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High Altitude Environment

High altitude environments provide several important ecosystem services including water supplies and recreational opportunities (Körner 2004).

From: Climate Vulnerability , 2013

Cold-Climate Aeolian Environments☆

S.A. Wolfe , in Reference Module in Earth Systems and Environmental Sciences, 2021

5.4 High-altitude environments

High-altitude environments represent unique aeolian settings where cold-climate processes may dominate locally. In North America, Ahlbrandt and Andrews (1978) describe features particular to the high-altitude cold-climate dune field in North Park, Colorado. The dune field occurs at an elevation of approximately 2500 m asl in a cold-temperate subhumid setting where the mean annual temperature is approximately + 3 °C, and mean January temperature is approximately − 7 °C. The area consists primarily of large parabolic dunes, superimposed by smaller migrating transverse-barchanoid ridges and parabolic dunes. As noted earlier, dune migration is slow in comparison to more arid dunes, despite a high wind energy regime, probably due to freezing of the moisture in the sand in winter or burial of sand by snow. Similar processes may occur in other high-altitude dunefields in North America including Great Sand Dunes National Monument in Colorado, and the Casper, Ferris, Seminoe, and Killpecker dune fields of Wyoming.

In the Lake Tekapo area of the alpine regions of New Zealand, McGowan (1997) documents entrainment of dust, primarily in late autumn and early spring, associated with foehn winds. Although residing at a local elevation of approximately 700 m asl, mountain peaks within glaciated ranges up-valley attain heights greater than 2800 m asl. In this setting, fine-grained sediments are locally sourced from modern glaciofluvial braided river channels and alluvium (Fig. 20). Down-valley topographic funneling of foehn winds creates wind gusts greater than 25–30 m s^{− 1} at 2.65 m height, well above the estimated 7–8 m s^{− 1} required to entrain local sediment. Entrainment of sediment may be further enhanced by freeze-thaw cycles, resulting in the formation of needle-ice growth in exposed glaciofluvial and lacustrine deposits. Foehn winds cause these surfaces to thaw and dry, and subsequently become the primary sources of wind-blown sediment.

High-altitude aeolian processes are also prevalent in the Qinghai-Xizang Plateau of Tibet, China, at the relatively southerly latitudes of 36° to 29°N. Altitudes greater than 3000 m asl, coupled with dry conditions and strong winds create an environment highly conducive to aeolian sediment transport (Wang and French, 1995).

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CubeSat Technology and Periglacial Landscape Analysis

Julie Loisel , in Reference Module in Earth Systems and Environmental Sciences, 2021

1 Introduction

High-latitude and high-altitude environments are experiencing some of the most rapid changes on the planet, although logistic difficulties and availability of accurate data at appropriate spatial and temporal scales represents an ongoing problem for Earth scientists. Equipment and technology must be adapted to withstand long periods of cold temperatures, strong winds, as well as ice and snow cover. Access to remote locations for field sampling or installing equipment tends to be opportunistic, intermittent, and often limited to the summer season. In the case of polar regions, the prolonged dark winter period adds another source of complication in terms of access, equipment logistics, and observation technologies; even during summertime, remote sensed data are greatly limited due to frequent cloud cover and low solar illumination angles. Yet the polar and high-elevation regions of the world are experiencing relatively high-magnitude process rates involving ablation, erosion, sediment fluxes, and surface deformation. Furthermore, these environments are experiencing the fastest rates of structural environmental transformation due to climate change and human activity (Serreze and Francis, 2006; Borgerson, 2008). Such changes to landscape structure and organization, vegetation, hydrological and topographic patterns, and process regimes governing the water, carbon (C), and energy balance of these regions have local and global consequences (McGuire et al., 2009). It is therefore critical to better characterize the landscape and produce baseline information to accurately assess the impact of such changes, as well as to overcome the aforementioned challenges and utilize advances in remote sensing science and technology for characterization and monitoring, understanding the cryosphere, and providing insights into complex-system dynamics.

Recent developments in remote sensing technology have made it possible to use above-ground information to delineate, differentiate, measure, and track a number of periglacial processes and landform types. Most remote-sensing observations, however, still tend to be limited in terms of sensor and platform characteristics related to spatial, spectral, radiometric, and temporal resolutions, which dictate the level of generalization associated with information extraction, acquisitions times, and the ability to accurately assess and monitor change. In the coming years, nano-satellites such as CubeSats could help alleviate these notorious issues by providing new sensors and imagery that can accurately characterize the landscape and be used to actively monitor rapidly changing ecological, hydrological, and geomorphological systems in these remote environments. Indeed, the relatively new platform and sensor technologies enable acquisition of imagery at high spatial, spectral, radiometric, and temporal resolutions possible at a reasonable cost. Specifically, the miniaturization of a rapidly increasing number of sensor systems (e.g., multispectral, hyperspectral, magnetometers, radars) also makes CubeSat platforms ideal for capturing diverse environmental datasets that support multidisciplinary investigations of complex-system dynamics.

