Effectiveness of Native Grassland Restoration in Restoring Grassland Bird Communities in Tennessee

Grassland bird populations have declined more than any other group of birds over the last 37 years, based on Breeding Bird Survey (BBS) data (Hunter et al. 2001, Sauer et al. 2003). In Tennessee, significant effort is underway to restore native grasslands through partnerships between Tennessee Wildlife Resources Agency (TWRA), U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) and private landowners. This partnership has put thousands of hectares of native grasslands back on the Tennessee landscape. It is unknown, however, whether there has been a positive response by grassland birds to this restored habitat. Furthermore, the restoration has proceeded on an opportunistic basis, with emphasis placed on willing landowners, rather than conducting the restoration where wildlife benefits might be maximized.

Forty-five and forty-three restored native warm season grass (NWSG) fields were evaluated in 2002 and 2003, respectively. Three native grassland fields at Fort Campbell Military Reservation (FCMR) where viable populations of grassland birds are regularly found breeding were also evaluate each year for comparison. All fields were evaluated for vegetative species composition and structure and avian use. Effects of management practices for each field (mowing and burning) were also evaluate.

Restored program and FCMR fields were predominantly NWSG and forbs. Vegetative height in FCMR fields did not exceed 50 cm in either year while restored program fields exceeded 90 cm in both years. In restored program fields, bare ground cover was reduced from 16.7% in 2002 to 7.47% in 2003 (P < 0.05). Burned fields had significantly less litter cover ( x ̅ [sample mean] = 7%) than fields being mowed ( x ̅ [sample mean] = 17.24 %) or not being managed ( x ̅ [sample mean] = 13.7%) (P < 0.05). Litter depths were also greater in fields being mowed ( x ̅ [sample mean] – 1.06 cm) and not being managed ( x ̅ [sample mean] = 0.90 cm) than litter depths in fields being burned ( x ̅ [sample mean] = 0.45 cm), (P = 0.0004). Forb cover was greater in burned fields ( x ̅ [sample mean] = 33.75%), than forb cover in fields being mowed (x ̅ [sample mean] = 19.86%) or fields not being managed ( x ̅ [sample mean] = 22.95%) (P = 0.0006).

Eight-eight species of birds were noted in and around restored NWSG fields in Tennessee. Field size was the best explanatory variable for observed species richness of grassland species in restored NWSG fields in both years (P < 0.005). Nearly all of the grassland species in this study were positively associated with larger (> 30 ha) field sizes. Many species showed a negative relationship with increased vegetative heights and increased cover by NWSG. Many species also showed a positive relationship to increased levels of bare ground in both years. Henslow’s sparrow (Ammodramus henslowii) showed a positive relationship with increased litter depths. Grasshopper sparrows (Ammodramus savannarum), Henslow’s sparrows, eastern meadowlarks (Sturnella magna), dickcissels (Spiza Americana), and northern bobwhites (Colinus virginianus) were found in fields where average vegetative height was ≤ 52 cm. Northern bobwhites were found in restored field where average litter depths were < 1 cm. Northern bobwhites were found in restored NWSG fields in all size classes; Grasshopper sparrows, Henslow’s sparrows, eastern meadowlarks, and dickcissels occurred more often in larger patches when available.

Observed vegetative composition and structure were a result of management within the restored NWSG fields. Fields at FCMR are burned on a 1-3 year rotation, whereas 70% of the fields evaluated in this study were being managed by mowing or were not being managed. If the managing organizations in Tennessee do not coordinate their management efforts, then grassland management in Tennessee will probably never reach its full potential. Restored NWSG fields in Tennessee need to be managed using rotational (every three to four years) burning. In areas where burning is not an option, moderate discing could be used instead of mowing. With appropriate management, NWSG restoration in Tennessee could ultimately be more successful than previously thought possible.