@article {JRN55042, title = {The interactive role of wind and water in functioning of drylands: what does the future hold?}, journal = {BioScience}, volume = {68}, year = {2018}, month = {09/2018}, pages = {670-677}, chapter = {670}, abstract = {

Feedback mechanisms between abiotic and biotic processes in dryland ecosystems lead to a strong sensitivity to interannual variations in climate. Under a future regime of higher temperatures but potentially increased rainfall variability, drylands are anticipated to experience changes in wind and water transport that will alter plant community composition and feedback on landscape connectivity. Here, we present a conceptual framework for understanding the coupling of vegetation productivity, aeolian transport, and hydrologic connectivity under anticipated changes in future climate, which suggests that a more extreme climatic regime will lead to more connected landscapes with attendant losses in soil, nutrient, and water resources. When enhanced connectivity triggers state changes, irreversible changes in ecosystem functioning can occur, with implications for the future of global drylands.

}, keywords = {aeolian, connectivity, deserts, precipitation, runoff, wind erosion}, doi = {10.1093/biosci/biy067 }, url = {files/bibliography/JRN55042.pdf}, author = {Gregory S. Okin and O. E. Sala and Enrique Vivoni and J. Zhang and Abinash Bhattachan} } @article {JRN54144, title = {Connectivity in dryland landscapes: shifting concepts of spatial interactions}, journal = {Frontiers in Ecology and the Environment}, volume = {13}, year = {2015}, month = {02/2015}, pages = {20-27}, chapter = {20}, abstract = {

Dryland ecosystems are often characterized by patchy vegetation and exposed soil. This structure enhances transport of soil resources and seeds through the landscape (primarily by wind and water, but also by animals), thus emphasizing the importance of connectivity {\textendash} given its relation to the flow of these materials {\textendash} as a component of dryland ecosystem function. We argue that, as with the fertile-islands conceptual model before it, the concept of connectivity explains many phenomena observed in drylands. Further, it serves as an organizing principle to understand dryland structure and function at scales from individual plants to entire landscapes. The concept of connectivity also helps to organize thinking about interactions among processes occurring at different scales, such as when processes at one scale are overridden by processes at another. In these cases, we suggest that state change occurs when fine-scale processes fail to adjust to new external conditions through resource use or redistribution at the finer scale. The connectivity framework has practical implications for land management, especially with respect to decision making concerning the scale and location of agricultural production or habitat restoration in the world{\textquoteright}s drylands.

}, keywords = {conceptual model, dryland landscapes, landscape connectivity, soil transport, spatial interactions, state changes}, doi = {10.1890/140163}, url = {/files/bibliography/15-003.pdf}, author = {Gregory S. Okin and Moreno-de las Heras, Mariano and Patricia M. Saco and Heather L. Throop and Enrique Vivoni and A.J. Parsons and John Wainwright and Debra C. Peters} } @proceedings {JRN54044, title = {The southern Kalahari as a dust source: preliminary results from the field}, year = {2014}, month = {07/2014}, pages = {p. 326}, publisher = {International Society of Aeolian Research (ISAR)}, address = {Lanzhou, China}, abstract = {

The Kalahari encompasses one of the largest drylands in the Southern Hemisphere and it is a potentially large source of atmospheric dust in its relatively low-dust region.\  The severe iron depletion in the southern Indian and Atlantic Oceans, the ocean basins that receive much of the Kalahari dust, suggests that even incremental increases in dust export to these basins could have significant impact on ocean productivity. The Kalahari also provides an excellent \“natural laboratory\”, due to its consistent Kalahari Sands existing along a strong precipitation gradient (from ~850 mm in southern Zambia to ~150 mm in southwestern Botswana) with a range of different land uses and land use intensities. A large-scale field campaign to evaluate the potential of the southern Kalahari to produce atmospheric dust was established in August, 2013. The goal of the experiment is to evaluate the potential of climate change and land-use to contribute to dust production. The experiment includes measurement of horizontal flux, vegetation structure, and meteorological variables. Novel estimates were made of dust production efficiency (vertical flux produced per unit of horizontal flux) through the coordinated use of active aerosol samplers and passive horizontal sediment traps.\  In addition, a new stereophotographic method using an unmanned aerial vehicles for the estimation of wind-relevant vegetation parameters has been developed for this project. Our preliminary field data and modeling results indicate that land use and climate can have a significant impact on the potential for dust emission from the region, but new field estimates of dust emission efficiency suggest that the absolute magnitude of dust emitted from the region might, at present, be lower than previously thought.

