Table 3.
Shown are the minimum, 10th, and 50th percentile for the empirical CLs of nitrogen from Pardo et al. (2011a, b) that were applied to individual NLCD classes. Cells with NA indicate no range was reported and blank cells indicate no CL of that type. For the Northwestern Forested Mountains and Mediterranean California ecoregions, cells with more than one NCLD Class (i.e., have at least two of Forest, Herbaceous, and Shrubland land covers), the full range of CL values associated with the land covers was used. For the other three CLs examined (Lichen, Terrestrial Acidification, Aquatic Acidification), statistics were calculated in each 12-km grid cell rather than at the ecoregion level and thus are not shown here.
| Ecoregion | NLCD class | Empirical critical loads: minimum, 10th percentile, 50th percentile per ecoregion (kg N [eq]) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
| ||||||||||
| Nitrate leaching | Plant community composition | Forest-Tree health | ||||||||
|
| ||||||||||
| Min | 10th | 50th | Min | 10th | 50th | Min | 10th | 50th | ||
| Northern forests | Forest | 8 (571) | NA | NA | 7 (500) | 8.4 (600) | 14 (1000) | 3 (214) | 5.3 (378) | 14.5 (1035) |
| Northwestern forested mountains | Forest | 4 (285) | 5.3 (378) | 10.5 (750) | 17 (1214) | NA | NA | |||
| Herbaceous | 4 (286) | 4.6 (328) | 7 (500) | |||||||
| Marine west coast | Forest | 5 (357) | NA | NA | 5 (357) | NA | NA | |||
|
| ||||||||||
| Eastern temperate forests | Forest | 8 (571) | NA | NA | 3 (214) | NA | NA | |||
| Mediterranean California | Forest | 10 (714) | 10.7 (764) | 13.5 (964) | 24 (1713) | 24.9 (1778) | 28.5 (2035) | 17 (1214) | 19.2 (1371) | 28 (1999) |
| Herbaceous | 10† (714) | 10.4 (743) | 12 (857) | 6 (428) | 6.4 (457) | 8 (571) | ||||
| Shrubland | 7.8 (557) | 8 (571) | 8.9 (635) | |||||||
| Tropical humid forests | Forest | 5 (357) | 5.5 (393) | 7.5 (535) | 5 (357) | 5.5 (393) | 7.5 (535) | |||
|
| ||||||||||
| Great Plains (herbaceous) | Herbaceous | 10 (714) | 11.5 (821) | 17.5 (1249) | 5 (357) | 7 (500) | 15 (1071) | |||
|
| ||||||||||
| North American desert | Mixed‡ | 3 (214) | 3.5 (250) | 5.7 (407) | ||||||
CLs for nitrate leaching in the Mediterranean California ecoregion were from a mixed system of chaparral and oak woodlands, so we assigned those CLs to both Herbaceous and Shrubland NLCD classes.
CLs for this Plant community composition in the North American Desert came from mixed systems of the Southwest near Joshua Tree National Park and so were assigned to Herbaceous, Shrubland, and Forest NLCD classes.