Woody vegetation of an old-growth creekbottom forest in north-central Texas.
Old-growth forests are not easily defined. Runkle (1982) indicated that they are without obvious large-scale human or natural disturbances and contain large trees. Abrell and Jackson (1977) indicated they are near virgin. There is a streamside bottomland forest in Garland, Texas, that generally fits these descriptions and thus needs to be characterized.
In Texas, old-growth forests are rare. Nixon et al. (1977, 1980) described two such forests in eastern Texas, one associated with the Neches River and dominated by Carpinus caroliniana Walt., Quercus nigra L., and Fraxinus caroliniana Mill., and a second on the shore of Toledo Bend Reservoir that is dominated by Fagus grandifolia Ehrh. Old-growth hardwood communities exist elsewhere in the eastern United States, and most have been analyzed and described (for example, Abrell and Jackson, 1977, in Indiana, and Adams and Barrett, 1977, in Ohio). It is important that we characterize these old-growth forests because they suggest the past structure and composition of such communities. Furthermore, central Texas bottomland communities have received little attention. The purpose of this study, therefore, is to provide a description of a rare old-growth streamside forest in north-central Texas and to compare it with other forests previously described. Of additional interest is the purchase of this site by the city of Garland and its designation as the Spring Creek Forest Preserve. Our study should provide basic information to aid in the management of this preserve.
The Spring Creek Forest Preserve is located within the Blackland Prairies Vegetational Area of Hatch et al. (1990). It is a forested site situated along Spring Creek in northeastern Dallas County just north of Garland, Texas. More specifically, it is at the junction of Spring Creek and Holford Road. Characterized by rather steep banks and a deep and wide channel, Spring Creek meanders somewhat as it borders the study area. Occasional flooding occurs, with water overflowing the channel into the creekbottom. Woodlands are generally restricted to the creekbottom but occasionally extend onto adjoining slopes, where they may be disrupted by pastures, farmland, quarries, or gravel pits. The study area, as such, was approximately 500 meters long and 50 to 100 meters wide.
Dallas County is transitional between the Subtropical Humid climatic region of eastern Texas, which is characterized by warm summers, and the Subtropical Subhumid climatic region of central Texas, which is characterized by hot summers and dry winters (Larkin and Bomar, 1983). The average annual precipitation for the study area is about 89 centimeters; highest monthly totals occur in April, May, and September. The average annual temperature is 19[degrees]C, with an average annual low of 12[degrees]C and an average annual high of 25[degrees]C (Larkin and Bomar, 1983).
Three habitat types were designated--creekside, creekbottom, and slope. A total of 10 forest stands were analyzed, three at creekside, five in the creekbottom, and two on the slope. Stands were studied using the quadrat method. Quadrats were five by five meters, with each positioned end to end within belt transects. Transects were systematically placed adjacent to, and parallel with, the creek in creekside stands and in the center area of each of the creekbottom and slope stands. Fifty quadrats in each stand were sampled to estimate stand composition. Frequency, density, and basal area data were obtained. Importance values were determined by summing relative frequency, relative density, and relative basal area. Only those trees, shrubs, and woody vines with diameters at about 1.4 meters above ground equal to or greater than half a centimeter were included. Scientific nomenclature followed Hatch et al. (1990).
To compare stands, a polar ordination (Bray and Curtis, 1957) was developed following procedures outlined by Cox (1980). Community species diversity also was measured using the Shannon-Weiner diversity index (Shannon and Weaver, 1949): [H.sup.1] = -[SIGMA] pi [log.sub.2] pi, where pi is the decimal fraction of the individuals belonging to the i th species. Species richness is the number of species per stand.
Seven soil samples were collected from the study area--one from the slope, three from creekside, and three from the creekbottom. Soil samples were taken from the top 20 centimeters of the soil. Analyses were performed by the Stephen F. Austin State University Soil Testing Laboratory. Ion levels were determined for Ca, P, K, and Mg by atomic absorption spectrophotometry and soil texture by the hydrometer method (Bouyoucos, 1962).
Statistical analyses of vegetation and soil parameters were carried out using a one-way analysis of variance (ANOVA). An alpha level of .05 was used to determine significance.
