Cynthia S.A. Wallace

Estimation of Perennial Vegetation Cover Distribution in the Mojave Desert Using MODIS-EVI Data

This paper details a method to create regional models of perennial vegetation cover using pre-existing field data and satellite imagery. Total cover of perennial vegetation is an important ecological attribute of desert ecosystems, including the Mojave Desert, USA, an area of 125,000 km2. Moderate-Resolution Imaging Spectroradiometer Enhanced Vegetation Index (MODIS-EVI) data were coupled with measurements of total perennial cover and plot elevation using stepwise linear regression and linear regression techniques to create two models of cover. The final models produced R 2 of 0.82 and 0.81, respectively, and yielded maps of perennial cover distribution in the Mojave Desert at 250 m spatial resolution.

An Annual Plant Growth Proxy in the Mojave Desert Using MODIS-EVI Data

In the arid Mojave Desert, the phenological response of vegetation is largely dependent upon the timing and amount of rainfall, and maps of annual plant cover at any one point in time can vary widely. Our study developed relative annual plant growth models as proxies for annual plant cover using metrics that captured phenological variability in Moderate-Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) satellite images. We used landscape phenologies revealed in MODIS data together with ecological knowledge of annual plant seasonality to develop a suite of metrics to describe annual growth on a yearly basis. Each of these metrics was applied to temporally-composited MODIS-EVI images to develop a relative model of annual growth. Each model was evaluated by testing how well it predicted field estimates of annual cover collected during 2003 and 2005 at the Mojave National Preserve. The best performing metric was the spring difference metric, which compared the average of three spring MODIS-EVI composites of a given year to that of 2002, a year of record drought. The spring difference metric showed correlations with annual plant cover of R2 = 0.61 for 2005 and R2 = 0.47 for 2003. Although the correlation is moderate, we consider it supportive given the characteristics of the field data, which were collected for a different study in a localized area and are not ideal for calibration to MODIS pixels. A proxy for annual growth potential was developed from the spring difference metric of 2005 for use as an environmental data layer in desert tortoise habitat modeling. The application of the spring difference metric to other imagery years presents potential for other applications such as fuels, invasive species, and dust-emission monitoring in the Mojave Desert.

Biodiversity losses and conservation trade-offs: assessing future urban growth scenarios for a North American trade corridor

The Sonoran Desert and Apache Highlands ecoregions of North America are areas of exceptionally high plant and vertebrate biodiversity. However, much of the vertebrate biodiversity is supported by only a few vegetation types with limited distributions, some of which are increasingly threatened by changing land uses. We assessed the impacts of two future urban growth scenarios on biodiversity in a binational watershed in Arizona, USA and Sonora, Mexico. We quantified and mapped terrestrial vertebrate species richness using Wildlife Habitat Relation models and validated the results with data from National Park Service (NPS) biological inventories. Future urban growth, based on historical trends, was projected to the year 2050 for (1) a ‘Current Trends’ (CT) scenario and (2) a ‘Megalopolis’ (MEGA) scenario that represented a transnational growth corridor with open-space conservation attributes. Based on CT, 45% of existing riparian woodland (267 of 451species) and 34% of semi-desert grasslands (215 of 451 species) will be lost, whereas in the MEGA scenario, these types would decline by 44% and 24%, respectively. Outcomes of the two models suggest a trade-off at the taxonomic class level: CT would reduce and fragment mammal and herpetofauna habitat, while MEGA would result in loss of avian-rich riparian habitat.

