State 1
Savannah State - Reference

Community 1.1
Oak Savannah/Tallgrass Community

Figure 9. 1.1 Oak Savannah/Tallgrass Community

The Oak Savannah/Tallgrass Community (1.1) is the reference community and is characterized as a live oak savannah with 30 to 35 percent woody species canopy cover. Live oak dominates the overstory. Texas oak (Quercus buckleyi), scrub oak (Quercus sinuata var. breviloba), sumacs (Rhus spp.), elm (Ulmus spp.), and hackberry (Celtis spp.) can also be important overstory species. Both percent species composition by weight and percent canopy cover are used in this ESD. Most observers find it easier to visualize or estimate percent canopy for woody species (trees and shrubs). Canopy cover drives the transitions between community and states because of the influence of shade and interception of rainfall. Species composition by weight remains an important descriptor of the herbaceous community and of the community as a whole. Woody species are included in species composition for the site. Calculating similarity index requires use of species composition. Little bluestem dominates the herbaceous component of the site. Other important grasses are sideoats grama, big bluestem, Indiangrass, green sprangletop (Leptochloa dubia), tall grama (Bouteloua hirsuta var. pectinata), slim tridens (Tridens muticus), tall dropseed (Sporobolus compositus), and silver bluestem (Bothriochloa laguroides). Forbs commonly found on the site include Maximilian sunflower (Helianthus maximiliani), awnless bushsunflower (Simsia calva), Engelmann’s daisy (Engelmannia peristenia), dotted gayfeather (Liatris punctata), and halfshrub sundrop (Calylophus serrulatus), and bundleflowers (Desmanthus spp.). Other shrub and tree species found in communtiy (1.1) include eastern redbud (Cercis canadensis), species of cherry (Prunus spp.), bumelia (Sideroxylon spp.), elbowbush (Forestiera pubescens), and saw greenbrier (Smilax bona-nox). Ashe’s juniper (Juniperus ashei) was historically restricted to rocky ledges and shelves, where it was protected from fire. Prior to settlement, this site functioned as a shifting mosaic with shrub-dominated areas expanding until a catastrophic fire killed woody species and opened areas for grasses and forbs. The site would recover to a grassland savannah until woody species encroached during longer fire-free periods. After 15-25 years without a fire regime, the site would cross the threshold between the Savannah State to the Shrubland State. This shifting mosaic would continue in a long term cycle. The reference savannah community will transition to the Oak Savannah/Midgrass Community (1.2) with lack of fire, lack of brush control, long-term drought, repeated, long-term growing season defoliation, and/or other repeated critical growing season stresses. The first species to decrease in dominance will be the grasses and forbs with the least shade tolerance and highest moisture requirements (i.e. Indiangrass, big bluestem, and Engelmann’s daisy). This will initially result in an increase in composition of little bluestem. As shrub canopy cover increases, little bluestem will decrease and shade and drought tolerant midgrasses and forbs will increase in composition. The soil surface of this site is characterized by stones and boulders covering 30 to 65 percent of the soil surface. Bare soil composes 10 percent or less of the ground cover. Plant basal cover and litter make up the remainder of the ground cover. The site is well drained with high infiltration and low runoff, despite the steep slope. The shrub canopy will intercept much of the rainfall. Although the stones and boulders on the soil surface increase runoff and lead to the development of water flow patterns, runoff is eventually intercepted by plants within the site. Soils are high in organic matter and the heavy plant cover contributes to increasing organic matter and soil building.

