Inspired by David Allen Sibley's recent post titled "Trees in their spring colors", I took this photo of a landscape near me. What species do you see? (Photo taken 5/17/12)
The evergreen trees that take up much of the frame are Eastern White Pines (Pinus strobus), a species that often establishes itself in open places, with sandy soil. The trees visible in the top center are Big-toothed Aspen (Populus grandidentata). Their slim profile, silvery young leaves, and light bark are helpful clues. Colonies of aspens also tend to grow on open, sunny sites.
The final species, in the bottom left, has small pines and aspens growing near it. The dark bark and flower bud clusters, visible as hundreds of white finger-like projections among the leaves, help to identify this sun-loving species as Black Cherry (Prunus serotina). I've included a close up of a few flower clusters (technically called racemes) in full bloom.