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An Environmental History of the Middle Rio Grande Basin

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An Environmental History of the Middle Rio Grande Basin CHAPTER 5 HISTORICAL IMPACTS AND CHANGES: BIOTIC RESOURCES AND HUMAN POPULATIONS As described in previous chapters, adverse impacts Turner 1965; Hennessy 1983; Humphrey 1958, 1987; generated by humans on the surface water, vegetation, Johnson and Elson 1977; Neilson 1986; Swetnam 1990; Vale soils, and fauna began with their arrival in the region more 1982, to name just some). Most of these studies examined than 10,000 years ago. In some instances these impacts climate and juniper-grassland savannas, pinyon-juniper and resulting environmental changes were interrelated woodlands, or ponderosa forests, as well as the interrela- with natural phenomena, such as extended droughts and tionships with other ecological factors, notably human- fires. These elements have been discussed in Chapters 2– caused modifications such as grazing, fire suppression, 4, so they will only be summarized in this chapter. fuelwood cutting, and logging. These studies also focused Generally, as Native American populations grew and on changes in the recent past, that is, when Anglo Ameri- technological innovations advanced, these impacts af- cans began colonizing the region in the mid 19th century. fected ever increasingly larger areas, with greater pres- The adverse effects of extended drought on vegetation sures on selected resources. Several events or series of re- were recognized as early as the mid 19th century. In 1857 lated events marked significant changes in impacts on the a geologist with the Lt. Joseph C. Ives military expedition environment. In the late prehistoric period the introduc- to the Colorado River recorded that the lower reaches of tion of the bow-and-arrow, cultigens, and associated ag- upland juniper stands were dead. Stands of dead “pine- ricultural knowledge were hallmarks in this evolution. trees,” including ponderosa, were also observed at this Relatively large villages were established along the Rio time. This phenomenon was attributed to the extant Grande and tributaries, and areas of bosque were cleared drought conditions. More recent die-offs of juniper due for cultivation by the Puebloan groups. to xeric conditions have also been noted on the Pajarito In the 16th century the first Europeans brought firearms, Plateau west of Santa Fe (Hewett et al. 1913: 56–57, 59, 62) metal tools, livestock, and a different view of the physical and on the Sevilleta National Wildlife Refuge due to the and biological world and their relationship with it, exert- 1950s drought. ing new pressures on the environment. The Spanish popu- A member of the U.S. Geographical Exploration and lation grew steadily, while Native American numbers, Survey team in northern New Mexico in 1875 speculated especially the Puebloans, decreased, primarily due to in- that the area was becoming increasingly xeric. This specu- fectious diseases, also introduced by the Spanish. Impor- lation was probably based in part on reports by local tantly, livestock numbers increased disproportionately; Hispanos, who related that springs and creeks had ceased grasslands around every Pueblo and Hispano settlement flowing between 1775 and 1800. Another possible indica- were intensively grazed. Irrigation farming expanded to tor of increasingly xeric conditions on the plateau was the the point that little floodplain land in the Middle Valley encroachment of pinyons into the lower elevations of the was uncultivated. By the early 19th century some water- ponderosa pine zone (Hewett et al. 1913: 52–53). logging and build-up of salts in the soil were underway Climate fluctuations through time, combined with in- due to intensive irrigation. Riparian forests and pinyon- tensive grazing of cattle, have resulted in changes in veg- juniper woodlands near settlements were reduced for use etative cover and composition across the Southwest. One as fuelwood and building materials. Fire was sometimes of the plant genera that has been most affected is Juniperus, employed by Hispanics in these botanical zones to create which has increased its range markedly (Davis 1987: 123). pasture or farm land. West (1984: 1310–1313) concluded that climate fluctua- tions were only one probable cause of vegetative change EFFECTS OF CLIMATE in pinyon-juniper in the late historic period. During wet periods, pinyon-juniper has invaded or reinvaded inten- The role of climatic fluctuations as related to short-term sively grazed grassland areas where fuels for fire had been vegetational change has been investigated by a number diminished and where juniper seeds were dispersed in of ecologists, botanists, environmental historians, geog- feces. Density of both species has increased generally over raphers, and range specialists across the Southwest since the region. Decreased understory vegetation and compac- the 1950s (Arnold and Reid 1964; Bahre 1991; Brown 1950; tion of soils by livestock grazing, coupled with droughts Dobyns 1981; Gehlbach 1981; Harris 1966; Hastings and and then intense precipitation, may have led to soil ero- USDA Forest Service Gen. Tech. Rep. RMRS–GTR–5. 