Contrasting Development of Canopy Structure and Primary Production in Planted and Naturally Regenerated Red Pine Forests

Laura J Hickey,Robert T Fahey,Mark T Kreider,Christopher M Gough,Jeff Atkins,Shea B Wales

doi:10.3390/f10070566

Laura J Hickey, Robert T Fahey + Show 4 more

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https://doi.org/10.3390/f10070566

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Abstract

Globally, planted forests are rapidly replacing naturally regenerated stands but the implications for canopy structure, carbon (C) storage, and the linkages between the two are unclear. We investigated the successional dynamics, interlinkages and mechanistic relationships between wood net primary production (NPPw) and canopy structure in planted and naturally regenerated red pine (Pinus resinosa Sol. ex Aiton) stands spanning ≥ 45 years of development. We focused our canopy structural analysis on leaf area index (LAI) and a spatially integrative, terrestrial LiDAR-based complexity measure, canopy rugosity, which is positively correlated with NPPw in several naturally regenerated forests, but which has not been investigated in planted stands. We estimated stand NPPw using a dendrochronological approach and examined whether canopy rugosity relates to light absorption and light–use efficiency. We found that canopy rugosity increased similarly with age in planted and naturally regenerated stands, despite differences in other structural features including LAI and stem density. However, the relationship between canopy rugosity and NPPw was negative in planted and not significant in naturally regenerated stands, indicating structural complexity is not a globally positive driver of NPPw. Underlying the negative NPPw-canopy rugosity relationship in planted stands was a corresponding decline in light-use efficiency, which peaked in the youngest, densely stocked stand with high LAI and low structural complexity. Even with significant differences in the developmental trajectories of canopy structure, NPPw, and light use, planted and naturally regenerated stands stored similar amounts of C in wood over a 45-year period. We conclude that widespread increases in planted forests are likely to affect age-related patterns in canopy structure and NPPw, but planted and naturally regenerated forests may function as comparable long-term C sinks via different structural and mechanistic pathways.

Highlights

Forested landscapes are increasingly a mosaic of naturally regenerated and planted stands varying in age and structure
Our analysis focuses on the structural complexity measure “canopy rugosity”, which summarizes the variance in vegetation density and distribution across horizontal and vertical canopy axes [26]
Though we found that planted red pine stands initially accumulated C rapidly in wood, naturally regenerated stands exhibited slightly lower, on average, but more stable net primary production (NPP) across ages, a pattern that was observed in other forest ecosystems [11,50,51] and which suggests a trade-off between NPPw stability and magnitude

Summary

Introduction

Forested landscapes are increasingly a mosaic of naturally regenerated and planted stands varying in age and structure. Forests 2019, 10, 566 with their naturally regenerated counterparts containing the same species assemblages, planted forests have higher stem densities and are less structurally heterogeneous, containing trees more uniform in height, diameter, and spacing [5,6]. In addition to the direct effects of natural and planted regeneration pathways on structure, stand characteristics with known linkages to ecosystem functioning such as stem density, leaf area index (LAI), and structural heterogeneity change as forests age [7,8,9,10]. Though the effects of stand regeneration pathways and age on structure are well-characterized, the functional implications of a global rise in planted forests— for rates of carbon (C) storage—are only minimally understood [4,11,12,13,14]

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