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2 - Spatial patterns
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp 18-45
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Summary
Key points
Remote sensing tools have greatly improved the mapping of both terrestrial and submarine landslides, particularly at global scales. At regional and local scales, environmental correlates are being found that help interpret spatial patterns and related ecological processes on landslides.
Landslides are frequent on only 4% of the terrestrial landscape and coverage varies over time because new landslides do not occur at a constant rate.
Multiple landslides triggered by the same event, such as an earthquake or severe rainstorm, can vary in physical characteristics. This variety contributes to a mosaic of landslide conditions across the landscape.
A landslide environment contrasts with the more stable conditions found in adjacent habitats. The transitions between landslide and adjacent habitats in light, fertility, stability, and other characteristics can be abrupt to gradual, sometimes making it difficult to define where a landslide begins or ends.
Introduction
The distribution of landslides is determined by background factors (ultimate causes) such as rock type and soil properties and by immediate triggers (proximate causes) such as rainfall or earthquake occurrence (Dai et al., 2002). While the prediction of the location and timing of a particular landslide remains inexact, mapping of existing landslides at global spatial scales is improving with the use of remote sensing tools such as satellite imagery (Hong et al., 2007). There are also discernible spatial patterns at regional and local scales, driven particularly by the location of landslide triggers (e.g., earthquake epicenters, regions of high rainfall) interacting with topography (Zhou et al., 2002). Within a given landslide, there can also be spatial patterns that influence local ecological processes. The dramatic impacts that landslides have on plants, animals, and soils represent important alterations of the spatial patterns of many ecosystems that can influence future ecosystem processes for decades (Foster et al., 1998).
References
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp 246-288
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4 - Biological consequences
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp 83-137
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Summary
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Landslide colonists have adaptations to survive low-nutrient, unstable substrates, where they may also experience temperature and water stress. Many of the species that colonize landslides are found exclusively in disturbed habitats and are known as gap specialists. Other colonists are common species in the adjacent undisturbed environment where their proximity to the landslide may have enabled rapid dispersal.
Microbes (including bacteria and fungi) are probably the first organisms to disperse to and colonize landslides. Symbiotic relationships, such as lichens, and plants with mycorrhizal fungi or nitrogen fixing bacteria, represent adaptations for survival in newly exposed, low-nutrient landslide substrates.
All plant life forms are found on landslides, but tend to segregate by slope. Small plants including bryophytes and forbs tend to dominate steep slopes, while tree ferns and trees tend to dominate less steep slopes. Grasses, vines, vine-like scrambling ferns, and shrubs, as well as most wind-dispersed plants, are common colonists on many landslides.
Arthropods are typically the first animals to colonize landslides, and include mites, Collembola, and ants, which are well adapted to temperature extremes and drought conditions.
Vertebrates associated with landslides are generally visitors rather than residents of the landslides. Birds and small mammals are the most common visitors, yet most vertebrates do not visit landslides until sufficient ground cover or foraging material has become established.
Preface
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp xi-xiv
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Summary
Landslides are fascinating because they are dangerous and remind us how powerless we are in the face of overwhelming geological forces. Some progress has been made on how to predict their occurrence and how to avoid or reduce the damage that they cause, but humans are still vulnerable to landslides. We find landslides fascinating for another reason. They create a new surface of exposed rock and soil to which plants, animals, and microbes respond. These habitat gaps in the landscape provide great habitats for rock hounds, plant collectors, bird watchers, and other outdoor enthusiasts, in addition to research opportunities for geologists and ecologists. Landslide surfaces are not at all homogeneous, but vary greatly in degree of plant and soil removal, subsequent stability, and soil fertility. Organisms respond to that variability with different patterns of colonization and community development. Understanding these responses can greatly improve landslide stabilization and ecosystem restoration. The new field of landslide ecology examines the biological responses to landslides, including human responses because we avoid, use, cause, and manage landslides. This book synthesizes the growing literature on landslide ecology and provides the first comprehensive examination of landslides as dynamic ecosystems rather than simply as physical phenomena to be predicted, avoided, and mitigated.
