I have planted several pecans and walnuts, as well as encouraged several volunteer hickories in my budding food forest in central TX. Some portions of my soil are shallow and rocky, and the heat is ubiquitous throughout most of the year; so heavy mulching is a necessity. During the fall months there are more bags of leaves waiting for me on the side of the road than one could ever use, so I have my choice of what types of leaves to mulch with during this time.
My question then is whether I would be better off mulching with leaves of the same species (or family) that I will be putting the mulch around? That is vs the cedar elm, hackberry, and live oak leaves that are also commonly available.
I see a few distinct advantages as well as some drawbacks to this strategy. On one hand all these leaves can be assumed to contain at least a trace amount of Juglone, which would be helpful in inhibiting weed competition if only a small amount. The other advantage is that it stands to reason (rather unscientifically) that if these leaves fell from pecans then they must contain the nutrients that a pecan would need in order to build leaves and thrive. The downside to this method as far as I see it would be that any diseases found on these mature pecans would be brought and hand placed right where they would need to be to spread to my saplings.
I think that if you gathered materials from places very close to home, you are likely to keep any problems from within your community, where they are, and you are less likely to bring any new problems.
Keeping the long-term goal in sight, the focus should be upon building soil and building the fungal network throughout the soil profile. Healthy soil should take care of any fungal or bacterial problems. Basically, let your good microbes fight it out with any bad pathogens. If there is concern with bringing bad stuff onto your property via someone else's leaves, then compost them for a few months. If you can heat the compost to 140 degrees, it will take care of most of your concerns. Whether those leaves be of the same species or something completely different, once the microbes get ahold of them, they'll be safe.
Keep your focus on the soil, not the trees. Build the soil and it'll take care of the trees. From that perspective, I wouldn't think that it makes much difference where the biomass comes from (from the same tree or from another) --- just add as much biomass as you can and keep as many living roots growing around the trees. The combination of carbon on top of the soil (mulch) and root exudates from plant roots (both your trees as well as other annual plants growing nearby) will keep the microbes happy.
Consider planting a diverse mix of cover crop seeds around the trees for the next couple of years. That will help feed the soil food web and build the kind of microbial community your trees will thrive on for years to come.
"The rule of no realm is mine. But all worthy things that are in peril as the world now stands, these are my care. And for my part, I shall not wholly fail in my task if anything that passes through this night can still grow fairer or bear fruit and flower again in days to come. For I too am a steward. Did you not know?" Gandolf
Great question (s) Jesse. Dale has brought up the Closed system which is grand especially if diseases are happening in the extended gathering area. If there are no diseases present at or close to you, then this is still a good idea but not as important to follow.
Marco also brought up some great ideas.
Pecans and Walnut trees are allelopathic species so there should be no need to introduce juglone to their soil.
Indeed, pecan leaves have what the tree used to form those leaves and keep them alive so that makes them a good choice for mulching.
One note about mulching, it is possible to have too much mulch around nut and fruit trees, granted it takes a lot but when you reach that thickness the roots will struggle. I use 4 inches deep as my cut off point.
Pecan tree leaf diseases are visible to the naked eye, if you are worried about diseases possibly being present, best to hot compost those suspect leaves then use the compost as your mulch around your trees.
Pecan saplings have a long road to survive before they will produce pecans (up to 20 years) so building their soil is paramount for good crops once they mature enough to start producing.
Minerals are very important for nut trees, Using something that contains a maximum number of the 5000 known minerals is always a good idea. Items like fish meal, bone meal, kelp powder, green sand, Sea-90, are all beneficial not just for trees but for all plants.
Most of the soil of planet earth is deficient in many of the minerals plants would love to have available for their best health.
If you have available as much organic material as it sounds like, you could use half for "fresh mulch" and compost the other half so that when you apply the compost you are also bulking up the soils microorganisms.
I wish I had access to about 100 cubic yards of leaves every fall, I would have enough compost in the spring, every year.