Ecological dynamics
The information in this ecological site description (ESD), including the state-and-transition model (STM), was developed using archeological and historical data, professional experience, and scientific studies. The information is representative of a complex set of plant communities. Not all scenarios or plants are included. Key indicator plants, animals, and ecological processes are described to inform land management decisions.
Introduction – Southern Arkansas, western Louisiana, and eastern Texas have been deemed the Pineywoods because of the vast expanse of pine trees. The region represents the western edge of the southern coniferous belt. Historically, the area was covered by pines with mixed hardwoods, sparse shrubs, and a diverse understory of grasses and forbs. Fire played a significant role in reducing the woody competition that generally out-competes the herbaceous understory layer. Fire suppression and land conversion have reduced the amount of historical communities in existence today.
Background – Prior to settlement by the Europeans, the reference state for the Loamy Claypan Uplands was a Shortleaf Pine/Post Oak (Pinus echinata/Quercus stellata) Woodland. Remnants of this presumed historic plant community still exist where natural conditions are replicated through conservation management techniques. Evidence of the reference state is found in accounts of early historic explorers to the area, historic forest and biological survey teams, as well as recent ecological studies in the last 30 years. The community is an uneven-aged woodland with a well-developed understory of grasses/forbs, shrubs, and overstory saplings.
Settlement Management – As human settlement increased throughout the area, so did the increase in logging and grazing by domestic livestock. The logging became so extensive that by the 1930’s most of the region had been cut-over. Replanting trees to historic communities was not common and early foresters began planting loblolly pine (Pinus taeda) for its quick growth. As more people colonized they began suppressing fire, which allowed dense thickets of shrubs to replace the herbaceous understory.
Current Management and State – Today much of the remnant forest is gone, replaced by pine plantations, crops, and pastures. The areas that were not converted have been fire-suppressed so long that loblolly pine and fire intolerant hardwoods populate the overstory structure. Currently, U.S Forest Service properties are the best place to view the remnant sites. Some private individuals have begun restoring communities through selective tree planting and retention of communities that remain. Other restoration efforts include mimicking natural-disturbance regimes through gap-phase regeneration on plantation sites.
Fire Regimes – Fire was a natural and important disturbance throughout the Western Gulf Plain. Fire occurred naturally from lightning strikes and was started by Native Americans for game movement. The reference community developed with a frequency of fire every 5 to 10 years. Fires usually occurred in early spring, removing senescent vegetation, recycling nutrients and minerals, and spurring new plant growth. Late summer fires occurred as well, but with a different community effect. Summer fires burned hotter and with more intensity, greatly suppressing the shrub canopy layer. The summer fires also shifted the ecological site transitional state by decreasing grass densities and increasing forb densities. The topography, fuel loads, and other conditions caused patchy burns throughout the region resulting in mosaic patterns of plant communities and a heterogeneous landscape.
Disturbance Regimes – Extreme weather events occur occasionally throughout the region. Tornados uproot trees and open canopies in the spring months. In the late summer and early fall, hurricanes or tropical depressions often make landfall, dumping excessive amounts of rain and toppling trees with high winds. Another cause of large canopy openings is the effects of the southern pine beetle (Dendroctonus frontalis). Starting in the late 1950’s, beetle outbreaks have occurred every 6 to 9 years (although a major attack has not occurred in some time), usually when the trees are stressed due to multiple environmental factors.
Plant Community Interactions – The length of fire intervals and position on the landscape create a moderate overstory-canopy cover (40 to 70 percent). The canopy cover is higher than the associated upland sandy sites with frequent fire, and much lower than the lower loamy-to-clayey sites with infrequent fire. The understory consists of small shrubs and a diverse layer of grasses and forbs. The claypan in the soil restricts the growth of some plants due to the abrupt increase in clay (less than 20 percent increase). Plants like American beautyberry (Callicarpa Americana) and longleaf woodoats (Chasmanthium sessiliflorum) are well adapted to this site, while less-adapted plants are hindered from growing into the subsoil and extracting moisture.
