Well... as to the life expectancy of Poplar
trees, there are about 40 species (all located in Nothern Hemisphere, 10 native to North America) the genus Populus contains
trees with common name of Poplar and Aspin. Generally those called Poplar are riparian species (live along water courses) in my expierence I would consider the useful life expectancy to be 20-30 years. The fact that your
trees are only about 10 years old i find puzzling. I think you could post some pics and perhaps we can give you more info. but the best answer would be to retain a qualified arborist to review your existing
trees and provide some ideas as to what else would be suitable to
plant. The one thing to always keep in mind is that there are always several suitable solutions (may times ppl what to act like there is one right answer). Oh one other thing,
trees are living things and therefore are unperdictable on an individual bases. As to Bess's idea of introducing new
trees to take the place of the Poplars I have successful used this method in the past. I have no idea if this long winded note is of much assistance but here it is. Good luck.