Old Field Succession

 Old Field Succession

An old field/powerline cut with bluestem, goldenrod, fleabane, ragweed

Ecological succession is the natural progression of a natural community over a period of time. This process starts with an area of land that has been disturbed or is in some cases completely barren and ends with a climax community such as an old-growth forest. Disturbances to an ecosystem reset the cycle of succession at anytime and in most cases this creates a diverse community of plants and animals. Primary succession takes the longest and often starts with a barren or rocky area, often after a large-scale event such as volcanic eruptions or glacial movements. This process takes millions of years as organisms must colonize the area, and produce enough biomass to support plants. Secondary succession is a much faster process that takes anywhere from a few decades to 200-500 years. This type of ecological succession is known as Old Field Succession and is often the result of natural or human-made disturbances and affects a much smaller area. We can find examples of secondary succession in almost any part of North America with most of the woodlands, meadows, coppices/shrub thickets, and wetlands being the result of secondary succession. There is only a small fragment of "Virgin Forest" left in North America and even these areas see fires, windstorms, and other disturbances. The process of natural succession is a fascinating subject that has interested me since I was a teenager. Additionally, disturbed habitat seems to be a magnet for birds and mammals as well as a good place to find wildflowers. In this article I will be discussing the process of Secondary Succession in the Carolinas and what plants and animals occupy each stage. 

What is Old Field Succession?

Capped landfills are an example of a grassland stage, NHC Landfill

Old-growth hardwoods in Appalachia  

For the purposes of this article "Old Field Succession" is the transition of an ecological community from an open field or meadow, to an old-growth forest. This differs from Primary Succession which usually takes place in areas completely devoid of plant life such a lava fields, where it takes thousands or even millions of years for the site to support more than lichens, moss, and other primitive lifeforms. Secondary Succession in turn usually starts with an area that already has some plant life nearby as well as the organic matter (i.e. soil, and detritus) to support herbaceous and woody plants.  Most sources say this process takes 200-500 years to go from a grassy field to a climax forest. However, we can see most of stages of succession within a few decades or as little as in 8-15 years with fast growing trees. There are many theories about how plant communities evolve overtime and respond to disturbances. The concept of Old Field or Secondary Succession remains widely accepted by many ecologists and foresters today (circa 2020). 

Learn about natural succession with these Wikipedia articles, Ecological Succession

The Stages of Secondary Succession 

The process of secondary succession consists of five stages with each one creating its own plant  community. In general biodiversity increases as the site progresses through the cycle. Because there are already plant communities nearby and the site is not rocky, it only takes one or two growing seasons for an area to become a meadow or old field. After that, woody plants begin to take over and within 15-20 years, that same field would become a woodland. However, it will take at least a century for the site to gain the characteristics of a mature forest as pioneer species get replaced by climax species. The 200-500 year cycle is often reset when there are fires, windstorms/tornados, insect outbreaks, or human disturbances such as logging. On a small scale, these disturbances are important for maintaining biodiversity and may be a reason why meadowlands, peatlands, and pine savannas exist. I will explain the stages of succession through a hypothetical story of a corn and soybean farm "Holly Farms" that went out of business in recent times but the family held on to the land instead of  selling is to developers. 

Stage 1 Meadow or Grassland Stage 

Fields and cropland, this site appears operational  

The first stage of Old Field Succession begins with a barren field or perhaps an abandoned pasture, or homesite. Some of these areas may be completely devoid of vegetation as is the case with a capped landfill or a ploughed field, although most sites already have herbaceous and woody plants growing in them. The Meadow or Grassland Stage takes place during the first two or three seasons after a cultivated site is abandoned or a major fire occurs in a forest. Annuals and other fast growing plants fill in the site during the first season, while biennials and perennials fill in during the second year, followed by perennial grasses. A few trees and shrubs may mix in later in this stage, although the site is mostly a grassland habitat.