State 1
Woodland
There are two communities in the Woodland State: the Shortleaf Pine/Post Oak Woodland Forest (1.1), the Fire-primed Understory (1.2). The reference state has a moderate overstory cover (40 to 70 percent) of Shortleaf Pine and Post Oak with a well-developed and diversified understory of grasses, forbs, and shrubs. The forest composition is uneven-aged with members of the pine community probably being over 200 years.
Natural disturbances of fires, lightning strikes, hurricanes (wind throw), ice events (rare), and beetle infestations create large canopy gaps from which the ecosystem is naturally regenerating. The natural canopy spacing is kept intact by periodic fires ranging from 5 to 10 years. Good representative basal areas are less than 70 square feet per acre. Growth competition can be seen in the outer rings on trees in locations where the basal area exceeds 80 square feet per acre.
Community 1.1
Shortleaf Pine/Post Oak Woodland
Shortleaf pine and post oak comprise the majority of the overstory. The occurrence of shortleaf pine in the overstory at any given site is usually 70 to 90 percent. Post oaks have established on the sites at 10 to 30 percent. Other hardwoods are sometimes found colonizing the areas in lesser amounts (less than 5 percent), including oak and hickory species. American beautyberry is extremely prevalent and makes up the majority of the understory shrub layer.
Table 6. Ground cover
| Tree foliar cover |
5-25%
|
| Shrub/vine/liana foliar cover |
10-50%
|
| Grass/grasslike foliar cover |
25-50%
|
| Forb foliar cover |
0-20%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
25-95%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
5-35%
|
Table 7. Canopy structure (% cover)
| Height Above Ground (ft) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.5 |
0-1% |
0-10% |
10-30% |
0-15% |
| >0.5 <= 1 |
5-25% |
0-30% |
10-40% |
0-15% |
| >1 <= 2 |
0-5% |
5-30% |
5-30% |
0-5% |
| >2 <= 4.5 |
0-5% |
5-50% |
0-5% |
0-1% |
| >4.5 <= 13 |
5-15% |
0-5% |
– |
– |
| >13 <= 40 |
15-25% |
0-1% |
– |
– |
| >40 <= 80 |
25-35% |
– |
– |
– |
| >80 <= 120 |
10-35% |
– |
– |
– |
| >120 |
5-10% |
– |
– |
– |
Community 1.2
Fire-primed Understory
Both communities are characterized by a diverse ground layer. Longleaf woodoats and Texas ironweed (Veronia texana) are especially common. This layer is thick enough to provide ground-nesting birds and fawns with adequate cover. In phase 1.1, the fire interval has been so recent that shrubs and tree saplings have not grown higher than three feet. Phase 1.2 has an increased abundance and height of the shrub layer. Under natural conditions, only fire tolerant saplings will grow into the overstory.
Pathway 1.1A
Community 1.1 to 1.2
The driver for the community shift is time since the last fire. As post-fire time increases, so does the foliar cover by shrub species. As the perennial grasses and forbs age, their senesced leaves increase fine fuel levels.
Pathway 1.2A
Community 1.2 to 1.1
The driver for the community shift is fire. As fire burns through the understory, it encourages a diverse herbaceous layer while suppressing shrubs and tree seedlings.
State 2
Mid-story Dominant Forest
The Mid-story Dominant State has crossed a threshold in which normal environmental events cannot transition the community back to State 1. The brush canopy has become so thick, it has begun to limit the productivity of the ground-layer. The limited ground layer does not provide enough fuel to harbor a burn with the intensity found in State 1.
Community 2.1
Mixed Mid-story
Yaupon (Ilex vomitoria) may begin to overpower the shrub layer. Yaupon has limited fire toleranance and takes advantage of the clay soil found below the loamy surface. Because of fire suppression, the American beautyberry will have several years of growth still attached to the plant. Frequent fires keep the plant pruned and vibrant.
