the geographic basis of geomorphic enquiry

The Geographic Basis of Geomorphic Enquiry

Nicholas Preston1, Gary Brierley2 and Kirstie Fryirs3*1School of Earth Sciences, Victoria University of Wellington2School of Environment, The University of Auckland3Department of Environment and Geography, Macquarie University

Abstract

Geomorphic enquiry ranges from interpretations of landscape evolution framed within geologicalsciences to contemporary process-form analyses that build upon engineering applications.Geographic discourse blends these perspectives, emphasizing spatio-temporal relationships across arange of scales. Following a brief historical overview, this article highlights how emerging themesin geomorphic enquiry emphasize nonlinear, emergent aspects of geomorphic systems. Suchunderstandings extend beyond traditional conceptualizations of landscapes that were based uponnotions of deterministic stability and predictability. The unique configuration and temporalsequence of drivers, disturbances and responses of each landscape, along with the historicalimprint, result in system-specific behavioural and evolutionary traits wherein landscape forms andprocesses are contingent upon a multitude of factors. This place-based perspective of landscapes isan inherently geographical approach to enquiry. Such geomorphic thinking provides a coherenttemplate for a range of environmental management applications, especially in interdisciplinaryfields such as landscape ecology and landscape engineering.

Introduction

… how to reconcile … views of what geomorphology is … is a topic that is perhaps too littlepursued.(Michael Church 2010, 282)

Geomorphic enquiry entails the description and explanation of landscape forms, processesand genesis. Implicitly, therefore, it requires both a generic understanding of the physicsand mechanics of process and an appreciation of the dynamic behaviour of landscapes asthey evolve through time (see, for example, Crozier et al. 2010). A large body of theoryhas been established to analyse patterns of landscape processes and forms across variousspatial and temporal scales. In developing this understanding, geomorphic enquiry extendsacross several disciplines, primarily housed within geography, geology and engineeringdepartments.

In recent years various authors have discussed prospective benefits and ⁄or limitations ofgeomorphic training received within geology and geography programmes, and prospectsrelated to the emergence of earth system sciences (see Church 2005; Dadson 2010;Keylock 2007, 2010; Paola et al. 2006; Parsons 2006; Ritter 1988; Slaymaker 2009; Summer-field 2005). These discussions build upon long-standing debate (see, for example, Brown1975; Bryan 1950). In many ways, the diversity of approaches to geomorphic enquirycan be viewed as a disciplinary strength, rather than a weakness (Butzer 1973; Jennings1973; Sherman 1996). Despite the range of perspectives on future geomorphologies, twoprimary threads of enquiry are emerging: large-scale modelling applications in earthsystem science, and applied (environmental) geomorphology. Our concern here lies with

Geography Compass 5/1 (2011): 21–34, 10.1111/j.1749-8198.2010.00404.x

ª 2011 The AuthorsGeography Compass ª 2011 Blackwell Publishing Ltd

the latter thread, striving to enhance the profile and uptake of geographic approaches togeomorphic enquiry (see Tooth 2009).

Geomorphologists have a long tradition of applying their science in environmentalmanagement (e.g. Cooke and Doornkamp 1974). Whether addressing concerns for globalchange, sustainability, natural resources management, natural hazards or conservation ⁄ res-toration issues, the spatial organization of landscapes and the way in which responses todisturbance or management treatments affect other parts of landscapes are innatelygeographic questions. Management efforts must build upon process-based understandingof landforms framed in their landscape and evolutionary context, giving due regard to theprimacy of location and spatial variability (i.e. system-specific understanding). As relation-ship to place is pivotal, there are highlight inherent dangers in resorting to the use ofoverly generalized relationships or modelled behaviour.

Our discussion of geographical applications of geomorphic enquiry builds upon a briefoverview of the history of geomorphological thought. We outline how recent develop-ments have arisen naturally from their predecessors, noting the complementarity betweenwhat have formerly been perceived as antithetical approaches to the study of geomor-phology. We highlight the way in which synthesis of various threads of geomorphologicalenquiry provides a more realistic basis for prediction and modelling of landscape behav-iour. As noted by Dadson (2010, 396):

Physical geographers have a significant contribution to make, not just in the integration ofknowledge of the biosphere, lithosphere, hydrosphere and atmosphere, but also to the detailedand nuanced ways in which the actions of and impacts upon human societies can be enumer-ated, quantified and communicated.

