The hot air is trapped in the trees during the day, especially if there is light breeze. If the wind strengthens this can disturb the stagnant hot air and cause it to burst from the trees; restitution thermal bubbles of a sort.
But as you will know, a stonking summer thermal will give 6 to 8 knots.
A good sunny thermal will give 4 to 6 knots.
An evening thermal over a forest in calm condition will give 1 knot at best.
An evening thermal over a forest in strong winds will give nothing, because the weak thermal will be broken to pieces.
The westerly turbulence at AMS is definitely a wave-rotor effect, which is why it occurs at low level.
And this really should be understood by AMS crews, because the effect is predictable and more easily countered if you understand why it is happening. (ie: it will more pronounced in stable warm-sector conditions with straight isobars, or at night under an inversion.)