For the study of periglacial environments, CubeSat technology provides new opportunities to perform, for example, detailed topographic and morphometric analyses (geomorphometry), detailed characterization of landscape surface biophysical properties (hyperspectral remote sensing), as well as chemical atmospheric measurements using LiDAR, optical imagery, and radar imagery. Such datasets can be used to quantify the rate of change of landforms and processes (e.g., erosion, deposition, ablation, evapotranspiration) that were previously undetectable, which ultimately can be linked to early-warning systems and decision-support systems that can guide management and planning activities. Changes in biomass, phenology, and phytogeomorphology—which alter surface energy balance and greenhouse gas emissions—can also be monitored across thawing landscapes. Along those lines, monitoring hydrological changes (i.e., wetting vs. drying) of lowland and upland soils and vegetation communities is sorely needed.

The objective of this chapter, therefore, is to provide Earth scientists with an overview of CubeSat technology, and how it can be used for improved assessment and monitoring of rapidly changing environments. Background information is presented to address historical, technological, and practical aspects of the technology and existing and planned missions. Earth observation capabilities are then addressed and spatial and temporal analysis for information extraction is briefly covered. Important Earth-science applications are then highlighted. Finally, the use of CubeSat imagery for studying rapidly changing periglacial landscapes is demonstrated. When combined with ground observations and process-based models, CubeSats could have a transformative impact on Earth-observation capabilities and promote high-impact science.

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Occupied and Empty Regions of the Space of Extremophile Parameters

Jeffrey M. Robinson , Jill A. Mikucki , in Habitability of the Universe Before Earth, 2018

2.7.3 Vacuum and Low Pressure

Humans and other mammals exhibit physiological acclimation to low pressure in high altitude environments, except on the highest mountains. The "death-zone" for mammals is ~ 8000 m, above which death occurs even after long-term acclimatization due to low oxygen and severe physiological impacts resulting in cerebral and/or pulmonary edema (for reference, Mt. Everest peaks at 8,848 meters). On Mars, surface pressure is much lower (0.6 kPa) than on Earth (101 kPa), and experimental exposure of bacteria to simulated Martian conditions shows that this low pressure is well within the parameter ranges for many species, even species not known as "hypo-barophiles" (Schuerger & Nicholson, 2016).

Mammals are able to survive several minutes when exposed to vacuum (Gosline, 2008). Remarkably, many common and extremophilic microbes tested exhibit resistance to simulated or real space vacuum (Olsson-Francis & Cockell, 2010). Numerous organisms including viruses, bacteria, fungi, and nematodes were tested in space during the Apollo 16 mission (Taylor et al., 1975). Fungi (Novikova et al., 2015), lichens (Sancho et al., 2007), and animals such as tardigrades and nematodes (Jonsson et al., 2008) have also been tested. Many are able to survive medium- to long-term space exposure, and some are shown to survive even re-entry and impact (Pasini & Price, 2015).

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Vulnerability of Ecosystems to Climate

M.A. Davis , in Climate Vulnerability, 2013

4.05.3.2 Particularly Vulnerable Environments

Some regions of the world are more vulnerable to species introductions if weather patterns change. These include high altitude environments and high latitude regions. High altitude environments provide several important ecosystem services including water supplies and recreational opportunities ( Körner 2004). To date, many high altitude sites have yet to experience high rates of species introductions, probably due to a combination of low levels of propagule pressure and habitat disturbance, both a result of low amounts of human activity in these environments. However, more than one thousand species of non-native plants have established in high altitude sites throughout the world and while local species richness may increase at some sites, there is growing concern that some of these plants may negatively affect the highly valued ecosystem services provided by these environments (Pauchard et al. 2009). For example, the replacement of herbaceous or shrub vegetation by trees might result in increased evapotranspiration and less water export down to lower elevations (Mark and Dickinson 2008). Moderating temperatures would inevitably make it easier for many non-native species to spread into higher altitude sites. Also, the spread of non-native plants is likely increasing due to the increased connectivity between high altitude sites, which is resulting from increased movements by humans between sites, often facilitated by the construction of roads and/or recreation areas. The establishment of some non-native plants at these higher elevations may also be facilitated by atmospheric nitrogen deposition (Price 2006), bringing in yet another environmental change driver to interact with invasive species and climate.

