Original: Failing human intervention , and assuming that a population of about 1000 can survive that long , natural tree hollows will begin to develop in the Black Friday regrowth as the trees reach about 150 years of age in the second half of the 21st century , and numbers begin to climb again .
Simplified: Without help from people , and if population of about 1000 can survive for another 150 years , natural tree hollows will begin to develop in the trees that started growing after Black Friday .