We begin this book by emphasizing the relevance of landslides to ecological processes. For instance, landslides act as conduits of soil nutrients and organic matter down slopes and into aquatic habitats including rivers and oceans. Landslides also provide habitats for colonization by early successional species. The spatial complexity of landslides comes both from the contrast with more stable, vegetated surfaces at the undisturbed edge and from variation in fertility and stability along lateral and vertical gradients within a landslide. Such heterogeneity often supports high regional biodiversity. We also discuss the physical causes and consequences of landslides, which is necessary information for any ecological study. These topics have been thoroughly addressed by geomorphologists, so we focus on their potential ecological consequences. For example, post-landslide erosion can reduce rates of ecosystem recovery, which are generally faster in warm, tropical regions than in cooler, temperate ones.
6 - Living with landslides
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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Human interactions with landslides have become more frequent and lethal as our populations expand into less stable terrain. This trend suggests that we must better understand what causes landslides and how to mitigate future damage.
Disturbances created by road construction, urban expansion, forestry, and agriculture are major contributors to anthropogenic landslides, and each has increased in frequency during the last several decades.
The field of landslide risk assessment is growing rapidly, and many new mapping and modeling tools are addressing how to predict landslide frequency and severity. Mitigation of landslide damage is also improving, particularly when new landslides follow patterns similar to previous ones. Despite a broad understanding of landslide triggers and consequences, detailed predictions of specific events remain elusive, due to the stochastic nature of each landslide's timing, pathway, and severity.
Biological tools are valuable additions to efforts to mitigate landslide damage. Biological protection of soil on slopes and restoration of species composition, food webs, and ecosystem processes ultimately must supplement technological approaches to achieve long-term slope stability because biological systems are generally more resilient than man-made structures.
Glossary
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 06 December 2012, pp 241-245
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Landslide Ecology
- Lawrence R. Walker, Aaron B. Shiels
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- 05 January 2013
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- 06 December 2012
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Despite their often dangerous and unpredictable nature, landslides provide fascinating templates for studying how soil organisms, plants and animals respond to such destruction. The emerging field of landslide ecology helps us understand these responses, aiding slope stabilisation and restoration and contributing to the progress made in geological approaches to landslide prediction and mitigation. Summarising the growing body of literature on the ecological consequences of landslides, this book provides a framework for the promotion of ecological tools in predicting, stabilising, and restoring biodiversity to landslide scars at both local and landscape scales. It explores nutrient cycling; soil development; and how soil organisms disperse, colonise and interact in what is often an inhospitable environment. Recognising the role that these processes play in providing solutions to the problem of unstable slopes, the authors present ecological approaches as useful, economical and resilient supplements to landslide management.
7 - Large scales and future directions for landslide ecology
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp 227-240
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Summary
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Landslide ecology is an emerging discipline that provides insights into both scientific and management issues. Scientifically, it explores nutrient cycling and soil development, plant physiological adaptations, dispersal and colonization dynamics, novel mixes of native and non-native species, and successional trajectories in an often inhospitable environment. Landslide ecology also integrates biological aspects of landslides into efforts to manage slope hydrology, soil erosion, and the stabilization of slopes.
Human–landslide interactions are becoming more common as human populations expand into mountainous terrain and climate change increases landslide frequency.
A landscape-level approach to landslide rehabilitation integrates topography, broad-scale climatic conditions, landslide density, patch dynamics, propagule dispersal, and coarse-scale predictive models.
We expect future contributions to landslide ecology will come from more effective technological tools to mitigate erosion and predict landslide hazards, an increased understanding of how plant–animal–soil interactions determine colonization patterns and successional trajectories, and practical contributions from efforts to use biological methods to stabilize landslides. Finally, we hope that the emergence of landslide ecology as a discipline will also improve our cultural perspectives of landslides, including the promotion of more sustainable uses of slopes and avoidance of erosion-prone areas.