A Brief History of Geomorphic Thought

Modern geomorphology grew out of the nineteenth century quest to understand theEarth (Church 2010, 265). It is not the purpose of this article to provide a history ofgeomorphology, for which the reader is directed to, for example, Burt et al. (2008),Chorley et al. (1964) or Grapes et al. (2008). Rather, this overview of the discipline’sevolution shows how various developments in geomorphology can be related to eachother and, in particular, the historical underpinning of more recent developments.

HISTORICAL-EVOLUTIONARY GEOMORPHOLOGY

The eighteenth and nineteenth century roots of geomorphic enquiry emerged at a timewhen both explorers and scientists of the Western world were engaged in cataloguingand classifying natural history. At this time, the study of landforms was descriptive and itwas inherently geographic (i.e. place mattered). Emerging approaches to landscape evolutionreflected, in part, a reaction to the perception of catastrophism as the key driver of physi-cal landscapes. Examples include the emergence of the principle of uniformitarianism (thepresent is the key to the past) proposed by Hutton (1788, 1795) and insights into processgeomorphology conveyed by Lyell (1837). Subsequent extensions to this work includedthe incorporation of uniformitarian principles as a basis to explain the origin of sedimen-tary rocks (Sorby 1859) and the emergence of ‘dynamical geology’ by Dana (1863).

Subsequent developments of geomorphology as an academic discipline in the late nine-teenth century were inevitably influenced by Darwin’s then recently published Origin ofSpecies, which proposed that life had evolved through a series of primitive forms, rather

22 Geographic basis of geomorphic enquiry

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than having been created in its present state (see Stoddart 1966). Although geologistswere beginning to grasp the immensity of geological time, this was not yet widely appre-ciated, and the notion that life and the Earth itself had evolved throughout time was aradical departure from accepted knowledge. The geomorphological parallel was clear: justas organisms could be considered as the culmination of a process of biological evolution,so too was it possible for a landscape to have evolved through a series of intermediatestages, before reaching its current stage of development. This evolutionary foundation ofgeomorphic enquiry is best exemplified by the Geographical Cycle of W. M. Davis(1899). Davis’ Cycle was inherently historic, outlining various stages as landscapesprogress towards an evolutionary endpoint. Landscapes are viewed as being subjected tocontinuous, albeit slow, change over time.

Alternative cycles were advocated, framed in terms of climatic determinism and associ-ated regional landforms that developed from different sets of processes than those charac-teristic of Davis’ humid-temperate zone ‘Normal Cycle’ (e.g. Budel 1977; Cotton 1961;King 1953; Tricart and Cailleux 1972; Wood 1942). Indeed, Davis himself contributedalternative cycles, highlighting the relative importance of differing geomorphic processesin determining the evolutionary sequence of landscapes in differing morphoclimatogeneticsettings (e.g. Davis 1905).

Although this cyclic view of landscape development dominated geomorphic thinkingfor some time, and has not necessarily been abandoned, it was not without its critics. Inparticular, Penck (1924) pointed out that regions experiencing constant uplift do notexhibit the characteristic hillslope forms postulated by Davis. This implied that time wasnot an absolute determinant; the cycle did not have fixed beginning and ⁄or endpoints,but could be punctuated or interrupted without having run its course.

QUANTITATIVE-DYNAMIC GEOMORPHOLOGY

In a sense, historical-evolutionary approaches to geomorphic enquiry were essentiallydescriptive, largely overlooking process drivers and the idea of landscape adjustment – oradaptation – to a set of controls. The emergence of process-based approaches was later cast,perhaps inappropriately, as the antithesis to Davisian evolutionary geomorphology, withG. K. Gilbert as its figurehead (e.g. Gilbert 1877). As Sack (1992) pointed out, Davis andGilbert were not the competitors that later geomorphologists made them out to be, andthere is not necessarily antipathy between the approaches. Certainly the roots of thisapproach lie in Gilbert’s more pragmatic approach to landform explanation. A contemporaryof Davis, Gilbert recognized that it is not simply the inevitable passage of time that deter-mines landscape form; rather, landforms can more properly be described and explained byreference to the action of geomorphic processes largely independently of time. Gilbert(1877) viewed topographic form as the manifestation of the balance that exists between theinternal resistance of the earth surface and externally applied forces of erosion. Landformdevelopment in this context is thus a far more complex phenomenon than simple increase inentropy, and time is not considered to be an important variable in the same sense as withinthe Davisian cycle. Davisian notions of cyclicity were rejected as being too simplistic (e.g.Chorley 1965), as was the notion of an evolutionary endpoint to landform development.

