Conversion of uniform broadleaved stands to an uneven-aged structure

The conversion of an even-aged (single tiered canopy) stand to a multi-tiered (uneven-aged) structure can be accomplished by vertically partitioning growing space among canopy layers. A successful example of this methodology was accomplished in an upland oak stand in the Ozark Highlands of Missouri, USA. The conversion process on the study area was initiated in 1961 and completed with the establishment of a third cohort resulting from a harvest in 2000. The prescription calls for allocating growing space among three canopy tiers (overstory, midstory, and understory) at a ratio of 3:2:1 based on regional stocking charts. This distribution ensures full site utilization and maintains approximately 60% of stand basal area in the sawtimber size classes while reserving sufficient growing space for the recruitment of new cohorts as needed. Further, the conversion prescription facilitates transition of the stand into a maintenance phase of management following completion of stand conversion; the 3:2:1 ratio equates to a negative-exponential diameter distribution defined by a q-value of 1.7 (for 5 cm diameter classes). During conversion, however, a q-value based target diameter distribution should never be used to determine the cut. Rather, each cohort is treated as a separate even-aged entity where proper spacing, species, and stem form are the factors determining removal.