Do harvest retention patches in the boreal forest emulate those resulting from wildfire? A comparison of understory vegetation a decade after disturbance

To sustain a breadth of ecosystem services, Ecosystem-based forest
management (EBM) aims to reduce differences between managed and natural
forests. Based on observed structural complexity of forests following
natural disturbance, retention of forest structure at harvest is being
implemented globally. Despite a decade of including retention patches in
managed forests, it remains unclear if patches in forests disturbed by
fire and harvest exhibit similar structural characteristics and
biodiversity as intact forest. Such knowledge is critical within an
adaptive management framework. We present the first study comparing
understory vegetation of post-fire and post-harvest remnants in the
boreal. A decade following disturbance, we examine forest structure and
plant diversity in key locations of harvests and burns: the disturbed
matrix, island remnants within the disturbance, adjacent undisturbed
forest, and edges of these. We utilize a trait-based framework for plant
diversity to test hypotheses about how traits vary in relation to
disturbance type, environmental variables, and with variation in
structure.  Edge effects were minor and didn’t differ between
burns and harvests. Both harvest and wildfire remnants maintained
understory communities and forest structure similar to adjacent forest,
but remnant and reference areas exhibited some compositional differences
between fire and harvest sites. Analysis of plant functional traits
revealed similar patterns across burns and harvests, with colonization
traits associated with disturbed areas, while persistence traits were
associated with island remnants.  Synthesis and applications: The
similarity of the understory community and forest structure of island
remnants to adjacent reference forest in burned and harvested areas
suggests remnants are effective reservoirs of undisturbed forest. This
provides evidence that implementation of aggregated retention at harvest
helps achieve a key objective of retention, i.e. maintaining structural
heterogeneity to support biodiversity.