The difference between these two approaches was made explicit in seminal papers byChorley (1962), Hack (1960) and Strahler (1952), and expressed in terms of von Berta-lanffy’s (1950) general systems theory. In the terminology of general systems theory,the Davisian cyclic model is a closed system, defined with reference to the first law ofthermodynamics as those that do not exchange matter or energy across their boundaries.

Geographic basis of geomorphic enquiry 23


Davis’ Normal Cycle also corresponds to the second law of thermodynamics, wherebylandscape development can be characterized as decay to maximum entropy.

Although not explicitly stated as such by Davis, geomorphic change within the NormalCycle can be envisaged as trending towards a state characterized by minimal flux ofenergy and matter, i.e. increasing in entropy. In contrast, notions conveyed by Gilbertand others viewed the landscape as an open system or series of sub-systems. Both energyand matter could be introduced into the landscape system from external sources (e.g. pre-cipitation, streamflow), and each part of the landscape could be seen as a sub-systemexchanging matter and energy with adjacent sub-systems. The important distinction thusrelated to the notion of entropy. Rather than increasing with time as an ever-growingproportion of the landscape reached a state of geomorphic stasis, entropy was seen asbeing distributed throughout the landscape (Leopold and Langbein 1962). Definingentropy as the amount of energy not available for geomorphic work, Leopold andLangbein (1962) argued that landforms adjust following the principle of least work to astate in which energy would have the highest probability of being dissipated either kineti-cally or as heat. Thus, entropy would be located not in restricted parts of the landscape,but distributed everywhere throughout landscapes that had achieved steady state, ‘grade’(Mackin 1948) or ‘dynamic equilibrium’ (Strahler 1952). Quantitative-dynamic geomor-phology, as this approach was termed by Strahler (1952; see also Strahler 1992), wasdefined explicitly as the antithesis to Davisian historical or evolutionary geomorphology.However, as Chorley (1962) points out, for all the perceived failings of Davisian cyclicnotions, the quantitative-dynamic approach cannot fully explain ‘whole’ landscapes.While they may exhibit dynamic equilibria – which Davisian schemes did not readilyembrace – landscapes change over time, introducing an ‘unwelcome historical parameter’(Chorley 1962, 3). Clearly, as Chorley concluded, the quantitative-dynamic behaviour oflandscapes must be considered alongside the historical behaviour of systems. This entaileda shift in focus from broad landscape scales to a more detailed level of analysis, with anexplicit emphasis on quantitative rigour (e.g. Horton 1945; Strahler 1957). From thisemerged a suite of major developments in process-based understanding of landforms. Thistransition was assisted by notable technological developments after the second world war(Church 2010). Remote sensing applications alongside new computation and dating tech-niques enhanced surface and subsurface mapping capabilities and measurement ofgeomorphic process activity. Increased appreciation of the diversity of landscape formsand the plethora of controls upon them brought about the conceptualization of geomor-phology as a system science.

SYSTEMS APPROACH TO GEOMORPHIC ENQUIRY

Within a systems approach – as most clearly expressed in Physical Geography: a SystemsApproach by Chorley and Kennedy (1971) – landscapes can be conceived as comprisingany number of components with behavioural relationships. This reductionist approach toquantitative-dynamic geomorphology emphasizes the relation between the processes bywhich matter and energy move through the landscape and the forms that result from thatmovement.