Community 1.2
Oak Savannah/Midgrass Community

Figure 12. 1.2 Oak Savannah/Midgrass Community

The Oak Savannah/Midgrass Community Phase (1.2) typically results from lack of fire over a long period of time (transition 1.1A). During this period, indigenous or invading woody species increase on the site. The site will return to the Oak Savannah/Tallgrass Plant Community (1.1) when brush control (albeit infrequent due to slope) and/or repeated fires allow competition from a vigorous grass component to dominate open savannah areas while shrubs dominate mottes and constitute 35 percent or less woody canopy cover (transition 1.2A). When the Oak Savannah/Midgrass Community (1.2) is continually overgrazed and fire is excluded, the community crosses a threshold (T1A) to a state that is dominated by woody plants, the Mixed-Brush/Midgrass Community (2.1). Important grasses are little bluestem, sideoats grama, silver bluestem, tall dropseed, and Texas cupgrass (Eriochloa sericea). More grazing-resistant shortgrasses and less palatable forbs begin replacing the midgrasses. Some of the perennial forbs persist, but less palatable forbs will increase. Woody canopy varies between 35 and 60 percent, depending on the severity of grazing, fire interval, and availability of increaser shrub species. Numerous shrub and tree species will continue to increase because shrub canopy intercepts rainfall and creates drier growing conditions for understory species, reducing their vigor and competitiveness. Typically, trees such as oak (Quercus spp.), elm, hackberry, and ash (Fraxinus spp.) will increase in size, while other tree and shrub species such as bumelia, sumac (Rhus spp.), elbowbush, agarito (Mahonia trifoliolata), honey mesquite, juniper, and pricklypear (Opuntia spp.) will increase in density. The composition of hardwood species tends to increase on north and east aspects while west and south aspects favor softwood species. To control woody species populations, prescribed grazing (browsing) and fire can be used to control smaller shrubs and trees, and mechanical removal of larger shrubs and trees may be necessary in older stands. The time frame for woody species to dominate a healthy community is unknown, but reference sites indicate re-growth of woody species reached 75 percent canopy cover in about 25 years. Fire and brush control are difficult to use on this site. Examples exist of restoration using strategic burning with small fires. Chemical control may require hand spraying or aerial application to create openings in a closed shrub canopy. It may take several years to achieve change, depending upon growing conditions and the aggressiveness of treatment. Large scale fires historically burned this site only during hot, dry, windy conditions. Large scale prescribed fires require careful fuel management and generally involve burning this site at the same time as surrounding more productive sites with plentiful fine fuels. The transition 1.1A will result in an increase in bare ground, shrub density, and length of water flow patterns, in addition to decreased infiltration. Heavy continuous grazing will reduce plant cover, litter, and mulch. Litter and mulch will move off site as plant cover declines. Ashe’s juniper is a particularly aggressive shrub on this site. Once the midgrasses decrease below 25 percent of composition, woody species cover exceeds 60 percent canopy cover, and the woody plants within the grassland portion of the savannah reach fire-resistant size (about 3 feet in height), the site crosses a threshold into the Shrubland State (2) and the Mixed-Brush/Midgrass Plant Community (2.1). Until the Oak Savannah/Midgrass Plant Community (1.2) crosses the threshold (T1A) into the Mixed-Brush/Midgrass Community (2.1), this community can be managed back toward the reference community (1.1) through the use of cultural practices including strategic burning and strategic brush control. Once invasive woody species become established, returning fully to the reference is difficult, but it is possible to return to a similarly functioning plant community. The risk of soil erosion under shrub canopy is much less than deeper sites due to shallow soil depths. The large fragments that cover 35 – 65 percent of the soil surface provide numerous interruptions to waterflow that reduces the opportunity for soil to flow off site. Unlike sites with deeper soils, changing management practices (improving grazing management and controlling brush) can create sufficient change in growing conditions for the site to follow restoration pathway R2A to the Savannah State within a reasonable time frame.

Pathway 1.1A
Community 1.1 to 1.2

Oak Savannah/Tallgrass Community

Oak Savannah/Midgrass Community

The Oak Savannah/Tallgrass Plant Community will shift to the Oak Savannah/Midgrass Plant Community when there is continued growing season stress on palatable grass species. These stresses include: lack of fire, lack of brush control, long-term drought and/or other repeated critical growing season stress. Increaser species (midgrasses and woody species) are generally endemic species released from competition as vigor of tallgrasses declines. Woody species canopy exceeding 35% and/or dominance of tallgrasses falling below 50% of species composition indicate a transition to the Oak Savannah/Midgrass Plant Community. Presettlement, this site was dependent on fire to maintain the savannah’s balance of grass and shrubs. Currently, fire and/or brush management are required to maintain the reference community. Due to the infrequent and irregular nature of fire presettlement, one can theorize the site transitioned between the two communities within the Savannah State, and even across the threshold to the Shrubland State, under natural influences. This site would be less stable than the surrounding prairie sites. The driver for this transition is increasing canopy cover of woody species. Contemporarily this transition is often driven by introduction and expansion of invasive shrubs. Cattle grazing management tends to not drive this transition, as the site is not well suited to cattle grazing due to steepness and rockiness. Examples exist of Steep Rocky sites that were overgrazed by cattle, particularly less steep slopes and areas when access to more favorable sites was limited. The driver for community shift 1.1A for the herbaceous component is improper grazing management on sites with grazing. On ungrazed or lightly grazed sites increased competition from invader midgrasses and forbs and increasing shrub cover drive herbaceous shifts. The driver for the woody component is lack of fire and/or brush control.

