It depends on the plant in question, both to the degree of allelopathy and how it functions. In most cases, allelopathy is a function of the root, with the chemicals/hormones exuded creating an inhospitable growing habitat for other plant species. And generally not all plant species uniformly......the allelopathic properties are typically directed at select species or plant types.

There certainly can be allelopathic effects felt from wood chips or ground remains of plants in question but they tend not to be overwhelming compared to the effect created by the living specimens. Allelopathic properties leach out of plant parts and to a very large degree, are neutralized by decomposition and certainly by a composting process. Allelopathy is still not well understood and a lot of research is being conducted on this phenomenon with respect to creating natural pre-emergent "herbicides". A lot of trees exhibit some degree of allelopathy - far more species than most suspect - but with the exception of few well-known trouble makers, like black walnuts, the effects are generally quite mild and easy to work around/with.

Personally, I wouldn't have many worries about using the wood chips as mulch for pathways. I'd not even be overly concerned about mulching planting beds with it. If anything, it may make an even more effective weed suppressing mulch compared to other mulch products. Eucalyptus, which has known allelopathic properties, makes an excellent mulch and is bagged and sold as such.

"Allelochemical concentrations in the producer plant may also vary over time and in the plant tissue produced. Foliar and leaf litter leachates of Eucalyptus species, for example, are more toxic than bark leachates to some food crops"

Here is a link that might be useful: Allelopathy: How Plants Suppress Other Plants

Thanks both of you.
Great article, now I wish black cottonwood grew in Florida so I could have info about it.
Interesting note on Broccoli.

Anyway I had to do something with all the chips, so I started placing them in the lower part of the woodland where plants were not in proximity, but then went ahead and put them on the paths, just will have to wait and see.

I have used Cottonwood chips for years with no observable negative affects. I don't treat Cottonwood any different from other types of wood and welcome any kind I can get. No Black Walnut yet though.

{{gwi:1076859}}
Acer macrophyllum in winter with no leaves or seeds. Perfect for a path. Minimum tracking.

Good to know Botann.
The only negative effect so far is the headache I seem to be getting working around the chips. That cottonwood smell--yikes! it is so strong--is it off gassing something? References say "Balsam smell" --I don't think so.
Way more intense than just passing one by in the forest.

Fresh chips soon foster molds which give off an aerosol when disturbed. Inhalation of this should be avoided, a nasty condition called farmer's lung is associated with exposure to moldy grass parts. It has also been known to afflict a nurseryman using peat from a particular source. He did not notice anything until knocked to his knees by sudden severe pain.

Treatment involved an extended hospitalization.

If I spread a load of chips right away, I'm just fine. If I wait until it is moldy and the spores look like smoke, I develop a bad cough that lasts for several days. I wait now until the mold is done before handling the chips. Lesson learned.
I should point out the vapor released when the pile is hot is different than mold spores. The vapor is harmless. The spores are not.