Landscape Ecology And Natural Disturbances: Relationships To Biodiversit Y
10Extension NoteLandscape Ecology and NaturalDisturbances: Relationships to Biodiversity BiodiversityManagement Conceptsin Landscape EcologyJohn Parminter and Patrick DaigleB.C. Ministry of ForestsResearch Program31 Bastion SquareVictoria, BC V8W 3E7(250) 386-6810July 1997“. . . if the effects of forestmanagement activitiesclosely resemble those ofnatural disturbances, therisk of losing native speciesand altering ecologicalprocesses is lowered . . .”Natural disturbance statistics grabyour attention: Hurricane-force winds flatten over ha of forest land on northern Vancouver Island in the winterof .Smallisolated “hot spots” of moun tain pine beetle infestations aredetected in southwestern BritishColumbia in the early s. Theseinfestations irrupt rapidly a decadelater into massive outbreaks covering ha of lodgepole pineforests. Wildfire burns over ha ofBritish Columbia’s forest land in . One fire alone covers ha—more than half of the totalarea burned.These extraordinary events canmean different things to differentpeople: a reduced timber harvest, alost wilderness reserve, an unsightlyrecreation area. Many of the feelingsgenerated embrace a sense of loss andthe belief that nature is on the rampage. But while these scenarios mayappear to conflict with and impair amultitude of forest resource values,these natural disturbances show evolution in action and can actuallymaintain that increasingly preciousglobal treasure—biodiversity.British Columbia’s natural ecosystems have all evolved, and are stillevolving, under the influence ofnatural disturbances such as wildfire,wind, and insects (Figure , Table ).To maintain a range of ecosystems andhabitats and to maintain biodiversity,a new approach in forest managementapplies the concepts of landscape anddisturbance ecology.The field of landscape ecologyintegrates natural disturbance regimesand their effects on the distribution ofecological types across a landscape,the dispersal and movement of plantand animal species, and the flow ofenergy and nutrients. The Forest Practices Code explicitly recognizeslandscape ecology by designatingplanning areas called Landscape Units,each with specific Landscape UnitObjectives. The Biodiversity Guidebook (B.C. Ministry of Forests andB.C. Ministry of Environment, Landsand Parks ), a component of theCode, focuses on the significance ofsustaining naturally occurring landscape patterns.The guidebook recommends aprocedure for establishing and meeting objectives to maintain biodiversityat both landscape and stand levels.Ecological principles form the basis ofthis approach, which assumes that ifthe effects of forest management activities closely resemble those ofnatural disturbances, the risk of losingnative species and altering ecologicalprocesses is lowered. January 2000. Policy direction for biodiversity is now represented by the Landscape Unit PlanningGuide. This Extension Note should be regarded as technical background only.Ministry of Forests Research Program
Disturbance history of British Columbia’s forests for insects, wildfires, and forestharvesting.The other biologicalconcepts documented asindividual extension notesinclude: management concepts forlandscape ecology(Extension Note No. 07), spatial patterns, connectivity, riparian areas, interior habitats andedge effects, and seral stages acrosslandscapes.This extension note is the second ina series designed to raise awareness oflandscape ecology concepts and toprovide background for the ecologically based forest managementapproach recommended in theBiodiversity Guidebook. The emphasisis on natural disturbance ecology(Parminter ). We first define anddescribe natural disturbances, theagents responsible, and the ecologicalprinciples of natural disturbances, andtheir effects on landscape patterns,processes, and functions. We concludeby examining how the concepts ofnatural disturbance ecology are incorporated into the Forest Practices Codeand the biodiversity guidelines.What Is Natural DisturbanceEcology?Until relatively recently, natural resource management decisions andactivities were based on the idea thatecosystems existed in a steady, selfreplacing state (sometimescorresponding to “old-growth” conditions) and that natural disturbanceswere unimportant. Some peoplesought to protect old-growth forestsfrom human intervention, believingthat this was the appropriate way topreserve all species.However, scientists have increasingly recognized that forest, shrub,and grassland ecosystems are dynamicentities. This view, referred to in ecology as the “non-equilibrium model,”considers ecosystem structure to bedetermined by interactions betweenthe long-term forces of ecologicalsuccession, fluctuations in climate,and the more immediate effects ofnatural disturbances.Natural disturbances are defined asrelatively distinct events in time thatdisrupt ecosystem, community, orpopulation structure and that changeresources, the availability of suitablehabitat, and/or the physical environment. These events occur at varyingintensities across various space andtime scales and have contributed,along with climate, soils, andgeomorphology, to producing thediverse landscape patterns we seetoday.Disturbance Agents and RegimesWildfire, wind, drought, insects, anddisease cause some of the most Parminter’s chapter in Voller and Harrison’s Conservation Biology Principles for Forested Landscapesprovides a valuable reference for those wanting an in-depth understanding.