Analysis of the individual components of landscapes highlighted the degree of separa-tion between a system and its surroundings (i.e. open versus closed systems) and thestructural criteria that can be used to differentiate (in order of increasing integration andsophistication) between morphological, cascading and process–response systems (Chorleyand Kennedy 1971). Disparate geomorphologies embraced a particular process domain in



a particular climatic zone (e.g. karst geomorphology, fluvial geomorphology, coastalgeomorphology, permafrost geomorphology, etc.; Harrison 2001). Within each sub-disci-pline, considerable progress was made in understanding the mechanics of process, build-ing largely upon the engineering literature. Increasingly fine resolution analyses usedunderstanding of Newtonian mechanics to relate direct measurements of process activityto resulting forms. Statistical analyses brought about more acute description of the rangeof landforms (see Strahler 1952, 1954). Prior to this time, the consideration of processes(at all scales) was ignored. As in other disciplines, the time was ripe for more precise(quantitative) descriptions of landforms to take precedence. Access to electronic calculat-ing machines facilitated this transition in approach. Horton’s (1945) articulation of thehydrophysical properties of drainage basins, Strahler (1950) and Strahler (1952) advocacyof general systems theory and dynamic geomorphology and Leopold and Maddock’s(1953) rationalization of the hydraulic geometry of river channels are but three illustra-tions of this new geomorphology. Many sophisticated numerical models were developedto characterize these processes. In many instances, these various suites of landforms wereappraised in relation to the notion of constant process-characteristic form, which suggests thatan idealized or characteristic landform is adjusted to the most effective magnitude ofprocess. These understandings built upon historical precedents. For example, hydraulicgeometry relations to channel form are an extension of regime theory principles(Kennedy 1895; Lindley 1919). As with Davis’ Geographical Cycle, the notion of con-stant process-characteristic form has elegance, and intuitively seems reasonable. Implicitly,the notion assumes that there is a normal, predictable state for the landscape – the formfrom which landscapes in dynamic equilibrium will be perturbed and to which they mayreturn. This reductionist Newtonian paradigm dominated geomorphic enquiry fromapproximately 1960–1990 (Church 2010).

For all the considerable progress geomorphology has made in terms of mechanisticunderstanding of morphodynamics, there is a limit to what this offers in terms of under-standing the landscape in its entirety (Baker and Twidale 1991). Increasingly, geomorphicinvestigations extend beyond analyses that reduce phenomena to their form and processcomponents at the individual landform scale. Nature is rarely neatly compartmentalized,and beyond reductionism there must be synthesis. True understanding of landscape func-tion requires knowledge of how the pieces of the landscape fit together. Focus uponlandscape-scale phenomena requires a parallel increase in the temporal dimension andrecognition of history (Brierley 2010; Schumm 1991).

Unfortunately, whenever the process-driven frequency ⁄magnitude ⁄effectivenessapproach to enquiry has been tested against historical data on actual change, it has beenfound wanting, as it often cannot predict past rates of process activity and associated land-scape responses. Similarly, difficulties in predicting the future have gone awry when trig-gering events fall outside the ‘known’ range of behaviour. As a result, increased emphasishas been placed upon understanding relationships between forcing processes (drivers,energy) and geomorphic response (the landform product), and associated notions of boththresholds (Schumm 1973, 1979) and landscape sensitivity (Brunsden and Thornes 1979;Selby 1974; Wolman and Gerson 1978). In addition, characterization of morphologicalresponse to environmental change or external perturbation must take into account theconcept of reaction and relaxation times (Allen 1974; Brunsden and Thornes 1979). Inturn, reaction and relaxation time needs to be considered in relation to the recurrenceinterval of forcing process (Brunsden and Thornes 1979; Selby 1974), and indeed to thesequence of forcing events of given magnitude (e.g. Beven 1981). Feedback scenarios canproduce circumstances wherein the relationship between forcing process and geomorphic



response is not constant in time, and neither stationarity nor constancy of threshold valuescan be assumed (e.g. Preston 1999, 2000).

In summary, it has become evident that landscapes respond to perturbing impulses incomplex, nonlinear ways (Schumm 1973, 1991). Process and form cannot be simplylinked together in terms of frequency, magnitude and effectiveness. Disrupted evolution-ary pathways, variable historical imprints and system-specific configuration ⁄ connectivityensure that there may be pronounced variability in behavioural responses to disturbanceevents. Related notions of emergence and contingency have promoted moves towardswhole-of-system applications at the landscape scale.

