Original: Failing human intervention , and assuming that a reduced population could have survived that long , natural tree hollows were expected to develop in the Black Friday regrowth as the trees reached about 150 years of age in the second half of the 21st century , and numbers to begin climbing 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 .