Pathway 1.2A
Community 1.2 to 1.1

Oak Savannah/Midgrass Community

Oak Savannah/Tallgrass Community

The Oak Savannah/Midgrass Plant Community will return to the Oak Savannah/Tallgrass Plant Community under grazing management that provides sufficient critical growing season deferment in combination with proper grazing intensity as long as the seedbank or seed source is still present. Favorable moisture conditions will facilitate or accelerate this transition. The understory component may return to dominance by tallgrasses in the absence of fire, however, reduction of the woody component to reference conditions of 35% or less canopy cover will require inputs of fire and/or brush control. Due to the steepness of the site, brush control may be limited to hand work or chemical control using aerial or all-terrain vehicle (ATV) application because site conditions hinder use of heavy machinery. The driver for community shift 1.2A for the herbaceous component is proper grazing management. The driver for the woody component is fire and/or brush control. Brush control can also benefit tallgrasses and drive community shift 1.2A for the herbaceous community.

State 2
Shrubland State

Community 2.1
Mixed-Brush/Midgrass Community

Figure 15. 2.1 Mixed-Brush/Midgrass Community

The Mixed-Brush/Midgrass Community (2.1) presents a 60 percent woody plant canopy, with live oak as the dominant species within the oak mottes and honey mesquite and juniper invading the former grassland areas. The community loses its savannah appearance with invasive shrubs beginning to fill the open grassland portion of the savannah. The oak mottes remain, but are no longer the only areas with trees. This community type is the result of lack of fire and accompanying increase in shrub canopy cover. Alternatively, groups of Ashe’s juniper can replace oak mottes. Much of MLRA 85 was cleared of hardwoods around 1900. Hardwood species were also impacted by overgrazing by sheep and goats in the early 1900s. After the hardwoods were harvested, re-growth was primarily by juniper. These dense juniper stands are commonly referred to locally as “old growth cedar” or “cedar brakes”. These juniper stands can occur in either the Mixed-Brush/Midgrass community (2.1) or Mixed-Brush Shrubland community (2.2) depending on the composition of the understory. Canopy cover of these juniper stands can reach 80 percent. Once juniper stands have become dense and extensive, it is difficult to reestablish oaks. Although difficult, managers can restore the grassland openings within the shrubs through properly executed brush management. The degree of treatment depends upon practicability. The success of reestablishment of desirable native grasses and forbs is dependant upon soil being left when juniper are removed. Brush removal that leaves the thin layer of soil can increase the likelihood of success of reseeding efforts. Reclamation success is often dependant on the skill of those removing brush. The slope of this site makes restoration a difficult practice and often limits the size of restoration operations. In areas where high deer densities occur, heavy browsing can decrease preferred woody plants. There is a continued decline in diversity of the grassland component and an increase in woody species such as sumac. Unpalatable forbs such as western ragweed (Ambrosia psilostachya) increase in species composition. Annual herbage production decreases due to a decline in soil structure and organic matter and has shifted toward the woody component. All unpalatable woody species have increased in size and density. Honey mesquite is an early increaser throughout the MLRA. Redberry juniper (Juniperus pinchotii) occurs only in the southern counties of the MLRA and eastern redcedar (Juniperus virginiana) occurs only in the northern portion. Ashe’s juniper occurs mostly in the southern portion, but can be found throughout the MLRA. Many of the reference community (1.1) shrubs are still present. Sideoats grama and other reference community (1.1) midgrasses decrease to the point that grasses no longer form the dominant component. Shortgrasses/grasslikes such as low panicums (Panicum spp.) and threeawns (Aristida spp.) increase. Remnants of the reference community (1.1) grasses and forbs along with unpalatable invaders occupy the interspaces between trees and shrubs. Cool-season species such as Texas wintergrass (Nassella leucotricha) and sedges (Carex spp.) can be found under and around woody plants. Plant vigor and productivity of the grassland component is reduced due to competition for nutrients and water from woody plants. Common herbaceous species include tall grama, and Mexican sagewort (Artemisia ludoviciana ssp. mexicana). Buffalograss (Bouteloua dactyloides), western ragweed, and curly-mesquite (Hilaria belangeri) are persistent increasers until shrub density reaches maximum canopy. As the grassland vegetation declines, more soil is exposed, leading to crusting and erosion. Due to the shallow depth to limestone bedrock and steep slope, erosion can be severe. Higher rainfall interception losses by the increasing woody canopy combined with increased evaporation and runoff can reduce the effectiveness of rainfall. Soil organic matter and soil structure decline within the interspaces, but soil conditions improve under the woody plant cover. Soil loss can occur during rainfall events. Excessive grazing by other deer or goats will create a community dominated by large trees. Few remnant midgrasses and opportunistic shortgrasses, annuals, and perennial forbs occupy the woody plant interspaces. Characteristic grasses are threeawns and cedar sedge (Carex planostachys). Grasses and forbs make up as little as 5 percent of annual biomass production. Excessive cattle grazing tends to create a different response and structure to the community than does excessive deer or goat grazing. Excessive cattle grazing tends to accelerate invasion of shrubs because it creates conditions where young shrubs increase in vigor and size while palatable grasses decrease in vigor and abundance. Excess deer or goat grazing tends to create a dominance of large trees by removing both young shrubs and the young growth that grows below the browse line on larger shrubs and trees. While large trees will continue increase in size, they will have very little production below the browse line. The site becomes dominated by large trees with little forage available for livestock or wildlife. Large trees with little understory provide much less soil protection than do dense stands of grass. As soils erode, understory species have reduced potential to revegetate the site. The bare area under the browse line creates a situation that provides poor forage conditions and poor visual cover for wildlife. Annual primary production is approximately 700 to 2000 pounds per acre. In this plant community, annual production is balanced between herbaceous plants and woody species. Browsing animals such as goats and deer can find fair food value if browse plants have not been grazed excessively. Forage quantity and quality for cattle is low. Unless brush management and proper grazing management are applied at this stage, understory composition will continue to shift towards shortgrasses and unpalatable forbs, causing the community to convert to the Mixed-Brush Shrubland Community (2.2). Aggressive shrubs (such as juniper) can facilitate this shift even under proper grazing management.

