Sam Drake

Biophysical characterization and management effects on semiarid rangeland observed from Landsat ETM+ data

Semiarid rangelands are very sensitive to global climatic change; studies of their biophysical attributes are crucial to understanding the dynamics of rangeland ecosystems under human disturbance. In the Santa Rita Experimental Range, AZ, the vegetation has changed considerably, and there have been many management activities applied. This study calculates seven surface variables: the enhanced vegetation index, the normalized difference vegetation index (NDVI), surface albedos (total shortwave, visible, and near-infrared), leaf area index (LAI), and the fraction of photosynthetically active radiation (FPAR) absorbed by green vegetation from the Enhanced Thematic Mapper (ETM+) data. Comparison with the Moderate Resolution Imaging Spectroradiometer vegetation index and albedo products indicates they agree well with our estimates from ETM+, while their LAI and FPAR are larger than from ETM+. Human disturbance has significantly changed the cover types and biophysical conditions. Statistical tests indicate that surface albedos increased and FPAR decreased following tree-cutting disturbances. The recovery will require more than 67 years and is about 50% complete within 40 years at the higher elevation. Grass cover, vegetation indexes, albedos, and LAI recovered from cutting faster at the higher elevation. Woody plants, vegetation indexes, and LAI have recovered to their original characteristics after 65 years at the lower elevation. More studies are needed to examine the spectral characteristics of different ground components.

Fine-Scale Analysis of Mount Graham Red Squirrel Habitat Following Disturbance

Abstract Habitat destruction and degradation are major factors in reducing abundance, placing populations and species in jeopardy. Monitoring changes to habitat and identifying locations of habitat for a species, after disturbance, can assist mitigation of the effects of human-caused or -amplified habitat disturbance. Like many areas in the western United States, the Pinaleño Mountains of southeastern Arizona, USA, have suffered catastrophic fire and large-scale insect outbreaks in the last decade. The federally endangered Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis) is only found in the Pinaleño Mountains, and to assess effects of forest disturbance on habitat we modeled their potential habitat by identifying characteristics of cover surrounding their centrally defended middens. We classified high-spatial resolution satellite imagery into ground cover classes, and we used logistic regression to determine areas used by squirrels. We also used known midden locations in conjunction with slope, elevation, and aspect to create a predictive habitat map. Squirrels selected areas of denser forest with higher seedfall for midden sites. Among active middens, those in the densest and least damaged forests were occupied in more seasons than those in more fragmented and damaged areas. The future conservation of red squirrels and the return of healthy mature forests to the Pinaleño Mountains will rely on preservation of mixed conifer zones of the mountain and active restoration of spruce–fir forests to return them to squirrel habitat. Our ability to evaluate the spectrum of fine- to coarse-scale disturbance effects (individual tree mortality to area wide boundaries of a disturbance) with high-resolution satellite imagery shows the utility of this technique for monitoring future disturbances to habitat of imperiled species.

Comparison of Seed Germination of Agriophyllum squarrosum (L.) Moq. and Artemisia halodendron Turcz. Ex Bess, Two Dominant Species of Horqin Desert, China

Both Agriophyllum squarrosum and Artemisia halodendron play essential roles in the vegetation rehabilitation process in Horqin desert. Responses of germination to temperature, water potential, and burial depth in the two species were studied experimentally. The results showed that: (1) seeds of the two species could germinate with high final percentages (> 67%) at prevailing surface soil (0–5 cm) temperatures from April to July. However, Agriophyllum squarrosum had more efficient mechanisms to ensure that seeds germinate quickly at prevailing May temperatures but slowly at the temperatures of April and July, in comparison to Artemisia halodendron; (2) Artemisia halodendron had higher final germination percentages than Agriophyllum squarrosum when water potential was low (p < .0.01); and (3) seedlings of Artemisia halodendron emerged well only at a depth less than 1 cm and did not emerge at all when the burial depth reached 4 cm, while those of Agriophyllum squarrosum emerged with a final percentage of 21.6% even at the depth of 4 cm. These different characteristics of seed germination and seedling emergence could partially explain the phenomenon that Agriophyllum squarrosum always precedes Artemisia halodendron in establishing on moving sand dunes in Horqin desert.

The Recent Evolution of the Oasis Environment in the Taklimakan Desert, China

Numerous natural and anthropogenic factors have caused soil salinization, land surface degradation, and desertification in Keriya County in China’s Xinjiang region. Information from multi-temporal remotely sensed data such as the Soil Salinity Index (SSI) has contributed significantly to an understanding of these environmental changes. The approach to calculating SSI is based on the spectral bands of Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper Plus (ETM+). A soil salinity map of the Keriya County area was produced from Landsat ETM+ images, with an overall accuracy of 72.73% and kappa coefficient of 0.6689. The analysis of the recent evolution of the oasis of Keriya County was carried out by coupling climatic and socioeconomic data with information derived from multi-temporal remotely sensed data such as the SSI, Normalized Difference Vegetation Index (NDVI), and different land use classes. Such analysis appeared to be very useful in identifying and monitoring changes occurring in the oasis ecosystem and for understanding the consequences of human-induced land degradation processes.

Old and New: Changing Paradigms in Arid Lands Water Management

Water management paradigms and practices have evolved markedly from the post-World War II years to the twenty-first century. Changes have been particularly urgent and visible in water-limited arid lands. Notable trends include movement from an emphasis on technological, supply-side solutions toward sociological, demand-side management; from rigid top-down state control toward decentralized management; and from local or regional management arenas toward integrated, multilateral formation of water policy from a global perspective. Efforts continue to augment water supplies, but practice has shifted from tactics such as weather modification to energy-efficient desalination, wastewater reuse and, significantly, conservation, which was hardly considered in previous periods of perceived abundance. Overtaking even these efforts in importance is a growing intellectual elaboration of an integrated water management paradigm, which recognizes that each element on both the supply and demand sides of the equation contributes to the total water availability and requires consideration of linkages between urban and rural water use as well as between the domestic, industrial, and agricultural sectors. This awareness has spurred the establishment of “global water initiatives,” marking a shift toward globalization of water management to achieve higher levels of integration.

Deriving land surface biophysical parameters from satellite data for soil carbon sequestration

We apply a hybrid inversion algorithm to estimate land surface biophysical variables (e.g., leaf area index) from the CHRIS (Compact High Resolution Imaging Spectrometer), and ETM+. Field campaigns were conducted over Tucson, Arizona to validate the algorithms and the products. The derived products were compared for different human management activities. These products are then available for input to a plant growth model for calculating the potential for carbon sequestration