Arctic regions have been reported to have experienced dramatic temperature increases over the past few decades, exceeding recent historical trends by 1.4 °C (Kaufman et al. 2009), although other data questions the magnitude of this increase [Alexeev et al 2012]. If surface temperature increases over the Arctic, which then warm the soils, and melt the permafrost, snow and ice, this would transform the terrestrial and marine arctic environments and making them amenable to more species. For example, it is estimated that 219 shallow water mollusk species in the northern Bering Sea have the potential to spread into the North Atlantic due to warming arctic waters without any human assistance (Vermeij and Roopnarine 2008). Increase shrub growth has been documented (Sturm et al. 2001) and the spread of other plants northward, some facilitated by humans and some not, is assumed. Like plants everywhere, they will alter ecosystem processes such as nutrient cycling and carbon sequestration. Some of the changes we may view as enhancing ecosystem services; some we may not. Antarctica currently has only two native vascular plants, Antarctic hairgrass, Deschampsia antarctica, and Antarctic pearlwort, Colobanthus quitensis (Caryophyllaceae). If surface temperatures warmed and increasing human travel to Antarctica by scientists and tourists, new plant species, as well as animal species, would be arriving soon, if they have not done so already. The number of species in high latitude regions would almost certainly increase since the number of introductions will likely exceed the number of extinctions, perhaps substantially. It is also expected that hybridization will be common between some of the new and long-term residents (Vermeij and Roopnarine 2008).

Environments experiencing increased resource availability are particularly vulnerable to the establishment of new species (Davis et al. 2000). As described above, if climate permits increased water and/or nutrient availability in an environment, it would be more invasible to many plant species. Similarly, if the local and regional climate results in an increase in primary productivity, the increase of food availability would likely make the habitat more invasible for herbivores.

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Weathering and Soils Geomorphology

P.A. Warke , in Treatise on Geomorphology, 2013

4.12.4.2.3 Form convergence (equifinality)

The surfaces of many desert regions are mantled with angular shattered debris similar to that observed in many cold high-latitude and/or high-altitude environments but the production of this debris in both hot and cold regions probably reflects the action of quite different processes exploiting structural weaknesses within the rock but resulting in a similar debris endform. For example, in hot deserts thermal fatigue and salt weathering may have a significant role to play in the generation of angular shattered debris. It is important to recognize that different processes can give rise to similar weathering forms and because arid environments are widely recognized as being rich in salts due to high rates of evaporation and a lack of fluvial outflow, there has been a tendency to associate salt weathering with the widespread breakdown and release of debris. Too often, weathering processes that are immediately associated with observed rock weathering forms are judged to be solely responsible for their formation. But this assumption of 'guilt by association' can obscure the role of both past and present processes. For example, repeated heating and cooling of rock surfaces over many years, while leaving no obvious physical trace, may have contributed to microscopic alteration through a thermal fatigue effect, whereby intergranular bonds are gradually weakened, facilitating the ingress of moisture and contributing to the apparent efficacy of salts (Smith and Warke, 1997).

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Fluvial Geomorphology

S. Tooth , in Treatise on Geomorphology, 2013

9.31.1 Introduction

'Drylands' is a collective term for the Earth's extensive hyperarid, arid, semiarid, and dry-subhumid environments, and includes many regions commonly referred to as deserts or semideserts. Drylands occur in cold, high-latitude, or high-altitude environments (e.g., Antarctica's Dry Valleys or the Tibetan Plateau) but most drylands are in warm, low-latitude, or low-altitude environments, being particularly prevalent within the subtropical, high-pressure belts of the Northern and Southern Hemispheres. These warm drylands are characterized by high (but variable) degrees of aridity, reflecting low precipitation totals and high potential evapotranspirative demands, yet nonetheless many support numerous river systems. 'Dryland rivers', 'desert rivers', and 'arid-zone rivers' are synonyms commonly used to describe these systems, many of which only flow infrequently but play a central role in landscape dynamics and exert a strong influence on human use of these marginal environments. A common assumption is that the dryland climate sets these rivers apart from rivers in wetter and/or cooler climatic settings (e.g., tropical, temperate, or polar environments), as expressed by differences in flow and sediment transport processes, by distinctive channel morphologies, or by characteristic spatial and temporal patterns of channel change. The idea that climate is the primary factor that determines river process, form, and behavior is similar to the climatic geomorphology school of thought, which was popular in mid-twentieth-century continental Europe. The central thesis of this school was that the Earth's surface could be divided into morphogenetic regions that are characterized by distinctive, climatically determined, landform assemblages (e.g., Büdel, 1982). Although climatic geomorphology has been subject to critiques that have downplayed the overriding importance of climatic factors in landform development (e.g., Twidale and Lageat, 1994), by-and-large similar critiques have not been applied to our thinking about dryland fluvial environments. As a result, the idea that dryland fluvial environments are somehow distinctive or even unique compared to fluvial environments in other climatic settings is entrenched in much of the literature, and indeed the inclusion of a specific chapter on drylands in this volume might be taken as reinforcing that idea. However, why should this be? Given the vast geographic extent of drylands, which cover a wide range of local climatic, tectonic, structural, lithological, and phytogeographical settings, should we not expect just as much diversity in fluvial process, form, and change within drylands as between drylands and other climatic settings?

