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Sounds like a question for "Homework or Poetry" catagory. You're in "Garden/Landscape" but it's an interesting question so lets see:

If my decomposing carcass helps nourish the roots of a juniper tree or the wings of a vulture – that is immortality enough for me....

You want help with this part? (And as much as anyone deserves). Edward Abbey, In Death

It means that if we can replenish the earth, give back, contribute- this would be enough immortality for anyone & no one deserves any better than this. It's a quote about afterlife, circle of life & life feeds on life. Maybe this will help~

It's a quote from Edward Abbey who didn't want burial in a cemetery and had his wife and friends transport him in his sleeping bag to a burial in the desert. If you do a search of "poem if my decomposing carcass" you'll come up with several links with information on him.

have your carcass burned ground and put into a compost pile ,then mulch many plants .spread the immortality around .leave it in the wild for the birds and that is immortality too.regardless ,your molecules will get redistributed anyway ,ashes to ashes ,dust to dust.