}, author = {Gregory S. Okin and Nicholas Webb and Abinash Bhattachan and Dintwe, Kebonye and Paolo D{\textquoteright}Odorico} } @article {49967, title = {Dust: small-scale processes with global consequences}, journal = {EOS Transactions, American Geophysical Union}, volume = {92}, year = {2011}, pages = {241-243}, abstract = {

[1] Desert dust, both modern and ancient, is a critical component of the Earth system. Atmospheric dust has important effects on climate by changing the atmospheric radiation budget, while deposited dust influences biogeochemical cycles in the oceans and on land. Dust deposited on snow and ice decreases its albedo, allowing more light to be trapped at the surface, thus increasing the rate of melt and influencing energy budgets and river discharge. In the human realm, dust contributes to the transport of allergens and pathogens and when inhaled can cause or aggravate respiratory diseases. Dust storms also represent a significant hazard to road and air travel. Because it affects so many Earth processes, dust is studied from a variety of perspectives and at multiple scales, with various disciplines examining emissions for different purposes using disparate strategies. Thus, the range of objectives in studying dust, as well as experimental approaches and results, has not yet been systematically integrated. Key research questions surrounding the production and sources of dust could benefit from improved collaboration among different research communities. These questions involve the origins of dust, factors that influence dust production and emission, and methods through which dust can be monitored.

}, keywords = {desert dust, dust emissions, remote sensing, small-scale processes}, doi = {10.1029/2011EO290001 }, url = {files/bibliography/JRN00562.pdf}, author = {Gregory S. Okin and Joanna E. Bullard and Reynolds, R. L. and Ballantine, J.-A. C. and Schepanski, K. and Todd, M. C. and Jayne Belnap and Matthew C. Baddock and Thomas E. Gill and M. Miller} } @article {49968, title = {Impacts of atmospheric nutrient deposition on marine productivity: Roles of nitrogen, phosphorus, and iron}, journal = {Global Biogeochemical Cycles}, volume = {25}, year = {2011}, pages = {GB2022}, keywords = {atmospheric deposition, iron, marine productivity, nitrogen, nutrient deposition, phosphorus}, author = {Gregory S. Okin and Baker, A. R. and Tegen, I. and Mahowald, N. M. and Dentener, F. J. and Duce, R. A. and Galloway, J. N. and Hunter, K. A. and Kanakidou, M. and Kubilay, N. and Prospero, J. M. and Sarin, M. M. and Surapipith, V. and Uematsu, M. and Zhuo, T.} } @article {50052, title = {The contribution of brown vegetation to vegetation dynamics}, journal = {Ecology}, volume = {91}, year = {2010}, pages = {743-755}, chapter = {743}, abstract = {

Indices of vegetation dynamics that include both green vegetation (GV) and non-photosynthetic vegetation (NPV), that is, brown vegetation, were applied to MODIS surface reflectance data from 2000 to 2006 for the southwestern United States. These indices reveal that the cover of NPV, a measure of vegetation brownness and a component of ecosystems worldwide, is highly variable in both space and time in the study region. In the more mesic regions of the study area, the timing of peaks in NPV appears to result from simple senescence of GV at the end of the growing season. In these regions, the amplitude of GV cyclicity dominates the total vegetation signal. In contrast, in arid and semiarid regions, the amplitude of cyclicity of NPV dominates the total vegetation signal, showing the vegetation of these regions to be unexpectedly dynamic. Shrublands of southwestern United States exhibit temporal behavior in which the annual peak in NPV cover precedes the annual peak in GV cover by a few months. Several explanations for this behavior are offered. This study shows the importance of vegetation indices that include NPV, or vegetation brownness, in understanding terrestrial ecosystem dynamics, as well as the response to change for these ecosystems.

