Is it okay to throw away the non-edible part of the apple - the apple core / or in general fruit waste? Does it decompose on the rock (maybe with the help of animals) and temperature, or does it interfere negatively with the nature?
The problem with food waste at that elevation is that there is very little soil to bury things and that decomposition happens much slower at those altitudes.
Sometimes there are still marmots/pikas at that elevation who will eat left over apples and such, the problem with that is then they become dependent on humans and can even become aggressive. Aggressive marmots will chew through your backpack while aggressive pikas will bark at you.
At that elevation food waste should be packed out, at least to lower elevations where it can be buried.
My viewpoint: If it is unlikely to be seen before natural processes take care of it then disposal in the wilderness isn't unreasonable. Thus, below timberline, outside Jasper National Park, walking 10 feet off the trail to bury my orange peel is reasonable.
At high elevation the decomp times are large -- years.
There are situations where disposal of anything in unwarranted. A lake in the Sierra that by reputation gets about 100,000 mountain bikers per year. Some stay overnight. Some do it as a day trip. The crap load alone is enormous, mostly being concentrated at the (unknown) latrines at the lake, and on a narrow trail right of way too and from. (I doubt many people go even 10 meters off the trail to pee, and little more than out of site to crap. So all the disposal, including my exemplar orange peel happens on a 15 km x 100m strip.
Ecologists, the old fashioned kind, talk about carrying capacity. An eco-system can deal with a certain amount of 'stuff' or a certain level of harvest without much change. There are tipping points, however where the ecology changes radically. Examples:
A creek tumbling over rocks quickly reaches saturation for dissolved oxygen. Your left over mac and cheese dumped into the stream adds an oxygen load. Bacteria or detritivores, or fish eat the food, and take oxygen from the water. Drop the dissolved O2 by 5-10% not much effect. Drop it by 50% and the trout may be in trouble. Drop it by 90% and you will get a huge change in what lives in the creek.
Carrying capacity isn't usually a line in the sand. For orange peels and apple cores I expect that most temperate softwood forests with more than 20" of precipitation per year can tolerate a peel per square meter per year with very little effect. Indeed, the skyline trail in Jasper could probably still handle people discarding their peels this way -- if they were disposed of in the right section of trail, and done so by people with full understanding of the conditions necessary for it to degrade.
But I tend to be conservative both of the quanities that can be disposed of this way, and of people's ability to make good choices.
I don't like Jasper. I don't like trails where the number of people I meet is measured on a 'per hour' rate rather than a 'per week' rate.
I don't have a need to bury my peel. I carry it with me to camp. Since I use wilderness areas, not national parks, I cook on a fire, and burn my peel.
Story time: I was on a canoe trip in the Aylmer lake region of the North west territory. This area is a hundred miles north of tree line, and has a climate much like the grass/moss to lichen transition.
We stopped at a trappers shack ruin. In the ruin was a 50 year old copy of Saturday Evening Post. The magazine was pristine. We went through it, laughing at the WWII era ads, and put it back for the next person.
You brought the apple in. Take the core out.