Unveiling the Diversity of Tree Growth Patterns in Boreal Old-Growth Forests Reveals the Richness of Their Dynamics

Maxence Martin,Nicole J Fenton,Cornélia Krause,Hubert Morin

doi:10.3390/f11030252

Abstract

Research Highlights: Radial growth patterns of trees growing in old-growth boreal forests in eastern Canada can be grouped into a small number of simple patterns that are specific to different old-growth forest types or successional stages. Background and Objectives: Identifying the main radial growth trends in old-growth forests could help to develop silvicultural treatments that mimic the complex dynamics of old-growth forests. Therefore, this study aimed to identify the main radial growth patterns and determine how their frequencies change during forest succession in old-growth forests, focusing on boreal landscapes in eastern Canada. Materials and Methods: We used dendrochronological data sampled from 21 old-growth stands in the province of Quebec, Canada. Tree-ring chronologies were simplified into chronologies of equal length to retain only primary growth trends. We used k-means clustering to identify individual growth patterns and the difference in growth-pattern frequency within the studied stands. We then used non-parametric analyses of variance to compare tree or stand characteristics among the clusters. Results: We identified six different growth patterns corresponding to four old-growth forest types, from stands at the canopy breakup stage to true old-growth stands (i.e., when all the pioneer cohort had disappeared). Secondary disturbances of low or moderate severity drove these growth patterns. Overall, the growth patterns were relatively simple and could be generally separated into two main phases (e.g., a phase of limited radial increment size due to juvenile suppression and a phase of increased radial increment size following a growth release). Conclusions: The complexity of old-growth forest dynamics was observed mainly at the stand level, not at the tree level. The growth patterns observed in true old-growth forests were similar to those observed following partial or stem-selection cuts in boreal stands; thus, these silvicultural treatments may be effective in mimicking old-growth dynamics.

Highlights

The development of industrial-scale forestry since the end of the industrial revolution has eroded much of the primary forest coverage around the world [1,2]
Recent studies have highlighted the complex dynamics of forest succession within the eastern Canadian boreal forest [21,22,23]; the processes explaining these results were poorly known
The radial growth patterns identified in this study could serve to develop forest dynamics models that provide a better description of fine-structural changes in boreal old-growth forests

Summary

Introduction

The development of industrial-scale forestry since the end of the industrial revolution has eroded much of the primary forest coverage around the world [1,2]. Forests 2020, 11, 252 rejuvenating or fragmenting these stands [3,4,5] Such changes can threaten biodiversity [6,7,8] and the provision of ecosystem services in these forests [9,10,11]. To address these problems, new approaches to forest management have been proposed in recent decades, such as emulating natural disturbance regimes [12,13] or mimicking stand-scale natural processes [14,15]. Forest managers face a major “complexity challenge” by having to find economically viable silviculture treatments that can reproduce the complexity of natural disturbances observed in old-growth forests [15]

Objectives

Methods

Results

Discussion

Conclusion