More info required I'm afraid - where did you buy the tree? Was it in a plastic covering when you bought it, and if so, did you harden it off first? Did you improve the planting area with humus rich material, such as garden compost or composted animal manure before planting? How small is small? And please describe exactly how you've been watering, such as every 3 days with the spray gun on the end of the hose, once a week with a gallon can, whatever....

I should imagine the soil would be very poor in nutrients and also very dry too when the conifers were removed. Did you enrich the soil at all? I have a newly planted sorbus in my garden....I planted it 2 years ago.....and it is doing fine. I watered it twice a week throughout the spring and summer of its first year and am still watering now but not so frequently. Can we have more info?