Tree seedlings have grown higher and are beginning to escape the effects of fire and will become part of the overstory given more time with lack of management. The species present in the reference community will still be found, only in lesser amounts because the canopy cover is creating a better environment for fire-intolerant and shade-loving species.
Table 8. Ground cover
| Tree foliar cover |
10-25%
|
| Shrub/vine/liana foliar cover |
35-75%
|
| Grass/grasslike foliar cover |
10-25%
|
| Forb foliar cover |
0-10%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
50-100%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0-20%
|
State 3
Mixed Forest
A long-term lack of fire and management has now caused the plant community to cross two major thresholds resulting in a very-closed canopy community. Fire intolerant hardwoods have become part of the overstory. The overstocking reduces the overall value of the timber stand. The value is decreased because of reduction in shortleaf pine numbers and an increase in hardwoods.
Community 3.1
Dense Pine/Hardwood Forest
The understory plant layer only contains remnants of longleaf woodoats and only a few forb species. The shrub layer is dominated by large, dense patches of yaupon. Because the site lacks the diversity found in the reference state the wildlife diversity is reduced to only generalist species and those seeking refuge.
Similar to State 2, this ecological state requires management to restore the reference community. Selective timber harvest to remove unwanted hardwood species is the first step to allow the understory to return. Frequent prescribed burns (1 to 3 years) will help suppress the hardwood regeneration. Intense summer fires may also be required. The suppression of overstory seedlings will allow grasses, forbs, and shrubs to reestablish.
Table 9. Ground cover
| Tree foliar cover |
80-95%
|
| Shrub/vine/liana foliar cover |
35-75%
|
| Grass/grasslike foliar cover |
0-10%
|
| Forb foliar cover |
0-5%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
25-100%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0-5%
|
Community 3.2
No Overstory
The No Overstory community is the result of a natural disaster or clearcutting in which the entire overstory has been removed. Immediately after the event, the understory may begin to resemble State 1. Although given enough time without fire or management, the area will return to a Dense Pine/Hardwood Community (3.1).
Pathway 3.1A
Community 3.1 to 3.2
The driver for the shift is a natural disaster or clearcut situation. Examples of natural disasters include hurricane, wind throw, severe ice storms, or severe fires. Following timber harvest by clearcut, little of the State 1 vegetation remains. Primary vegetative succession occurs post clearcut.
Pathway 3.2A
Community 3.2 to 3.1
The driver for the community shift is time and lack of fire. Shrubs and tree saplings will not be suppressed without return fire intervals.
State 4
Plantation
The Plantation State is a result of conversion activities. The landowner has maximized silviculture production by planting a monoculture of tree species.
Community 4.1
Pine/Hardwood Plantation
In the immediate years following the initial plantation tree planting, the understory community will resemble State 1. During this early growth period, the landowner will typically remove unwanted hardwoods and herbaceous plants to reduce competition with the planted trees. As the overstory canopy closes, less understory management is required due to sunlight restrictions to the ground layer.
State 5
Pasture and Cropland
The Pasture and Cropland State is a result of conversion activities. The landowner has maximized agriculture production by planting a monoculture of introduced grass species or agricultural row crops.
Community 5.1
Planted Pasture and Row Crop
Typical introduced pasture grass species include bahiagrass (Paspalum notatum) and different varieties of bermudagrass (Cynodon dactylon). The grasses are grown for livestock production through direct grazing or baling hay for later use. Agricultural row crops are grown for food and fiber production. Many farmers use herbicides to reduce unwanted plant competition which yields a plant community unrepresentative of State 1 or subsequent vegetative states.
Transition T1A
State 1 to 2
The transition from a State 1 to State 2 is a result of time and long periods (greater than 10 years) of no fire. Without fire to suppress shrubs and tree seedlings, biomass and diversity will be lost from the grass and forb layers of the system. The transition is also characterized by tree sapling’s bud zones beginning to escape the height at which fire is effective at suppression.
Transition T1B
State 1 to 4
The transition is due to the land manager maximizing silviculture potential. Merchantable timber is harvested by clearcut, then the site is prepared and planted to a monoculture of trees.