}, keywords = {deserts, grasslands, green photosynthetic, non photosynthetic, phenology remote sensing, savannas, shrublands, stress vegetation dynamics, vegetation, woodlands}, doi = {10.1890/09-0302.1}, url = {/files/bibliography/10-051.pdf}, author = {Gregory S. Okin} } @article {50126, title = {Do changes in connectivity explain desertification?}, journal = {BioScience}, volume = {59}, number = {3}, year = {2009}, month = {March 2009}, pages = {237-244}, abstract = {Desertification, broad-scale land degradation in drylands, is a major environmental hazard facing inhabitants of the world{\textquoteright}s deserts as well as an important component of global change. There is no unifying framework that simply and effectively explains different forms of desertification. Here we argue for the unifying concept that diverse forms of desertification, and its remediation, are driven by changes in the length of connected pathways for the movement of fire, water and soil resources. Biophysical feedbacks exist that increase the length of connected pathways explaining the persistence of desertified landscapes around the globe. Management of connectivity in the context of environmental and socioeconomic change is essential to understand, and potentially reverse, the harmful effects of desertification.Desertification, broad-scale land degradation in drylands, is a major environmental hazard facing inhabitants of the world{\textquoteright}s deserts as well as an important component of global change. There is no unifying framework that simply and effectively explains different forms of desertification. Here we argue for the unifying concept that diverse forms of desertification, and its remediation, are driven by changes in the length of connected pathways for the movement of fire, water and soil resources. Biophysical feedbacks exist that increase the length of connected pathways explaining the persistence of desertified landscapes around the globe. Management of connectivity in the context of environmental and socioeconomic change is essential to understand, and potentially reverse, the harmful effects of desertification.}, keywords = {connectivity, desertifiction, erosion, fire, vegetation dynamics}, url = {/files/bibliography/09-007.pdf}, author = {Gregory S. Okin and A.J. Parsons and John Wainwright and Jeffrey E. Herrick and Brandon T Bestelmeyer and Debra C. Peters and E.L. Fredrickson} } @conference {50250, title = {Feedbacks between aeolian processes, vegetation productivity, and nutrient flux in deserts}, booktitle = {Geological Society of America Meetings}, series = {Geological Society of America Meetings}, year = {2008}, abstract = {Wind is a key abiotic factor that influences the dynamics of arid and semiarid systems. A series of experiments and models will be presented that show the important feedbacks that exist between Aeolian processes and biotic process in deserts. Wind impacts vegetation by both changing the composition of the soils, mainly by winnowing fines from erosional areas and redeposition of fines in deposition areas, and by direct physical effects on plants. The former leads to significant loss and redistribution of soil organic matter and plant nutrients as well as the disruption of nutrient cycling