What kind of mushroom is this in central Europe?

Question

I found some mushrooms in the forest and I'd like to know what kind it is, for being able to tell how to protect the trees from it.

Growing Info

growing location: central Europe, forest
host plant: beech tree, alive
season: late Summer (Sept. 15th 2020)

The area where the mushrooms were found is a typical beech forest with unusually low water levels, as the last few summers have been drier and warmer than usual. I presume the trees suffer more from these mushrooms because the trees are weakened due to the hot weather and little rain.
Some of the mushrooms dry out while on the host tree.

Picture Taking Conditions

The closeup pictures were taken at home. This was after transporting the mushrooms and storing them in the fridge for 2 days. They got a bit squeezed during this procedure.

Pictures

host tree:

host tree from below:

multiple mushrooms, pic A:

multiple mushrooms, pic B:

bright mushroom, pic A:

bright mushroom, pic B:

bright mushroom, pic C:

cream colored/older mushroom, pic A:

cream colored/older mushroom, pic B:

cream colored/older mushroom, pic C:

Answer 1

Based on the lateral stem, fan-like shape, and growth on wood, I believe these are Pleurotus or a closely related genus. Pleurotus are generally soft, while Hohenbuehelia are more rubbery (David Arora, Mushrooms Demystified, 1986). Telling the species definitively will be more difficult, though they do resemble P. ostreatus, which grows throughout Europe. A number of similar species are difficult to tell apart.

^{Fig. 1. Pleurotus ostreatus. source: iNaturalist}

P. ostreatus is only weakly parasitic, which suggests to me that the beech may be already dying from the stressors you mention. A professional silviculturist would be able to make recommendations for forest management.