The purpose of this chapter is to assess the distinctiveness and diversity of dryland fluvial environments from a global perspective. The focus is on warm drylands, and rather than attempting to cover all aspects of dryland fluvial environments, this chapter mainly emphasizes dryland rivers because typically they are the most imposing and identifiable features of fluvial landscapes, and they represent the main conduits for water and sediment movement (Tooth, 2000a). Many excellent reviews of other aspects of the dryland fluvial environment exist, including for hillslope runoff generation and sediment supply, gullies, alluvial fans, and pediments (e.g., see contributions in Thomas, 1997a; Bull and Kirkby, 2002a; Parsons and Abrahams, 2009). This chapter consists of five main sections. Section 9.31.2 traces the growth of the idea that there is a distinctive fluvial geomorphology of drylands. Section 9.31.3 highlights more recent findings that demonstrate greater diversity of dryland river process, form, and change than has hitherto been appreciated. Section 9.31.4 reviews the main characteristics of dryland rivers, including the different flow and sediment transport conditions, channel forms and dynamics, channel and floodplain sedimentology, and equilibrium and nonequilibrium behavior. Section 9.31.5, in the light of this review, questions whether we can make any sound generalizations regarding dryland rivers, and whether there are indeed any features distinctive or unique to dryland rivers. Section 9.31.6, by focusing particularly on findings emerging over the last decade or so, assesses recent trends in the study of dryland rivers, and identifies where the research frontier currently lies.

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Slow Periglacial Mass Wasting (Solifluction) on Mars

Andreas Johnsson , ... Harald Hiesinger , in Dynamic Mars, 2018

8.1.1 Context

The following paragraphs examine hillslope landforms on Mars that show remarkable morphological resemblance to terrestrial solifluction lobes where solifluction is a collection of slow mass-wasting processes associated with freeze–thaw action that always involves liquid water (e.g., Matsuoka, 2001). They are common landforms in Earth's cold nonglacial (periglacial) environments; i.e., an environment of perennially frozen ground overlain by a layer of seasonally thawed ground (active layer) or in high-altitude environments of seasonal frost (French, 2007). Their close spatial proximity to other relatively young landforms such as polygonal patterned ground (e.g., Levy et al., 2009) and gullies (e.g., Reiss et al., 2003) suggests that they are of similar age and formed within the last few million years. If the martian features are indeed formed by solifluction then they would be potentially important climate indicators hinting to environments where transient liquid water occurred on Mars in the Late Amazonian Epoch. However, the question of whether liquid water has been a landscape-modifying agent in the very recent climate history on Mars (i.e., within the time period of spacecraft observations) is debated with vigor (e.g., Pilorget and Forget, 2016; Conway et al., 2015; Malin and Edgett, 2000; Dundas et al., 2015, 2017a) and these debates propagate to the interpretation of landforms formed over the whole Amazonian Epoch. Although small quantities of flowing salty water (brines) have been proposed as an agent for the recurring slope lineae on Mars (Ojha et al., 2015; Stillman, 2017), most of the Mars' water, at or close to the surface, is believed to be currently locked in frozen reservoirs such as the polar caps (e.g., Byrne, 2009), i.e., ground ice (Feldman et al., 2004; Mellon and Jakosky, 1995; Mellon et al., 2009; Wilson et al., 2018), and debris-covered glacial ice (e.g., Levy et al., 2014; Holt et al., 2008; Plaut et al., 2009). The martian surface hosts numerous likely ice-related landforms such as glacier-like viscous flow features (e.g., Milliken et al., 2003; Souness and Hubbard, 2012; Hubbard et al., 2014), concentric crater fill (e.g., Levy et al., 2010), lineated valley fill (e.g., Squyres, 1979), and atmospherically derived dust/ice "mantle" deposits (e.g., Mustard et al., 2001). Collectively, these features likely reflect morphogenesis in subfreezing conditions. Other landforms are more ambiguous and have been reported to evolve entirely under subfreezing conditions or to have evolved by freeze–thaw cycling (Balme et al., 2013). These landforms include polygonally patterned ground (e.g., Mellon, 1997; Mangold, 2005; Levy et al., 2009; Soare et al., 2014a), scalloped depressions (e.g., Morgenstern et al., 2007; Soare et al., 2007; Lefort et al., 2010; Zanetti et al., 2010; Séjourné et al., 2011), and pingo-like fractured mounds (e.g., Burr et al., 2009; Soare et al., 2013, 2014b). However, due to the ambiguity (equifinality) of the processes leading to their formation, they are poor diagnostic landforms from which to infer the action of liquid water (e.g., Ulrich et al., 2011). Recent observations of hillslope landforms resembling retrogressive thaw slumps (Balme and Gallagher, 2009), seemingly sorted clastic patterned ground (Balme et al., 2009; Hauber et al., 2011a; Gallagher et al., 2011; Gallagher and Balme, 2011; Soare et al., 2016; Barrett et al., 2017), and solifluction lobe–like landforms (Gallagher et al., 2011; Hauber et al., 2011b; Johnsson et al., 2012; Soare et al., 2016) are more difficult to explain by subfreezing conditions alone (Gallagher and Balme, 2015). These observations raise the question as to whether Mars, at least locally, may have developed a relatively deep active layer (a layer that undergoes thermal cycling below and above the freezing point for water) allowing for transient liquid water and subsequent landform development.