process. The latter leads to burial, pedestaling, leaf stripping and branch abrasion that lead to increased plant mortality. There is significant evidence that this leads to state changes in deserts, namely replacement of grasses by shrubs, which in turn create landscapes that are far larger emitters of dust. Changes in aridity have, in the past, caused changes variations in dust emission associated with vegetation state changes and, models suggest, aeolian processes will be increasingly important in vegetation change and dust emissions in deserts.}, keywords = {abstract, aeolian, arid, biotic, semiarid, wind}, author = {Gregory S. Okin and Junran Li and Lorelei Alvarez and Debra C. Peters and Paolo D{\textquoteright}Odorico} } @article {50251, title = {Spatial patterns of soil nutrients in two southern African savannas}, journal = {Journal of Geophysical Research - Biogeosciences}, volume = {113}, year = {2008}, pages = {G02011}, doi = {10.1029/2007JG000584}, author = {Gregory S. Okin and Mladenov, N. and L. Wang and Cassel, D. and Caylor, K. K. and Ringrose, S. and Stephen A. Macko} } @article {50480, title = {Multiscale controls on and consequences of aeolian processes in landscape change in arid and semi-arid environments}, journal = {Journal of Arid Environments}, volume = {65}, year = {2006}, month = {April 1, 2006}, pages = {253-275}, abstract = {Aeolian processes are tightly linked to soil and vegetation change in deserts at multiple spatial and temporal scales. Wind influences patterns of vegetation and soil within the landscape, while these patterns control wind erosion at patch to landscape scales. Aggregated at larger scales, patterns in soil and vegetation distributions influence global distributions of dust and its biogeochemical impacts. Understanding the controls on aeolian processes is, therefore, important not only in understanding the biogeochemistry and land cover patterns in dryland environments but also in understanding global land cover, climate, and biogeochemistry. These relationships are poorly understood, particularly for structurally complex plant communities such as shrub-invaded grasslands. The objective of this paper is to review the controls on aeolian processes and their consequences at plant-interspace, patch-landscape, and regional-global scales. Based on this review, we define the requirements for a cross-scale model of wind erosion in structurally complex arid and semi-arid ecosystems. http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WH9-4H1004J-1-1N\&_cdi=6845\&_user=1496926\&_orig=browse\&_coverDate=04\%2F30\%2F2006\&_sk=999349997\&view=c\&wchp=dGLbVtb-zSkWA\&md5=e74666463d89e6fd5315d4fde2958934\&ie=/sdarticle.pdf}, keywords = {aeolian processes, desertification, dust emission, landscape change, wind erosion}, url = {/files/bibliography/06-010.pdf}, author = {Gregory S. Okin and D. E. Gillette and Jeffrey E. Herrick} } @inbook {50696, title = {Modelling wind erosion and dust emission on vegetated surfaces}, booktitle = {Spatial Modeling of the Terrestrial Environment}, year = {2004}, note = {//USDA//LTER IV// Listed in LTER IV 2004 annual report}, month = {2004}, pages = {137-156 pp}, publisher = {Wiley, and Sons, Ltd}, organization = {Wiley, and Sons, Ltd}, abstract = {

