colonization: seeds bare ground with initial flora using raw climate values.
 	## Uses temperature/moisture directly (not biome climate range) because abiotic-classified
 	## tiles may have narrow climate ranges that don't match their actual climate conditions
 	## (e.g., a temperate tile classified as polar_desert before biology establishes).
 	## Does NOT run for abiotic worlds (ecology is disabled when abioticWorld = true).
+	## Respects the O2 minimum threshold — no pioneer seeding in anoxic atmospheres.
+	var o2_mult: float = _o2_growth_mult(o2_fraction)
+	if o2_mult <= 0.0:
+		return
 	var pioneer_rate: float = veg.get("pioneer_rate", 0.002)
 
 	for tile: Variant in tiles:
diff --git a/packages/engine-ts/src/EcologyPhysics.generated.ts b/packages/engine-ts/src/EcologyPhysics.generated.ts
index 17973a5d..47664018 100644
--- a/packages/engine-ts/src/EcologyPhysics.generated.ts
+++ b/packages/engine-ts/src/EcologyPhysics.generated.ts
@@ -391,12 +391,17 @@ function _getStage(stage_index: number, stages: Record<string, number>[]): Recor
 // Flora tick functions (auto-transpiled from flora.gd)
 // ---------------------------------------------------------------------------
 
-function tickPioneer(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>): void {
+function tickPioneer(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>, o2_fraction: number = 0.21): void {
   // Pioneer colonization: seeds bare ground with initial flora using raw climate values.
   // Uses temperature/moisture directly (not biome climate range) because abiotic-classified
   // tiles may have narrow climate ranges that don't match their actual climate conditions
   // (e.g., a temperate tile classified as polar_desert before biology establishes).
   // Does NOT run for abiotic worlds (ecology is disabled when abioticWorld = true).
+  // Respects the O2 minimum threshold — no pioneer seeding in anoxic atmospheres.
+  let o2_mult = _o2GrowthMult(o2_fraction)
+  if (o2_mult <= 0.0) {
+    return
+  }
   let pioneer_rate = (veg as any)["pioneer_rate"] ?? 0.002
 
   for (const tile of tiles) {
@@ -1160,7 +1165,7 @@ export class EcologyPhysics {
 
     // Flora dynamics (order matches flora.gd process_turn)
     const o2 = grid.o2_fraction ?? 0.21
-    tickPioneer(tiles, bf, veg)
+    tickPioneer(tiles, bf, veg, o2)
     // Reclassify pioneer-seeded tiles immediately so subsequent ticks use the correct biome.
     // A tile seeded from canopy=0 to canopy>0 may be in an abiotic biome (polar_desert,
     // chaparral) that won't match its actual climate, causing tick_canopy/tick_undergrowth
diff --git a/tools/sprite-generation/spritegen.db-shm b/tools/sprite-generation/spritegen.db-shm
index 35ce2169..e7186dc0 100644
Binary files a/tools/sprite-generation/spritegen.db-shm and b/tools/sprite-generation/spritegen.db-shm differ
diff --git a/tools/sprite-generation/spritegen.db-wal b/tools/sprite-generation/spritegen.db-wal
index 4470d33c..f5638cd1 100644
Binary files a/tools/sprite-generation/spritegen.db-wal and b/tools/sprite-generation/spritegen.db-wal differ
diff --git a/tools/transpile-engine/ecology_assembly.py b/tools/transpile-engine/ecology_assembly.py
index c46126ad..85c339bc 100644
--- a/tools/transpile-engine/ecology_assembly.py
+++ b/tools/transpile-engine/ecology_assembly.py
@@ -220,7 +220,7 @@ def _read_functions(path: Path) -> dict[str, str]:
 # ---------------------------------------------------------------------------
 
 FLORA_TICK_SIGS: dict[str, str] = {
-    "tick_pioneer":       "tickPioneer(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>): void",
+    "tick_pioneer":       "tickPioneer(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>, o2_fraction: number = 0.21): void",
     "tick_canopy":        "tickCanopy(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>, o2_fraction: number = 0.21): void",
     "tick_undergrowth":   "tickUndergrowth(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>, o2_fraction: number = 0.21): void",
     "tick_fungi":         "tickFungi(tiles: TileState[], biomeFlora: Record<string, Record<string, number>>, veg: Record<string, number>): void",
@@ -657,7 +657,7 @@ export class EcologyPhysics {{
 
     // Flora dynamics (order matches flora.gd process_turn)
     const o2 = grid.o2_fraction ?? 0.21
-    tickPioneer(tiles, bf, veg)
+    tickPioneer(tiles, bf, veg, o2)
     // Reclassify pioneer-seeded tiles immediately so subsequent ticks use the correct biome.
     // A tile seeded from canopy=0 to canopy>0 may be in an abiotic biome (polar_desert,
     // chaparral) that won't match its actual climate, causing tick_canopy/tick_undergrowth