Limits to growth of forest biomass carbon sink under climate change

Abstract

Widely recognized as a significant carbon sink, North American forests have experienced a history of recovery and are facing an uncertain future. This growing carbon sink is dictated by recovery from land-use change, with growth trajectory modified by environmental change. To address both processes, we compiled a forest inventory dataset from North America to quantify aboveground biomass growth with stand age across forest types and climate gradients. Here we show, the biomass grows from 90 Mg ha^-1 (2000-2016) to 105 Mg ha^-1 (2020 s), 128 Mg ha^-1 (2050 s), and 146 Mg ha^-1 (2080 s) under climate change scenarios with no further disturbances. Climate change modifies the forest recovery trajectory to some extent, but the overall growth is limited, showing signs of biomass saturation. The future (2080s) biomass will only sequester at most 22% more carbon than the current level. Given such a strong sink has limited growth potential, our ground-based analysis suggests policy changes to sustain the carbon sink.

Fig. 1

Forest aboveground biomass current recovery with stand age across forest-type. Observed and modeled aboveground biomass and stand age in 23 primary forest types across North America are summarized for the current period, 2000–2016. Observed values (gray boxplots) are collected from the National Forest Inventory programs in the United States and Canada. Modeled values (red lines and ribbons) are calculated as the posterior means (lines) and 95% credible intervals (ribbons) from the hierarchical Bayesian growth model fitted to the current data. Each forest-type is fitted to the model separately

Fig. 2

Geographic distributions of current forest aboveground biomass. Both the observed and modeled maps are averaged at the 10-min longitude by latitude resolution from inventory plots for the current period, 2000–2016. GIS data source: GADM database of Global Administrative Areas (https://gadm.org)

Fig. 3

Trends of the current and future forest aboveground biomass. The current period (2000–2016) is summarized as observed and modeled values. The future periods (2020s, 2050s, 2080s) are summarized as two IPCC scenarios (RCP4.5 and RCP8.5) under the best-case circumstances of no disturbances. Points are means, error bars are standard deviations, thick lines are 50% quantiles (25% and 75%), and thin lines are 90% quantiles (5% and 95%)

Fig. 4

Geographic distributions of future forest aboveground biomass and current vs. future ratio. The modeled aboveground biomass across North America during the future period, 2080s, under the RCP8.5 scenario, is used together with the current biomass (Fig. 2) to calculate the ratio of current vs. future biomass. The ratio summarizes the extent to which the current biomass approaches the future biomass potential under the best-case circumstances of no disturbances. Both maps are averaged at the 10-min longitude by latitude resolution from inventory plots. GIS data source: GADM database of Global Administrative Areas (https://gadm.org)