This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Chapter 7 Plants, Arthropods, and Birds of the Rio Grande Deborah M. Finch, Gale L. Wolters, and Wang Yong USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Albuquerque, New Mexico Mary J. Mund, Department of Biology, University of New Mexico, Albuquerque, New Mexico INTRODUCTION forest in this stretch, (2) the extent of past and cur­ rent research conducted in the bosque, and (3) the Human populations have increased dramatically apparent public, political, governmental, and aca­ along the Rio Grande since European settlement. demic interest in this area owing to its urbanization, Human use of water for irrigation and consumption, recreational opportunities, habitat alteration, water and human use of land for agriculture, urban cen­ usage and pollution, and need for conservation and ters, livestock grazing, and recreation have changed restoration. We refer to the Middle Rio Grande as the Rio Grande ecosystems by altering flood cycles, chan­ portion of the river, restricted to New Mexico, from nel geomorphology, upslope processes, and water Elephant Butte Reservoir to Cochiti. quality and quantity. Such abiotic changes have in­ fluenced the biological diversity and ecological func­ RIPARIAN VEGETATION tions of the Middle Rio Grande Basin, altering the distribution, structure, and composition of riparian Historical Overview plant and animal communities. We review the literature and identify research Riparian ecosystems, according to Lowe (1964), are needs pertaining to the flora and fauna of the Middle associations of any kind in or adjacent to drainages Rio Grande bosque, focusing on plants, arthropods, and/ or their floodplains. They are further character­ and birds. These groups serve as model taxa for moni­ ized by species and/ or life forms different from that toring population changes and trophic level interac­ of the immediate surrounding non-riparian associa­ tions in response to natural and human-caused tion. Although riparian ecosystems have existed changes in function, structure, and dynamics of ri­ along the Rio Grande and its maj()r tributaries for parian ecosystems. Many arthropod species are first perhaps a million years (Scurlock 1':)88), they occupy order herbivores, so the composition and structure less than 1 percent of the land area in New Mexico of plant communities are likely to influence their and adjacent states. Nevertheless, they are extremely presence, absence, and reproduction. Birds forage on important to the biological diversity and ecological food supplies that range from seeds, fruits, and integrity of arid southwestern ecosystems. leaves, to insects and small vertebrates. Thus, the The Pleistocene epoch, lasting from around 2 mil­ distribution, dispersal, migration, and demography lion to 10,000 years ago, was characterized by south­ of avian species will likely be affected by changes in ward glacial advances and retreats. Vegetation ex­ riparian plant communities and by interactions hibited similar movement, by retreating south ahead among plant and insect associations. Birds and in­ of the advancing glacial ice and advancing to the sects are dispersal agents of seeds of many plant spe­ north to occupy the land exposed by melting ice. cies, and so they contribute to the growth and com­ Scurlock (1988) speculated that cottonwood bosque position of plant communities. (woodland fringing a body of water) probably ex­ In this chapter, we focus on the Middle Rio Grande isted along the Rio Grande since the colder times of because of (1) the availability of cottonwood gallery the early Pleistocene. During the late Pleistocene and 133 early Holocene epoch, the climate apparently dra­ ciation dominated by JllnCllS balticlls and Houttllynia matically changed to warmer and drier conditions. californica. Associated species were Baccharris wrightii, As a result, rich mixed coniferous forests expanded Helianthus annUllS, Dyssodia papposa, 011agra jamesii, in range to occupy the area (Axelrod and Bailey 1976). Amorpha fruticosa, and Rumex berlandieri. As the climate became more arid, coniferous forests Van Cleave (1935) described five Rio Grande flood­ were replaced by woodlands, grasslands, and plain plant communities: (1) cottonwood-willow for­ shrubI and (Van Devender et al. 1984). ests several hundred yards wide along the stream McKinley and Brown (1982) theorized that south­ with little understory vegetation except scattered western riparian deciduous forests reflect a contrac­ clumps of saltgrass; (2) grass-woodland bosque oc­ tion of the formerly widespread Early Tertiary mixed cupying elevated floodplain sites dominated by coy­ mesophytic forest. Riparian ecosystems are