WESTERN OKLAHOMA WETLANDS 5 A Classification and Analysis of Emergent Wetland Vegetation in Western Oklahoma Bruce W. Hoagland Oklahoma Biological Survey and Department of Geography, University of Oklahoma, Norman, OK 73019-0575 Vegetation classification is an important tool for researchers and resource managers. In the case of wetland vegetation, there is a paucity of quantitative data and analysis for classification purposes. This study analyzed quantitative vegetation data from 55 sites in western Oklahoma. Eight vegetation classes were identified. The two most common vegetation types were dominated by Schoenoplectus americanus and Typha domingensis. Previous studies had not identified vegetation dominated by Heteranthera limosa-Bacopa rotundifolia-Marsilea vestita. One site was dominated by Thalia dealbata, which had not been reported from western Oklahoma in the past. © 2002 Oklahoma Academy of Science INTRODUCTION Information classification is a crucial aid in types (7,8). Penfound (9) recognized 27 the interpretation of the relationships wetland vegetation types in western Okla- between categories (1). The classification of homa in a study of vegetation associated vegetation into units facilitates communi- with reservoirs and natural lakes. The cation between researchers and resource results of this study were based presence/ managers (2,3). For wetland managers and absence data but were not quantitatively researchers the Cowardin et al. (4) classi- analyzed. fication system has become an integral The structure and dynamics of vege- component of wetland inventory and tation in buffalo wallows is probably the conservation efforts (5). The goals set forth most extensively studied wetland habitat in by Cowardin et al. (4) include (a) the western Oklahoma (10-14). Buffalo wallows description of ecological units with homo- are small-scale landscape features with low genous natural attributes, (b) arrangement species diversity and with vegetation of those attributes in order to aid resource composed of primarily perennial wetland managers, (c) identification of units for species (14). Vegetation structure of playa classification and inventory, and (d) pro- lake wetlands were analyzed by Hoagland vision of uniformity in concepts and ter- and Collins (15), including sites in Texas and minology (5). At the base of the Cowardin Cimarron Counties. et al. (4) classification are the dominance The goals of the current study were to types which provide a description of provide a quantitatively derived classi- vegetation units within a region. fication and description of herbaceous Information on wetland dominance wetland vegetation. Such a classification types for a region or state can be obtained will be of value to wetland conservation and through field studies or through a review management efforts in Oklahoma. of the published literature. Unfortunately, there is a paucity of literature regarding the METHODS vegetation of western Oklahoma herb- aceous wetlands. The need for increased Study area: Study sites were located in 16 quantitative data for wetland vegetation in western Oklahoma counties (Fig. 1). Within Oklahoma has been noted (6). Recent the study area, latitudinal variation in studies of western Oklahoma wetlands do temperature and longitudinal variation in not provide a classification of dominance precipitation combine to produce a south- Proc. Okla. Acad. Sci. 82:5-14(2002) 6 B. W. HOAGLAND Figure 1: Location of western Oklahoma emergent wetland study sites. The number of sites quantitatively sampled in each is numerically designated. east-to-northwest environmental gradient that support halopyhtic vegetation (20-22). (16). For example, mean annual temper- In excess of 40 hydric soil types have been ature in the southeastern portion of the identified in western Oklahoma (8). study area is 17.2oC and in the northwest is Data collection and analysis: Study 13.3oC (17). Likewise, the mean annual low sites were located by review of 1:24,000 scale temperature decreases from 18oC in the US Geological Survey topographic quad- southeast to 1.7oC in Cimarron County, and rangles and National Wetland Inventory the mean annual high temperature from maps. Sites were excluded from this study 28.9oC to 25.6oC. There are 200 frost free if they met any of the following criteria: (a) days in Jefferson County as contrasted with heavily grazed (i.e., vegetation cropped to 170 days in the northwest (17). Mean annual less than 3 cm and trampled), (b) converted precipitation ranges from 83 cm to 41 cm to exotic pasture grasses (i.e., Cynodon along a southeast to northwest axis. dactylon), (c) currently or recently in row Physiographically, the study is char- crop production, or (d) evidence of acterized by gently rolling