Historical analysis of landscape change in the eastern boreal mixedwood: A case study in the context of cohort-based management

Maintenance of forest spatial structure through forest management is increasingly recognized as an important landscape-level aspect to maintaining biodiversity. In this study, we use forest inventory maps dating from 1965, 1972, 1983, and 1994 to describe the recent historical spatial structure at the Lake Duparquet Research and Teaching Forest (LDRTF) in northwestern Quebec, Canada. Mapped forest stands were classified according to a conceptual cohort model of stand development based on species composition and other stand attributes. Contiguous forest stands of the same cohort class were agglomerated to form relatively uniform patches containing a single cohort class. Landscape spatial structure was defined using four landscape characterization indices: proportion of the landscape, mean patch size, mean distance to nearest neighbour and mean patch shape index. Cohort 1 patches occurred as both small and large units that had complex shapes while Cohort 2 patches occurred as small dispersed units that had simple shapes. Cohort 3 patches dominated the landscape matrix and formed both small and large units that were generally agglomerated in the same vicinity. Our cohort classification of mapped stand polygons was validated by comparing the proportion of land occupied by each cohort in two natural fires (1923 and 1760) that have shaped this area. Theoretical local targets for maintaining cohort structure in the landscape were then formulated based on these historical landscape characteristics.