The poplar trees here have been suffering an epidemic of leaf miners for about 7 years. These bugs are native to this area but a series of warmer-than-average winters has allowed their population to explode. Every year seems to be worse than the last.
The leaf miner lays its eggs on poplar leaves and the larvae munch their way through them, creating tunnels that meander through the leaf until they end up at an edge, where they create a little coccoon. A tiny moth eventually hatches out and goes on to lay the next generation's eggs.
Nearly every leaf on every tree is affected now. The beautiful bright green of the poplars turns into a silvery grey earlier every year. When the leaf-miner population explosion started, I remember hearing that the trees could only stand three or four years of it before they'd start dying. They've done well, but we're starting to notice stands of dead poplars here and there, or trees with dead branches.
Lots of other deciduous trees, like the alders and birches, seem to be untouched by the infestation. Maybe they'll move into the spaces that the dying poplars leave, or maybe the bugs will eat themselves out of existence and the millions of tiny new poplars that are popping up everywhere will be able to grow. We'll just have to wait and see.