Analyzing spatial patterns of old-growth red pine dominated forests in Wisconsin and Minnesota as a tool to increase forest resilience

Heterogeneous spatial patterns are an important characteristic of forests and central to forest functioning and resilience. Old forests typically have complex structures and provide useful starting points from which to understand processes assembling forest communities and in turn managing for resilience. In the U.S. Lake States, extant old growth forests are rare, especially dry, frequent fire forest types. In this study we analyzed components (e.g., canopy characteristics) and spatial patterning (tree density, arrangement) of old growth red pine stands for developing metrics of silviculture prescriptions. Our data indicate that reference red pine stands are currently > 6 times denser than historical (ca. 1860) conditions, and current tree spacing formed a single large clump after just 4–6-meter inter-tree distances. Historically, these stands had complex spatial arrangements and contained a diversity of size, age, height, and canopy structures. By characterizing spatial arrangements of stands in terms of individuals, clumps, and openings, we offer both a reference point, and basis of management for dry, red pine dominated forest types in Wisconsin and Minnesota to maintain or restore more spatially complex forests. • Historically red pine forests had a diversity of spatial arrangements. • Red pine stands are currently > 6 times denser than historically. • Stands currently are comprised of single large clump within 6-m inter-tree distance. • Individual, Clumps, & Openings (ICO) methods are applicable in Lake States forests. • ICO methods can help add complexity by restoring spatial patterns.