Yes - the area where the fir tree was will have had all the nutrients sucked out of it. It will need plenty of 'food' in the shape of well-rotted manure/home made compost, chicken manure pellets, etc, dug in or mulched if digging isn't possible.

If you can gradually remove the roots, that would help, but in the meantime, let the worms take compost into the soill for you, and 'tickle' the surface with your fork, adding a sprinkling of pellets. I'd also suggest that every time you plant anything, you 'try' to make the planting hole bigger than normal, and back-fill with compost.

The manure could be used when the plants are dormant - as a mulch again.

In addition to the ferilizing Spritzhenry recommends, put earthworm castings over the soil, about 1/2 liter per square meter (different brands differ in concentration) and spray stale beer (ale, stout, bitters, etc.) on the bed, about 1 pint per 9 sq. meters, then sprinkle long enough to put on at least 10 cm of water. That will greatly speed up the decay of the fir roots, which are probably still sucking nitrogen out of the ground.

Tug - I don't think we can buy earthworm castings here - I've never seen them for sale, anyway. Can you get them over there easily?

Several different national brands that I know of, Spritzhenry, plus a bunch of local wormeries. Never imagined that they wouldn't be available in the UK.

What a great idea! I'll have to look around, but it's not a common product here, or I'd have seen it, I think.