Community 2.2
Mixed-Brush Shrubland Community

Figure 18. 2.2 Mixed-Brush Shrubland Community

The Mixed-Brush Shrubland Community (2.2) is the result of many years of improper grazing management, lack of periodic fires, and/or lack of proper brush management. Oaks, honey mesquite, and/or juniper dominate the Mixed-Brush Shrubland Community (2.2), which has greater than 60 percent woody canopy cover and little or low understory production. It is now essentially a dense shrubland with remnant grasses, sedges, and forbs under the canopy and within interspaces. As brush canopy increases, annual production for the understory declines to very low levels, due to shading, competition for nutrients, and interception of rainfall by the shrub canopy. Most of the remaining understory is shade tolerant, grazing tolerant, and/or unpalatable. Common understory shrubs are pricklypear, agarito, sumacs, and elbowbush. Grazing pressure generally becomes less of a factor once the community has reached this stage, particularly if junipers have replaced shrubs with browsing value. Canopy cover will increase until the site is covered with a dense stand of brush. Juniper stands may become so dense as to provide little wildlife browsing or cover. Reference sites demonstrate that the Steep Rocky site is highly resilient when brush control is accompanied by favorable growing conditions. Because soils on this site are shallow to very shallow even at reference conditions, erosion is not severe under shrub canopy. Additionally 35-65 percent of the soil surface is covered with large fragments (stones, boulders, and limestone outcrops) which create favorable microsites for seed germination in the spaces between the rocks. If remnant plants are present, aggressive tallgrasses such as big bluestem, little bluestem, and Indiangrass reestablish and increase following brush control or fire accompanied by grazing deferment. Remnant grasses are protected between the rocks so that once the overstory is removed, they can express themselves. Cleared sites frequently re-grow to dense juniper stands that can reach 75 percent cover in approximately 25 years unless juniper control measures are taken. These dense stands of juniper can reach 80 percent canopy cover with an understory that is primarily cedar sedge with trace amounts of reference community species. The shrub canopy acts to intercept rainfall and increase evapotranspiration losses and interception losses, creating a more xeric microclimate. Soil fauna and organic mulch are reduced, exposing more of the soil surface to erosion in interspaces. The percent of exposed limestone bedrock increases with erosion. However, within the woody canopy, hydrologic processes stabilize and soil organic matter and mulch begin to increase and eventually stabilize under the shrub canopy. The Mixed-Brush Shrubland Community (2.2) provides good habitat cover for wildlife, but only limited forage or browse is available for livestock or wildlife. At this stage, highly intensive restoration practices are needed to return the shrubland to grassland. Alternatives for restoration include: brush control and range planting, proper stocking, prescribed grazing, and prescribed burning following restoration to maintain the desired community.

