Post Oak Savanna restoration plan

1. Introduction

1.1 Texas post oak savannas

Oak savannas of the mid-western U.S. are found in a wide swath running from Minnesota down to Texas. Savannas are defined as having scattered, open-grown trees with or without a shrub layer and herbaceous ground cover dominated by grasses. Varying landscape and climactic conditions coupled with biotic interactions and fire history resulted in a mosaic of forest, savanna, and prairie communities across the Midwest (Anderson 1983). Savannas are ecosystems which fall somewhere in the middle of the mosaic representing a continuum from forest to prairie (Barbour et al. 1980).

The post oak savanna ecoregion of Texas is positioned in an ecotone between the Piney Woods deciduous forests to the east and the Blackland prairies to the west. The plant community of this region prior to European settlement was a savanna dominated by tussock grasses and forbs punctuated with scattered groves of trees, primarily post oaks (Quercus stellata) and blackjack oaks (Quercus marilandica). The post oak savannas were formed and maintained by disturbance. Frequent fires, both anthropogenic and natural in origin, were the driving force behind the savanna landscapes; these fires were typically broad in scope and would burn until landforms, soil change, or weather conditions would contain them. These fires maintained the diverse plant communities by suppressing woody species and stimulating prairie grass and forb species (Schmidly 2002). Bison herds grazed the savannas, increasing spatial and temporal heterogeneity in plant community structure, plant productivity, species richness and diversity, nutrient redistribution and cycling, and a variety of other ecosystem processes (Knapp et al. 1999).

 

1.2. Ecology and Natural Resource Teaching Area (ENRTA) site description

The ENRTA is a 180-acre preserve located in the southern reaches of the post oak savanna ecoregion in College Station, Texas (Fig. 1). The preserve is under the management of the Department Ecosystem Science and Management at Texas A&M University.  The ENRTA is part of a larger, 1000-acre experimental range owned by Texas A&M University near campus in the west central portion of Brazos County, Texas (30°34’46″N, 96°21’47″W). The preserve is a mosaic of savanna, forest, and grasslands which is home to several A&M facilities, including a field laboratory, teaching pavilion, mechanical shop, greenhouses, and a physics observatory. The ENRTA currently functions as a teaching and research environment for Texas A&M faculty, staff, and students.

The climate at the site is semi-arid, with hot summers and mild winters. Mean annual temperature is 20°C, with mean high temperatures ranging from 36°C in July to 10°C in January. Mean annual precipitation is 101.8 cm, with most falling in spring and the least in summer. The terrain is relatively flat, frequently cut by large actively eroding gullies. Soils are deep, somewhat poorly drained fine sandy loams of the Boonville series and have both low fertility and water permeability. The preserve is mainly comprised of post oak savanna, and also includes seasonal wetlands, riparian woodlands along White Creek, two sizeable ponds, and several remnant prairies.

 

1.3 Restoration importance

The ENRTA and surrounding range are highly suitable for environmental conservation as it provides a habitat island for many bird, mammal, reptile, and fish species in a heavily urbanized and cultivated part of Brazos County. The rich diversity of species found in savanna habitats makes the identification, preservation, and management of remnants critical for conserving the biodiversity of the North American prairie-forest transition zone; the fragmentation and conversion of open savannas to closed woodland or cultivated land upon settlement has led to oak savannas being among the rarest plant communities in the world (Taft 1997). The land use history the ENRTA is representative of the fate of much of the prairie-forest transition zone. Prior to its acquisition by the university in 1946, the area had been cultivated for the farming of cotton and ranching of cattle; overgrazed and depleted of soil productivity, the land was subsequently abandoned (Anderwald 1949). Decades of undesirable management practices had left the land overrun with undesirable species and the soil, lacking proper nutrient and water cycling, unsuitable for many native plant species and prone to erosion. After the university took over, the land was managed for education and research in agricultural range management, which, while more beneficial for the diversity of the savanna than abandonment, was not actively seeking the restoration of this rare plant community.

Shifts in the academic climate at the university led to the removal of cattle and the focus at the ENRTA shifting towards management for ecosystem conservation. The ENRTA has the potential to act as a habitat island in the sea of anthropogenic activity, preserving rare and endemic species threatened by the expansion of human activities (Caughley 1994). Capturing the dynamic spatial heterogeneity of savanna ecosystems within narrow preserve boundaries will be particularly challenging in such a fragmented landscape; intensive management will be required to restore species diversity, and prescribe fire, the primary management tool, lacks the natural spatial heterogeneity of the landscape-scale fires which formed the savanna (White and Bratton 1980, Stritch 1990). However, with the association between the ENRTA and Texas A&M University, as well as its location in a highly threatened ecosystem, these challenges provide a unique opportunity for research, education, and the development of protocols for the restoration of degraded savanna communities which could have lasting impacts in the field of conservation biology.