topography with extensive physical modification. In the local occurrences of dissected hills. The field, sites were assigned to the appropriate surface geology is composed primarily of class in the Cowardin et al. (4) system. shallow-marine deposits (18). However, Quantitative vegetation data were collected Tertiary sands, clays, and gravels are from acceptable sites using randomly prominent in Ellis, Harper, and the Pan- placed 0.25 m2 quadrats. This sample size handle Counties (18). Several soil great was chosen because of the small size and groups are present in the study area, ranging linear nature of many western Oklahoma from darkly colored loams and clay loams wetlands. A larger sample size would developed under mid and shortgrass increase the amount of upland vegetation prairies which are typical of the panhandle, in the quadrat. The number of quadrats to dark or dark-reddish clay and clay-loam sampled depended on the total area of the developed under tall, mid, and shortgrass site. All species occurring within a quadrat prairie which are prominent in the remain- were recorded, and percent cover was then der of the study area (19). Stabilized and visually estimated to the nearest 5%. active sand dunes along major streams are Vegetation data from each site were another important group of soils. They are compiled into a matrix of mean species mostly brown and light brown loams and cover values-by-site. Vegetation data were sands with clay lenses that support semi- classified into floristic associations by using permanently flooded habitats (19). Gypsum two-way species indicator analysis (1,23). outcrops and saline springs produce soils These data were subsequently analyzed by Proc. Okla. Acad. Sci. 82:5-14(2002) WESTERN OKLAHOMA WETLANDS 7 using detrended correspondence analysis nutans. (DCA; 24,25) to identify regional gradients Cluster 3 contained the greatest num- and trends in species composition. ber of sites and the highest species diversity. The greatest mean cover value and highest RESULTS frequency was T. domingensis. Frequently co-occurring species included Lippia nodi- Vegetation classification: A total of 55 sites flora, P. lapathifolium, P. pensylvanicum, were sampled and 182 species encountered. Panicum virgatum, Salix nigra, and S. ameri- The greatest number of sites where located canus. Sites for this vegetation occurred in in Blaine and Cimarron Counties. The a broad array of habitats, including palus- distribution of sites reflects the availability trine and riverine. and access to sites which met the sampling Cluster 4 was dominated by S. ameri- criteria. Table 1 lists all species encountered canus. Frequently occurring species includ- during the sampling, the TWINSPAN ed Cephalanthus occidentalis, Lycopus ameri- clusters into which they were classified, and cana, P. virgatum, and S. tabernaemontanii. No species richness, diversity, evenness values clear vegetation type emerged from cluster for each cluster. TWINSPAN analysis 5. Species with high cover values in this produced eight vegetation clusters (Table 2). cluster included one site dominated by Echinochloa crusgalli, Eleocharis palustris, Nelumbo lutea and two by Thalia dealbata. Polygonum pensylvanicum, Rumex altissimus, Cluster 7 contained playa lakes. Pasco- Schenoplectis americana, S. tabernaemontanii, pyrum smithii, a mesic C3 grass, was the and Typha domingensis were the most dominant species at these sites. L. cuneifolia frequently encountered species. All vege- and Oenothera canescens co-occurred in all tation clusters were dominated by perennial playa lake. Guymon playa, which captured plant species. irrigation run-off, was the only playa Cluster 1 was composed of pond sites dominated by obligate wetland species (P. that occurred in the swales of stabilized sand coccinea and P. lapathifolium). dunes. These ponds and attendant vege- Sites in Cluster 8 occurred in saline tation were encountered throughout central areas and were dominated by Distichlis Oklahoma, but not in far northwest Okla- stricta-S. americana. Frequently occurring homa or in the Panhandle. The dominance species included Aster subulatus, E. palustris, type at these sites was described as Heter- and L. lanceolata. Boggy Creek salt flats, anthea limosa-Bacopa rotundifolia-Marsilea located in a gypsum outcrop area in Beck- vestita. Associated species included Am- ham County, a unique salt tolerant species, mania coccinea, P. pensylvanicum, P. coccinea, Cressa truxillensis, which had been pre- and Sagittaria latifolia. The most abundant viously documented from only one site in plants on pond shorelines were Leptochloa Oklahoma and not collected since the 1950 fasicularis and E. crusgalli. Upland vege- (26). tation was dominated by Artemisia filifolia, Ordination: