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Comparison of native brushland, replanted, and unaided secondary succession plant communities in the Lower Rio Grande Valley of Texas.

Abstract

Agriculture and urban development have destroyed 95% of native brushland habitat in the Lower Rio Grande Valley (LRGV) of south Texas. Therefore, habitat restoration is an important issue in the LRGV. Since 1982, the U.S. Fish and Wildlife Service has been replanting areas in the LRGV to native brushland species to establish a wildlife corridor along the lower reach of the Rio Grande. Vegetation composition of a mature brushland, a replanted habitat and an unaided secondary succession site (fallow field) were examined at one locale in the LRGV in 1999. The mature brushland edge plot had the highest species richness (43) followed by the replanted edge plot (37), mature brushland interior (35), replanted interior plot (33) and fallow field interior (12) and edge (11) plots. Edge and interior plots in the same habitat were similar in species composition (mature brushland, 74%; replanted, 63%; fallow field, 70%). Community similarity was greater for mature brushland and replanted habitats (47%) than th e mature brushland and fallow field (32%), or the replanted and fallow field habitats (28%). These data suggest that current replanting techniques used by the U.S. Fish and Wildlife Service in the LRGV achieve a more diverse plant community in a shorter length of time than unaided secondary succession of fallow fields.

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The Lower Rio Grande Valley of Texas (LRGV) marks the northernmost extension of the range of many tropical species of flora and fauna (Blair 1950; Oberholser 1974; Jahrsdoerfer & Leslie 1988; Lonard & Judd 1993). Since 95% of the LRGV native brushland has been destroyed (Purdy 1983; U.S. Fish and Wildlife Service 1985) and as existing sites of brushland are fragmented among a landscape of agricultural and urban development, habitat restoration is necessary to sustain the brushland ecosystem of the region. Herein, the term mature brushland is used to describe an undisturbed thorn woodland. These south Texas plant communities are commonly referred to as brushlands (Scifres 1980; Scifres & Hamilton 1993).

The vegetation of the LRGV is well known (Clover 1937; Correll & Johnston 1970; Judd et al. 1977; Vora 1990; Vora & Jacobs 1990; Vora & Messerly 1990; Lonard et al. 1991; Lonard & Judd 1993; Wright 1996; Ewing 2000), but studies that have examined brushland succession in the LRGV are meager (Johnston 1963; Vora & Messerly 1990; Judd et al. 2002). Brushlands in the LRGV are typically dominated by native species such as Fraxinus berlandieriana, Ulmus crossifolia, Celtis laevigata, Chloroleucon ebano, Ehretia anacua or Prosopis glandulosa with ground layers dominated by Chromolaena odorata, Rivina humilis, Malpighia glabra, Setaria leucopila or Panicum maximum.

Current land management initiatives of the U.S. Fish and Wildlife Service (USFWS), Texas Parks and Wildlife Department (TPWD) and The Nature Conservancy of Texas (TNC) focus on the objective of acquisition of brushlands and restoration of degraded habitats in LRGV. Brushland restoration techniques were first used in the LRGV by TPWD in 1958 to establish nesting habitat for white-winged doves (Zenaida asiatica). The USFWS started planting native vegetation in an effort to reestablish a wildlife corridor along the Rio Grande in the LRGV in 1982 (Vora 1992). The LRGV reforestation effort has used two methods, direct-seeding and seedling plantings. Direct-seeding was first used in the LRGV by TPWD in 1959, and by the USFWS throughout the 1980's and until 1995 when seedling-only replanting became the favored technique.

The differences between the replanting methods involve a trade-off between the diversity of the group of plant species to be used, and the amount of time, labor and money required to implement the method. The seedling approach consists of planting 20-47 native brushland species in weed-free agricultural fields. After planting, the area may be irrigated and grass-specific herbicide may be used to prohibit the establishent of invasive grasses. Since 1995, the replanting methods used by the USFWS in the LRGV have produced higher plant survivorship and greater species diversity than in previous years (C. Best pers. comm.).

Although USFWS replants about 325 ha/year with species such as C. laevigata, Leucaena pulverulenta, Chloroleucon ebano, no studies have been published on the post-planting vegetation composition of these areas. Consequently, this study examined the species composition of a mature brushland, a replanted site and an unaided secondary succession site (hereafter fallow field) at one locale in the LRGV.

By providing data on species richness, percent cover and percent similarities of the plant communities, this study will assist land managers in assessing the efficacy of revegetation efforts at hastening brushland succession in the LRGV and it provides one of only two comparative analyses of vegetative cover between a mature brushland, a replanted field and a fallow field in the LRGV (Judd et al. 2002). The following hypotheses were investigated: (1) replanting native plants provided a species composition more similar to a mature brushland than unaided secondary succession on a similar site, (2) species-specific mean percent cover was more similar between mature brushland and replanted areas than between mature brushlands and unaided secondary succession sites in the ground, midstory and over-story layers, (3) there was significantly greater total cover on mature brushland and replanted plots than on fallow fields.

