Where brush has grown into small trees, crushing the growth is a plausible alternative to poison.
Aerators can sometimes work where grades or topography make subsoil plowing impractical. Once plants are thinned, aerators might be followed by subsoiling. Smaller is better. Use of contours is essential. Applications must vary since no two properties are the same.
This will be cheaper than poisons, kinder to habitat & soil life, and healthier for wild and domestic animals.