Without fruits, and in most cases without leaves and twigs, interspecific differences between Ulmus americana L. and U. rubra Muhl. and between Fraxinus pennsylvanica Marsh. and F. americana L. were not easily determined. This was especially the case for mid- and upper canopy trees where access to leaves and twigs was utterly impractical. As a result, these are listed as Ulmus sp. and Fraxinus sp.
The 10 forest stands were located on two soils--the Frio silty clay, frequently flooded phase, and the Austin-Lewisville complex. The creekside and creekbottom stands were on the Frio silty clay. This is a deep, well drained, nearly level soil that occurs on flood plains (Coffee et al., 1980). It is a calcareous, moderately alkaline soil with a dark grayish color. The Austin-Lewisville complex was formed over chalky limestone and is located on slopes up from floodplains. The slopes are usually five to eight percent and eroded. These soils are calcareous and moderately alkaline and are usually dark grayish in color.
Our soil analyses indicate that surface soils of the study area were basic calcareous clays (Table 1). Soil pH ranged from 7.6 to 7.8 and showed no significant difference between stands. Creekside sites had significantly less phosphorus (P = .014); although potassium ranged from 360 parts per million at creekside to 473 in creekbottom sites, differences were not significant. There were no significant differences between sites in regard to sand, silt, and clay content.
The polar ordination displayed a vegetational continuum with creekside stands at one end of the spectrum and slope stands at the other (Fig. 1). In creekside stands, overstory species with the greatest basal area were, in descending order, Quercus shumardii Buckl., Fraxinus sp., Juglans nigra L., and Quercus macrocarpa Michx. (Table 2). Celtis laevigata Willd. and Ulmus sp. had the greatest densities and highest importance values. Although these same species occurred in the overstory of creekbottom stands, their basal area generally declined. Carya illinoensis (Wang.) K. Koch and Quercus muhlenbergii Engelm. had considerably higher basal areas in creekbottom stands, whereas Fraxinus sp. and Ulmus sp. had the greatest densities and highest importance values (Table 2).
The greatest basal areas of overstory species on the slope were exhibited by Q. shumardii, C. illinoensis, Fraxinus sp., and Q. muhlenbergii (Table 2). Fraxinus sp. and Ulmus sp. displayed the highest density, whereas Fraxinus sp., Q. shumardii, and C. illinoensis had the highest importance values.
[FIGURE 1 OMITTED]
The more prevalent shrubs and small trees in the creekside stands were Cornus drummondii C. A. Mey., Viburnum rufidulum Raf., Rhamnus caroliniana Walt., and Juniperus virginiana L. These sames species, along with Prunus mexicana S. Wats. and Ilex decidua Walt., were common creekbottom stand components. Common vines at the three sites were Vitis riparia Michx., Toxicodendron radicans (L.) Mill., Parthenocissus quinquefolia (L.) Planch., and Berchemia scandens (Hill) K. Koch. The first three listed were more notable creekside and creekbottom constituents, whereas Berchemia scandens was the most common slope species.
Species richness was relatively constant with means of 32, 29, and 31 species in creekside, creekbottom, and slope communities, respectively. Total density at creekside was 2374 plants per hectare, whereas the creekbottom was 1894 and the slope 3040. Thus density decreased from creekside to creekbottom and increased to highest values in the slope stands. There were no significant differences among the three groups. Total basal area of creedside, creekbottom, and slope stands was 49.56, 39.31, and 32.14 square meters per hectare, respectively. These differences were not statistically significant. The slope stands had the highest mean species diversity ([H.sup.1] = 4.02) (Fig. 2). Conversely, the creekside stands had the lowest value ([H.sup.1] = 3.40). Creekbottom stand species diversity was 3.60.