Summary

This chapter contains sections titled:

}, keywords = {book, books, chapter, chapters, model, dust emission, model, wind erosion, report, reports, wind erosion, dust emission, wind erosion, modelling}, doi = {10.1002/0470094001.ch7}, author = {Gregory S. Okin and D. E. Gillette}, editor = {R. Kelly and Drake, N. A. and Barr, S. L. eds.} } @article {51027, title = {Degradation of sandy arid shrubland environments: observations, process modelling, and management implications}, journal = {Journal of Arid Environments}, volume = {47}, year = {2001}, note = {//USDA//LTER IV// In file and Updated 12/15/2005}, month = {2001}, pages = {123-144}, abstract = {

Field remote sensing, and modelling observations from a degraded Mojave Desert shrubland were used to develop a model of the progressive degradation of areas adjacent to sites of direct anthropogenic disturbance. Aeolian removal and transport and dust, sand, and litter are the primary mechanisms of degradation, killing plants by burial and abrasion, interrupting natural processes of nutrient accumulation, and allowing the loss of soil resources by abiotic transport. It is concluded that any arid shrubland with wind-erodible soils is susceptible to degradation, and where possible development of these lands should be avoided.

}, keywords = {agriculture, article, articles, desertification, journal, journals, landscape, ecosystem dynamics, management, shrublands, model, process, Mojave Desert, paleolakes, shrubland, degradation, shrublands, wind erosion}, doi = {10.1006/jare.2000.0711}, url = {files/bibliography/JRN00324.pdf}, author = {Gregory S. Okin and Murray Bruce and W. H. Schlesinger} } @inbook {51026, title = {Desertification in an arid shrubland in the southwestern United States}, booktitle = {Land Degradation}, year = {2001}, note = {//NMSU,USDA//LTER IV//ProCite field[6]: In}, month = {2001}, pages = {53-70}, publisher = {Kluwer Academic Publishers}, organization = {Kluwer Academic Publishers}, address = {Dordrecht}, abstract = {

In the Mojave Desert of the southwestern U.S. human destruction of soil crusts and removal of vegetation have led to progressive, expanding degradation of adjacent arid shrublands. Aeolian mobilisation of dust, sand and litter triggered by anthropogenic disturbance contributes to the destruction of islands of fertility in adjacent areas by killing shrubs through burial and abrasion. This interrupts nutrient-accumulation processes and allows the loss of soil resources by abiotic transport. Thus the processes of degradation spread across the landscape driven largely by abiotic processes.

Soil chemical analyses and remote sensing observations presented here are designed to test a model hypothesis of degradation of arid shrublands. Nutrient and non-nutrient chemical species in the soil act as tracers of material transport and provide clues as to the nature of progressive anthropogenic degradation in arid shrublands. Remote sensing yields information about short- and long-term effects on the landscape as well as important constraints on the magnitude of degradation. Field, chemical and remote sensing observations argue for an extension of recent definitions and models of desertification to include the loss of islands of fertility in established shrublands. This extended model places arid shrublands in a continuum of physical and ecological processes and ecosystems that links semiarid grasslands with Sahara-like hyperarid barren lands.

}, keywords = {book, books, chapter, chapters, desertification, shrubland, Model Hypothesis, Mojave Desert, report, reports, Semiarid Grassland, shrubland, desertification, soil crust, wind erosion}, doi = {10.1007/978-94-017-2033-5_4}, url = {files/bibliography/JRN00325.pdf}, author = {Gregory S. Okin and Murray, B. and W. H. Schlesinger}, editor = {Conacher, A. J. ed.} } @article {51025, title = {Distribution of vegetation in wind-dominated landscapes: implications for wind erosion modeling and landscape processes}, journal = {Journal of Geophysical Research}, volume = {106}, year = {2001}, note = {//USDA//LTER IV//}, month = {2001}, pages = {9673-9684}, abstract = {

Dust emission and wind erosion from arid and semiarid environments provide a major source of global atmospheric aerosols. Well-known relations between wind stress and saltation sand flux for sand sheets and relations between sand flux and dust emission by sandblasting have enabled construction of dust models that have only been partly successful in predicting atmospheric mineral dust concentrations. Most models of wind erosion assume that vegetation is evenly distributed. Through the use of field, Fourier transform, and semivariogram analysis, we show that mesquite dunelands in the Chihuahuan Desert of southern New Mexico, United States, have anisotropic shrub distributions. Elongated areas of bare soil, {\textquotedblleft}streets,{\textquotedblright} which are aligned with the prevailing winds may partially explain discrepancies between observed and predicted atmospheric dust concentrations. Soils in the streets are not protected from winds blowing down the streets and may therefore produce more dust than if vegetation were more evenly distributed. Currently, few desert landscape evolution models take the role of wind explicitly into account. The existence of streets implies that wind plays a major role in the evolution of vegetated arid and semiarid landscapes with wind-erodible soils. Here wind acts in tandem with water to enforce islands of fertility centered around individual shrubs and may provide an explanation for reduced soil fertility observed in shrublands. Furthermore, in order for mathematical models of dust flux to be successful in these landscapes, new landscape models are required which incorporate the existence and orientation of streets.

}, keywords = {aeolian processes, vegetation effects, aeolian processes, wind erosion, article, articles, journal, journals, model, wind erosion, wind erosion, }, doi = {10.1007/978-94-017-2033-5_4}, url = {files/bibliography/JRN00327.pdf}, author = {Gregory S. Okin and D. E. Gillette} }