1998 265 sion as well. Donart (1984: 1249) determined that drought dates from the 1820s (Bayer et al. 1994: 90; Snow 1976: can cause considerable damage to grazed and nongrazed 172–175). Beginning about the same time, the Rio Grande vegetation, which can result in high levels of mortality of in the Alameda area began to move westward and by 1768 herbaceous plants. Drought-tolerant species or new spe- flowed in or near its present channel. Alameda, originally cies of plants can then invade the open areas created within located on the west bank of the river, was resettled on the a plant community. east side (Chavez 1957: 3; Sargeant 1987: 38–39). Veblen and Lorenz (1991: 173–176) attributed historic changes in the ponderosa zone along the Front Range in EFFECTS OF FIRE Colorado to climatic variability, fire (before 1920), logging, and grazing. Except for logging, these factors have con- The effects of fire on vegetation in the Southwest have tributed to ponderosa invasion of grasslands. Reduction been investigated since the 1920s (Arnold et al 1964; Bahre of natural and human-caused fires since 1920, a possible 1991; Hough 1926; Humphrey and Everson 1951; shift to a more mesic climate, and livestock overgrazing Kozlowski and Alhgren 1974; Leopold 1924; Pyne 1982; were cited as the agents of change. Stewart 1956; Weaver 1951, 1974; Wright 1980, to list only A recent study of vegetational change in southeastern a few). Studies have centered on invasion or reinvasion Arizona indicates that “no directional vegetation changes of grasslands due to fire suppression, floral structure and since 1870 have been clearly linked to any trends, changes, composition of woodlands, availability of nutrients in soil, or fluctuations in the climate” (Bahre 1991: 103). This study and other soil characteristics. Although much more is now and others, however, do support the hypothesis that short- known about the impacts of fire on flora, these phenomena term climatic changes or deviations do exacerbate human- are still poorly understood (Covington and DeBano 1990: caused modifications of plant communities, as indicated 78–79). above. Thus, biologists and eco-culturists (anthropolo- Impacts and changes caused by fire on grasslands re- gists, environmental historians, and geographers) must lated to juniper movement in the Southwest have been continue to direct their research at understanding the com- addressed by Bahre (1991); Humphrey (1974); Johnsen plex interactions between humans and their environment, (1962); Komarek (1969); and Vogl (1974). These investiga- including climate, through time (Bahre 1991: 105; Worster tors, in general, agree on the following historical impacts 1984). and changes produced by lightning or human-caused Periodic Rio Grande floods caused by melt of above- fires: normal snowfall or intense rains on the watershed im- pacted various eco-cultural resources in the Middle Val- 1. grassland fires were more frequent and widespread ley. One result of the high runoff was avulsion, or move- before 1900, ment of the river from its current channel to a new one. 2. fires were “hotter” on the ground due to the pres- From the 1600s to early 1900s the Rio Grande channel gen- ence of more grass biomass, erally shifted to the west side of the floodplain from An- 3. fires killed seedling or young woody shrubs and gostura to Belen (Fig. 57), although there were some east- trees up to 5 years old, and ward movements. 4. fires have been just one of several interrelated fac- Perhaps the earliest historic movement of the Rio tors producing change in the grasslands. Grande occurred near Tome Hill in Valencia County. Some time between 1692 and 1750 the river left its channel, Fire History which ran around the west end of the hill and along the south side of the eminence, and moved westward to near Prior to 1900, human-ignited fires and natural fires were or at its present location (Scurlock et al. 1995: 118–119). relatively frequent in grasslands, woodlands, and forests Fray Dominguez (Adams and Chavez 1956: 8) recorded at a given locale. Fire frequencies in the last 300 years, or a story about the eastward shift of the river in the Belen intervals over the last 300 years, range from 1.9 to 25 years. area, causing severe flood damage at Tome in 1769. In the Some presuppression or pre–1900 fires burned as long as early 1800s the Rio Grande again shifted westward in the several months over thousands of acres (Ahlstrand 1980: Bernalillo area, forcing residents on that side of the river 4, 6; Cooper 1960: 137–138; Foxx 1981: 7). Clearly, vegeta- to resettle on the new east bank at the present town site tion associations and composition in the study region have (Bowen and Sacca 1971: 48–49, 60; Lange and Riley 1970: evolved with periodic fire. 176). The major flood of 1884 caused a westward shift of In the early to mid 1800s there seems to have been a the river in the Los Lunas area (Crawford et al.
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