I killed a tree

First time this has happened and I'm very surprised.
I've been coppicing my alder for four seasons now, and the regrowth has been great. However one tree that I cut last year has not grown back. The only thing I can think of is that I had carelessly left some prunings around the stump and this must have casued a problem. Either the harboured damp led to an infection, or nibblers ate all the shoots. I'm inclined to the former explanation.
I'm surprised because I'm sure I've read that piling brash around stools is actually suggested in a few places, to keep browsing animals like deer away from the  regrowth. Maybe my climate is just too damp for this strategy. Anyhow I'll not be doing that again! I'll make sure any piles are well clear. Actually I'm planning to move the brash to my 'natural farming' area to give a organic material boost to the soil for next year. Luckily I've got deer fencing (and a cat) so large and small browsers are not a problem at the moment.
I'll attach a photo of the stump, you can see the healthy regrowth of the trees behind that were cut at the same time. I have pulled the twigs to one side exposing the dead stump.

Are you cutting them every year? My step father used to manage a lot of hazel coppice and that was done every 7-10 years they were after poles for hurdles etc so obviously use effects how often you cut. I'm just wondering because cutting every year is how I go about killing trees I don't want!

Hi Skandi, No - I'm cutting trees every year, but not the same ones. I'm hoping that I'll cut the same tree in between 5 - 20 years depending on the species. Alder is my quickest growing tree, and I have cut those for the last four years. This is the first year I'm cutting some birch, and I do expect to have some losses from those. It's a balance between the tree being too 'mature' in some way, but this depends on the species. The hazel is all still too twiggy to be of much use to me yet. It seems to need more shelter to grow well.
In my secret permaculture garden I am trying to kill a sycamore that is growing in the patio beds. I actually cut it at about 4 feet, because I'm hoping to make a bird table base out of it - it's just outside the kitchen window. I have been rubbing all regrowth from it all summer....