Ground reflectances were measured in the blue, green, red and near infrared (NIR) regions of the spectrum in a set of recently thinned pine- and spruce-dominated stands near Umea, Sweden. Compared with the untouched reference stands, the change in ground reflectance of the thinned stands was approximately linearly related to the thinning grade and to the coverage of the cutting waste left on the ground. Typically, thinning resulted in a reflectance increase in the red and decrease in the NIR band. The major effects of the presence of cutting waste on the ground reflectance can be simulated following a rather simple theoretical analysis. It appeared to be more difficult to quantitatively describe the effects on reflectance caused by the successional changes in the ground and field layer vegetation.