Area affected by some natural and cultural disturbances in British Columbia(from Parminter 1997)Disturbance agentArea (ha)Insects (1921 1995)Wildfire (1912 1995)Forest harvesting (1913 1993)Slash burning (1913 1993)Land clearing (1913 1958)Wildlife habitat burning (1982 1993)Total24 274 99010 577 1518 289 0961 744 789438 164551 98045 876 170widespread landscape disturbance.They affect most ecosystems, but notwith equal frequency or magnitude.Catastrophic events, such as wildfire,wind, landslides, snow avalanches,flooding, and certain other weatherrelated phenomena, can be intenseand act over large areas, resulting inthe death of entire populations andcausing major changes to ecosystems.However, a relatively minor disturbance, involving tree death or treefallgaps, would affect only one or a fewindividuals.Two categories of natural disturbances are: . Abiotic: from non-living agents,such as wildfire, flood, landslidesand snow avalanches, and weatherrelated phenomena (e.g., wind,drought, frost/ice/snow). . Biotic: from living agents, such asdisease organisms, or grazing andbrowsing by mammals or insects.The combined effects of abioticand biotic natural disturbance agentsdetermine natural disturbance regimes. These regimes are defined byvariables such as the area disturbedand the frequency and magnitude ofthe disturbance (expressed as eitherintensity or severity).Disturbance frequency, size, andintensity vary among ecosystems,helping to create landscapes withdifferent attributes. Landscape attributes include the relativeabundance of seral stages, or thestages of ecosystem development thatfollow a major disturbance event.Other attributes relate to specifichabitats, such as riparian and wetlandareas, or to the spatial relationshipsthat influence landscape connectivityand edge or interior forest habitats.British Columbia’s forests haveevolved under the influence of severalnatural disturbance regimes, whichhave created the composition, size,age, and distribution of specific foresttypes, as well as the structural characteristics of forest stands.Seven Generalizations about theImportance of DisturbanceDisturbances are fundamentallyimportant in controlling landscapepattern and ecological function. PeterWhite ( ) listed seven generalizations that help to explain naturaldisturbances and their effects onecosystems. . Disturbances occur on a variety ofspatial and temporal scalesLandscape mosaics reflect the temporaland spatial distributions of disturbances. Disturbances can be of: small spatial scale (e.g., an individualtree dies or falls, creating a treefallgap), or large spatial scale (e.g., fire may return a large forested area to an earlyseral stage or wind may advancesuccession by releasing anunderstorey of shade-tolerant advanced regeneration).Both small- and large-scale disturbances can occur, resulting in landscapemosaics with patches of varying size,species composition, and age structure.
