The photos are of a vilmori mountain ash. It was loosing upper limbs and looked so unhealthy we cut it down. I want to plant a Saskatoon very close to where it was and am concerned that a soil borne disease could have caused the vertical trunk splitting ( before the sapsuckers had their way with it) It is not sun scald as it was in a shady area that gets very little sun. The other reason google gave was wet conditions following dry conditions. There was a rhodo next to it and whenever it started to wilt in the summer, it was watered..
Sorbus vilmoriniana is a bit on the tender side, yours might have been damaged by cold. Too bad, it looks like it was comparatively big for the species.
Going out on a limb here, I am inclined to think your mountain ash did not die of a soil borne disease. I don't know where you could have the soil tested to find out for sure. There is a damp area in my garden where I do think a soil pathogen lingers; for example, branches on a pieris die from time to time and a fairly large old rhodo completely died for no apparent reason. To hedge your bets, you may want to do what I have - plant a shrub in a large barrel that does not touch the ground. It's not an ideal solution but does fill up a space without risk of disease.
Along with other means water molds are spread by splashing so growing in elevated containers does not reliably escape them when infested surface water is ever neaby. Also Phytophthora ramorum actually falls out of the sky in rain drops to cause a foliar blighting that looks like fire damage. And of course all involved materials at time of planting would need to be completely free of water molds in order for any attempted physical isolation to produce the desired effect. Using an anecdotal example of involved processes there was an incident produced by the aforementioned P. ramorum wherein salal (Gaultheria shallon) growing along a stream began having leaf damage. Subsequent investigation determined that an infested container nursery set up to drain into the same stream was the source. With splashing by rain drops hitting the stream being the means of transference to the salal.
Before I forget, @janepots, if you really want to plant something else in the space where your mountain ash was - and if you're worried about a soil fungus - there are a number of plants that are reputed to be resistant to phytophthora or whatever that you can look up on the web. To minimize the risk of a new plant becoming infected, you might also want to put it in a large container like an oak half-barrel, kept above the ground on bricks. Put clean mulch over the ground to further minimize the chances of potential spores splashing up. Phytophthera killed 3 Cornus nutallii and dozens of native trilliums in my last garden but lots of other plants were unscathed. If you are actually dealing with a root disease, your challenge is to find plants that are not susceptible. Good luck!
