Creating un-evenaged stands through gap cutting – production losses, growing stock and harvest impacts during the transition period

Continuous Cover Forestry (CCF) is currently a much-debated issue in Sweden. Although there are several options qualifying as CCF, the most frequently invoked system is the individual tree selection. Popular opinion ascribes to it many benefits for which there is only ambiguous evidence, as long-term trials are lacking. Long-term production, the site properties and the degree of thinning necessary for successful stand regeneration are not yet fully known.

Against this background, gap-cutting of the checkerboard type appears to be an advantageous compromise. It allows for the use of artificial regeneration and established machine systems while causing smaller openings compared to standard clear cuts. Furthermore, we can predict some aspects of the transition from even-aged stands using existing forest growth models with much less uncertainty than for individual tree selection.

A key parameter of the gap system is the cutting schedule. It determines, among other things, how large production losses are incurred due to harvesting the original stand at a sub-optimal age, the age structure of the future stand and its fluctuations over time, which includes how large a portion of the stand is cleared at once. At the landscape scale, these effects aggregate into changes in harvest flow and growing stock dynamics during the transition period.

In this lecture, I aim to present results from two ongoing studies that explore the transition from even-aged to uneven-aged stand structures through gap cutting at the stand and the landscape levels. Furthermore, I aim to discuss the principal research needs and challenges for enhancing the modelling capacity of CCF in Sweden.