2. Restoration goals

The primary restoration goal for the Ecology and Natural Resource Teaching Area is:

• to rehabilitate degraded areas into diverse communities of the Texas post oak savanna ecoregion.

The secondary restoration goals (where compatible with the primary goal) are:

• to recreate oak savanna, prairie, wetland, and forest communities typical of the post oak savanna ecoregion similar to those expected to have occurred historically in the area.
• to increase plant species diversity and richness through the establishment of locally rare or extirpated species found in comparable, healthy ecosystems.
• to increase use of the area by wildlife through the creation and maintenance of natural habitats.
• to control or eradicate invasive plants and animals which would threaten the restored ecosystems.
• to facilitate use of the ENRTA by the public as well as Texas A&M faculty, students, and staff by:
  • meeting the needs of students, faculty, and staff for education and research.
  • providing public outreach focusing on education through community interaction.
  • improving site accessibility with redesigned parking and trail systems.
  • increasing awareness of the ENRTA through enhanced communication and online presence.

3. Action plan

3.1 Conservation protocol

The protocol which will be used to restore the post oak savannas has been adapted from McCarty (1998). Conservation will happen in two phases: restoration and maintenance. Restoration is the attempt to restore functioning ecosystems from degraded remnants of the original. Maintenance is the preservation of functionality within natural or restored ecosystems. Species diversity, richness, and the presence of conservative species can be used as indicators of restoration success, as they all were characteristically high in savannas.

The basic procedure for restoring existing savanna ecosystems has two parts: first, the mid-stories must be reopened, and second, a fire regime needs to be reinstated (i.e. thin and burn). By reducing the density of woody species in the mid-story, the conditions become favorable for suppressed forbs and grasses in the understory to grow and propagate. Reinstating a fire regime protects the reviving plants from competition by the more fire sensitive woody mid-story species. The fire regime must be designed such that it maintains an open mid-story, stimulates the reproduction and development of the herbaceous community, and remove accumulated litter which would smother sites for herbaceous establishment (Nielsen et al. 2003). As fire is returned to this fire-dependent ecosystem, development progresses through somewhat predictable stages. The first phase is dominated by woody shrubs, which is the normal beginning state for savannas having several decades of pastoral grazing and fire exclusion. In the second phase, the woody mid-story species remain, but forbs and grasses will begin to increase, developing a vigorous herbaceous understory often dominated by a few less desirable species. The final phase accompanies the development of a diverse herbaceous community, including more conservative species, dominated by grasses, sedges, and forbs (Mccarty 1998).

3.2 Four restoration actions for the ENRTA

1. Reintroduce disturbance (i.e. thin and burn)

The Texas post oak savanna was formed and maintained by two major disturbances: migratory herds of grazing bison and periodic fires. In the absence of natural disturbances, what used to be savannas and prairies have undergone intense thicketization, turning the more open savanna into dense woodland. Savannas and prairies can be recreated in these areas if encroaching woody biomass can be reduced (thinning) and subsequent growth suppressed (burning). Thinning will consist of using various mechanical (i.e. chainsaw, grubbing) and chemical (i.e. foliar spray, basal spray) means; once the woody biomass has been sufficiently reduced, burning will be reintroduced to the landscape in the form of prescribed fire, in order to maintain woody suppression and promote the development of the herbaceous community.

2. Stabilize soils at risk due to erosion

The intensive agricultural and ranching activities which occurred in the area prior to its acquisition by the university led to a steep decline in soil fertility and stability. The soils generally consist of sandy topsoils over a clay subsoil; these are by nature unstable and prone to erosion when the protective vegetation cover is decreased or removed (Anderwald 1949). This instability is subjected to intense runoff load from impermeable surfaces on campus and Easterwood Airport which flows through the ENRTA, which has led to deep channel and gully formation. Precipitation events result in local sheet, rill, and gully erosion from increased runoff and loss of vegetation-induced soil stability. The soil instability threatens to undermine any actions taken to remediate the plant communities. Therefore, efforts need to be taken to preserve the integrity of the soil structure. Sites where there is active gully formation or sheet and rill erosion need to be addressed by controlling water flow above the site, stabilizing the soil in the affected area, and establishing vegetation into the eroded soils. Overland water flow through the ENRTA also needs to be managed, with the installation of pipes, rock vanes, and other channeling structures as necessary to prevent further damage to streambanks, surrounding soils, and existing infrastructure.