vernally ote willow (Salix exiglla), cottonwood, salt cedar adapted to Early Tertiary climates and retreated to (Ta11larix penta11ara, T. clzi11e11sis), and Russian olive pockets where the warm temperate climate persisted (Elaeagnlls (l1lg11stijolia) with a herbaceous understory (McKinley and Brown 1982). Nineteenth century of saltgrass, yerba mansa (Ane11lopsis calijorJlica), flea­ southwestern riparian plant communities, as we bane (Erigero11 plziladelplzicllS), and horseweed know them today, probably developed during this (Leptilol1 c{l1wdeJlse); (3) wet meadow-like community, period of climatic change. with the water table at or just below the soil surface, In his comprehensive chronological description of dominated by sedges, rushes U1l11CllS spp.), saltgrass, 19th century riparian vegetation along the Rio and yerba mansa; (4) swampland (marsh) dominated Grande, Scurlock (1988) speculated that stands of by cattail, sedges, spikerush (Eleoclwris spp.), scour­ valley cottonwood (Populus fremontii var. wislizel1ii) ing rush (Eqlliset1l11l lzye11lale), watercress (Radicllla and willow (Salix spp.) were interspersed with 11astllrti1l11l-aqllatic1l111), and buttercup. (Ra111111CulliS marshes dominated by sedge (Carex spp.), tule bul­ cy11lbaliria) and generally encompassed by a band of rush (Scirpus acutus), cattail (Typha latl/olia), and woody vegetation; and (5) small lakes occupied by saltgrass (Distichlis spicata) at the end of the last ice aquatic plants. age. He also suggested that the first significant hu­ man impact on the Rio Grande riparian ecosystem Current Vegetation CompOSition was probably clearing of the bosque vegetation for and Structure cultivation between 1,500 and 2,000 years ago. Woodbury and Zubrow (1979) reported that many In New Mexico, floodplain riparian vegetation has large American Indian farming villages were cen­ probably been impacted more by human activities tered along the Middle Rio Grande valley by the mid than any other type of riparian vegetation (Dick­ 1500s, and Harper et al. (1943) estimated about Peddie 1993). Current Rio Grande floodplain vegeta­ 100,000 acres of former bosque vegetation was un­ tion greatly differs in both composition and extent der cultivation by the mid 18th century. from that described by Van Cleave (1935). Cotton­ The first comprehensive description of Rio Grande wood and willow were, and remain, primarily re­ floodplain vegetation was authored by Watson (1912) stricted to the immediate floodplains. The bosque, who described open and more or less pure forests of though much reduced in extent, is still represented valley cottonwood along the Rio Grande where the by some individual cottonwood trees of extremely water table was near the surface in the open. Accord­ large size. With some notable exceptions, the historic ing to Watson, the trees were small because native cottonwood and willow forests have been reduced ranchers harvested them for fuel and fenceposts, al­ to a narrow band of mid- to old-age forest stands though protected individual trees were veritable gi­ between levees in the Middle Rio Grande floodplain. ants in girth. Scattered throughout this forest and Many cottonwood/willow communities were lost to especially along the banks of the streams were a few expanding agriculture, the demand for fuel and willows, clumps of Baccharris wrightii and Cassia wood products, channelization and flood control bauhinioides, and an herb layer consisting of Juncus projects, urbanization, transportation systems, inun­ balticus, Trifolium rydbergii, Aster spinosus and a few dation by large impoundments, and the introduction grasses. Watson described this riparian forest as and escape of exotic plants. monotonously uniform and poor in species. Watson The phreatophyte vegetation on the Rio Grande (1912) also described a riverbank wet meadow asso- floodplain today is found in relatively hydric, mesic, 134 and xeric conditions (Campbell and Dick-Peddie planted in Albuquerque as an urban ornamental. Salt 1964). Some species have moved into the bosque from cedar became naturalized and by the 1920s was a up and down stream communities and other species dominant shrub along many southwestern rivers have moved from adjacent upland plant communi­ (Horton 1977). Van Cleave (1935) also referred to both ties, but the greatest factor influencing the composi­ salt cedar and Russian olive as dominant plant spe­ tion of bosque communities, according to Campbell cies in the grass-woodland bosque floodplain of the and Dick-Peddie (1964), has been the introduction Middle Rio Grande. The invasion of salt cedar on of plants such as salt cedar and Russian olive. floodplains in New Mexico was rapid and dramatic. In a comprehensive