MATERIALS AND METHODS

Study sites are the McManus Unit of the Las Palomas Wildlife Management Area and the La Coma tract of the Lower Rio Grande Valley National Wildlife Refuge in Hidalgo County, Texas, approximately 6 km south of Donna and 1 km north of the Rio Grande (Fig. I). The study sites are managed by TPWD and USFWS, respectively. The McManus Unit is 22 ha of undisturbed native brushland. The banks of a resaca (oxbow channel) from the Rio Grande are evident running approximately north-south through the center of the tract, and the northernmost area of the resaca contained water for most of the year of the study. McManus Unit is separated from the southern portion of La Coma tract by a dirt road bordered by Panicum maximum. Two plots on the McManus Unit served as the mature brushland controls for the study. These plots were located approximately 1300 m south of the wet portion of the resaca.

Two plots were established in the southern portion of the La Coma tract in an area that was replanted with 592 native seedlings per hectare in October 1995. The abundances of the species planted are listed in Table 1. In July 1996, the percent survival of the planted individuals was estimated by USFWS to be 85% (C. Best pers. comm.). The fallow field on the La Coma tract was in agricultural production until 1985 when USEWS purchased the land. Two plots were established in the fallow field on the northeastern portion of the La Coma tract.

Edge and interior plots were randomly located at each site as follows. Edge habitat was a zone of vegetation between two distinct habitats such as brushland and grassland. Edge habitat was defined as a 50 m wide zone along the periphery of each habitat. The interior plot was located within each habitat type more than 80 m from the habitat boundary. Plots consisted of five adjacent and parallel, 50 m line transects that were oriented east to west and separated by 10 m. The west end of the northernmost transect of each plot was permanently marked using a steel t-post to allow for temporal resampling in TPWD and USFWS monitoring programs. Stratifying samples by edge and interior plots within each habitat permitted elucidation of variation in the plant communities.

Vegetation was sampled once at each plot between 3 November 1999 and 2 January 2000. Because on average there is more rainfall in September in the LRGV than in any other month (Jacobs 1981), these months correspond to a time of year when vegetation is lush. Vegetative cover was assessed using the line intercept method (Canfield 1941). Vegetation was separated into three layers. Height ranges were: ground layer < 1.5 m, midstory [greater than or equal to] 1.5 [less than or equal to] 3.0 m, overstory > 3.0 m. Length (cm) of each transect intercepted by vertical projections from plants was recorded for each plant species. Intercepts from fallen or standing woody debris were recorded as large plant debris (pieces [less than or equal to] 2 cm diameter) or small plant debris (pieces < 2 cm diameter).

Cover is the amount of ground occupied by perpendicular projections to the ground from each species. Overlaps of species also were recorded; therefore, in dense vegetation percent cover could exceed 100. The total length intercepted by each species from each of five transects per plot was used to calculate mean cover per plot. The mean of species-specific percent cover from ground, midstory and overstory layers was calculated for each species on each plot and the means that satisfied the assumptions of normality and homogeneity of variances were compared among plots using one-way analysis of variance (ANOVA) followed by Tukey multiple comparisons (Sokal & Rohlf 1995) using the statistical program SPSS (SPSS 1988). Non-normal, heteroscedastic means were transformed using the arcsine function prior to ANOVA tests. Tables, however, are presented using the untransformed means and the standard error of the untransformed means (Sokal & Rohlf 1995). Kolmogorov-Smirnov tests were used to examine mean cover of species among plots when samples could not be transformed to fit assumptions of ANOVA. Differences were considered significant at [alpha] = .01. The mean total cover for each layer was compared using A NO VA and multiple comparisons as explained above. Sorensen's coefficient (Brower et al. 1998) was used to compare species similarity within and among habitats. Taxonomy follows Jones et al. (1997).

RESULTS

The mature brushland edge plot had the highest species richness (43) followed by the replanted edge plot (37), mature brushland interior (35), replanted interior plot (33) and fallow interior (12) and edge (11) plots. Species on plots within the same habitat were similar (mature brushland, 74% similarity; replanted, 63% similarity; fallow field, 70% similarity). While mature brushland and replanted areas shared 23 species, mature brushland and fallow areas only shared 10 species. Similarly, only nine species occurred in both replanted and fallow areas. Analysis of species composition between habitats showed that the mature brushland and replanted habitats were more similar (47%) than the mature brushland and fallow field (32%), or the replanted and fallow field habitats (28%).

Chromolaena odorata dominated the ground layer of the mature brushland plots, contributing 52% of the total cover on the interior plot and 41 % of the total cover on the edge plot. Average percent ground cover of C. odorata was significantly different among plots (F = 19.14, df = 19, P = .0001) with mature brushlands plots having the most ground cover (Table 2). Ground cover of Ehretia anacua was significantly different among plots (F = 7.06, df = 24, P = .001) with the mature brushland interior having significantly more E. anacua than the replanted edge (P = .004) and the fallow edge plots (P = .008). Dicliptera sexangularis also provided a high percentage of cover for the ground layer on the mature brushland edge plot. Panicum maximum was the dominant species in the ground layer of the fallow edge and fallow interior plots and its abundance was significantly different among plots (F = 13.80, df = 24, P = .0001). The ground layer of the replanted edge plot also was dominated by P. maximum whereas the ground layer of the replanted interior plot was dominated by Baccharis neglecta.

Large plant debris provided significantly more ground cover in the mature brushland than in the replanted and fallow habitats (Table 3).

The replanted habitat had large plant debris from Baccharis neglecta, L. pulverulenta and Acacia minuata. Most of the large debris on the fallow plots were from Helianthus annuum and Abutilon incanus while the large plant debris on the brushland plots consisted of a variety of woody species, such as Ulmus crassifolia, P. glandulosa, S. celastrina and C. Iaevigata.

The midstory of the mature brushland edge plot was dominated by Celtis pallida and the midstory of the mature brushland interior plot was dominated by S. celastrina (Table 3). One shrub species, C. odorata, was abundant in the midstory layer of the mature brushland edge plot. Prosopis glandulosa dominated the midstory of the fallow edge plot and fallow interior plot. Baccharis neglecta dominated the midstory of the replanted edge and interior plots.

Ulmus crassifolia dominated the mature brushland edge plot overstory followed closely by C. Iaevigata and S. celastrina (Table 4), whereas P. glandulosa dominated the overstory of the fallow edge plot and fallow interior plot. The replanted edge plot was dominated by L. pulverulenta whereas the replanted interior plot was dominated by B. neglecta. Sideroxylon celastrina dominated the mature brushland interior plot overstory.

While mean percent cover in the ground layer was similar between mature brushland and fallow plots for species such as Clernatis drummondii and Z. obtusifolia, the mature brushland had more similarity in species-specific mean cover with the replanted plots. Mean percent cover of Ehretia anacua, P. glandulosa and Z. obtustfolia also was more similar between mature brushland and the fallow plots in the midstory and overstory layers. Overall, more species-specific similarities were found between the mature brushland and the replanted plots.

Significant differences in mean total percent cover were found among plots in all three habitat layers (ground: F = 14.81, df = 29, P <.001; midstory: F = 17.72, df = 29, P <.001; overstory: F = 13.90, df = 29, P <.001) (Table 5). Mean total percent cover of ground layer was highest for the mature brushland edge plot and the fallow edge plot. The replanted interior plot had the lowest mean total percent ground cover. The mean total percent ground cover of the mature brushland edge plot was significantly higher than the brushland interior plot (P = .002), replanted interior (P < .001) and the fallow interior plot (P < .001). The fallow edge plot had the lowest mean total percent midstory cover. Mean total percent overstory cover was high for the mature brushland edge and mature brushland interior plots and the replanted interior plot and lowest for the fallow plots. The replanted interior plot was significantly higher in mean total percent overstory cover than the fallow edge (P < .001) and interior plots (P = .001).

DISCUSSION

Only two publications (Vora 1990; Judd et al. 2002) quantify cover characteristics of brushland communities in the LRGV. Only Judd et al. (2002) and this study compare cover characteristics between mature brushland, replanted area and secondary succession areas. Such comparative studies are needed to evaluate revegetation efforts in the LRGV.

Judd et al. (2002) examined the species composition, richness and diversity among an undisturbed native woodland, a facilitated succession site (i.e., a naturally revegetated site) and an unaided succession site in Cameron County, Texas. They found higher species richness and diversity of trees and shrubs at the undisturbed woodland compared to the facilitated succession site and the unaided succession site. Their site is the oldest known replanted area in LRGV, but only four woody species were replanted there (Judd et al. 2002). Thus, their site may not be representative of more recent revegetation efforts (i.e., since 1995) although it does provide insight into successional processes that similar replanting treatments may undergo in forty years.

Wright (1996) documented woody plant composition, structure and principal species planted on two revegetated sites in the LRGV, but he did not compare these sites to other stages of habitat development in the LRGV. Young & Tewes (1994) tested the survival and stem characteristics of planted brushland species at Laguna Atascosa National Wildlife Refuge, but did not examine the entire replanted community.

The unaided secondary succession of the fallow habitat had much more time to develop (14 years) into a community representative of mature brushland than the replanted habitat (four years). However, the replanted and mature brushland habitats were more similar in plant composition than either was to the fallow habitat which shows that replanting brushland species establishes a plant community representative of mature brushland more quickly than unaided secondary succession from fallow fields.

Dominance of mature brushland plots by shade-tolerant species such as Chromolaena odorata and Ehretia anacua compared to the shadeintolerant species P. maximum, B. neglecta and Clematis drummondi at the replanted and fallow plots shows that the latter areas are in an early stage of the succession. Prosopis glandulosa, Z. obtusifolia, C. pallida and S. celastrina are established at the fallow plots and may provide more cover in time. How long it may take for tree and shrub cover to approach that of the mature brushland is unknown. Van Auken & Bush (1985) reported that fallow fields in Central Texas, similar to fallow fields in this study, become dominated initially by a shade-intolerant species such as A. minuata or P. glandulosa, but after 25 years become dominated by shade-tolerant species such as C. laevigata. Based on their site in south Texas, Judd et al. (2002) suggest that it will take more than 27 years for a fallow area to become dominated by a shade-tolerant species such as C. Iaevigata.

Dominance of B. neglecta at replanted plots may subside if the areas become dominated by A. minuata or L. pulverulenta. Archer et al. (1988) suggest that P. gLandulosa serves as a nurse plant, assisting in the establishment of other woody species by attracting birds that deposit seeds. In this way, species such as A. minuata, L. pulverulenta and P. glandulosa may serve as successional intermediates to a more diverse and shade-tolerant community representative of an undisturbed mature brushland.

Mature brushland plots in this study had a species composition similar to the riparian vegetation near Alamo, Texas reported by Clover (1937), and the former resaca bottom of Santa Ana National Wildlife Refuge (SANWR) described by Vora (1990). Both sites are about 7 km east of my study area. Notable differences between the Alamo and SANWR habitats and the mature brushland plots of this study were the absence of Fraxinus berlandieriana and the presence of P. glandulosa and Acacia greggii var. wrightii at this study area. Habitats at SANWR may have been different from the sites in this study due to the closer proximity of SANWR to the Rio Grande (hence, more prone to natural flooding) and, in more recent decades, the artificial flooding regimes used at SANWR. The species composition of the fallow plots was similar to the species composition of an abandoned field south of Penitas, Texas (55 km east of study sites) described by Clover (1937) which contained Celtis pallida, C. drummondii, Opuntia engelmannii var. Iindheimeri, P. glandulosa and Z. obtusifolia.

Clematis drummondii was found climbing over vegetation on the replanted plots and the fallow interior plot. It may be impeding growth of planted individuals. Burton & Bazzaz (1991) found that the presence of Poa or Setaria at planting sites had more negative influence on tree emergence than soil series or yearly fluctuations in weather parameters. Similarly, Bush & Van Auken (1989; 1990) have found that Prosopis glandulosa growth is reduced from herbaceous competition.

Non-native grasses are abundant and prolific in the LRGV. Cynodon dactylon, Pennisetum ciliare and P. maximum are common invasive species in replanted fields. These grasses are common on disturbed areas such as roadsides and field margins, and if not controlled may spread into adjacent fields. Pennisetum ciliare may inhibit plant growth by competition for water, light and through the release of allelopathic agents (Akhtar et al. 1978; Hussain et al. 1982), whereas C. drummondii may reduce the establishment of woody plants due to its habit of growing in a dense mantle over vegetation, thereby prohibiting light penetration (Vora & Messerly 1990).

The dominance of B. neglecta in all habitat layers of the replanted interior plot was likely a result of the timing of site preparation. The replanted interior plot was plowed and bedded (in preparation of replanting) two weeks after the area containing the edge plot, and when B. neglecta had dropped seed (C. Best pers. comm.). Consequently, seeds on the soil surface were incorporated into the soil during site preparation and B. neglecta became the dominant species. The difference in importance values of planted and invasive species between the replanted plots demonstrates the need for consistency in the application of restoration techniques. The abundance of B. neglecta cover at the replanted interior plot caused the replanted interior plot to have a significantly greater mean percent overstory cover than the fallow plots.

The lowest total cover and lowest survival of planted species on the La Coma tract occurred where B. neglecta had greater than 25% cover

(K. Ewing pers. comm.). Although B. neglecta may compete with replanted species for light, it may provide beneficial shade for young plants (Vora & Messerly 1990) and it attracts songbirds that may help disseminate brushland seeds (Fuentes et al. 1986; Guevara et al. 1986; Archer et al. 1988). The role of B. neglecta as a competitor with replanted native species in the LRGV should be examined.

In addition to studying species composition and percent cover, it would be beneficial to examine the density of woody and herbaceous plants in mature brushlands so that replanting efforts could mimic the spacing of mature brushlands. Therefore, supplementing line transect data with density surveys from plots (as per Judd et al. [2002]) when sampling vegetation composition in the LRGV is preferred.

Only a small number of studies have examined the vegetation composition of undisturbed riparian brushlands of the LRGV (Clover 1937; Vora 1990; Judd et al. 2002). With the current state of limited water resources in the southwestern U.S. and the promise of further economic growth in the LRGV, continued fragmentation of habitat is likely as well as a loss of integrity of the remaining undisturbed areas. Consequently, there is an urgent need to continue replanting programs and to document floral characteristics of remaining tracts of undisturbed brushland in the LRGV so that agencies involved in land restoration have a model by which to guide their efforts.
Table 1

Abundance of seedlings replanted in a 13.4 ha field at the La Coma tract
in October 1995.

Species replanted Abundance

Havardia pallens 925
Acacia rigidula 764
Celtis laevigata 740
Acacia greggii var. wrightii 606
Adelia vaseyi 522
Chloroleucon ebano 448
Ehretia anacua 418
Prosopis glandulosa 306
Ziziphus obtusifolia 292
Lucaena pulverulenta 275
Karwinksia humboltiana 237
Acacia minuata 229
Parkinsonia aculeata 224
Amyris madrensis 192
Diospyros texana 169
Ulmus crassifolia 150
Castela texana 139
Phaulothamnus spinescens 135
Celtis pallida 133
guaiacum angustifolium 132
Capsicum annuum var. aviculare 124
Sideroxylon celastrina 123
Forestiera angustifolia 115
Mimosa asperata 104
Randia rhagocarpa 77
Lycium berlanderiana 76
Cordia biossieri 71
Colubrina texana 67
Condalia hookeri 56
Zanthoxylumfagara 51
Malpighia glabra 48

Total plants 7948

Table 2

Means of the percent cover with standard error of the mean in
parentheses for ground layer species.

