Why the different colours?

[Rough Hewn]

To the best of my Knowledge and I'm a proper amateur, all Poplar. Both were laying on the ground and had been for some time. In my (proper amateur) mind, the one of them could have still been alive and the other not seems to make sense.

Alder, willow, lime and birch will often turn orange when exposed to light and air when freshly cut.
[emoji106]

[AJStrees]

I see ash and willow. Willow can go an orange colour too when cut. Just saying...... 

[Unframed Dave]

Thanks all for the suggestions, there is no willow anywhere in the woods. The two trees I cut in that stack were 10 metres plus in height and no lower branches, so I'm fairly confident that's Holly out. There is birch in the woods, quite a lot, but I'm familiar with birch and both trees have been down long enough for substantial moss growth to set in, I believe birch would be rotten in that time scale. Ash is a possible, as is alder. Although I haven't seen any alder, but then haven't been looking for it.