Answer: Cotinus (smoke tree) grows best in poor and rocky soils. Since your soil is basically alkaline and your pine tree has been dropping needles for several years, I suspect the final result is a soil that is relatively close to neutral. Smoke trees do not have a preference to soil type, other than the requirement that it drains quickly. Make sure you loosen the soil in a large area before planting your new smoke tree (to encourage good drainage) and then simply backfill the planting hole with native soil. Water regularly while the roots are becoming established and then you can practically ignore the tree and it should thrive in the garden site you describe.
Best wishes with your landscape!
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