diff --git a/src/simulator/crates/mc-flora/src/engine.rs b/src/simulator/crates/mc-flora/src/engine.rs
index 286a60fb..ab07fdc2 100644
--- a/src/simulator/crates/mc-flora/src/engine.rs
+++ b/src/simulator/crates/mc-flora/src/engine.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{BTreeMap, HashMap};
 
 use mc_core::grid::GridState;
 use rayon::prelude::*;
@@ -74,7 +74,7 @@ const EMERGENCE_INTERVAL: u64 = 10;
 /// Owns per-tile flora populations and the species registry.
 pub struct FloraEngine {
     /// Per-tile flora populations, keyed by (col, row).
-    pub tile_populations: HashMap<(i32, i32), Vec<FloraSlot>>,
+    pub tile_populations: BTreeMap<(i32, i32), Vec<FloraSlot>>,
     /// All known flora species, keyed by id.
     pub species_registry: HashMap<u32, FloraSpecies>,
     /// Next species ID to assign on generation.
@@ -86,7 +86,7 @@ pub struct FloraEngine {
 impl FloraEngine {
     pub fn new() -> Self {
         Self {
-            tile_populations: HashMap::new(),
+            tile_populations: BTreeMap::new(),
             species_registry: HashMap::new(),
             next_species_id: 1,
             tick_count: 0,