3. Invasive species identification, eradication, and control

Upon its acquisition, the cultivated land in the ENRTA was dominated by undesirable weedy and invasive herbaceous species. Various treatments have been applied since then, with varying degrees of success, but invasive species will continue to be a problem due to the fragmentation, urbanization, and general poor health of the ecosystem and its surroundings. Invasive species reduce biodiversity and pose a threat to the restoration of stable and diverse savanna communities. Following the identification of an invasive species, there are two options for management: eradication or control. Eradication is the preferred option, but is only viable during the early stages of invasion. It will be done through mechanical and chemical treatments or habitat management, depending on the target species. Where eradication is infeasible, the remaining management alternative is control, which seeks to reduce the density and abundance of the invasive organism to beneath an acceptable threshold (Wittenberg and Cock 2001). Repeated assessments will be done to ensure that new invading species are identified and managed before they become permanently established.

4. Recover and reintroduce native species

In addition to invasive species management, the development of diverse communities will be facilitated through the establishment and growth of native species. Ideally, habitat management will allow natural regeneration via the seed bank. However, as the seed bank at the ENRTA may have decreased species diversity, richness, and composition due to the historical plant community, the seeding or planting of native grasses, forbs, and shrubs will occur as necessary. Species selected for importation will be chosen from plants which are a part of healthy post oak savanna ecosystems.

3.3 Restoration agenda

These four restorative actions will be applied to the ENRTA wherever necessary to achieve the primary and secondary restoration goals. To facilitate the planning of restorative and maintenance actions, the ENRTA has been divided into three management units (Fig. 2). The boundaries for these management units were selected based on a combination of property lines, natural and artificial barriers (i.e. roads, White Creek), existing plant communities, and similarity of necessary management actions. The management units encompass the entirety of the ENRTA as well as extending beyond its borders along natural barriers into lands which are a part of the TAMU Experimental Range Area, as natural ecosystems do not recognize human-established boundaries. The names and descriptions of each unit, as well as the general timeline for restoration, can be found in detail below.

Figure 2 Map of the restoration plan of the Ecology and Natural Resource Teaching Area (ENRTA) by unit. The ENRTA boundaries are in black. Post Oak unit is shaded blue, Riverwood unit is shaded white, and Whiterun unit is shaded red.

3.3.1. Post Oak Unit

The Post Oak Unit encompasses the northern half of the ENRTA. It is the smallest of the three units at 55 acres. The unit primarily consists of degraded upland post oak savanna, with an overstory of post oak (Quercus stellata) and other brush species, including eastern juniper (Juniperus virginiana), Chinese privet (Ligustrum sinense), and yaupon holly (Ilex vomitoria). The area has undergone intense thicketization to the point where large, open areas are rare, except for one on the southern side. The unit is bounded on all sides by either paved or gravel roads. Special considerations will need to be taken during restoration for a pond on the southwestern edge and a seasonal drainage creek which runs along the length of the unit from north to south, ending in a wetland near the southeastern edge.

The Post Oak Unit will be the initial focus for restoration efforts; this is due to its small size, relative uniformity of restoration actions required, well defined boundaries, and the fact that it is the first area seen upon entering the ENRTA. The objective is to turn this unit into a demonstration post oak savanna. To accomplish this, it will require the removal of the brush which has encroached into the open areas surrounding the oak mottes. This will be accomplished via mechanical removal both with equipment and by hand followed by herbicide application. Once the woody biomass has been sufficiently reduced, routine prescribed fire will be reintroduced to the unit to suppress the growth of woody species and encourage the development of the herbaceous community.

The pond on the south side is used by faculty and students for teaching and research; it also provides habitat for a variety of animal species. As such, it will be maintained and protected from nutrient or chemical inputs resulting from management activities. The seasonal creek drains the surrounding unit as well as the airport to the north; thus, it is dry for most of the year but responds very quickly to any precipitation. There is substantial erosive activity along much of the waterway, with some spots cutting ravines twenty feet deep into the ground. Precautions need to be taken not to destabilize the soil surrounding the creek when restoring this unit. Actions should also be taken to stabilize the overland water flow to limit damage to restored areas and seasonal wetland via erosion. The wetland is currently poorly accessible and littered with debris (wooden frames, chunks of cement and rock); as such, cleaning up the area and improving accessibility needs to happen before further restoration efforts can be taken.

