| Vegetation USGS Navajo Nation Studies |
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| USGS Navajo Nation Studies Map of Study Area Bedrock Mapping Surficial Mapping Land Surface Changes Vegetation Drought Conditions 1999-2005 Traditional Knowledge and the Native Perspective Project Participants Web Links Selected References Publications & Presentations |
Vegetation imvestigations will include:
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 Project members Kathryn Thomas and Harris Francis identifying plants. |
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Bimodal precipitation in the southwest is characterized by winter snowfall and summer monsoons that have different relative effects on the survival and germination of shrubs vs. C4 grasses (Neilson, R.P., 1986). Yet, the general shift in landscape conditions, from grass dominated to shrub dominated that has been well documented in the southwest, is often attributed to desertification and overgrazing (Humphrey, 1958; Savage and Swetnam, 1990). In addition, changes in land use practices on the Navajo Nation that began in the mid- 1970’s, from sheep (that forage on shrubs and grass) to cattle (that graze on grass almost exclusively) may contribute to a decrease in grass vs. shrub vegetation cover. Shrub dominated surfaces with a low relative percentage of surface cover provide less surface stabilization, and are more vulnerable to erosion by wind and water (Schlesinger et al., 1990). A comparison of satellite imagery from wet years in the early 80’s, and successive drought years will help to delineate trends in vegetation change and landscape change related to drought. Recent environmental changes that could contribute to increased drought severity and desertification include 1) changes in the types of precipitation, and timing and intensity of events 2) resulting changes in groundwater and surface water interactions and recharge, and 3) landscape and vegetation response to these changes. The current drought, as well as the droughts of 1908-1913, 1934-1935, 1951-1956, 1963-1965, were generally dry in both winter and summer, but also accompanied by short bursts of intense summer rain (Neilson, 1986). These traits, characteristic of drought in the past century, may become a more general characteristic of southwest precipitation with Global Warming (Trenberth, 1998). Although local climatic conditions are usually determined by temporally and spatially averaging precipitation patterns, sessile organisms, and the ecosystem in which they inhabit respond to the timing and sequences of weather events. Plants that provide surface stabilization require the successful completion of every stage in their life history, each of which is sensitive to different frequencies of meteorological variability (Neilson, 1986). The current drought in northeastern Arizona is characterized by less overall precipitation, but is accompanied by increased temperatures beginning in 2000, and a relatively late monsoon compared to earlier observations by Humphrey (1958) and Douglas et al. (1992). These current environmental trends, resulting in both drought and intermittent floods, will be examined in order to understand climate-landscape interactions that contribute to drought severity in the southwest. |
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U.S.
Department of the Interior - U.S.
Geological Survey - Geology
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