Site descriptions and experimental design
To examine plant community and soil type controls on belowground C
fluxes in temperate forests, we worked in six eastern U.S. temperate
forests within the Smithsonian Forest Global Earth Observatory
(ForestGEO) network (Anderson-Teixeira et al. 2015): Harvard
forest (HF; 42° 32’ N, 72° 11’ W) in North-Central Massachusetts, USA;
Lilly-Dickey Woods (LDW; 39° 14’ N, 86° 13’ W) in South-Central Indiana,
USA; the Smithsonian Conservation Biology Institute (SCBI; 38° 54’ N,
78° 9’ W) in Northern Virginia, USA; the Smithsonian Environmental
Research Center (SERC; 38° 53’ N, 76° 34’ W) on the Chesapeake Bay in
Maryland, USA; Tyson Research Center (TRC; 38° 31’ N, 90° 33’ W) in
Eastern Missouri, USA; and Wabikon Lake Forest (WLF; 45° 33’ N, 88° 48’
W) in Northern Wisconsin, USA. At each of the six sites, we established
nine 20m × 20m plots spanning a gradient of ECM tree dominance (by basal
area) for a total of 54 plots. At each site, the three plots with the
lowest ECM tree dominance and the three plots with the highest ECM tree
dominance were designated as AM and ECM ‘end-member’ plots. The
remaining three plots per site were designated as AM/ECM ‘mixed’ plots.
The sites vary in climate, soil type, and plant species composition but
each host a diversity of AM and ECM associated canopy tree species. For
the most dominant tree species at each site, see Table 1. Soils are
predominantly Oxyaquic Dystrudepts at HF, Typic Dystrudepts and Typic
Hapludults at LDW, Typic Hapludalfs at SCBI, Typic or Aquic Hapludults
at SERC, Typic Hapludalfs and Typic Paleudalfs at TRC, and Typic and
Alfic Haplorthods at WLF. For site-specific soil properties, see Table
2.