Is my cherry tree dying?
I planted a yoshino cherry in 2007 which has been healthy until this year. It had less blooms than usual and now the leaves are very sparse. Is there something wrong with it? It is the front most tree in the first picture. Many of the little branches are dead. The tree is on a slight slope so the tree is not sitting in wet ground.
We cannot see any particular disease or insect in these photos.
That suggests that the problem is environmental/cultural. The large ferns (ostrich ferns?) in the background hint that the site is wet. A slight slope would not necessarily save a tree from saturated soils in a large areas. It's possible some roots rotted due to the abnormally high rainfall last year.
Though we can't see it well, the base of the tree looks odd. You might want to send us clear closer shots of the base.
Here is a good fact sheet about abiotic (not insect or disease) problems which will kill trees: https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs/HG86%20Common%20Abiotic%20Plant%20Problems_2018.pdf
This is simply showing the juncture of the graft. That is not harming the tree; it is typical.
With all the wet weather this spring, many cherry trees had a lot of fungal leaf diseases. Cherry shot hole is common: https://extension.umd.edu/hgic/topics/cherry-shot-hole-flowering-cherries
Otherwise, it's possible the site just has soggy soil and some of the roots died. If so, the tree will either bounce back or continue declining. When there is an obvious direction of run-off, sometimes it is possible to divert excess water, but then, of course, in droughty times, it will make the site dryer. If the tree is not happy in the site, ultimately it's best to just replace with a tree happier there.