It has been found that mice carry an important bacteria back to the site necessary for soil reconstruction and root development of conifer seedlings. If we were to broadcast spray and remove the grass species we also would remove the mice by removing their food source. We could plant conifers again and even have good survival, but root growth would be severely restricted and grass would again take over the site as the plantation failed. Poor growth and form can readily be blamed on the nurseries supplying the trees, planting quality, the site preparation methods, or numerous other factors. Many of our problems stem from harsh continuous treatments with too much change too fast for the site without attention to the invisible organisms that are essential to establishing a healthy fast growing forest.
Many similar circumstances occur world wide and more research is needed.