Annual aboveground carbon uptake enhancements from assisted gene flow in boreal black spruce forests are not long-lasting

Martin P Girardin,Xiao Jing Guo,Nathalie Isabel,Isabelle Duchesne,Patrick Lenz,Manuel Lamothe

doi:10.1038/s41467-021-21222-3

Abstract

Assisted gene flow between populations has been proposed as an adaptive forest management strategy that could contribute to the sequestration of carbon. Here we provide an assessment of the mitigation potential of assisted gene flow in 46 populations of the widespread boreal conifer Picea mariana, grown in two 42-year-old common garden experiments and established in contrasting Canadian boreal regions. We use a dendroecological approach taking into account phylogeographic structure to retrospectively analyse population phenotypic variability in annual aboveground net primary productivity (NPP). We compare population NPP phenotypes to detect signals of adaptive variation and/or the presence of phenotypic clines across tree lifespans, and assess genotype‐by‐environment interactions by evaluating climate and NPP relationships. Our results show a positive effect of assisted gene flow for a period of approximately 15 years following planting, after which there was little to no effect. Although not long lasting, well-informed assisted gene flow could accelerate the transition from carbon source to carbon sink after disturbance.

Highlights

Assisted gene flow between populations has been proposed as an adaptive forest management strategy that could contribute to the sequestration of carbon
We examined 51,029 tree rings from 1560 trees growing since 1974 in two common gardens located at Mont-Laurier and Chibougamau (Fig. 1a)
Using net primary productivity (NPP) phenotypes to compare populations for their mitigation potential, we found historical and present-day adaptive variation to temperature (GDD5p) and precipitation (MAPp) over the 42-year growth period

Summary

Introduction

Assisted gene flow between populations has been proposed as an adaptive forest management strategy that could contribute to the sequestration of carbon. Countries have agreed that large net global greenhouse gas (GHG) emission reductions (i.e., the sum of gross emissions to the atmosphere plus removals of carbon from the atmosphere) are required to hold this warming to less than 2 °C above pre-industrial levels This level is considered the most the Earth could tolerate without risking catastrophic changes to ecosystem health and human safety[4]. The foremost drivers of tree growth performance and survival, whether it is abiotic or biotic stress (e.g. late frost, drought, defoliation, etc.), or their cumulative impacts along a tree’s lifespan have to be identified and taken into account[19,20,21,22] Even adaptive measures such as assisted gene flow carry the risks of negative feedback on carbon if relocated genotypes (as a group of individuals) are exposed to climatic stresses for which they are not adapted[16,17,23]. Reduced carbon uptake in trees growing under climatic stresses[12,24] and increased release of carbon via mortality[25,26] could offset benefits of mitigation activities aimed at the enhancement of forest carbon stocks[17]

Methods

Results

Conclusion