📊 Long-term impacts of uneven-aged development on the quantity and fragmentation of old-growth forest in a landscape (University of Alaska Fairbank)

Uneven-aged management is currently seen by many forest ecologists as an extensive management approach when compared to more traditional even-aged methods, offering interesting compromises between timber production and other important ecosystem services. But uncertainties remain concerning its impacts on longer time periods and broader spatial scales, where harvesting activities and forest roads construction extend over larger areas.

Here, we explored the impacts of uneven-aged management on the composition and fragmentation of a 800 000ha landscape over a 150 years-planning horizon. To that end, we used the forest landscape model LANDIS-II, along with an extension that simulates the expansion of the forest road network. We compared 30 different management scenarios that varied the proportion of even- and uneven-aged management, the level of aggregation of the harvested areas, and the presence of pre-existing forest roads on a forested landscape of Mauricie (Québec, Canada).

Our results show that compared with even-aged management, uneven-aged management increased both the quantity of forest roads and their operational costs, the fragmentation per se of the older forests, and the quantity of forest with older tree cohorts. In addition, differences in landscape fragmentation between even-aged and uneven-aged management were reduced in the northern region of the landscape, in the boreal forest, where forest fires tended to fragment old forests irrespectively of the type of management approach employed.

We conclude that the choice of uneven-aged over even-aged management should depend on the type of fragmentation and habitat considered, the patterns of fragmentation resulting from natural disturbances, and on the perceived effects of fragmentation per se in the landscape. We also conclude that aggregation of the harvested areas could help reduce the negative impacts of uneven-aged management, but that they are unlikely to compensate them entirely.