Cotton and corn cultivation were important in central Georgia until the boll weevil struck in the 1920’s. Then the depression bankrupted many farmers who tried to persevere, despite this agricultural pest. This economic calamity gave ecologists the opportunity to study forest succession as fallow fields eventually were transformed into climax forests. In less than a year bare soil becomes covered in grass and weeds 2 feet tall. Ragweed, asters, and broomsedge (a type of bunch grass) take over in the 2nd year, and by the 3rd year broomsedge and pine saplings up to 3 feet tall predominate. These 1st three years are known as the “grassland stage.”
If left unmodified, years 3-10 are known as the “grass and shrub stage.” Broomsedge and pine saplings are joined by blackberry, blueberry, sumac, greenbrier, and persimmon often covered by grape vines, Virginia creeper, Carolina jessamine, and honeysuckle–all plants that thrive in the sun. Eventually, pine trees emerge above this tangled mess. During years 11-30 the landscape is known as a “young pine forest.” An “old pine forest,” years 31-60, hosts tall pine trees but with a dense oak understory. This mixed pine/oak forest is habitat for more species of birds than any other stage. Lightning strikes, red heart disease, and pine beetles kill many pine trees during this stage, opening up the forest canopy and creating uneven-aged stands of trees beneficial for many different species of birds. After 60 years left fallow the land becomes a climax oak/hickory forest.
Below is a chart interspersed with photos showing the association of bird species with each stage of forest succession.
Years 1-3 (Grassland Stage)–grasshopper sparrow, field sparrow, song sparrow, meadowlark, killdeer plover, quail, junco, horned lark.
Grasshopper sparrows (Ammodramus summurum) are abundant in old fields.
Years 3-10 (Grass and Shrub Stage)–Add white-throated sparrow, rufus-sided towhee, cardinal, catbird, mockingbird, mourning dove, Carolina wren, and brown thrasher.
Covey of quail. This species becomes most abundant 3-5 years after cleared land is left fallow.
Years 11-30 (Young Pine Forest)–Subtract most of the grassland species but add flicker, blue jay, chickadee, titmice, pine warbler, and white-eyed vireo.
Rufus sided towhees move into young pine forests.
Years 31-60 (Old Pine Forest Stage)–Subtract mourning dove, catbird, mockingbird, brown thrasher, and white-eyed vireo, but add summer tanager, woodpeckers, yellow-throated warbler, black and white warbler, wood thrush, flycatchers, red-eyed vireo, and kinglets.
Carolina wrens are abundant in old pine forests with an hardwood understory.
> 60 years (Climax Oak/Hickory Forest) Subtract towhee, pine warbler, and tanager, but add white breasted nuthatch.
White breasted nuthatches won’t move into a forest until it is at least 50 years old. Last time I saw this species was when I visited Marshall Forest in Rome, Georgia which is a virgin forest.
Forest succession from bare soil to climax forest has occurred in Georgia ever since Indians began cultivating the land here over 1000 years ago. However, habitat including each successional stage is much older than this because our present day species of song birds, especially habitat specialists, have existed for over 1 million years. Before man impacted the environment, changes in the landscape depended upon natural disturbances. Heavy acorn consumption by megafauna along with trampling and bark-stripping suppressed tree recruitment and growth. Lightning-ignited fires thinned forest into open woodlands. Tornadoes and downbursts flattened wide swaths of trees. Drought, ice storms, floods, and fluctuating climate cycles also changed forest structure and tree species composition. Landscapes are never eternally permanent.
Johnson and Odum
“Breeding Bird Populations in Relation to Plant Succession on the Piedmont of Georgia”
Ecology 37 1956
Meyers, J.M. and A.S. Johnson
“Bird Communities Associated with Succession and Management of Loblolly-Shortleaf Pine Forests”
U.S. Forest Service General Technical Report