Pathway 2.1A
Community 2.1 to 2.2

Mixed-Brush/Midgrass Community

Mixed-Brush Shrubland Community

Without fire (natural or human-caused) and/or brush control, woody density and canopy cover will increase in the Mixed-Brush/Midgrass Plant Community until it converts into the Mixed-Brush Shrubland Plant Community. Improper grazing management and/or long-term drought (or other growing season stress) will accelerate this transition. Due to the shallow nature of the soils, woody species (particularly live oak and juniper) may die off under severe drought conditions. This may facilitate a transition back to the Savannah State by providing canopy openings for grass cover to increase when favorable growing conditions return. While woody species canopy may continue to increase, the indicator for this transition is the change of the understory from domination by midgrasses to a sparse understory of shortgrasses and unpalatable forbs. There may be areas under dense shrub cover with almost no understory. Improper grazing management or other long-term growing season stress can decrease the composition of midgrasses and palatable forbs in the herbaceous component. Even without grazing, in the absence of fire, the woody component will increase to the point that the herbaceous component will shift in composition toward shortgrasses and forbs suited to growing in shaded conditions with little available soil moisture. The driver for community shift 2.1A is lack of fire and/or brush control.

Pathway 2.2A
Community 2.2 to 2.1

Mixed-Brush Shrubland Community

Mixed-Brush/Midgrass Community

Brush management and/or fire can create great openings in the canopy so that remnant midgrasses and shade intolerant forbs can increase in vigor and composition. Large groups of dense forbs may remain with stands of good herbaceous growth in the openings of shrub canopy. Continued fire and/or brush management will be required to maintain openings in the canopy. Fire management is challenging on this site, particularly on steeper slopes, which may burn only during wildfire conditions. Prescribed fire requires special precautions and prudence due to difficulty in both carrying a fire and controlling the fire once moving. This site is usually in small spot treatments or burned along with adjacent ecological sites. If the herbaceous component has transitioned to shortgrasses and low forbs, proper grazing management (combined with favorable moisture conditions) will be necessary to facilitate the shift of the understory component to the midgrass-dominated Mixed-Brush/Midgrass Plant Community. Range planting may accelerate the transition of the herbaceous community, particularly when combined with favorable growing conditions. However, range planting is very difficult on the Steep Rocky site and will be limited to hand seeding of small areas or ATV broadcasting due to the steepness and rockiness of the site. Range planting is more commonly associated with restoration efforts associated with Restoration Pathway R2A. The driver for community shift 2.2A is fire and/or brush control.

Transition T1A
State 1 to 2

While the Savannah State has some resistance to shrub dominance, long-term lack of fire or brush control will allow brush to dominate the site even under proper grazing management. Shrubs make up a portion of the plant community in this state, therefore propagules are present. The mean fire return interval to maintain the Savannah State is 5-10 years. Even with proper grazing management and favorable climate conditions, lack of fire for 15-25 years will allow woody species to increase in canopy to reach the 60% threshold level. An infusion of invasive species (i.e. juniper or mesquite) will speed up the process. Improper grazing management, prolonged drought, and a warming climate will provide a competitive advantage to shrubs which will accelerate this process. Tallgrasses will decrease to less than 5% species composition. This transition can occur from any of the Grassland State Communities. The driver for Transition T1A is lack of fire and/or brush control. The Grassland State is always at risk for this transition because woody species are present in the grassland plant community. Introduction of aggressive woody invader species (i.e. juniper) increase the risk that this state transition will occur and accelerate the rate at which it is likely to occur.

Restoration pathway R2A
State 2 to 1

Restoration of the Shrubland State to the Savannah State requires substantial energy input. Mechanical or herbicidal brush control treatments can be used to remove woody species. A long-term prescribed fire program may sufficiently reduce brush density to a level below the threshold of the Savannah State, particularly if the woody component is dominated by species that are not re- sprouters. Brush control in combination with prescribed fire, proper grazing, and favorable growing conditions may be the most economical means of creating and maintaining the desired plant community. If remnant populations of tallgrasses, midgrasses, and desirable forbs are not present at sufficient levels, propagules from adjacent sites are frequently necessary to restore reference community species. Range planting will be limited to hand or ATV broadcasting due to the steepness and rockiness of the site. The driver for Restoration Pathway R2A is fire and/or brush control combined with restoration of the herbaceous community and proper grazing management. Restoration may require aggressive treatment of invader species.