Effects of historical land use and landscape configuration on forest plant diversity in an agroforested landscape of southern Quebec, Canada

Background/Question/Methods

Past land use affects present-day biodiversity, in particular through the type of land use and the resulting forest fragmentation. While past land use modifies soil properties, past landscape configuration affects plant species dispersal. Both can induce changes in the composition of a plant community and lower the abundance of less competitive species. Moreover, these effects can last for centuries after the disturbance. In southwestern Quebec, Canada, plant communities have been subject to three centuries of intensifying land use, including agriculture and urbanization, which have created pressure on a reduced and fragmented forest area. The main objective of this study was to evaluate the effects of past land use and landscape configuration on current plant diversity in remnant forest patches of the Vallée-du-Richelieu County in southwestern Quebec. We first analyzed the evolution of the abundance and spatial configuration of forest patches from the 1860s to the 1990s using historical topographical maps and analysis of landscape change trajectories with Affinity Propagation algorithm. Secondly, we collected plant species data in forest plots (n=52) with different land-use histories and different connectivity to surrounding forest patches through time; effects on current plant diversity were analyzed using Non-metric Multidimensional Scaling ordination (NMDS).

Results/Conclusions

The landscape change trajectory analysis showed that, unlike much of the rest of eastern North America, the majority of the landscape remained relatively stable in forest or non-forest land cover type throughout the entire period from the 1860s to the 1990s. But other important trajectories included: a clearing of the forest seen in the 1910s map that was maintained through the 1990s; and a clearing of the forest only found in the 1990s map. This could be explained by a slow evolution of agriculture from a traditional and non-productive farming in the 1860s to a slight improvement in farming techniques at the beginning of the XX^th century followed by a gradual increase in farms’ area generalized in Quebec’s Saint-Lawrence Lowlands starting in the 1970s. The NMDS analysis showed a clustering of study sites that have remained forested and connected to neighbouring forest patches through time vs forest patches that were in agricultural land use in the 1860s and isolated from other patches through time. The results suggest that both past land use and past landscape configuration affect current plant diversity. Current analysis is being conducted to identify which species and functional groups are indicative of these differential histories.