A meadow in late spring (note this is actually part of a Pine Savanna)

Holly Farm Site: In our example, we will look at an abandoned corn or soybean field in Pender or Northern New Hanover County. This site was part of a large farm that ceased operations this past autumn. The fields were ploughed regularly and was well-maintained. In addition to the fields there are hedgerows, a stand of pines, and a rundown homesite with a 200 year-old Live Oak. Within one growing season of the field going fallow, we have a mixture of annual and some fast-growing perennial colonizers, and several warm-season grasses. There may be Bahia Grass, Bluestem "Broomsedge", Timothy Grass, or Common Crabgrass although the majority of the plants are species like dandelion, sow thistle, mullen, bitterweed, horse nettle, and maybe some naturalized sorghum or wheatgrass. There might even be Dogfennel, coreopsis, and morning glory by summer's end. Cool season plants like henbit, ryegrass and chickweed take over in the winter. 

Wildlife: You will see bees, wasps, and various butterflies visiting flowers while some ground nesting bees and wasps will make burrows. Vesper Sparrows, Horned Larks, and Killdeers love barren fields, as do White Ibis and Sandhill Cranes. Aside from these birds, you won't see too much although some migrating warblers may visit clumps of weeds. 

Stage 2 Old Field Stage 

An old field example with herbaceous and woody plants

The next stage of succession begins after 3-5 years depending on the site, location, and soil type. Meadowlands peak during their second and third seasons before hardy perennials, vines, and the first woody shrubs begin to takeover the site. In many areas there are already trees springing up by the end of the first growing season, although it usually takes several years for those to reach significant  size. At this stage, the vegetation may be up to our waists and most annuals and "weedy" species have shaded out. These sites are known as old fields

Holly Farm Site: Our cornfield has been abandoned for four years and it is already unrecongizable. The third growing season brought a sea of color as native and nonnative wildflowers and short-lived shrubs flowered from May to November. There were Swamp and Savannah Sunflowers, salvias, meadow beauties, blazing stars, coneflowers, goldenrods and asters. Hibiscus (maybe Seashore Mallow), Wild Indigo and Groundsel Tree have filled nicely, while some shrubs such as Wax Myrtle, Common Juniper, and sapling pines can be seen in some areas. This year also saw lots of prairie and grassland birds including nesting Meadowlarks, Savannah Sparrows, and Common Yellowthroats. However, by the fourth season, the wildflowers have begun to give way to shrubs, vines and aggressive perennial species. The birds brought in more than Wax Myrtles, junipers, and Red Cedars. There is Black Cherry coming up along the fencerow as well as invasive Chinese Privet and Tallow Trees, while squirrels and crows have buried acorns, and nuts from hickories, creating new trees. This is beginning Old Field Stage and marks an important transition between grassland and woodland.  

Wildlife: During the Old Field Stage you will see a wide diversity of birds, insects, mammals, and reptiles. Green Anoles, Fence Lizards, and Tree Frogs live in the dense clumps of shrubs and small trees, while Field Mice and Meadow Voles scurry under the thicket to avoid Red Tailed Hawks soaring above. While there are still Meadowlarks and even a Kestrel nesting in a nearby tree hole, most of the grassland birds are gone as it has the undergrowth has become too thick. During the spring and summer, Mockingbirds, Cardinals, Indigo Buntings, Blue Grosbeaks, and Field Sparrows sing all day long, while autumn brings a large flocks of sparrows and doves going after the seeds from the wildflowers. Those wax myrtles and privets that took over the cornfield are now magnets for Myrtle Warblers, robins, starlings, and waxwings all winter long. One day you spot a family of deer browsing on plants, or a Grey Fox running across the dirt road. 

Stage 3 Shrubland/Copse

An example of a shrubland, mix of pines, oaks, privet, and briers

The third stage of succession can begin as early as eight years after a disturbance, the transition normally occurs after 15 years. This stage is known as the Shrubland, Copse, or Bramble stage which are all terms for a landscape dominated by shrubs, vines, brambles (i.e. blackberry) and small trees. There are some cases when a field or garden will become a shrubby thicket in only a few seasons, especially if invasive exotic species such as Buckthorn Kudzu and Japanese Wisteria are present, skipping the grassland and old field stage entirely. Wax Myrtle, Loblolly Pine, and Sweet Gum are examples of native trees that can overtake a field or garden in a few seasons. At this stage, the site is nearly impenetrable and almost all traces of the meadow and its wildflowers are gone. 