3.3.2. Riverwood Unit

The Riverwood Unit encompasses much of the southern half of the ENRTA as well as the neighboring woodland running along White Creek. It is the largest of the three units at 88 acres. The unit consists of a mix of prairies and wooded areas in a gradient of lowland forest to upland savanna, all overgrown with brush. The unit is bounded by gravel roads on the north and west sides, White creek along the lengthy south side, and the property line on the east side. Special considerations will need to be taken during restoration around White Creek, a pond along the western edge, power lines running through the unit, two large gullies forming in open areas, and the lighted approach to Easterwood Airport.

The restoration of the Riverwood Unit will follow Post Oak Unit. The heterogeneity of plant communities, difficulty of terrain, large number of obstacles to restoration, and large size make this unit more difficult to manage than Post Oak Unit. The objective is to rehabilitate the variety of plant communities in this unit to create a diverse landscape for education, research, and community involvement. To accomplish this, encroached oak savannas will be restored using protocols developed in the restoration of Post Oak Unit. In the open prairies, woody growth will be suppressed using fire, mechanical, and chemical treatments to ensure these areas remain open.

Before significant time or resources can be spent rehabilitating the riparian and lowland forests near White Creek, the systemic problems associated with flashiness and water quality need to be addressed, otherwise any restoration efforts area at risk of being damaged or destroyed. As the source of these problems originates outside of the TAMU Experimental Range and the effort required to address them enormous, restoration of the lowlands and riparian areas may be limited. The pond and its surrounding vegetation will be maintained, as it provides habitat for many bird and fish species. Chinese tallow (Triadica sibifera) is beginning to invade around the pond’s edge and will be eradicated. Texas A&M University’s Physical Plant periodically mows the areas beneath the power lines and in the approach to Eastwood Airport to keep them free of woody species. Any additional management actions in these areas would need to conform to the current management plan. There are several large gullies in this unit which are in the early stages of being treated; management of these gullies will progress until they are stabilized.

3.3.3. Whiterun Unit

The Whiterun Unit encompasses two small sections of the ENRTA, on the northern and southern side of the property, as well as a large section of heavily disturbed and developed land bordering the ENRTA. It is nearly as large as the Riverwood Unit at 87 acres. The unit contains several Texas A&M facilities, including the ENRTA Field Lab, Physics and Astronomy Teaching Observatory, ESSM greenhouses, parking lots, and waste water treatment pipelines, interspersed with patches of grassland and forest. The unit is bounded by gravel roads running the length of the east side, extending from the ENRTA property line north to south; the western edge runs along a gully which used to be White Creek in the southern half and along fence-line in the northern half. Special considerations will need to be taken during restoration for the various facilities in this unit as well as several sites of severe erosion.

The objectives for this unit are to restore the fragmented patches into diverse savanna and prairie communities wherever possible and to preserve areas at-risk due to erosion. The grassland and savanna patches will be restored using techniques developed in the restoration of the other two units, though the use of fire will be limited by proximity to existing facilities. Restoring these patches is a lower priority than the savanna and prairie restorations in Post Oak and Riverwood units. Erosion control will begin immediately and occur as needed throughout the restoration project. A comprehensive erosion management plan will be designed according to the ‘Ten Commandments of Erosion and Sediment Control’ (Waikato Regional Council, 2009, Table 1).

Table 1: The ‘Ten Commandments’ for preparing an erosion control plan

1	Minimize disturbance	6	Install perimeter controls
2	Stage construction	7	Employ detention devices
3	Protect steep slopes	8	Training and experience
4	Protect watercourses	9	Make sure the plan evolves
5	Stabilize exposed areas rapidly	10	Assess and adjust

 

3.4 Responsibilities

The Ecology and Natural Resource Teaching Area manager (Jake Gaster) is responsible for implementing this ecological restoration plan. The work will be carried out or supervised by the ENRTA manager, with the help of student workers and/or volunteers. All work will be accountable to department head of the Ecosystem Science and Management (ESSM) department of Texas A&M University (Dr. Katy Kavanagh). ESSM faculty will provide specialist technical advice and assistance, including the planning for and permitting of prescribed burns, to assist with the realization of restoration goals. The resources required for this project will be provided by the ESSM department.

 

References

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