Changing forestry with an improved TRIAD approach for diversity, resilience and connectivity.

Background/Question/Methods

The TRIAD zoning forest management approach was proposed three decades ago to address conflicting environmental and economic priorities. Under this approach, part of a forest landscape is set aside for protected areas, and counterbalanced by intensive and extensive management zones in the rest of the landscape. More recently, novel management approaches have been proposed to improve the resilience of forest landscapes to uncertain future conditions by increasing the functional trait diversity and functional connectivity of forest landscapes. In this perspective, we revisited the TRIAD approach by integrating these new concepts. We developed "TRIAD+++" scenarios across a 4 million hectares forest landscape in the Mauricie region of Quebec, Canada. These scenarios used strategic plantations that varied functional groups in the intensive management zones to increase local functional diversity (FD). We compared four different scenarios: a novel TRIAD+++ with these strategic plantations, a normal TRIAD, a business as usual (BAU) with strategic plantations, and a BAU without plantations. We simulated our scenarios using the spatially explicit forest landscape model LANDIS-II. We assessed the resilience of the landscape to natural disturbances affected by climate change (fire, drought and spruce budworm outbreaks) and the harvestable wood volume over a planning horizon of 150 years.

Results/Conclusions

Our results suggest that this novel TRIAD+++ approach can improve forest resilience to the simulated disturbances and help foster the overall functional diversity of the landscape. While BAU with FD-enhanced plantations had effects similar to the TRIAD+++, it also showed less stable harvestable volumes. Indeed, wood volume stability in the TRIAD++ scenario was possible despite the decreased biomass of some economically important tree species, due to the increased biomass of rarer and less common species. In contract, the scenarios of the normal TRIAD and the BAU without FD-enhanced plantations had less effect on both forest resilience and harvestable volume. We conclude that this new TRIAD+++ approach has the potential to prepare forests for an uncertain future and hence ensure their ability to provide important ecosystem services, while keeping forests "stocked" for the industry. The most important factor contributing to this success is the use of FD-enhanced plantations in areas of intensive forestry, and the spatial distribution of these intensive areas in low-diversity stands. As a result, the forest industry will have to develop new technologies to accommodate for timber coming from a more diversified set of tree species.