(ME = mature brushland edge; MI = mature rushland interior; RE =
replanted edge; RI = replanted interior; FE = fallow; FI = fallow
interior). The symbol ++ denotes a significant difference (P<0.01) among
mean percent cover estimates among plots. A letter following the
estimate notes a significant difference (P<0.01) between plots with the
same letter.

Species Plots

 ME MI RE

Abutilon incanus -- 0.8 (0.5) 0.1 (0.1)
Acacia greggii var. wrightii 0.5 (0.4) 0.2 (0.1) 0.1 (0.1)
Acacia minuata 0.9 (0.9) -- 3.6 (1.6)
Acacia rigidula -- -- 1.0 (1.0)
Adelia vaseyi -- -- 1.1 (1.1)
Amyris madrensis 0.1 (0.1) 0.2 (0.2) --
Amyris texensis 2.7 (2.0) 9.3 (3.6) --
Asclepias -- -- 0.4 (0.3)
Baccharis neglecta -- -- 5.3 (2.5)
Bothriocloa saccharoides -- -- --
Brassicaceae -- -- --
Capsicum annuum * 0.7 (0.4) -- --
Celtis laevigata 2.6 (1.6) -- 0.7 (0.6)
Celtis pallida 10.4 (3.7) 0.7 (0.4) --
Chloroleucon ebano 0.4 (0.4) -- 0.5 (0.5
Chromolaena odorata ++ 41.5 (11.3) 52.2 (6.2) 5.4 (2.6)
Cissus incisa 0.5 (0.4) -- 0.1 (0.1)
Clematis drummondii ++ 1.6 (1.6) -- 19.9 (4.5)
Cocculus diversifolius 0.5 (0.2) 0.2 (0.1) <0.1
Condalia hookeri 2.6 (1.2) 0.4 (0.3) --
Cordia boissieri -- -- 0.3 (0.2)
Croton incanus -- 1.8 (1.5) --
Cyperus rotundus -- -- --
Dicanthium annulatum -- -- <0.1
Dicliptera sexangularis 31.9 (13.9) <0.1 --
Diospyros texana -- -- --
Ehretia anacua ++ 4.9 (1.9) 6.7 (2.5)ab 0.2 (0.2)a
Forestiera angustifolia -- 0.7 (0.7) --
Guaiacum angustifolium 0.7 (0.7) -- --
Havardia pallens -- -- 1.0 (0.4)
Heimia sa1icifolia -- 0.2 (0.2) --
Heterotheca subaxillaris -- -- --
Karwinskia humboldtiana -- -- 0.3 (0.3)
Large plant debris ++ 3.8 (1.3) 4.3 (1.0)ab 0.3 (0.1)a
Leucaena pulverulenta ++ ++ 0.5 (0.4) -- 1.6 (0.7)
Lycium berlandieri -- -- --
Malphigia glabra 0.9 (0.7) 0.5 (0.4) <0.1
Malvastrum americanum -- -- --
Matelea reticulata -- -- --
Mimosa asperata -- -- 0.3 (0.3)
Opuntia engelmannii ** -- -- --
Panicum maximum ++ 4.4 (2.2)abc -- 73.1 (7.9)ad
Parkinsonia aculeata -- -- 0.3 (0.3)
Parthenium confertolium -- -- --
Paspalum lividum -- -- --
Pennisetum ciliare -- -- <0.1
Petiveria alliacea 0.8 (0.7) -- --
Phaulothamnus spinescens 5.5 (2.0) 8.4 (3.0) --
Plumbago scandens 14.6 (9.5) 0.8 (0.6) --
Prosopis glandulosa -- -- --
Rivina humilis <0.1 -- --
Salvia coccinea 0.6 (0.5) 0.9 (0.6) --
Sarcostemma cynan. *** 0.1 (0.1) -- 0.4 (0.3)
Serjania brachycarpa 0.8 (0.5) 0.2 (0.1) --
Setaria leucopila 1.7 (1.2) 1.2 (0.9) --
Sida physocalyx -- -- 0.7 (0.4)
Sideroxylon celastrina 4.3 (1.7) 4.7 (0.4) --
Small plant debris 3.3 (1.3) 1.6 (0.6) 0.5 (0.2)
Smilax bona-nox 1.6 (0.7) -- --
Solanum americanum -- -- --
Solanum triquetrum 0.1 (0.1) 0.1 (0.1) --
Sorghum halepense -- -- 4.1 (3.1)
Tillandsia usneoides -- 0.2 (0.1) --
Trixis inula -- 0.2 (0.2) --
Ulmus crassifolia 1.2 (0.6) 0.5 (0.2) 0.5 (0.5)
Unknown Brassicaceae -- -- --
Unknown Compositae -- -- 0.2 (0.2)
Unknown Poaceae -- -- --
Urvillea ulmacea 0.6 (0.6) -- --
Xylosma flexuosa 7.3 (3.0) 0.3 (0.3)
Zanthoxylum fagara 1.1 (0.8) 5.6 (2.7) --
Ziziphus obtusifolia 3.8 (2.7) 10.3 (4.7) --

