Plant Community Changes in Annual Production and Composition Through 8 Years of Warming Manipulations Under Ambient and Elevated Carbon Dioxide Atmospheres
Authors
Paul J. Hanson* (hansonpj@ornl.gov), Joshua M. Birkebak, Natalie A. Griffiths, Verity G. Salmon, Mark P. Guilliams, Keith C. Oleheiser, Michael W. Jones, Nikki J. Jones, Kyle J. Pearson, Melanie Mayes, Daniel Ricciuto
Institutions
Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN
URLs
Abstract
The Spruce and Peatland Response Under Changing Environments (SPRUCE) experiment has operated five warming manipulations (+0, +2.25, +4.5, +6.75, and +9°C) with and without elevated carbon dioxide atmospheres (eCO2 of +500 ppm) for 8 full calendar years (since August 2015). Researchers have tracked shrub-layer vegetation responses to the treatments using annual destructive plot sampling within each of the experimental plots. In 2023, the team sampled three 0.4 m2 plots from three random locations with each of the treatment enclosures (plus two ambient plots) to evaluate the influence of the warming and eCO2 treatments on community composition, standing biomass, and annual above ground net primary production (ANPP). Plot-level cumulative stand biomass has increased with warming treatments. Pretreatment and colder plots have standing mass in the range from 147 to 300 gC m-2 with warmer treatment plots ranging from 462 to 640 gC m-2. The 2023 assessment shows standing biomass combined across species for the +4.5, +6.75, and +9°C warming treatments with a trend of higher biomass under eCO2. Within the mid-summer standing biomass pool woody tissues drive the difference with foliage being very similar across all experimental treatments. ANPP is quite constant across treatments for the 2023 assessment ranging from 60 to 150 gC m-2 y-1.
The plant community composition was assessed for key ericaceous shrubs (Rhododendron, Chamaedaphne, Kalmia), two Vaccinium species (V. angustifolium, V. oxycoccos), graminoid species (mostly Eriophorum) and one common forb Maianthemum trifolium, plus a few minor understory and two tree species (Picea, Larix). The composition has changed with 8 years of treatments. Under all warmed scenarios >+4.5°C Kalmia, V. oxycoccos, and M. trifolium are largely absent from the plots. Rhododendron and Chamaedaphne have maintained their presence in the community and V. angustifolium plants and Picea rubrum seedling are showing increases.