Beyond Reductionism to Whole-of-system (Geographic) Perspectives

Geomorphology is simultaneously developing in diverse directions: on one hand, it is becominga more rigorous geophysical science – a significant part of larger earth science discipline; onanother, it is becoming more concerned with human social and economic values, with environ-mental change, conservation ethics, with the human impact on the environment, and withissues of social justice and equity.(Michael Church 2010, 265)

As noted at the outset of this article, recent developments in geomorphology have beencharacterized by a split in approaches to enquiry, with the emergence of earth systemscience on the one hand and applied (environmental) geomorphology on the other. Under-standing of the earth system at a large scale has increasingly incorporated understandingsof erosion and sedimentation alongside tectonic processes, facilitating the re-emergence ofhistorical approaches to analysis of big-picture landscapes (Brocklehurst 2010; Church2005; Summerfield 2005). Numerical modelling exercises apply geophysical principlesalongside geomorphic understanding to fashion new understandings of landscape evolu-tion (Church 2010). These studies are complimentary to geomorphic applications in envi-ronmental management, where ‘whole of system’ understanding increasingly emphasizessystem-specific attribute at the landscape scale, highlighting distinctly geographic relation-ships to place.

It is axiomatic that ‘the whole is generally greater than the sum of its parts’. Landscapesystems exhibit emergent properties. History matters (Time) and disturbance matters(Change) (Fryirs and Brierley 2009). Embracing history and change at the landscape scaleas central themes of geomorphic enquiry reaffirms the integral role of historical-evolu-tionary geomorphology, while building upon the gains achieved by quantitative-dynamic(process) geomorphology. As noted by Bracken and Wainwright (2006, 176):

The implicit assumption of equilibrium (or tendency towards it) leads to an approach that isinherently static and linear. Even where geomorphologists assume variability from equilibrium(‘dynamic’ equilibrium or relaxation periods), they have tended to look for straightforwardcorrelations between landscape variables. This approach leads to both errors of omission (processignored because landscape variables do not correlate as expected for a static state) and ofcommission (due to spurious correlations). Deeper understanding requires the investigation oflandscape-forming processes within their phase space and historical context. It is time to gobeyond the limitations of short-termist, process-based geomorphology. … Difference and thedynamics of landscape change should thus play a more central role in geomorphological investi-gations.

Geomorphology as practiced today is rarely exclusively either evolutionary or process-based. Emerging themes of enquiry recognize: (i) the importance of location andspatial relationships, (ii) the central role played by disturbance to, and perturbation of,



geomorphic systems and (iii) the importance of evolution (i.e. past trajectory of change)in dictating current conditions (and likely trajectories of adjustment). Landscape behaviouris thus contingent on a multitude of interacting factors. Simply bolting together modelsof individual processes cannot explain whole-of-system changes over time. Increasedemphasis is now being given to the nature of process interaction, highlighting the mannerin which compartments function in concert.

Landscapes comprise mosaics of landforms of differing sizes and longevity, representingcomplex open systems characterized by morphological responses to differing processesoperating over multiple time scales. Different components of landscapes can be primed tochange in response to a diverse array of triggers. Impacts in one place may dampen orbuffer effects elsewhere (Brunsden 1993). As landscapes are constantly adjusting to myriadperturbing impulses, they are best described as nonlinear systems, wherein responses toexternal stimuli reflect initial conditions, the history of change and perturbation, proxim-ity to threshold conditions and the degree to which forcing processes and geomorphicforms are in-synchronicity with each other (Phillips 2003).

Each landscape reflects the cumulative history of responses to disturbance events andthe spatio-temporal propagation of those responses. Earlier views of landform develop-ment towards a climax or equilibrium endpoint are now considered to be overly naıveand simplistic. Geomorphic stability is no longer conceived of as an endpoint, or evennecessarily as a ‘normal’ state. In a sense, exceptions from a notional equilibrium condi-tion are now viewed as the norm (Phillips 2007). Landscape behaviour – both processoperation and the complex suite of landforms that result – is contingent on a wide range offactors, and deterministic prediction of system behaviour will rarely, if ever, be possible.This explicitly requires an acceptance of probabilistic rather than deterministic prediction.Landscapes are emergent (Harrison 2001). Although we can make statements about thelikelihood of occurrence of an event of given magnitude within a given spatio-temporalcontext, and under certain conditions (e.g. Crozier 1999), we cannot make absoluteprediction about time, location or magnitude of process occurrence or indeed of anythingmore than its immediate consequences. Although frequency ⁄ magnitude spectra of processbehaviour remain important, it is their statistics that are of interest as probabilistic(stochastic) approaches to qualitative understanding of system behaviour progressivelyreplace deterministic process models (Church 2003; Preston and Schmidt 2003; Wilcockand Iverson 2003).

