In the context of a wooded scene like the one described, the element that typically helps to create harmony is monochromatic color. This refers to the use of a single color in various shades and tones, which can unify the visual elements in a landscape and create a cohesive look.
While perspective, line, and emphasis can contribute to the composition, they may not necessarily create harmony in the same way that a monochromatic color scheme would. Therefore, the correct answer is:
monochromatic color