Table 1. County level mean ± standard error effective number of crop species (ENCS) for each ERS Farm Resource Region (calculated using US Census of Agriculture data collected during 1978, 1982, 1987, 1992, 1997, 2002, 2007, and 2012.
| Year of the Census | ||||
|---|---|---|---|---|
| Region | 1978 | 1982 | 1987 | 1992 |
| Heartland | 3.79±0.05d | 3.95±0.05c | 3.88±0.05d | 3.41±0.05d |
| Northern Crescent | 5.85± 0.10a | 6.21 ± 0.10a | 6.56 ± 0.12a | 6.19 ± 0.11a |
| Northern Great Plains | 5.26±0.16ab | 5.66±0.18a | 5.86±0.15b | 5.61 ± 0.16a |
| Prairie Gateway | 4.06±0.09cd | 4.00±0.09c | 4.29±0.09cd | 4.52±0.09b |
| Eastern Uplands | 4.43±0.07c | 4.64±0.08b | 4.77±0.08bc | 4.24±0.07bc |
| Southern Seaboard | 4.29±0.09c | 4.73±0.09b | 5.18±0.10b | 4.07±0.09c |
| Fruitful Rim | 5.57±0.27ab | 5.97±0.27a | 6.61±0.29a | 6.38±0.29a |
| Basin and Range | 3.95±0.19cd | 4.16±0.21bc | 4.28±0.21cd | 3.96±0.21bcd |
| Mississippi Portal | 2.90±0.08e | 3.63±0.08c | 4.11±0.10d | 3.55±0.08cd |
| Region | 1997 | 2002 | 2007 | 2012 |
| Heartland | 3.31± 0.04e | 3.31±0.04d | 3.17±0.04d | 3.06±0.03e |
| Northern Crescent | 6.60±0.12a | 6.42±0.14a | 6.06±0.11a | 5.49±0.10 a |
| Northern Great Plains | 5.32±0.14b | 5.79±0.16a | 5.43±0.14a | 5.06±0.13ab |
| Prairie Gateway | 4.66±0.08c | 4.43±0.08c | 4.31±0.08b | 3.98±0.08c |
| Eastern Uplands | 3.87±0.08d | 3.59±0.08d | 3.37±0.08d | 3.47±0.08d |
| Southern Seaboard | 3.94±0.08d | 4.25±0.09c | 4.24±0.09b | 3.90±0.08c |
| Fruitful Rim | 6.66±0.29a | 6.43±0.28a | 6.03±0.24a | 4.94±0.19b |
| Basin and Range | 4.13±0.20cd | 3.72±0.18cd | 3.50±0.17cd | 3.47±0.17cde |
| Mississippi Portal | 3.37±0.08de | 3.90±0.10c | 4.07±0.10c | 3.86±0.09 cd |
Within each year, differences among regional ENCS values are denoted by differing lowercase letters (P<0.05).