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The Trace-Fossil Record of Vertebrates

Stephen T. Hasiotis , ... Michael J. Everhart , in Trace Fossils, 2007

Modern Aestivation and Hibernation Burrows

Aestivation and hibernation burrows are used by extant amphibians, reptiles, and mammals as temporary shelters from extreme, short-term climatic or environmental conditions. Aestivation and hibernation behaviors allow animals to occupy a wide variety of habitats and climate settings. For example, the anuran Scaphiopus couchii inhabits California deserts with a mean annual precipitation of less than 6 cm, no permanent water bodies, air temperatures that reach 50°C, and soil temperatures of over 30°C at a depth of 25 cm (Pinder et al., 1992). Simple to complex burrows are constructed to create a microenvironment more suitable for the animal's survival. These burrows are occupied from a few months to several years and are generally used only once. Successions of cross-cutting burrows can result from several years of seasonality producing many generations of burrows originating from the same surface.

Aestivation is a state of inactivity and metabolic reduction in response to a lack of water or high temperature. It is a common part of the life cycle of vertebrates that occupy periodically dry habitats. In general, the animal burrows into moist soil or mud, forms a cocoon to slow water loss, and becomes inactive to conserve energy (Pinder et al., 1992). By creating burrows, aestivators can rely on the soil-buffered burrow microenvironment rather than the surface environment. Daily temperature variation decreases with depth in the soil. Below 40 cm there is little to no daily temperature fluctuation. Decreasing moisture levels and increasing temperature are considered the signal for entering and leaving a state of aestivation. Extremes of either environmental variable can lead to extensive periods of aestivation. Some anurans can survive up to five years without leaving the aestivation state, although only a small percentage of the population survives (Pinder et al., 1992).

Hibernation is a state of inactivity in response to seasonally low temperatures in high-latitude or high-altitude environments. Animals have developed a number of responses to these conditions, including physiological means of tolerating freezing, submergence under water, or hibernating on land in a burrow to avoid freezing (Pinder et al., 1992; Butler, 1995). Burrowing hibernators must deal with prolonged cold and starvation by accumulating fuel reserves and adjusting their metabolic rates. Hibernation burrows must discourage desiccation, retain heat, provide protection from predators, supply environmental cues to trigger emergence, and maintain oxygen levels (Zug et al., 2001).

Fish inhabiting lakes and floodplain ponds in regions subject to drought use burrows to provide protection from desiccation. Gobies, catfish, mudskippers, and African and South American lungfish use burrows as aestivation chambers (Atkinson and Taylor, 1991). The African lungfish Protopterus annectens lives in floodplain swamps of the Gambia River (Greenwood, 1986). The climate has alternating wet and dry seasons in which rainy seasons may last 3–5 months and flood large areas of the alluvial plain. At the end of the rainy season, lungfish burrow into the floor of the drying swamps and aestivate while other fish re-enter the river. Protopterus constructs aestivation burrows by biting into the moist sediment of the pond floor and lateral motion of the body and tail (Greenwood, 1986).

Aestivation is most common among amphibians. Aestivating amphibians may be active for as few as 2 months of the year, their lives condensed into brief active periods during favorable conditions (Pinder et al., 1992). Aestivating anurans (frogs and toads) are mainly terrestrial or freshwater aquatic and inhabit regions with arid to semiarid climates subject to variable and seasonal rainfall (Pinder et al., 1992). The spadefoot toads of North America, Scaphiopus (Pelobatidae), the Australian Cyclorana (Hylidae), and the African bullfrog Pyxicephalus (Ranidae) are some of the best-documented terrestrial aestivators (Zug et al., 2001). These anurans aestivate for 7–10-months per year, and are active for short periods of time after seasonal rains create ephemeral ponds in which they breed (Pinder et al., 1992). The larvae develop quickly and metamorphose into adults before the waters evaporate. Amphibian aestivation burrows vary in depth depending on the season, average temperature, and the density of the soil. Spadefoot toad burrows range from 20–70-cm deep, while African bullfrog burrows are 80–150-cm deep (Pinder et al., 1992). Aestivation burrows are non-randomly distributed, occurring as small areas of high burrow density surrounded by large areas with no burrows. Over 39 spadefoot toad burrows have been reported from one 6 m² area (Pinder et al., 1992). Many amphibian aestivators form cocoons composed of one to several layers of shed skin or a layer of secreted mucus in order to reduce evaporative water loss (Pinder et al., 1992). Aquatic anurans form cocoons that reduce evaporative water loss by 90% and enable survival up to 150–250 days in dry soil (Pinder et al., 1992). Some salamanders produce cocoons of dried mucus similar to those of lungfish that allow survival for up to 110 days (Pinder et al., 1992).