[FIGURE 2 OMITTED]
The overall dominants in the Spring Creek forest are Fraxinus sp., Ulmus sp., Carya illinoensis, Celtis laevigata, Quercus shumardii, and Q. muhlenbergii. Upper Trinity River Basin forests in north-central Texas are generally characterized by an abundance of Ulmus crassifolia Nutt., Fraxinus pennsylvanica, and C. laevigata (Nixon and Willett, 1974). In the Spring Creek forest, U. crassifolia is of minor importance. Ulmus americana is consistently associated with these Trinity riverbottom species, oftentimes being among the dominants (Nixon and Willett, 1974). The association of C. laevigata, U. americana, and F. pennsylvanica, therefore, is not uncommon. In fact, these species occur together throughout the southern deciduous forest, having been designated the Sugarberry-American Elm-Green Ash Forest Cover Type (Eyre, 1980). C. illinoensis and Q. shumardii also occasionally are present in bottomland forests in north-central Texas and they, too, may be among the dominant species (Nixon and Willett, 1974; Cox, 1983). They also occur eastward as associated species of various forest cover types (Eyre, 1980). Thus the more notable inconsistency of the Spring Creek forest is the presence of Q. muhlengergii among the dominants. Robertson et al. (1978) found this species to be more representative of transitional sites up from bottomland. There are many more plants of Q. muhlenbergii on the slope at Spring Creek, but basal area is less than that in the creekbottom. Of interest is the recent designation of a Q. macrocarpa-Q. muhlenbergii forest community type, which ranges from Kansas and Nebraska into Wisconsin (Monk et al., 1990). Additional studies are needed to better understand the distribution and importance of Q. muhlenbergii in northcentral Texas.
When comparing the vegetational composition of the Spring Creek forest with bottomland vegetation of nearby regions, it was found that 18 of the 28 most common bottomland forest species of north-central Oklahoma were found at Spring Creek, including nine of the 10 dominant Spring Creek species (Rice, 1965; Collins et al., 1981). U. americana is the principal tree species of Oklahoma bottomlands. Petranka and Holland (1980) found that mature stands of forest vegetation of creekbottoms in south-central Oklahoma contained Celtis sp., U. americana, Sapindus saponaria L., Acer negundo L., C. illinoensis, Q. macrocarpa, F. pennsylvanica, and Q. shumardii in decreasing order of importance. These species, with the exception of S. saponaria, were dominants at Spring Creek. Shrub and woody vine species were also similar. Six of nine shrubs and five of nine vines mentioned by Rice (1965) also occurred at Spring Creek.
Riparian communities associated with the Guadalupe and San Antonio rivers and with creekbottoms on the Edwards Plateau in south-central Texas display affinities to Spring Creek woody vegetation (Van Auken et al., 1979; Ford and Van Auken, 1982; Bush and Van Auken, 1984). Celtis laevigata, Carya illinoensis, Acer negundo, Juglans nigra, Ulmus americana, and Sapindus saponaria are important components. Twenty-one of 32 species present in the Guadalupe floodplain were in common with Spring Greek communities (Ford and Van Auken, 1982). Only four of 32 species recorded in south-central Texas were not found in eastern Texas; however 28 appear to be at the westernmost margin of their range.
Species diversity and evenness in Spring Creek communities increased with distance from the creek ([H.sup.1] = 3.40 for creekside, 3.60 for creekbottom, and 4.02 for slope). Bush and Van Auken (1984) also found that diversity increased as distance from the San Antonio River increased. It was obvious that the Spring Creek bottomland was subjected to flooding. Studies have shown that species diversity increases with decreasing flood stress (Bell and del Moral, 1977). It is not uncommon for species diversity to increase from dry to mesic (Cox, 1983) and from wet to mesic (Nixon et al., 1983). Stressful environments tend to reduce diversity (Barbour et al., 1980).