Index
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 06 December 2012, pp 289-300
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Frontmatter
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp i-vi
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1 - Introduction
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 05 January 2013
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- 06 December 2012, pp 1-17
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The geological characteristics of landslides and their management as physical hazards are well documented. In contrast, the ecological processes that are initiated by landslides, and their relevance to efforts to restore stability to unstable slopes, have never been synthesized.
Landslides can cause intense human suffering and human activities can aggravate natural causes of landslides. However, we can ameliorate many of the worst effects of landslides through improved prediction and restoration of landslides and adjoining slopes.
Landslides initiate many ecological processes at landscape to local scales, including the process of ecological succession. Although landslides have negative effects on the survival of many terrestrial and aquatic organisms, they also recycle nutrients and provide habitats for colonizing species.
Landslides encompass many types of gravity-driven movements of mass. A typical landslide often has material that falls, slides, and flows, thereby creating geologically and ecologically heterogeneous substrates. Landslides cause and are caused by other disturbances, an interaction that creates a disturbance regime.
Relevance of landslides
A landslide is broadly defined as a sudden mass movement of substrate downhill and occurs on sloping terrain. Landslides can be localized slumps several square meters in size or so large that they are visible from space. Why are landslides important to you? Perhaps your property or farm has been damaged by landslides, or road access to your workplace or vacation site has been blocked. Maybe your telephone, water, or electrical power services were once disrupted. Or perhaps you follow reports of landslides because your home is on a steep slope and you wonder whether or when your property will slide. Regardless of your personal experience with landslides, we demonstrate in this book that landslides are relevant at many levels, both personal and ecological. Landslides are geological events that have obvious immediate impacts on landscapes and humans, but they also provide such ecological services as nutrient enrichment of rivers and creation of new habitats for colonizing organisms unable to survive in the surrounding ecosystem. The geology of landslides and hazard management (e.g., how to minimize property losses through landslide prediction, prevention, and restoration) are well-studied, with several recent summaries of research progress (e.g., Sidle & Ochiai, 2006; Sassa et al., 2007). However, the ecology of landslides (the interaction of organisms with the landslide environment) has received surprisingly little attention, given the dramatic influences that landslides have on the environment. Less than 1% of papers published on landslides between 1970 and 2010 address ecology (Web of Science, 2011). Landslides are a severe type of disturbance because they damage or remove plants, animals, and soil organisms. Landslide habitats are therefore of interest as examples of places where plant and animal communities assemble following disturbances that leave little or no biological legacy (primary succession). These ecological responses, when better understood, can be manipulated to augment restoration efforts that have, until recently, relied largely on modifications of the physical environment such as the construction of debris dams or re-contouring of slopes. Landslide ecology can thus be compared with other disturbances that initiate primary succession (e.g., volcanoes, retreating glaciers, and floods; Matthews, 1992; Reice, 2001; Walker & del Moral, 2003; Elias & Dias, 2009). This book attempts to fill the gap in our ecological understanding of landslides by presenting the first synthesis of the widely scattered literature on landslide ecology.
Plate Section
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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Contents
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 06 December 2012, pp vii-x
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3 - Physical causes and consequences
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 06 December 2012, pp 46-82
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Summary
Key points
The propensity for a landslide to occur is largely determined by potential slip planes, or weakness planes in the geological substrate, where the driving forces exceed resisting forces.
Landslide occurrence across the landscape is often unpredictable; substrates can be resistant to slippage for centuries and then suddenly experience instability that may result from human or non-human changes that disrupt the balance between driving and resisting forces at a slip plane.
Post-landslide erosion is common and can contribute as much as 33% of the total sediment loss from the site of landslide initiation. Such post-landslide erosion can continue for years, which reduces rates of ecosystem recovery on landslide scars and alters down slope habitats and watersheds.
Landslides greatly alter soils through physical losses, gains, and mixing, as well as through chemical changes. Soil organic matter contains critical nutrients and retains moisture; it facilitates soil and plant recovery in microhabitats present after a landslide. In warm, tropical regions, some landslide soil chemistry may recover to pre-landslide conditions within 55 years, yet such recovery is much slower in cooler, temperate regions.
