Maybe the Tsuga canadensis is allelopathic. Maybe not. Maybe it is intercepting precipitation, light, or roots are outcompeting the other plant. And the hemlock poison was actually the Conium maculatum. And deer damage should be very easy to confirm.

Dan

I have Tsuga canadensis growing near Picea pungens (and other spruces, for that matter) with no ill effects.

"Wasn't hemlock a poison of choice in Shakespeare?"

The neighbor doth process too much, methinks. That hemlock is a form of nightshade. An herbaceous perennial.

tj

Definitely not.
What are the symptoms of the spruce's decline?

needle loss, bare branches and gappy. I can't remember if the gaps were after cutting off dead branches or just pure blank gaps.

That conium reference is great. What a good example of how common names can be so misleading. I think that will suppress their poisoning suspicions.

Most (and maybe all, to some degree) trees (and plants for that matter) produce some degree of allelopathic chemical. Few produce effects great enough to be noticed in normal circumstances. If you google the name of the plant together with the word allelopathic and you don't get a lot of results, chances are good you aren't looking at an allelopathic problem.

That conium reference is great. What a good example of how common names can be so misleading.

We have it on some of our nature walks and like to point it out to the high-schoolers and above, wrt Socrates. 'Maculatum' means 'spotted' and the stem has 'blood-red' spots that help your remembery.

Dan

tsuga .... hemlock is shade tolerant ...

picea pungens is not ... for prime growth ...

ergo.. i think you deserve the props the others have missed..

i think YOU WERE RIGHT .... when you said: but I suspect that lack of sunshine is involved

you dont mention size of anything.. but if its been there a long time .. as the shade cover has grown and exceeded the pungens.. it is probably now suffering .... due to lack of sun [among other things]

one would expect with the razor sharp needles that pungens would be SOMEWHAT deer proof ... but the bottom line is usually... it only depends how hungry or desperate they are ...

very simply put.. with 15 to 20 feet between them.. i just dont see how something could mysteriously move thru the soil .. like some bizarre sci-fi creature.. to attack its neighbor ... in any significant manner ...

is it possible.. sure why not..

is it probable .. well.. probably as likely as a common name not misleading you to a wrong answer ... lol ...

i think you are in good shape with your initial gut reaction ....

good work

ken

Brandon is correct in the assumption that most trees have some sort of allelopathic properties but few possess this attribute in sufficient concentrations to be of concern or are restricted in the type of plants their specific allelopathy pertains to. FWIW, Picea pungens is considered to have a higher degree of allelopathic effect than Tsuga canadensis, so if this WAS the issue, your neighbor's tree would be of greater suspect in causing distress for your own tree rather than the other way around.

I think we are looking at other reasons - several of them already posed - that are causing the Fat Albert's distress.

btw, poison hemlock, Conium maculatum, is not a type of nightshade but a member of the carrot family, Apiaceae (formerly Umbelliferae), which includes a number of common herbs and weeds. It grows freely all over the very rural area where I live and considered a noxious weed. It also has minimal allelopathic characteristics so even if growing adjacent to the picea and/or the hemlock, unlikely to be causing problems for them but could very well cause problems - lethal problems - for any humans or animals that may accidentally ingest it.

Here is a link that might be useful: allelopathy of various tree species