TABLE 1. Mean values of the chemical and physical properties of the soil at the Spring Creek study area. Sample sizes are in parenthesis. Communities pH Ca P K Mg Sand Silt Clay Texture Slope (1) 7.6 >6000 30 400 >400 16 32 52 Clay Creekbottom(3) 7.7 >6000 31 473 >400 17 34 49 Clay Creekside(3) 7.7 >6000 18 360 >400 29 25 46 Clay TABLE 2. Comparison of density, basal area and importance value of the six dominant woody species occurring in creekside, creekbottom, and slope communities. Species are ranked according to basal area. Creekside Density Basal area (stems/ha) ([m.sup.2]/ha) IV Carya illinoensis 48 5.40 16.1 Quercus shumardii 152 9.03 32.6 Quercus muhlenbergii 21 5.00 12.3 Fraxinus sp. (1) 312 8.62 43.4 Juglans nigra 29 6.70 16.8 Ulmus sp. (2) 456 4.46 48.6 Quercus macrocarpa 29 6.42 16.3 Celtis laevigata 725 2.33 51.5 Others (4) 511 1.02 62.4 Total 2283 48.98 300.0 Creekbottom Density Basal area (stems/ha) ([m.sup.2]/ha) IV Carya illinoensis 77 12.32 41.5 Quercus shumardii 27 1.87 8.1 Quercus muhlenbergii 45 8.56 27.8 Fraxinus sp. (1) 386 3.29 45.5 Juglans nigra 21 2.27 8.4 Ulmus sp. (2) 333 3.10 42.0 Quercus macrocarpa 8 1.41 4.7 Celtis laevigata 274 2.85 33.3 Others (4) 504 2.60 88.6 Total 1675 38.27 299.9 Slope Density Basal area (stems/ha) ([m.sup.2]/ha) IV (3) Carya illinoensis 142 8.49 35.3 Quercus shumardii 200 9.27 40.4 Quercus muhlenbergii 208 4.57 27.5 Fraxinus sp. (1) 623 5.56 53.8 Juglans nigra 23 1.98 7.9 Ulmus sp. (2) 373 0.87 27.4 Quercus macrocarpa 12 0.07 1.2 Celtis laevigata 92 0.14 6.9 Others (4) 1340 1.13 99.6 Total 3013 32.08 300.0 (1) Includes Fraxinus pennsylvanica and F. americana. (2) Includes Ulmus americana and U. rubra. (3) Importance value is equal to the sum of relative frequency, relative density, and relative basal area. (4) Other species present and their importance values (creekside, creekbottom, slope): Acer negundo (8.7, 24.2, 2.1), Acer rubrum (0.0, 0.0, 0.4), Amorpha fruticosa (0.0, 0.0, 0.3), Berchemia scandens (0.4, 0.4, 7.5), Bumelia lanuginosa (1.4, 2.4, 2.5), Callicarpa americana (0.0, 0.0, 0.3), Catalpa speciosa (0.3, 0.0, 0.0), Cercis canadensis (0.6, 0.0, 0.0), Cocculus carolinus (0.3, 0.0, 0.0), Cornus drummondii (9.3, 0.4, 4.5), Euonymus atropurpureus (0.0, 0.9, 0.0), Forestiera pubescens (0.0, 0.2, 3.8), Gleditsia triacanthos (0.6, 1.2, 1.9), Ilex decidua (0.0, 1.1, 3.0), Juniperus virginiana (1.6, 2.4, 13.5), Maclura pomifera (2.3, 3.1, 1.0), Melia azedarach (0.8, 0.0, 0.0), Morus rubra (5.2, 13.2, 10.5), Parthenocissus quinquefolia (3.2, 2.0, 4.6), Platanus occidentalis (1.4, 0.0, 0.0),, Prunus mexicana (0.5, 2.6, 5.0), Rhamnus caroliniana (1.9, 1.7, 10.5), Toxicodendron radicans (1.7, 1.5, 0.3), Sambucus canadensis (0.0, 1.0, 0.0), Sapindus saponaria (2.5, 2.5, 0.0), Smilax bona-nox (0.3, 0.0, 0.3), Smilax hispida (0.3, 0.0, 0.0) Sophora affinus (0.0, 0.0, 2.0), Ulmus crassifolia (8.2, 18.3, 12.1), Viburnum rufidulum (2.2, 4.3, 11.2), Vitis cinerea (0.0, 0.0, 0.7), Vitis riparia (8.1, 4.8, 1.5), Zanthoxylum clava-herculis (0.4, 0.9, 0.0).
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E. S. NIXON, J. R. WARD, E. A. FOUNTAIN, AND J. S. NECK
Department of Biology, Stephen F. Austin State University, Nacogdoches, Texas 75962-3003
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|Author:||Nixon, E.S.; Ward, J.R.; Fountain, E.A.; Neck, J.S.|
|Publication:||The Texas Journal of Science|
|Date:||May 1, 1991|
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