Controls and reference conditions in forestry: The role of old-growth and retrospective studies

Forest stands that experience only natural disturbance can serve as controls to provide a scientific basis for comparison with harvested forests to help determine when harvesting has been done in a sustainable manner. Primary stands can serve as references for silvicultural trials that attempt to mimic the primary forest structural attributes on shorter time scales of a few decades. At the landscape scale, retrospective techniques can he used to examine proportion and variation in proportion of stands among structural and successional stages expected under the natural disturbance regime. These analyses are referred to as range of natural variation and serve as landscape-scale reference conditions for comparison with the managed forest landscape.