Hi Cornelp Every time you re-populate - it will (pseudo) randomise the placement. Remember that by shrinking the scale of plant instances, it creates more space between them, and then rules of distribute of placement and desnity will therefore change for everything else too - make sense? It's worthwhile just playing around with EcoSystems first to understand the relationship of different parameters. For example, if you drop a (non-infinite) plane (next to Torus primitive) to the ground - create an EcoSystem (e.g. Garden preset) and do a test render. Then physically resize the plane, and you will see everything scale as it resizes. However, edit the material and hit clear and then re-poupulate, and the scale will reset to original, but cover the same area more densely. I'm assuming the trees are part of the Eco System (hence them moving when repopulating, due to the shift in instances), but if you wanted them to remain fixed, i'd recommend removing them from your EcoSystem and manually placing them, or else to make a Mixed Eco Material - with the trees in one half and plants in another... Hope this helps to explain a little better? Kind regards