Hibernation occurs in all major reptile groups in temperate and subtropical regions. In arid regions, aestivation occurs in response to seasonal drought. North American gopher tortoises use underground burrows as a general shelter, nest, and refuge from daily to seasonal temperature fluctuations (Zug et al., 2001). Skinks construct burrows or use those of other animals for winter refuges (Zug et al., 2001; Chapple, 2003). Australian skinks of the genus Egernia construct deep, complex burrow systems with multiple entrances and chambers (Chapple, 2003). While these burrows are used as permanent dwellings, the entrances are sealed prior to hibernation during winter months. Monitor lizards also construct simple burrows as refuges from daily to seasonal temperature variations (Traeholt, 1995).

Burrowing mammals are present in all continents. Many carnivores and omnivores burrow for denning purposes as well as for shelter from daily to seasonal temperature fluctuations (Butler, 1995). North American grizzly bears enter a period of dormancy from October to April. Their winter dens are not natural cavities but are excavated into the soil (Butler, 1995). Most of these dens collapse, however, during the spring snowmelt and summer rain, so reoccupation and preservation is unlikely. Grizzly dens are simple structures, consisting of a tunnel leading to a large interior chamber (Butler, 1995).

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SFAP Survey Planning and Implementation

James S. Aber , ... Susan E.W. Aber , in Small-Format Aerial Photography and UAS Imagery (Second Edition), 2019

9-4 High-Altitude SFAP

Humans are an unmistakably low-altitude species (Rankin 2016). Half of all people live below 165 m altitude, > 85% are below 1000 m, and only 6% live more than a mile (~ 1600 m) high. Thus, it is no surprise that most SFAP has been undertaken at relatively low altitudes. Chorier attempted kite aerial photography at 5600 m at Khardung La pass in the Jammu and Kashmir province of northern India, but was thwarted with strongly gusty wind and temperature of − 15 °C. He did succeed nearby in the village of Khardung just below 4000 m altitude (Chorier 2016). This is the highest successful kite aerial photography known to the authors.

Even higher altitudes of ~ 4300 m were reached in a study by Immerzeel et al. (2014), who monitored the debris-covered tongue of the Lirung Glacier in the Nepalese Himalaya using a small fixed-wing UAV. The current record lies with a custom-built quadcopter UAV (a Black Snapper type, see Chap. 8-3) that was flown at 8000 m ASL below the summit of Mount Everest in 2016 (Fischer 2016)—the pilots did, however, wisely shun the even thinner air, higher wind speeds, and incalculable risks for man and machine at the actual summit.

For purpose of this discussion, high altitude is considered to be those regions above ~ 1000 m in elevation, and tremendous scientific interest exists for all types of environments at these high elevations. Global warming in mountain regions and related geomorphological changes provide a challenge for SFAP. Retreat of alpine glaciers around the world documents the shrinking cryosphere, for example (Burkhart et al. 2017). Changes in permafrost soils, landslides, debris flows, and mountain floods are some short-term processes whose spatial distribution and change dynamics are of great interest in the near future. The same applies for vegetation including subalpine forest and alpine tundra impacted by climate change. Human activities such as forest cutting, overgrazing, building operations, and hiking and sports tourism also have consequences in high-altitude environments.

The force that holds up a winged aircraft is determined by relative wind speed and air density acting on the lifting surface. At high altitude, lower air density means that fewer and lighter molecules (per air volume) flow over the lifting surface at a given wind speed. Air density is governed by three factors—pressure, temperature, and humidity. The combination of these factors determines potential lifting power of a particular winged platform for a given wind speed.

The standard atmosphere is an ideal model of atmospheric conditions (Table 9-1). These values reveal that density decrease is fairly slight up to about 1000 m high. At higher altitudes, however, air density declines significantly. At 3000 m, for example, air density is only about ¾ that of sea-level density. However, this assumes the standard atmospheric temperature of − 4.5 °C at that altitude. At higher temperature comfortable for field work and full battery power, say 20 °C, air density is considerably less.

Table 9-1. Standard atmospheric conditions for temperature, pressure, density, and density percentage according to altitude. Based on data from Engineering ToolBox (2003).

Altitude (m)	Temp (°C)	Pressure (hPa)	Density (kg/m³)	Percent
Sea level	15.0	1013	1.23	100
1000	8.5	900	1.11	90
2000	2.0	800	1.01	82
3000	− 4.5	700	0.91	74
4000	− 11.0	620	0.82	67
5000	− 17.5	540	0.74	60

These conditions impact all types of winged platforms, both manned and unmanned. In the case of kites, for example, several components could be adjusted to compensate for decreased air density at high altitude—use a kite with greater intrinsic lift, increase the size of kite, use a train of multiple kites, and reduce the weight of the camera rig (Aber et al. 2008). In general, rigid kites, particularly the rokkaku type, provide the greatest intrinsic lifting power compared with other types of kites (see Chap. 7-4). For fixed-wing aircraft, lower air density would lead to higher flight speed at the same energy input. At the same speed, accordingly, the available weight-bearing capacity would be lower. Multirotor small UAS would likewise expend more battery power to stay aloft, thereby reducing flight time. Many UAS manufacturers are currently testing their aircraft under high-altitude conditions in order to offer customers more specific details on their performance for high-mountain applications.