Process–response relationships are fashioned by the way in which a system is puttogether, i.e. its configuration (Lane and Richards 1997; Wainwright 2006), defined by thespatial distribution of various components and their topological relationships. Of particularimportance are the make-up of landscape compartments and the degree of landscapecoupling – the connectedness of differing parts of landscapes, associated residence times,and the frequency of events that drives change along with the spatial ramifications ofthose changes (Brierley et al. 2006; Fryirs et al. 2007a,b; Harvey 2002). For example, thequalitative model of interim storage of sediment as it moves through the landscape devel-oped by Lang and Honscheidt (1999) is inherently configurational: it consists of a seriesof storage units that are linked topologically. Interpretation of sediment output dependson landscape topology and implicitly to the interaction of this with frequency ⁄magnitudeof redistributive processes.

A ‘constructivist’ (building block) approach to landscape analysis recognizes how eachpart of the system relates to its whole (Brierley 1996; Brierley and Fryirs 2005).Constructivism is by definition a ‘bottom-up’ approach, differing subtly from reduction ⁄synthesis only in the implicit sense that the end product is not predetermined. In this



approach, efforts to synthesize the behaviour and evolution of landscape compartments asa coherent whole can be considered as a sequence of steps:

1 Determine and define the components of landscape systems.2 Develop models that explain the behaviour of those components.3 Elucidate the interaction of those components.4 Develop models explaining how the landscape behaves.

If geomorphologists are to explain complex landscape behaviour and provide appropriatetools for effective management practice, process knowledge must be related to spatialconfiguration and the changing nature of process linkages over time to convey a coherentview of landscape forms, processes and their evolution. These innately geographic consid-erations highlight the importance of system-specific understanding as a basis for manage-ment applications.

Geographic Underpinnings of Landscape-scale Geomorphic Applications

The most engaging and interesting intellectual work on geomorphic forms such as river chan-nels has not come from computer specialists and theoretical models but from field measurementsand observations.(Luna B. Leopold 2004, 10)

The impact of human disturbance to landscapes has long been acknowledged (e.g. Marsh1864). Growth in human population and technological advances have massively increasedthese impacts in recent decades, such that human agency is now viewed as a dominantcontrol upon contemporary modification the Earth’s terrestrial surface (e.g. Hooke 2000;Montgomery 2007). In this light, the importance of geomorphic understanding in pro-viding a fundamental landscape template for management applications has becomeincreasingly recognized.

End users of geomorphological research are typically land or resource managers,addressing societal concerns for issues such as erosion and sedimentation, stability of slopesand channels, hazard mitigation, pollution and contamination of soils, water and air,ecosystem management, animal and plant pests, water supply and quality, planning forcompeting land use demands and so on. The goal of management now is often definedby legislation and expressed in terms of ‘ecological health’, ‘sustainability’ and ‘biodiver-sity’, and is typically framed as a ‘catchment management’ plan. Increasingly, the ques-tions being asked of environmental scientists relate to ‘big picture’ issues concerning wholelandscapes, and to changing systems. Recent developments in approaches to enquiry placegeographically trained geomorphologists in an ideal position to build upon traditionalstrengths in efforts to provide coherent guidance with which to frame solutions to envi-ronmental management issues. This entails working integratively with other physical ⁄natural scientists – and social scientists – at a wide range of spatial and temporal scales.Landscape-scale analysis of physical interactions provides an integrative physical templatefor research and management applications, viewing attributes of any given site in theirspatio-temporal context (Brierley and Fryirs 2005, 2008). As noted by Rhoads (2006),prospects for enhanced collaboration between physical and human geographers may beimproved through more effective grounding in process philosophy – enhanced apprecia-tion and understanding of the historical origin of concepts and ideas.

Geomorphological understanding thus frames site-specific process knowledge inrelation to position within a catchment and the trajectory of landscape evolution.



Geomorphic skills such as ‘reading the landscape’, unravelling human impacts on land-scape in relation to ‘natural’ variability and understanding past responses to climate changeprovide valuable guidance in forecasting the future.