Disturbances can affect an ecosystem for: a relatively short time period (e.g.,a tree falls; subsequent canopyclosure occurs within a decade), or a relatively long time period (e.g., alandslide or intense wildfire;complete ecosystem recovery topre-disturbance conditions maytake centuries). . Disturbances affect many levels ofbiological organizationMost biological communities are recovering from the last disturbance.The effects of disturbance are felt atmany levels of biological organization—from the individual toecosystem-wide. Natural disturbancescan: disrupt ecosystem and standdevelopment, return areas to earlier stages ofsuccession, and change habitat mosaics.For example, severe fires may consume organic matter in soils, killdominant tree species, change streamchemistry, and shift the patterns ofmammal movements, thus affectingecological, physiological, and behavioural processes and landscapepatterns. . Disturbance regimes vary, bothregionally and within one landscape.Disturbances vary among specificgeographic areas and biogeoclimaticzones. Some regions or landscapes aresubject to wind, landslides, and flooding, while fire, insects, and diseaseaffect others more.For example, damage during severewind events is strongly associated withelevation and aspect, as well asvegetation structure. Extremely largeareas can be disturbed, especiallyalong or near the west coast, wherelarge-scale storms with hurricaneforce winds come ashore. Some %of individual tree mortality in coastalSitka spruce–western hemlock forestsis wind-induced, compared to lessthan % in interior ponderosa pineforests where conditions are differentand fire is the prevalent disturbanceagent.Small-scale wind events may createdisturbances of varying size in thelandscape because of specific topographic or vegetation conditions.Trees susceptible to blowdown includethose that are: situated in rain-saturated soils; located where airflow may be funnelled and thus accelerated (e.g., ona mountain ridge, at the head of avalley, or next to clearcuts); and weakened by age, root disease, orinsect damage. . Disturbances overlay environmental gradients, both influencing andbeing influenced by those gradientsUnderlying environmental gradientsaffect some natural disturbances. Forexample, fires have the potential toburn more intensely when movingacross dry terrain as opposed tomoister areas, where less fuel mightburn. Some disturbances, however,operate independently of physicalgradients, as when severe windstormsrandomly destroy trees over wideareas. The landscape patterns thatresult from this type of disturbanceare thus patchy and unrelated to theunderlying environmental gradients.Alternatively, some disturbancesreinforce changes in landscape composition and structure along physicalgradients. Such events are importantmechanisms for energy flow and nutrient cycling and for maintaining age,species, genetic, and structuraldiversity.5. Disturbances interactVarious disturbance agents affect analready diverse physical and biologicallandscape to create and maintain ecosystem diversity. Some disturbanceagents may promote or inhibit theoccurrence and effects of other disturbance agents.For example, windthrow may affect
areas with root rot, or insect attackmay increase in fire-damaged trees.Or, stands regenerating after a wildfiremay be less prone to bark beetle attackfor several decades, at which time thetrees may become susceptible.the establishment of early seral species. In contrast, windthrown forestsmay be accelerated towards a laterseral stage if shade-tolerant advancedregeneration forms the bulk of thenext stand. . Disturbances may result fromfeedback between the state of theplant community and itsvulnerability to disturbanceCertain landscape characteristics reinforce either shorter or longerdisturbance return intervals becauseof the composition and structure ofthe vegetation. So while the frequencyand intensity of disturbances caninfluence the types of ecosystems, andthus the vegetation present, theseecosystems can also develop distinctfeedback reactions that can, in turn,control the nature of the disturbance.For instance, stand-maintainingsurface fires were common in interiorDouglas-fir and ponderosa pine forests. Historically, these forests wereall-aged and consisted of distinctgroups (or clumps), usually of similarly aged trees, with a relatively openunderstorey and interspersedgrasslands. Such fires maintainedthese forests in this condition by essentially fire-proofing them: theirvulnerability to crown fires was reduced, which effectively reduced thepotential for succession to communities composed of later seral plantspecies.Natural Disturbances, EcosystemRecovery, and Biodiversity . Disturbances produce variabilityin communitiesDisturbances can impact a stand orlandscape unevenly. Natural disturbances (and those created by humanaction) can promote plant and animaldiversity by influencing the speciescomposition, age, edge characteristics,and distribution of stands across thelandscape.Because disturbance regimes canbe variable, resulting successionalpathways may also vary. For example,a stand-destroying wildfire may favourIn landscapes solely affected by natural processes, disturbances vary intime and space