1. We are given that 70% of the woodland area in the county is native woodland. 2. We know the native woodland area is 350 km². 3. Let the total area of woodland be $A$ km². 4. Since 70% of $A$ equals 350, we write the equation: $$0.7A = 350$$ 5. Solve for $A$: $$A = \frac{350}{0.7} = 500$$ 6. The total woodland area is 500 km². 7. Find the non-native woodland area by subtracting the native area from the total: $$500 - 350 = 150$$ 8. Therefore, the area of woodland that is not native is **150 km²**.