Transition T1C
State 1 to 5
The transition is due to the land manager maximizing agricultural production. Merchantable timber is harvested by clearcut, then the site is prepared and planted to either an improved grass or row crops.
Restoration pathway R2A
State 2 to 1
The driver for restoration is fire. Enough fuel is still left in this community to carry a fire through the site. More frequent burns (1 to 3 years) may be required, initially, to suppress the woody vegetation. Some tree species may have escaped the effective fire height and will have to be selectively cut down to return to State 1.
Transition T2A
State 2 to 3
The transition from a State 2 to State 3 is a result of time and long periods (greater than 20 years) of no fire. Without fire to suppress fire intolerant trees, they become part of the overstory canopy. The overstory is so saturated that the understory herbaceous layer is almost non-existent. As the overstory canopy closes, the mid-story becomes well established with shade tolerant species.
Transition T2B
State 2 to 4
The transition is due to the land manager maximizing silviculture potential. Merchantible timber is harvested by clearcut, then the site is prepared and planted to a monoculture of trees.
Transition T2C
State 2 to 5
The transition is due to the land manager maximizing agricultural production. Merchantable timber is harvested by clearcut, then the site is prepared and planted to either an improved grass or row crops.
Restoration pathway R3A
State 3 to 1
This restoration path is the most energy intensive. Restoration of this community to the reference state begins with a selective timber harvest. Removing unwanted trees (shade and fire intolerant) opens up the canopy allowing sunlight penetration to the ground. Years of overstory growth have limited the fuel necessary to have an effective fire. Time will be needed to encourage an understory and, if possible, mowing the understory may help. Once the herbaceous layer has established, frequent burns (1 to 3 years) may be required to suppress the woody vegetation.
Transition T3A
State 3 to 4
The transition is due to the land manager maximizing silviculture potential. Merchantible timber is harvested by clearcut, prepared, and planted to a monoculture of trees.
Transition T3B
State 3 to 5
The transition is due to the land manager maximizing agricultural production. Merchantable timber is harvested by clearcut, then the site is prepared and planted to either an improved grass or row crops.
Restoration pathway R4A
State 4 to 1
This restoration pathway can be accomplished in different ways depending on goals. One option is to create canopy openings by reducing the number of overstory trees. Then, restore the resulting canopy gaps with species from the State 1 understory. Restoring the understory may include planting shortleaf pine and post oak. This method keeps the forest structure intact and slowly changes the species composition.
Another restoration method is to selectively harvest and remove brush (via mechanical or chemical means), followed by re-planting shortleaf pine and oak species (using reduced planting rates.) The herbaceous understory will take time to develop, but this process can be expedited if adapted plant material is available. Fire is the best option to maintain desired canopy cover for enhancement of the understory, and reduce undesirable woody species. Fire frequencies of 1 to 3 years during both growing and cool seasons may be desired in order to maintain an open canopy and reduce undesirable plant competition. If fire is not a viable option, management of woody encroachment could be controlled by mowing or the use of herbicides.
Transition T4A
State 4 to 3
This community transition is caused by neglecting the plantation understory. Without mowing or herbicides, the brush canopy becomes a dense thicket.
Transition T4B
State 4 to 5
The transition is due to the land manager maximizing agricultural production. Merchantable timber is harvested by clearcut, then the site is prepared and planted to either an improved grass or row crops.
Restoration pathway R5A
State 5 to 1
This restoration path can be accomplished by planting a mix of shortleaf pine and oak species to their natural frequencies (see State 1 Overstory Composition table), trying to attain a 40 to 70 percent mature overstory canopy. Management will be required to control unwanted species by burning, mowing, and/or herbicides. Controlling introduced pasture grasses is difficult, with complete control likely not attainable. The herbaceous understory will take time to develop, but this process can be expedited if adapted plant material is available.
Transition T5A
State 5 to 4
The transition is due to the land manager maximizing silviculture potential. The site is prepared and planted to a monoculture of trees.