Emerging nonlinear approaches to system-specific landscape analysis provide a coherentplatform for cross-disciplinary applications. For example, landscape ecology examines theinfluence of spatial pattern on ecological processes, considering the ecological con-sequences of where things are located in space, where they are relative to other things,and how these relationships and their consequences are contingent on the characteristicsof the surrounding landscape mosaic. The pattern of a landscape is derived from its com-position (the kinds of elements it contains), its structure (how they are arranged in space)and its behaviour (how it adjusts over time to various impulses for change). A landscapeapproach to analysis of ecosystems elucidates the links between pattern and process acrossscales to integrate spatial and temporal phenomena, to quantify fluxes of matter andenergy across environmental gradients, and to study complex phenomena such as succes-sion, connectivity, biodiversity and disturbance (Brierley and Fryirs 2005, 2008; Tockneret al. 2002; Townsend 1996; Ward et al. 2002; Wiens 2002).

Many contemporary approaches to landscape rehabilitation and management endeavourto ‘heal’ systems by enhancing natural recovery processes (Gore 1985). Assessment ofrecovery potential is a predictive process that is based on the trajectory of change of asystem in response to disturbance events (Brierley and Fryirs 2005; Fryirs and Brierley2000). Working with, or enhancing, natural recovery processes provides an appealingoption because many of these actions cost nothing in themselves (although they may costsomething to initiate), they are likely to be self sustaining (although they may neednurturing in some situations), and they can be applied on a large scale (Bradshaw 1996).Holistic approaches to landscape ecology present opportunities for geomorphologists tocontribute substantially to policy and planning at regional and national levels, enhancingprospects for landscape rehabilitation.

The shift in focus to large spatio-temporal scales of management presents a challengeto mechanistic models that strive for deterministic prediction, in part because of difficul-ties with parameterization and computation. Many existing models incorporate only alimited range of processes – although the ability to represent individual processes inmodels is becoming increasingly sophisticated. More importantly, however, incorporationof multiple processes introduces elements of contingency such that simple inference ofpast landform on the basis of process magnitude is likely to result in misleading postdic-tions. Because processes exhibit different frequency ⁄magnitude spectra, and the inter-action between processes introduces complexity and contingency, stochastic orprobabilistic approaches are likely to prove more effective in modelling applications formanagement (e.g. Preston and Schmidt 2003; Schmidt and Preston 2003; Werner 2003).

Conclusions

Reductionist approaches can fail when one deals with highly complex systems, like those ingeomorphology, that operate at large time and space scales with embedded processes occurringover all scales. Moreover, some aspects of these systems, such as the geohistorical uniqueness ofparticular geomorphological features and the role of biological processes, may simply defymechanistic representation.(Rhoads 2006, 28)

Geomorphologists have considerable potential to make important contributions to a rangeof issues of global significance. To achieve this potential, better integration is required



between the many disciplines that pertain to geomorphology (Dadson 2010; Paola et al.2006). The right questions must be asked, communicating effectively with key decision-makers (Brierley 2009). System-specific knowledge is required. Numerical treatments ofearth surface processes must be appropriately conceptually framed. There are many excit-ing opportunities for geomorphologists interested in multidisciplinary research (Keylock2010), as geographic skills and interests provide a significant bridge between natural andsocial sciences.

Geomorphic enquiry since the middle of the twentieth century has been dominated bya quantitative-dynamic approach. It has been explicitly reductionist, embracing the viewthat insight into how a geomorphic system works can be gained by breaking systems intotheir component parts. The challenge now is to synthesize and extend understandingbeyond the mechanics of process and into the holistic function of complex landscapesystems. Such a synthesis will of necessity embrace flux and change as the definingcharacteristics of geomorphic systems. Emerging perspectives in geomorphology framesmaller-scale interactions in relation to the spatial configuration of landscapes and their dis-turbance regime. Such thinking recognizes that it is difficult to predict the state of a systemat any point in time because of the multiplicity of factors upon which it is contingent.Nonlinear thinking explicitly recognizes the inherent complexity of landscape behaviourand responses to disturbance. Notions of contingency have replaced deterministic predict-ability at the heart of geomorphic enquiry.

