First off, i don't want to buy anything to add nutrients into my soil, especially chemically made ones but even organically made i prefer free, local and abundant sources of nutrients to those found in stores.
So lets say i have a property near a forest. There is often dead wood and leaf litter on the ground of the forest. If take that organic matter and use it in my garden for mulching and hugelkultur, am i essentially depleting the nutrients in the forest (used to grow the stuff i use for mulch etc, and so it doesn't breakdown into nutrients in the forest), and transferring that into my garden?
This is really concerning for me because im trying to revitalize my plot of formerly agricultural land and build up the soil structure + build up local habitats for plant and fauna, but don't want to deplete the nutrients from the forest soil overly.
Is taking organic matter from the forest not so much of a concern as it still allows the forest to recover? Or may I deplete the nutrients in the forest overly and hurt the local ecosystem?
If its lawful to gather from the forest, just gather from different areas when you harvest annually and don't strip anything bare. Spead your harvest around and don't take more then 25% from any given area annually, including from the annual litter shead like leaves.
But with all the free resources available, like free leaves, free grass clippings, free coffee grounds, and free woodchips. Why even harvest from the forest, when you can help your neighbors, friends and or family? With so many people who could use help, just ask if you can rake their leaves, or haul their leaves when you notice giant piles of leaf bags in fall. Coffee shops have giant bags of coffee grounds, that often get thrown out in rual areas. There are so many ways to use that same effort to help others, and get the same reward, without harvesting from the forest. Elderly and disabled people often need help, and mowing a lawn with a bagging mower, gets you more carbon faster then raking in the woods. A call to your local Tree Professionals or Line Clearance Contractors will get you more wood with less energy/resources expended, then getting wood from the forest. And I understand people have successfully used woodchips for hugoculture, though I need to research those results more before I make recommendations on that last statment.
A few ideas to think about, since it's better to feel good for helping someone, then feel bad for harvesting from the forest; however, with my suggestions regarding forest harvest it would at least be considered sustainable.
As the boundary and shelter plantings on our property get bigger, I've begun "mining" them for leaf and branch material. Sometimes I'll go fossicking around in one of these areas and notice that the leaves are up to my ankles, so that just means that next time I need some mulch or browns for the compost, that's where I head with the rake and wheelbarrow. Nothing ever gets stripped bare, and if I go back in 3-6 months I can't always tell where I made the collection...especially if it's on the side where the chickens have access. There are places where the humus has built up to the point where I don't mind taking a few shovelfuls for potting purposes.
I was facing the same issues as you a few weeks ago, until I discovered JADAM Korean organic gardening. https://en.jadam.kr/ All information I have found has been free, and the methods described are quite easy. In this system, you can essentially brew your own fertilzers and microbes. You can also make your own organic pesticides, if you wish, but this is more difficult.
The idea behind making your own fertilizer is easy. I take a 5 gallon bucket, put in a good handful of leaf mold gathered from local woods, and add yard trimming to fill the bucket, before filling up with pond, rain, or well water and sealing the bucket off. You can start using this after just 7 days! One 5 gallon bucket will make enough liquid fertilizer for my 500 sq ft garden for several months. You can wet compost many other things too, like food scraps(including cooked and salted,) urine, leftover or damaged crops(this is best to fertilize the same types of crops,) and even fish.
Brewing microbes is also easy. You take a handful of leaf mold and a half a boiled potato, blend it up, and put in a bucket of soft water. The microbes are ready to apply after a day or three, depending on outside temperature.
All the other advice given should be more than enough to get all your mulching needs for cheap too, good luck!