Species Plots

 RI FE FI

Abutilon incanus -- -- 5.9 (3.0)
Acacia greggii var. wrightii -- -- --
Acacia minuata -- -- --
Acacia rigidula -- -- --
Adelia vaseyi <0.1 -- --
Amyris madrensis -- -- --
Amyris texensis -- -- --
Asclepias 1.0 (0.5) -- --
Baccharis neglecta 22.1 (4.8) -- --
Bothriocloa saccharoides -- 8.7 (5.8) 25.18 (11.3)
Brassicaceae 0.1 (0.1) -- --
Capsicum annuum * -- -- --
Celtis laevigata 0.8 (0.8) -- --
Celtis pallida -- -- --
Chloroleucon ebano 0.8 (0.6) -- --
Chromolaena odorata ++ 0.8 (0.5) -- --
Cissus incisa -- -- --
Clematis drummondii ++ 17.4 (3.0) 25.2 (14.4) 0.9 (0.6)
Cocculus diversifolius -- -- --
Condalia hookeri -- -- --
Cordia boissieri 0.2 (0.2) -- --
Croton incanus -- -- --
Cyperus rotundus 2.0 (1.2) -- --
Dicanthium annulatum 1.3 (1.3) 38.5 (7.5) 22.7 (10.6)
Dicliptera sexangularis -- 0.1 (0.1) --
Diospyros texana 0.3 (0.3) -- --
Ehretia anacua ++ 1.1 (0.5) 0.8 (0.8)b --
Forestiera angustifolia -- -- --
Guaiacum angustifolium -- -- --
Havardia pallens 0.6 (0.4) -- --
Heimia sa1icifolia -- -- --
Heterotheca subaxillaris 0.1 (0.1) -- --
Karwinskia humboldtiana -- -- --
Large plant debris ++ 0.7 (0.3) -- 0.3 (0.2)b
Leucaena pulverulenta ++ ++ 0.4 (0.3) -- --
Lycium berlandieri 0.1 (0.1) -- --
Malphigia glabra -- -- --
Malvastrum americanum -- 2.0 (1.2) --
Matelea reticulata 0.1 (0.1) -- --
Mimosa asperata -- -- --
Opuntia engelmannii ** -- -- 0.2 (0.2)
Panicum maximum ++ 11.6 (4.8)de 61.7 (9.6)e 46.0 (10.5)c
Parkinsonia aculeata -- 0.1 (0.1) 1.0 (0.6)
Parthenium confertolium 0.1 (0.1) -- --
Paspalum lividum 9.2 (6.0) -- --
Pennisetum ciliare 0.6 (0.6) -- --
Petiveria alliacea -- -- --
Phaulothamnus spinescens 0.2 (0.2) -- --
Plumbago scandens -- -- --
Prosopis glandulosa -- 1.5 (1.1) 2.4 (1.9)
Rivina humilis -- -- --
Salvia coccinea -- -- --
Sarcostemma cynan. *** -- -- --
Serjania brachycarpa -- -- --
Setaria leucopila -- -- --
Sida physocalyx 1.1 (1.1) -- 3.5 (1.4)
Sideroxylon celastrina -- -- --
Small plant debris 0.7 (0.2) <0.1 <0.1
Smilax bona-nox -- -- --
Solanum americanum 1.3 (1.2) -- --
Solanum triquetrum -- -- --
Sorghum halepense 0.6 (0.6) -- --
Tillandsia usneoides -- -- --
Trixis inula -- -- --
Ulmus crassifolia -- -- --
Unknown Brassicaceae 0.1 (0.1) -- --
Unknown Compositae 0.1 (0.1) -- --
Unknown Poaceae 0.8 (0.5) -- --
Urvillea ulmacea -- -- --
Xylosma flexuosa
Zanthoxylum fagara 0.3 (0.3) -- --
Ziziphus obtusifolia -- <0.1 2.0 (1.4)

* Capsicum annuam var. aviculare

** Opuntia engelmannii var. lindheimeri

*** Sarcostemna cynanchoides

Table 3

Means of the percent cover with standard error of the mean in
parentheses for midstory layer species.


(ME = mature brushland edge; MI = mature brushland interior; RE =
replanted edge; RI = replanted interior; PE = fallow edge; FI = fallow
interior). The symbol ++ denote a significant difference
(Kolmogorov-Smirnov P<0.01) among mean percent cover estimates among
plots. A letter following the estimate notes a significant difference
(P<0.01) between plots with the same letter.

