Driving factors of conifer regeneration dynamics in eastern Canadian boreal old-growth forests.

Maxence Martin,Miguel Montoro Girona,Hubert Morin,Runguo Zang

doi:10.1371/journal.pone.0230221

Abstract

Old-growth forests play a major role in conserving biodiversity, protecting water resources, and sequestrating carbon, as well as serving as indispensable resources for indigenous societies. Novel silvicultural practices must be developed to emulate the natural dynamics and structural attributes of old-growth forests and preserve the ecosystem services provided by these boreal ecosystems. The success of these forest management strategies depends on developing an accurate understanding of natural regeneration dynamics. Our goal was therefore to identify the main patterns and drivers involved in the regeneration dynamics of old-growth forests with a focus on boreal stands dominated by black spruce (Picea mariana (L.) Mill.) and balsam fir (Abies balsamea (L.) Mill.) in eastern Canada. We sampled 71 stands in a 2 200 km2 study area located within Quebec's boreal region. For each stand, we noted tree regeneration (seedlings and saplings), structural attributes (diameter distribution, deadwood volume, etc.), and abiotic (slope and soil) factors. The presence of seed-trees located nearby and slopes having moderate to high angles most influenced balsam fir regeneration. In contrast, the indirect indices of recent secondary disturbances (e.g., insect outbreaks or windthrows) and topographic constraints (slope and drainage) most influenced black spruce regeneration. We propose that black spruce regeneration dynamics can be separated into distinct phases: (i) layering within the understory, (ii) seedling growth when gaps open in the canopy, (iii) gradual canopy closure, and (iv) production of new layers once the canopy is closed. These dynamics are not observed in paludified stands or stands where balsam fir is more competitive than black spruce. Overall, this research helps explain the complexity of old-growth forest dynamics, where many ecological factors interact at multiple temporal and spatial scales. This study also improves our understanding of ecological processes within primary old-growth forests and identifies the key factors to consider when ensuring the sustainable management of old-growth boreal stands.

Highlights

The global extent of primaryaold-growth forest has declined markedly over the past few centuries through the cumulative and increasing impact from anthropogenic activities within these forest landscapes [1,2,3]
This study determined how secondary disturbance regimes and topographic constraints explain the dynamics of black spruce and balsam fir regeneration in old-growth forests
Our study offers an alternative perspective to standard models of forest dynamics, which generally rely on chronosequences

Summary

Introduction

The global extent of primaryaold-growth forest has declined markedly over the past few centuries through the cumulative and increasing impact from anthropogenic activities within these forest landscapes [1,2,3]. Boreal old-growth forest has experienced rapid loss over the last centuries [1,4,5]. The remaining old-growth forests are critically important to biodiversity, water resources, carbon sequestration and storage, and these stands remain integral elements of indigenous societies and even human health [3,6]. The sustainable management of boreal forests has a primary goal of protecting the remaining old-growth forests. Restoring the integrity of intact forests is an urgent issue; this is especially true in Fennoscandia where old-growth forests have been almost completely eliminated [7]. We are facing a critical situation where novel silvicultural practices and restoration strategies are priorities in the context of the global biodiversity crisis, climate change, and forest sustainability

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Discussion

Conclusion