Uneven-aged forest management is currently seen by many forest ecologists as an extensive management approach offering interesting compromises between timber production and other important ecosystem services related to biodiversity conservation, carbon storage, and social acceptability. While benefits of uneven-aged management have been reported at the stand-scale and for short time periods, uncertainties remain concerning its impacts for longer time periods and broader spatial scales. Of concern is the impact of forest roads. Indeed, uneven-aged forestry requires that silvicultural operations extend over larger forest areas than even-aged forestry in order to harvest the same volume of wood. Consequently, uneven-aged forestry may require a larger and more permanent forest road network to reach distant stands over shorter rotation periods.
Here, we explored the impacts of uneven-aged management on the composition and fragmentation of a 800 000 ha landscape over a 150 years-planning horizon. 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, but also 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.