In the face of this inherent complexity and uncertainty, geomorphologists have devel-oped numerous tools with which to appraise system-specific spatial and temporal patternsand rates of fluxes. In general, this understanding is applied at the catchment scale,thereby providing an effective basis with which to predict landscape changes and interpretbiophysical interactions (e.g. habitat changes, biogeochemical fluxes, etc.). Analyses oflandscape configuration and its connectivity increasingly emphasize functional relationsbetween system components, rather than the form-process relation for any individualcomponent. Linking process-based insights with new technologies such as terrain analysistools provides much greater predictive capacity.

In some ways that which was lost – or temporarily misplaced – through reductionismis now being regained. Perspectives of interactions over time have moved beyond thesimple sense implied by Davisian evolutionary models, recognizing that the history ofchange and perturbation in landscapes is a key determinant of subsequent geomorphicactivity. At the same time, geomorphologists have embraced space in new and differentways, emphasizing the importance of spatial arrangement – the way that landscapes areconfigured and their topology. Taken together, these geographic perspectives provide anew way of framing the questions we address in our research and teaching, prospectivelyopening new challenges and opportunities for geomorphology to respond to changingsocietal and economic demands.

Acknowledgement

We gratefully acknowledge insightful comments on an earlier draft of this manuscriptmade by Mike Crozier, Paul Hesse and Andreas Lang. Insightful and constructivecomments by three anonymous reviewers and the Editor of Geography Compass, BasilGomez, aided the clarity and communication of this paper. Financial support from ARCDiscovery project DP0345451 awarded to GB and KF supported NP during his time inAustralia.



Short Biographies

Dr Nick Preston completed his MSc at Victoria University of Wellington. His researchinvestigated the change in geotechnical slope resistance to shallow landsliding with time,providing the first demonstration of increasing resistance resulting from successive land-slide events. He undertook PhD studies at the University of Bonn, examining the role ofhuman activity in soil erosion over millennial time scales. Returning to New Zealand in2001 he took up a position with the Crown Research Institute, Landcare Research Ltdwhere he worked on soil erosion modelling. Subsequently he worked as a Post DoctoralFellow at Macquarie University, Australia where he worked on long profile relationships,landscape connectivity, and sediment flux in river systems. Appointed as a lecturer inGeography at Victoria University of Wellington in 2008, Nick developed courses in pro-cess and field geomorphology. His most recent research involves sediment flux at a sourceto sink scale, focussing on the hillslope ⁄fluvial interface.

Professor Gary Brierley is presently Chair of Physical Geography in the School ofEnvironment at the University of Auckland, New Zealand. He completed his undergrad-uate degree in Geography at Durham University, UK, his postgraduate work at SimonFraser University, Canada, and his post-doctoral work at the Australian National Univer-sity. He worked for fifteen years at Macquarie University, prior to moving to Aucklandin 2005. His research focuses primarily on the use of river science to guide managementapplications, especially concerns for ecosystem management, river conservation ⁄ rehabilita-tion and integrated catchment management. He is co-developer, along with Kirstie Fryirs,of the River Styles framework, and together with Kirstie he has written and ⁄or editedtwo major books: ‘‘Geomorphology and River Management’’ (Blackwell, 2005) and‘‘River Futures’’ (Island Press, 2008). Gary is presently Section Editor (Geomorphology)for Geography Compass having previously been Section Editor for the Environment andSociety section of the journal. He is also Chair of the Geomorphology Commission ofthe International Geographical Union.

Dr Kirstie Fryirs is a Senior Lecturer in the Department of Environment and Geogra-phy at Macquarie University, Sydney. Her postgraduate work focussed on post-Europeandisturbance responses in rivers and development of frameworks for assessing the physicalcondition and recovery potential of river systems. Sediment budgets, sediment tracingand landscape (dis)connectivity were the focus of her postdoctoral research. She is co-developer of the River Styles framework and short course. Her research currently focuseson how geomorphology provides a physical template for ecosystem function (in particularseed dispersal and upland swamp hydrology) and how science can be better used in envir-onmental management. She has also undertaken research on the distribution of heavymetal contamination at Casey and Wilkes stations in Antarctica. She has written and ⁄oredited two books with Prof. Gary Brierley titled ‘‘Geomorphology and River Manage-ment’’ (Blackwell, 2005) and ‘‘River Futures’’ (Island Press, 2008).

Note

* Correspondence address: Kirstie Fryirs, Department of Environment and Geography, Macquarie University,North Ryde, NSW 2109, Australia. E-mail: [email protected].

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