Chinese Garden - Accumulation of leaf needles at tree base

The below would be an update for this post on de-compacting a tree base:
2017: http://openplants.blogspot.sg/2017/05/accumulation-of-years-of-leaves-and.html
2018: http://openplants.blogspot.com/2018/02/accumulation-of-leaf-needles-at-tree.html

Photos below taken on 4 May 2019

 The tree (Gymnostoma nobile) that I de-compacted the tree base looks good, albeit slightly assymetrical but that tree next was... gone, presumably dead.

From another view.

 Tree base that was de-compacted on Nov 2014.

  Tree base of the presumably dead tree, which was not de-compacted. Signs of dead leaf needles still on it. Could the tree have been done in by the short drought period earlier this year and exacerbated by the compacted tree base?

Drought at SBG Eco Lake. Taken on 8 Mar 2019.