Helium balloons and blimps, filled to capacity, have considerably less lifting ability at high altitude compared with lower altitudes. Likewise, hot-air systems at high altitudes have less lifting power for a given difference in air temperature than they would have in lower regions. On the other hand, the lifting power increases with a larger temperature gradient between the air outside and the air within the balloon. As high mountain areas are usually colder than lower regions, this effect compensates to a large extent for the change in lifting capacity. A hot-air balloon operated at 850 hPa pressure and 15 °C difference in air temperature, for example, can carry the same payload as it could at 1000 hPa and 25 °C temperature difference.

High-altitude SFAP often takes place in or near mountains. Mountain ranges typically create strong local climatic effects, which include colder temperature, enhanced cloud cover (Fig. 9-7), and more precipitation than for adjacent lowlands. Mountain peaks and valleys are well known for rapid weather changes. Swirling wind funnels along valleys and over passes with frequent and abrupt changes in direction and strength; alternating updrafts and downdrafts are routine.

In many high-mountain regions, airfields even for small single-engine microlight aircraft are either non-existent or not usable throughout the year. By using unmanned SFAP platforms, higher risks could be taken under difficult flight conditions. Finding a suitable open space for unmanned SFAP may be a challenge in forested mountains, and access to alpine areas above timberline may be quite limited. Areas with good access are often sites with other human structures and activities that could prove risky for tethered platforms (Fig. 9-8). The combination of cloud cover, variable wind, and limited access makes for difficult SFAP in many mountain settings, and small manned aircraft may be particularly dangerous to operate under these conditions as well.

The authors have conducted considerable high-altitude SFAP with both kites and blimps, in spite of such limitations. In general, thinner air with increasing elevation is not a serious problem up to about 2500 m. Thin air does become more significant above 2500 m, particularly at usual temperatures (20–30 °C) for typical field work during the growing season. High plains, mountain forelands, and broad intermontane valleys offer excellent SFAP situations with relatively open terrain (Fig. 9-9). Mountains are more difficult, however, because of frequent cloud cover, gusty wind, and limited ground access (Fig. 9-10).

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High-Elevation Andean Ecosystems

Mary T.K. Arroyo , Lohengrin A. Cavieres , in Encyclopedia of Biodiversity (Second Edition), 2013

Origin and Diversification of the High-Elevation Flora

How the high-altitude flora of the South America Andes has been assembled is a fascinating topic for evolutionary biologists and biogeographers. Phylogenetic studies reveal that multiple sources have been involved: the subtending lowland vegetation types, a wider neotropical source, an austral-Antarctic source and a holarctic source. Phylogenetic evidence also confirms that once clades are able to establish in the high-elevation belt, they are likely to undergo north–south migration (cf. Hughes and Eastwood, 2006). Evidence for more than one independent entry into the high-elevation belt has been found in several genera (e.g., Chaetanthera, Hershkovitz et al., 2006a, b; Halenia, von Hagen and Kadereit, 2003), leading in such cases to increased phylogenetic diversity.

Phylogenies containing páramo taxa were recently analyzed by Sklenář et al. (2011). These authors found that temperate and tropical sources contributed about equally to the páramo flora, but that temperate genera of true northern hemisphere origin contributed comparatively more species to the páramo than their southern hemisphere counterparts, in spite of the fact that the arrival of northern hemisphere groups would have occurred through chance long-distance dispersal.

The well known Espeletia complex (>130 species) was originally hypothesized to have an ancestor in the subtending montane belt (Cuatrecasas, 1986), and although important advances have been made in understanding the relationships of the complex (Rauscher, 2002), better taxon sampling is needed to iron out the fine details of the colonization process. Several high Andean clades involving a northern hemisphere origin such as Lupinus (Hughes and Eastwood, 2006), Astragalus (Scherson et al., 2008), Gentianella (von Hagen and Kadereit, 2001), Halenia (von Hagen and Kadereit, 2003), and Valeriana (Bell, 2004; Bell and Donoghue, 2005) have experienced huge radiations in the páramo and puna, and among these are found some of the highest divergence rates ever recorded (Scherson et al., 2008). Although Sklenář et al. (2011) found that temperate and tropical sources have contributed equally to the páramo flora, a huge proportion of the very large wet tropical lowland lineages subtending the páramo seem not to have been able to successfully colonize the páramo, presumably because they are less adaptable for life at high altitudes than incoming lineages of temperate origin. It is not clear at this point whether the same holds for the puna and southern Andean steppe. Here there are many examples of moderate to large-sized radiations in genera of South American origin as found in Chaetanthera (Hershkovitz et al., 2006a), Perezia (Simpson et al., 2009), Junellia (O´Leary et al., 2009), and especially the endemic high-elevation Nototriche (see Table 1), which is nested in the Tarasa clade (Tate and Simpson, 2003), with many other large genera still to be studied (e.g., Adesmia, Acaulimalva, Nassauvia, Leucheria, Werneria, Xenophyllum). The more gradual vegetation transition into the high-altitude environment in the puna and over a large part of southern Andean steppe could be expected to facilitate easier establishment and radiation of clades of South American origin into the high-elevation habitat.