Holly Farm Site: It is now fourteen years since the cornfield was abandoned and despite several hurricanes, and a period of drought the site has grown up into a small woodland. Wax Myrtles, privets, junipers, hollies, and dozens of other shrubs have filled in, and the hedgerow that bordered the field has now become a miniature woodlot. When walking through the underbrush your trousers get caught on Smilax Brier, Dewberry, and Carolina/Multiflora Rose. Virginia Creeper, Muscatine Grape, and unfortunately Japanese Wisteria that was in the hedgerow have become intertwined with the shrubs. You also notice Loblolly Pines, Sweet Gums, Red Maples, and Eastern Red Cedars towering over the shrubs, and clusters of sapling oaks, hickories, and sycamore trees underneath. Swamp sunflowers, broomsedge/bluestem, and some clumps of goldenrod are all that remain of the lush meadow that carpeted the field eleven years ago. The cornfield site was turned into an ecological preserve guaranteeing it will not be cleared for development.

Wildlife: Upon our visit to the cornfield site we notice that the wildlife has changed drastically. There are still insects everywhere and clumps of wildflowers or flowering shrubs still support bees, wasps and butterflies. Many of the native trees and shrubs are host plants so we see Black, Tiger, and Zebra Swallowtails, Viceroy Butterflies, and later in the summer/autumn Monarchs and Gulf Fritillaries (as there is both milkweed and passionvine in the copse). The birds on the site are also different with the Indigo Bunting, Blue Grosbeak, and Mockingbird being the only "old field" birds left on the site, and are limited to the outermost edges of the site. You hear Grey Catbirds, Eastern Towhees, White Eyed Vireos, and Prairie Warblers singing from the thickets, a Brown Thrasher singing from a pine (next to a Pine Warbler). In addition to these standouts the songs of cardinals, chickadees, wrens, and titmice fill the air. You also come across a Wild Turkey on the trail, and hear Bobwhites calling from another field that is still in the old field stage. In addition to all of the new birds, you see Grey Squirrels in the treetops, skinks in the underbrush, and a rat snake amongst an overturned pine (taken out by last year's hurricane). Autumn and winter brings large flocks of warblers, vireos, and other songbirds. 

Stage 4 Woodland/Mid-Successional Forest

Example of a early to mid-successional woodland 

It usually takes 30-50 years for an old field to develop into a woodland or forest, although this can be artificially sped up by replanting trees. By this stage, the pines, and pioneer hardwoods have reached maturity and are now towering over the shrub layers below. While hardy shrubs like Wax Myrtles and most of the invasives will persist in partial or full shade, almost all of the junipers, cedars, and alders are gone. This is also when climax species such as hickories, beeches, oaks, tulip polars, and other trees begin to fill in. Most woodlands and forests in Southeastern North Carolina are in the  Early and Mid-Successional Stage and have been cleared, logged, or hit by natural disasters within the last 100-150 years. This is the longest stage of Secondary Succession with the transition from Mid-Successional to Climax ecosystems taking at least a century, barring no disturbances and only low-heat fires. 

Holly Farm Site: Forty years after the cornfields were abandoned, the "Holly Farm Preserve" is now an established woodland with a mixture of hardwoods, pines, and a healthy amount of understory. Loblolly Pines are still abundant although the canopy layers now contain Sweet Gum, Red and Silver Maple, American Beech, Ironwood, Sycamore, Tulip Poplar, Red Hickory, Mockernut Hickory, and six species of Oaks. While invasive privet, buckthorn, and wisteria still cause problems along the edges and trail bank, native shrubs such as Fetterbush, Highbush Blueberry, various hollies, and even White Dogwood have filled in. On a spring visit, you come across Mayapple, Jack in the Pulpit, Wild Ginger, violets, and bluebells. Fallen trees from past storms and the skeletons of junipers and cherries add to the detritus and provide nurse logs for wildflowers and mosses. The site also has some surviving relics from the homesite including Camellias, Azaleas, and a 240 year-old oak tree growing next to the decrepit farmhouse. The site feels and looks like a forest although it still has a dense shrubby understory. You will still see sun-loving trees, wildflowers like goldenrod, and the invasives along the roadside.