Species Plots

 ME MI RE

Acacia greggii var. wrightii 0.9 (0.6) 6.0 (3.1) 0.2 (0.2)
Acacia minuata 2.0 (1.5) 10.9 (5.3)
Acacia rigidula -- -- 1.7 (1.3)
Adelia vaseyi -- -- 0.6 (0.6)
Amyris texensis -- 4.3 (2.1) --
Amyris madrensis <0.1 -- --
Baccharis neglecta -- -- 12.1 (5.5)
Celtis laevigata 4.5 (2.4) -- 0.5 (0.5)
Celtis pallida 12.7 (6.4) 7.6 (3.5) --
Chloroleucon ebano -- -- 0.6 (0.6)
Chromolaena odorata 4.9 (2.5) 3.2 (2.1) --
Cissus incisa 0.2 (0.2) -- --
Clematis drummondii -- -- 1.6 (1.0)
Cocculus diversifolius 1.8 (0.6) -- --
Condalia hookeri 4.1 (2.8) 0.8 (0.80) --
Cordia boissieri -- -- --
Diospyros texana -- 1.9 (1.1) --
Ehretia anacua 3.6 (1.8) 5.8 (1.6) --
Forestiera angustifolia 0.4 (0.4) 0.4 (0.4) --
Guaiacum angustifolium 0.5 (0.5) -- --
Havardia pallens -- -- 1.2 (0.6)
Ipomea sinuata -- -- 1.1 (1.1)
Large plant debris 0.1 (0.1) 0.5 (0.5) --
Leucaena pulverulenta 0.2 (0.2) 0.7 (0.5) 3.6 (1.7)
Mimosa asperata -- -- 0.3 (0.3)
Panicum maximum -- -- < 0.1
Parkinsonia aculeata ++ 0.2 (0.2) -- 0.6 (0.5)
Phaulothamnus spinescens 3.0 (1.5) 5.6 (1.9) --
Prosopis glandulosa 2.1 (2.0) -- --
Sarcostemma cynanchoides -- -- --
Serjania brachycarpa 0.8 (0.4) 0.5 (0.2) --
Sideroxylon celastrina 6.8 (0.7) 15.9 (5.2) --
Small plant debris 0.1 (0.1) 0.1 (0.1) < 0.1
Smilax bona-nox 0.9 (0.5) -- --
Sorghum halepense -- -- 0.2 (0.2)
Tillandsia usneoides -- 0.4 (0.3) --
Ulmus crassifolia 2.1 (1.6) 2.0 (0.9) 0.4 (0.4)
Urvillea ulmacea <0.1 -- 0.1 (0.1)
Xylosma flexulosa 3.4 (1.5) -- --
Zanthoxylum fagara 1.8 (1.7) 7.6 (3.3) --
Ziziphus obtusifolia 5.1 (2.6) 10.8 (4.5) --

Species Plots

 RJ FE FI

Acacia greggii var. wrightii -- -- --
Acacia minuata <0.1 -- --
Acacia rigidula -- -- --
Adelia vaseyi 0.1 (0.1) -- --
Amyris texensis -- -- --
Amyris madrensis -- -- --
Baccharis neglecta 58.6 (4.7) -- --
Celtis laevigata 0.1 (0.1) -- --
Celtis pallida -- -- --
Chloroleucon ebano 0.3 (0.3) -- --
Chromolaena odorata -- -- --
Cissus incisa 0.1 (0.1) -- --
Clematis drummondii 1.1 (0.5) -- <0.1
Cocculus diversifolius -- -- --
Condalia hookeri -- -- --
Cordia boissieri 0.6 (0.6) -- --
Diospyros texana -- -- --
Ehretia anacua 0.2 (0.1) 1.3 (0.9) --
Forestiera angustifolia -- -- --
Guaiacum angustifolium -- -- --
Havardia pallens 0.5 (0.3) -- --
Ipomea sinuata -- -- --
Large plant debris 0.1 (0.1) -- --
Leucaena pulverulenta 0.4 (0.4) -- --
Mimosa asperata -- -- --
Panicum maximum -- -- --
Parkinsonia aculeata ++ -- 1.9 (1.2) 3.0 (1.4)
Phaulothamnus spinescens -- -- --
Prosopis glandulosa -- 3.7 (2.5) 4.2 (2.9)
Sarcostemma cynanchoides 0.3 (0.3) -- --
Serjania brachycarpa -- -- --
Sideroxylon celastrina -- -- --
Small plant debris -- -- --
Smilax bona-nox -- -- --
Sorghum halepense -- -- --
Tillandsia usneoides -- -- --
Ulmus crassifolia -- -- --
Urvillea ulmacea -- -- --
Xylosma flexulosa -- -- --
Zanthoxylum fagara -- -- --
Ziziphus obtusifolia -- -- 2.3 (1.4)

Table 4

Means of the percent cover with standard error of the mean in
parentheses for overstory layer species.


ME = mature brushland edge; MI = mature brushland interior;
RE = replanted edge; RI = replanted interior; FE = fallow edge;
FI = fallow interior; The symbol ++ denotes a significant difference
(Kolmogoov-Smirnov: P <0.01) among mean percent cover estimates among
plots.