Apart from major radiations that commonly cover two and even three of the major vegetation zones, the high-elevation flora has been enriched by small numbers of high altitude species evolving at different places in the phylogenies of groups mainly centered at lower to midelevations (e.g., Tropaeolum, Hershkovitz et al., 2006b; Malesherbia, Gengler-Nowak, 2003; Ourisia, Meudt and Simpson, 2006) or from migration along the Andean corridor from the initial point of establishment, as seen in case of the arrival of Astragalus in páramo (Sklenář et al., 2011) and Ourisia in páramo and puna (Meudt and Simpson, 2006) where northward migration has been involved. Although good phylogenies do not exist to ascertain the directionality of colonization, an important source of enrichment in the far southern Andes concerns a number of small endemic South America genera today occurring in the Patagonian steppe as well as at high elevations (e.g., Benthamiella, Gamocarpha, Oreopolus, Hamadryas, Huanaca, Onurus, Bolax). These genera, along with larger-radiating genera in the southern Andes such as Azorella and Nassauvia, could have comprised very early constituents of the original South American high-elevation flora. Hamadryas is a recently diverged clade within the Ranunculus complex (Hoot et al., 2008) and knowledge about when it diverged would shed important light on this important question. Other sources of enrichment include dispersal from an austral-Antarctic quarter. For example, as was already mentioned, Oreobolus is hypothesized to have arrived by long-distance dispersal in the southern Andes from Australasia at 5.5–6 Ma (Chacón et al., 2006) to later colonize into the northern Andes. Abrotanella is hypothesized to have existed on Antarctica in the mid-late Tertiary, to disperse northward into the Andes as well as into Australasia at around 3 Ma (Wagstaff et al., 2006). Overall, chance long-range dispersal has played an important role in bringing distant clades into the Andean high-elevation flora. Long to intermediate range dispersal has probably also played an important role in extending the latitudinal distributions of many resident clades, and might explain the outstanding success of the Asteraceae, a family which is generally well adapted for wind dispersal.

Twenty-five high Andean endemic genera are monotypic (Table 1). This high Andean biodiversity component is an intriguing one. Phylogenetic studies are now revealing that many of these monotypic genera are turning out to be embedded in other larger Andean clades. For example, southern Andean steppe Laretia, a dominant cushion plant in the central Chilean Andes, is sister to Azorella madreporica distributed in the puna (Nicolas and Plunkett, 2009). Until recently, Urbania was recognized as a monotypic genus of the puna, where it occurs at very high elevations. O´Leary et al. (2009) showed that it is embedded within a well supported clade of Junellia. Subsequently, it was transferred to Junellia (O´Leary et al., 2011). The high Andean monotypic cushion genus Patosia forms a well-supported clade with Oxychlöe, another small Juncaceous cushion genus (Table 1) (Záveská Drábková and Vlček, 2009). Monotypic Oreithales centered in the puna and páramo is nested within a clade of Anemone (Meyer et al., 2010), as is the slightly larger southern Andean steppe endemic high-elevation genus Barneoudia (Ranunculaceae). Laccopetalum and Krapfia (occurring also at lower altitude) are sister to one another, and belong to a terminal branching clade of the core Ranunculus group (Hoot et al., 2008); however, taxon sampling in Krapfia is presently insufficient to determine whether Laccopetalum diverged earlier than Krapfia. Overall, phylogenetic results tend to suggest recent origins for many of the high-elevation monotypic endemic genera. However, in other cases, relictual status seems more likely, as seen in the basal position of the endemic monotypic Caloppapus (Asteraceae) of the central Chile Andes with respect to a clade of Nassauvia and Triptilion (Simpson et al., 2009). Likewise, Huarpea, which is basal to a clade of Barnadesia (Gruenstaeudl et al., 2009) – the latter a genus of montane and lowland forest habitats in the Andes and Brazil – could turn out to be a relic taxon. The rare monotypic austral alpine genus Saxifragella was found to be deeply embedded in arctic and northern hemisphere Saxifraga sensu stricto and is considered to have arrived in the South American Andes via long-distance dispersal (Soltis et al., 2001), perhaps at an early stage. A fascinating case concerns Kurzamra (Lamiaceae), a monotypic dwarf shrub occurring at the upper limits of the vegetation. In a well sampled phylogeny Kurzamra occurs in a fairly well-supported clade with species of Cuminia, a small woody endemic genus of the Juan Fernández islands (Bräuchler et al., 2010). This relationship suggests that extinction of intermediates in the intervening Atacama desert might have occurred. Alternatively chance of long-distance dispersal into the high Andes associated with rapid morphological evolution might have been involved. To advance in our understanding the evolution of these fascinating high Andean genera, dated phylogenies, and often better taxon sampling are badly needed.

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