Table S4.

Critical loads (CLs) of N deposition for level 1 ecoregions in the present study compared with previously cited estimates in Pardo et al. (18)

Level 1 ecoregionCL of N dep. cited in table 5 of ref. 18 (Pardo et al.), kg⋅ha−1⋅y−1CL of N dep. (total herbaceous richness) from present study, kg⋅ha−1⋅y−1Compared with Pardo et al. (18)
Northern forests7–21 (hardwood forest alteration of herbaceous understory)Open: 8.0–9.8 (mean = 8.9, n = 75)New
Closed: 8.0–18.9 (mean = 13.8, n = 1,955)Similar
Northwestern forested mountains4–10 (alpine grassland species composition change)Open: 8.0–10.2 (mean = 9.1, n = 1,429)Similar
Closed: 10.8–19.6 (mean = 15.3, n = 2,113)New
Marine west coast forestsNo vascular plant CLOpen: No data
Closed: 10.4–15.0 (mean = 12.8, n = 24)New
Eastern temperate forests<17.5 (hardwood forest declines in species-rich genera)Open: 6.6–9.7 (mean = 7.9, n = 947)New
Closed: 7.8–19.3 (mean = 12.5, n = 7,378)Lower
Great plains5–15 (tallgrass prairie community shifts)Open: 8.3–9.8 (mean = 9.3, n = 618)Similar
Closed: 11.3–19.6 (mean = 16.6, n = 274)New
North American desert3–8.4 (warm desert decrease of native forbs)Open: 8.3–9.9 (mean = 9.2, n = 240)Higher
Closed: 13.5–17.0 (mean = 16.5, n = 32)New
Temperate SierrasNo vascular plant CLOpen: 8.6–8.7 (mean = 8.65, n = 3)New
Closed: 14.8–14.8 (mean = 14.8, n = 42)New
  • Critical load estimates in the present study are calculated using the two equations in Table 2. “Open” refers to open canopy vegetation whereas “Closed” refers to closed canopy forest vegetation. We did not have any vegetation sites with critical loads to summarize for the remaining two ecoregions: namely the wet tropical forest and the Mediterranean California ecoregions.