Species Plots

 ME MI RE

Acacia greggii var. wrightii 3.2 (1.7) 7.4 (5.2) --
Acacia minuata 7.4 (4.5) 0.6 (0.6) 9.8 (5.3)
Amyris texensis <0.1 -- --
Baccharis neglecta -- 10.4 (4.8)
Celtis laevigata 12.1 (5.2) -- --
Celtis pallida 5.6 (3.3) 5.4 (2.2) --
Chromnolaena odorata <0.1 -- --
Cissus incisa -- --
Clematis drummondii -- -- --
Cocculus diversifolius 1.6 (0.9) -- --
Condalia hookeri 2.9 (2.0) 3.2 (1.9) --
Diospyros texana -- 2.2 (1.0) --
Ehretia anacua 7.8 (3.9) 3.1 (1.6) --
Havardia pallens -- -- 1.0 (1.0)
Large plant debris 0.7 (0.5) 0.3 (0.3) --
Leucaena pulverulenra 2.2 (1.8) 6.4 (2.3) 13.7 (6.2)
Parkinsonia aculeata ++ -- 0.3 (0.3) 0.4 (0.4)
Pisonia aculeata 0.1 (0.1) -- --
Prosopis glandulosa 5.6 (5.6) -- --
Sapindus saponaria * -- 1.1 (1.1) --
Seriania brachycarpa 0.8 (0.8) -- --
Sideroxylon celastrina 9.8 (2.6) 18.6 (7.5) --
Small plant debris 1.0 (0.8) 1.5 (0.6) --
Smilax bona-nox 0.4 (0.4) -- --
Tillandsia usneoides 0.1 (0.1) 0.4 (0.4) --
Ulmus crassifolia 14.5 (4.5) 11.5 (5.5) --
Urvillea ulmacea 0.8 (0.8) -- --
Xylosma flexulosa <0.1 -- --
Zanthoxylum fagara -- 1.4 (1.4) --
Ziziphus obtusifolia 0.4 (0.4) 1.8 (1.0) --

Species Plots

 RI FE FI

Acacia greggii var. wrightii -- -- --
Acacia minuata 0.9 (0.9) -- --
Amyris texensis -- -- --
Baccharis neglecta 61.5 (4.7) -- --
Celtis laevigata -- -- --
Celtis pallida -- -- --
Chromnolaena odorata -- -- --
Cissus incisa 0.5 (0.4) -- --
Clematis drummondii <0.1 -- --
Cocculus diversifolius -- -- --
Condalia hookeri -- -- --
Diospyros texana -- -- --
Ehretia anacua -- -- --
Havardia pallens -- -- --
Large plant debris -- -- --
Leucaena pulverulenra 2.0 (1.3) -- --
Parkinsonia aculeata ++ -- 1.0 (1.0) 3.5 (1.5)
Pisonia aculeata -- -- --
Prosopis glandulosa -- 2.9 (2.0) 3.9 (2.9)
Sapindus saponaria * -- -- --
Seriania brachycarpa -- -- --
Sideroxylon celastrina -- -- --
Small plant debris -- -- --
Smilax bona-nox -- -- --
Tillandsia usneoides -- -- --
Ulmus crassifolia -- -- --
Urvillea ulmacea -- -- --
Xylosma flexulosa -- -- --
Zanthoxylum fagara -- -- --
Ziziphus obtusifolia -- -- 0.6 (0.6)

* Sapindus saponaria var drummondii

Table 5

Total mean percent cover with standard error of the mean in parentheses
from ground, midstory and overstory layers at plots.

ME = mature brushland edge; MI = mature brushland interior;
RE = replanted edge; RI = replanted interior; FE = fallow edge;
FI = fallow interior; An asterisk * denotes a significant difference
(P<0.01) among mean percent cover estimates. A letter following the
estimate notes a significant difference (P<0.01) between plots with
the same letter.


Vegetation layer Plots
 ME MI RE

Ground * 159.3 (11.3)abc 113.2 (9.1)a 121.4 (3.6)d
Midstory * 74.3 (9.3)abc 62.2 (8.1)de 35.8 (8.5)a
Overstory * 65.2 (15.7)ab 77.1 (9.3)cd 35.3 (8.4)

Vegetation layer Plots
 RI FE FI

Ground * 75.3 (6.5)bde 138.8 (7.0)e 110.0 (3.7)c
Midstory * 62.3 (5.5)fg 7.9 (3.1)bdf 9.5 (3.7)ceg
Overstory * 64.9 (3.1)ef 3.9 (1.9)ace 8.0 (3.0)bdf


ACKNOWLEDGMENTS

Access to study sites and logistical support was provided by Texas Parks and Wildlife Department and the U.S. Fish and Wildlife Service. I am thankful to Christopher Best and Kern Ewing for personal communications regarding their field observations. I am grateful to Robert Lonard who assisted with plant identification. I thank Frank Judd, David Wester, Robin Vora, Stephen Winter and an anonymous reviewer for comments on previous versions of this manuscript. I thank Michelle Sternberg who provided assistance in the field. This study was supported in part by James-Ware-Foltz Awards that were granted to the author in 1998 and 1999.

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MAS at: mitch_sternberg@fws.gov
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Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:May 1, 2003
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