Wildlife: At this stage, most of the grassland and old field birds are gone. There are still Indigo Buntings, and a few Towhee along the entryway and near the farmhouse, but almost everything you hear at this site are woodland birds. You see White Breasted Nuthatches and Black and White Warblers creeping up and down trees, spot Downy and Hairy Woodpeckers working higher up before a Pileated Woodpecker drops down to a dead pine tree to feed her youngsters. The air is filled with the song of warblers, vireos, Brown Thrashers, Summer Tanagers, Wood Thrushes and the buzz of cicadas. An Acadian Flycatcher feeds her young in a tree overhanging the old farm road, while a Carolina Wren pair takes care of a nest of their own in the rootball of the fallen pine. The same site that the snake was found in 26 years ago, although there are now twelve species of snakes in this woodland alone. Other notable finds include a Barred Owl, Wild Turkeys, many deer, and a Black Bear den that we were allowed to approach with trained biologists. To many visitors, the Holly Farm Preserve is thought to be an old forest even though it was a series of barren fields only four decades earlier. The character who has watched this farm's transformation as a relatively young adult is now growing old,  although his children and the hundreds of people he took into the woods are now continuing his story.

Stage 5: Climax Forest/Old Growth

Old growth (or mature) oak, hickory beech forest at Raven Rock State Park

The Climax Stage is the final stage of succession and is considered by many experts to be the peak plant community for any forest habitat, although this is not always the case. It takes centuries for a Mid-Succession Forest to return to its climax ecosystem. In most of the Eastern Deciduous Biome including in the Carolinas, climax forests are dominated by hardwoods and have relatively open understories. Some exceptions include fire-maintained pine savannas, coastal habitats that are constantly battered by the sea, and Boreal type forests where conifers remain dominant. By this point, most of the pioneer trees have been shaded out by the climax species, and some trees are now as high as 30m (100ft), although some eastern trees including some of our pines can easily reach 45m (150ft). Late-successional and climax woodlands are the the closest thing to virgin forests with the ancient Bald Cypress stands along the Northeast Cape Fear River being one example of a climax forest. You may have to go to the Appalachian Mountains or parts of Canada to find similar forests and even these sites may have been logged at least once during 400-years of European Settlement. 

Holly Farm Site: It is now 220 years since the cornfields at Holly Farm were abandoned and future generations have done their part to preserve the site as a historic landmark and an ecological preserve. A descendent of the person who watched the fields transition into woodland habitats has continued to give tours within the forest park. The forest tracts consist of hickories, oaks, beeches, and elms that vary by age group as well as the victims of many hurricanes, ice storms, and even a forest fire 55 years ago. This created a patchwork of microhabitats that range from small meadows to patches of mid-successional forests that filled the void when a tree falls. There are still Loblolly Pines in the area with one 210 year old specimine towering 37m (120ft) above the canopy along with several supercanopy Tulip Poplars and Sweet Gums. The Holly Farm Oak is also still alive and is now 420 years old and is widely recongized as an icon. The forest has a healthy canopy with layers of understory trees, saplings, and carpets of moss, herbaceous plants, and ferns. While the house is little more than a chimney and slab, it still serves as a reminder of the past, and some of the depressions and banks remain to tell the story of the farm that once occupied this site. The Holly Farm site has a wide diversity of plants and is a popular destination for birdwatchers, botanists, and those looking for some hiking. 

Wildlife: As a climax ecosystem, most of the site is dominated by forest dwelling animals. Warblers, vireos, flycatchers, wrens, chickadees titmice, and other forest birds are numerous. The Wood Thrush, Ovenbird, Kentucky Warbler, Screech Owl, and Broad Winged Hawk are just some of the notable birds that are found deep in the forest. The edges and clearings have an assortment of songbirds including some familiar species such as Indigo Buntings, Blue Grosbeaks, and Grey Catbirds, while a tornado made a large enough clearing to support Field Sparrows, and Prairie Warblers again. Bears, bobcats, Grey and Red Foxes call this park home, as do many deer (with the second cornfield site becoming a public hunting range). Barred Owls and Red Shouldered Hawks keep the squirrels in check, while everything in this forest ecosystem become part of the landscape after the end of its life. Logs, stumps, and fallen trees were left in place creating homes for woodpeckers, raccoons, and flying squirrels. In a timeframe of 200 years this abandoned farm site has grown from a field of annual weeds to a forest of pines, oaks, and hickories. This hypothetical example shows how natural succession can create biodiversity and how quick (relatively speaking) an open area can revert to forest.