Influence of Mature Overstory Trees on Adjacent 12-Year Regeneration and the Woody Understory: Aggregated Retention versus Intact Forest

Miranda Curzon,Brian Palik,Anthony D’Amato,Susan Baker,Christel Kern

doi:10.3390/f8020031

Abstract

Retention harvesting, an approach that intentionally retains legacy features such as mature overstory trees, provides options for achieving ecological objectives. At the same time, retained overstory trees may compete with the nearby recovering understory for resources, and much remains to be learned about potential trade-offs with regeneration objectives, particularly over extended time periods. We assessed the influence of aggregated retention (reserved mature overstory and understory patches) versus intact forest on structure and productivity (standing biomass) of the adjacent woody understory and regeneration 12 years after harvest in northern Minnesota, USA. Each site was dominated by Populus tremuloides Michx., a species that regenerates prolifically via root sprouts following disturbance. Overall, fewer differences than expected occurred between the effects of intact forest and aggregated retention on regeneration, despite the small size (0.1 ha) of aggregates. Instead, harvest status and distance from harvest edge had a greater influence on structure and standing woody biomass. Proximity to aggregates reduced large sapling biomass (all species, combined) relative to open conditions, but only up to 5 m into harvested areas. This suggests the trade-off for achieving productivity objectives might be minimal if managers use retention aggregates in this region to achieve ecological objectives and meet management guidelines.

Highlights

Practices that maintain or enhance biodiversity and structural complexity in forest ecosystems may increase adaptive capacity [1], an increasingly emphasized management goal in light of ongoing environmental change [2,3]
This indicates that relative values for each of these structural components increased along a general gradient extending from the inner-most plots beneath mature overstory to harvested plots located furthest from harvest edges
Given these similarities, analysis of depth of edge influence suggests that forest influence exerted by even given these similarities, analysis of depth of edge influence suggests that forest influence exerted aggregates resulted in fewer significant effects on structural variables indicative of regeneration by aggregates resulted in fewer significant effects on structural variables indicative of regeneration success

Summary

Introduction

Practices that maintain or enhance biodiversity and structural complexity in forest ecosystems may increase adaptive capacity [1], an increasingly emphasized management goal in light of ongoing environmental change [2,3]. Residual live trees (as well as other structural and biological attributes that persist after disturbance) provide continuity both temporally between forest generations and spatially across a landscape. Such complexity and continuity positively influence many aspects of biodiversity [5,9,10] through provision of habitat for birds and mammals [11], maintenance of ectomycorrhizal communities [12] which influence nutrient availability and cycling, amelioration of the microenvironment [13,14], and other mechanisms. Retention harvesting systems that reserve mature, overstory trees after harvest have been developed to provide similar habitat, complexity, and services as natural legacies [4,7,8]. In addition to positive impacts for biodiversity evident in the short- and medium-term [5,12,15], model simulations of stand development over periods of up to 240 years suggest structure in at least some actively managed forests

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