DESERT FIRES FUELED BY NATIVE ANNUAL FORBS: EFFECTS OF FIRE ON COMMUNITIES OF PLANTS AND BIRDS IN THE LOWER SONORAN DESERT OF ARIZONA

Abstract In 2005, fire ignited by humans swept from Yuma Proving Grounds into Kofa National Wildlife Refuge, Arizona, burning ca. 9,255 ha of Wilderness Area. Fuels were predominantly the native forb Plantago ovata. Large fires at low elevations were rare in the 19th and 20th centuries, and fires fueled by native vegetation are undocumented in the southwestern deserts. We estimated the area damaged by fire using Moderate Resolution Imaging Spectroradiometer and Normalized Difference Vegetation Index, which are more accurate and reduce subjectivity of aerial surveys of perimeters of fires. Assemblages of upland and xeroriparian plants lost 91 and 81% of live cover, respectively, in fires. The trees Olneya tesota and Cercidium had high amounts of top-kill. King Valley was an important xeroriparian corridor for birds. Species richness of birds decreased significantly following the fire. Numbers of breeding birds were lower in burned areas of King Valley 3 years post-fire, compared to numbers in nearby but unburned Alamo Wash. Although birds function within a large geographic scale, the extent of this burn still influenced the relative abundance of local species of breeding birds. This suggests that breeding birds respond to conditions of localized burns and slow recovery of vegetation contributes to continued lower numbers of birds in the burned sites in King Valley. Resumen En el 2005, un fuego a causa humana arrasó desde Yuma Proving Grounds hasta el Kofa National Wildlife Refuge en el estado de Arizona, EEUU, quemando ca. 9255 hectáreas de un área silvestre. Los combustibles fueron predominantemente la hierba nativa Plantago ovata. Incendios grandes a elevación baja, fueron raros en los siglos diecinueve y veinte, e incendios a causa de vegetación nativa son sin precedentes de los desiertos del suroeste de los Estados Unidos. Usando un Espectroradiómetro de Imágenes de Resolución Moderada y el Índice de Vegetación de Diferencia Normalizada, se calculó el área dañada por el fuego con más precisión y menos subjetividad de los perímetros del incendio por medio de muestreos aéreos. Ensamblajes de plantas en ecosistemas de tierra alta y de ecosistemas xeroriparios perdieron el 91% y el 81% de cobertura viva, respectivamente. Los árboles Olneya tesota y Cercidium tuvieron mucha muerte de las partes superiores. El King Valley era un corredor xeroripario muy importante para las aves. La riqueza de especies de aves reproduciéndose disminuyó significativamente tras el incendio. Números de aves reproduciéndose fueron inferiores en las áreas quemadas hasta después de tres años en el King Valley, en comparación con los números en Alamo Wash, un área cercana no quemada. Reconociendo la gran escala geográfica dentro de la cual aves habitan, el alcance de este incendio aún tuvo influencia en la abundancia relativa de especies de aves locales que se reproducen allá. Esto sugiere que aves reproduciéndose responden a las condiciones de zonas quemadas locales y la lenta recuperación vegetal contribuye a los continuos números bajos de aves en los sitios quemados de King Valley.

Modeling Habitat of the Desert Tortoise (Gopherus agassizii) in the Mojave and Parts of the Sonoran Deserts of California, Nevada, Utah, and Arizona

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Fallow-land Algorithm based on Neighborhood and Temporal Anomalies (FANTA) to map planted versus fallowed croplands using MODIS data to assist in drought studies leading to water and food security assessments

An important metric to monitor for optimizing water use in agricultural areas is the amount of cropland left fallowed, or unplanted. Fallowed croplands are difficult to model because they have many expressions; for example, they can be managed and remain free of vegetation or be abandoned and become weedy if the climate for that season permits. We used 250 m, 8-day composite Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index data to develop an algorithm that can routinely map cropland status (planted or fallowed) with over 75% user’s and producer’s accuracies. The Fallow-land Algorithm based on Neighborhood and Temporal Anomalies (FANTA) compares the current greenness of a cultivated pixel to its historical greenness and to the greenness of all cultivated pixels within a defined spatial neighborhood, and is therefore transportable across space and through time. This article introduces FANTA and applies it to California from 2001 to 2015 as a case study for use in data-poor places and for use in historical modeling. Timely and accurate knowledge of the extent of fallowing can provide decision makers with insights and knowledge to mitigate the impacts of drought and provide a scientific basis for effective management response. This study is part of the WaterSMART (Sustain and Manage America’s Resources for Tomorrow) project, an interdisciplinary and collaborative research effort focused on improving water conservation and optimizing water use.