Introduction
What causes a landslide? This is an important question, both ecologically and for human safety and hazard management. Landslides occur on sloped terrain, making topography a crucial component for landslide occurrence. However, the underlying factors that control whether or not a landslide is triggered include the conditions of the local soil and rock substrate. Below the ground surface, a complex combination of geological, topographical, hydrological, historical, climatological, and biological factors in addition to random disturbances interact and influence whether a landslide occurs (Table 3.1). Most of the below-ground characteristics that affect landslide occurrence are not fixed, but instead constitute dynamic interactions that can fluctuate in minutes or seconds. Water is absorbed and drained from soils at multiple scales and rates, which disrupts balances between driving and resisting forces. Seemingly static components of a hill slope, such as rock and soil, are also in a state of flux. Rock slabs can be split or pulverized through mechanical weathering, such as when moisture or roots penetrate cracks in bedrock and expand either by freezing or growing, respectively. Moisture, and the organic acids exuded by plants, can degrade rock surfaces and alter soil chemistry. Earthworms may increase infiltration, aeration, and organic matter decomposition (see Section 4.6.1).
5 - Biotic interactions and temporal patterns
- Lawrence R. Walker, University of Nevada, Las Vegas, Aaron B. Shiels
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- Landslide Ecology
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- 06 December 2012, pp 138-180
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Summary
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Landslide succession is the sequential replacement of plant communities following landslide creation. It is affected by biotic interactions and abiotic conditions and occurs in the intervals between recurrent erosion events.
Plant species can facilitate or inhibit landslide succession by direct species interactions or indirectly by the alteration of resources including light levels, soil stability, soil moisture, or soil nutrients. Species replacements may also occur due to differences in the life histories of landslide colonizers.
Herbivores, pathogens, and non-native species influence landslide succession and contribute to the variety of successional trajectories found on landslides, potentially with long-term consequences.
Landslides contribute to temporal heterogeneity of landscapes through their destruction and creation of habitats and sharp physical gradients. This heterogeneity generally has a net positive effect on biodiversity at landscape scales, but landslides generally decrease biodiversity at local scales.
Introduction
As soon as organisms colonize new landslide surfaces, they begin to alter the environment, often in ways that are not favorable for continued establishment of additional individuals of the same species. When changes in the landslide environment favor a new set of species better adapted to the changing conditions, species replacements occur. This process is considered succession (i.e., the change of ecological communities in structure and composition through time) (Glenn-Lewin et al., 1992). Primary succession occurs on surfaces where a disturbance has left little or no biological legacy (e.g., new volcanic surfaces); secondary succession occurs where soils remain relatively intact (e.g., following logging). Landslides are generally categorized as examples of primary succession because the initial disturbance removes most of the soil and vegetation (Walker & del Moral, 2003). However, because landslides frequently contain remnants of pre-disturbance soils and plants, change on those remnants often occurs along a continuum of disturbance severity between primary and secondary succession (Vitousek & Walker, 1987).
Germination after simulated rat damage in seeds of two endemic Hawaiian palm species
- Hector E. Pérez, Aaron B. Shiels, Halina M. Zaleski, Donald R. Drake
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- Journal of Tropical Ecology / Volume 24 / Issue 5 / September 2008
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- 01 September 2008, pp. 555-558
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Seed predation by native and alien rodents can limit plant recruitment and ultimately affect forest dynamics and composition (Campbell & Atkinson 2002, Côté et al. 2003, Hulme 1998, Sánchez-Cordero & Martínez-Gallardo 1998). Even partial consumption of seeds by predators may affect plant community structure, though its importance is poorly understood (Steele et al. 1993, Vallejo-Marín et al. 2006). Despite consumption of relatively large portions of seeds by herbivores, seeds can retain their ability to germinate if the embryo remains intact (Dalling & Harms 1999, Janzen 1972, Mack 1998). Germination of damaged seeds may be accelerated or prolonged (Karban & Lowenberg 1992, Koptur 1998, Vallejo-Marín et al. 2006). Damage by seed pests also facilitates ageing stress; which manifests as decreased seedling vigour, decreased seed viability, lower germination percentages and slower germination rates (Priestley 1986).