and maintain manyseral stages and community types at aregional scale. In the middle part ofthis century, the forests of coastalBritish Columbia were often harvestedand left to regenerate naturally orrestocked with Douglas-fir, sometimesregardless of site suitability. Forestmanagement consisted of clearcutting,snag falling, and slashburning—practices that were considered tomimic wildfire effects.To maintain biodiversity, resourcemanagers should understand hownatural disturbances and ecosystemrecovery are linked, and how historicalnatural disturbance regimes haveproduced the current habitat patternsand attributes of the landscape(Rogers ).Immediately after trees die in aforest, the complex process of renewalbegins. The speed of this recovery willvary greatly depending on the character and intensity of the disturbanceand the type of ecosystem affected.Ecosystems are not equally resilient—that is, they do not possess an equalability to recover. The species diversitythat ultimately arises in the disturbedarea depends on the balance struckbetween disturbance frequency andintensity and the level of competitionthat exists between species. Factorssuch as predation, other forms ofmortality, and environmental influences are also involved.Ecosystem Management and theForest Practices Code
The coastal plantations had asimpler structure and compositionthan natural forests and it was anticipated that most stands would beharvested before they were yearsold. These plantations lacked themulti-layered canopy, range of treesizes, old live trees, and abundantstanding dead trees and coarse woodydebris that are often present in naturalforests, thus reducing habitat qualityfor some species.At the landscape level, this management approach tended to alterdisturbance regimes by breaking uplarge blocks of mature forest into amosaic of young plantations, matureforests, and non-forested land. Insome areas, scattered cutblocks fragmented the landscape. In others, theprocess of continuous clearcutting leftfew, if any, remnant patches. Theamount of edge, the degree of isolation of forest remnants, and the lengthof forest road networks increased.These factors further influenced natural disturbance regimes, oftenresulting in accelerated windthrow,pest outbreaks, wildfire, and landslides.Today, forest operations are nolonger viewed as discrete treatments.Management activities take place in asemi-natural matrix of “culturally Comparison of idealized development in stands for (a) both structural diversityand wood production and (b) maximum wood production only (from Hansenet al. 1991).
Cissel et al4 ) describeal. (199(1994a useful six-step process toanalyze disturbanceprocesses at the landscapelevel and to generatepotential managementactions:1. Assess historic and currentdisturbance regimes forterrestrial and aquaticecosystems.2. Integrate this informationusing an appropriatemapping and/or narrativetechnique and define adesired landscapecondition and associatedmanagement approach forsubareas, or strata, withsimilar disturbanceregimes, potentialvegetation, and humanuse patterns.3. Project this managementapproach into the futureusing a geographicinformation system;assume no naturaldisturbances, but allow fornatural succession; modelharvesting thatharvestingapproximates the naturaldisturbance regime.4. Analyze the resultinglandscape pattern to see ifadjustments are needed tomeet establishedmanagement objectives(current conditions may beoutside the range ofdesired conditions).5. Adjust the frequencyfrequency,,intensityintensity,, or location offuture harvesting units asharvestingrequired; change theamount or shape ofreserves; prescribereserves;ecosystem restorationpractices.6. Identify managementactions that willencourage development ofthe desired landscapecondition.modified” forests, grasslands, andwetlands that dominates at the provincial scale. Furthermore, the land inthis matrix is managed in variousways—ranging from concentrated andintensive, to dispersed and extensive—to use multiple resources. This matrixalso plays three important roles related to biodiversity: providing habitat at smaller scales, buffering and increasing the effectiveness of protected areas (e.g.,parks and wilderness), and controlling connectivity in thelandscape, including the movementof organisms between protectedareas (Franklin ).The Forest Practices Code addresses the management needs of thissemi-natural matrix by using an ecosystem approach that considers theforest as a functioning ecological system in which ecological processesform a blueprint for specific resourcemanagement activities. These activities must enable the harvest of woodfibre, as well as maintain native species, ecosystem processes andstructures, and long-term ecosystemproductivity (Figure ).The guidelines in the BiodiversityGuidebook ( ) help to incorporatethe principles of natural disturbanceecology into forest planning. Themajor premise underlying the guidelines is that if the effects of forestmanagement activities closely resemble those of natural disturbances, thennatural ecological processes will likelycontinue with minimal adverse impact. This approach ensures thatmanagement treatments are consistent with the conditions under whichnatural species, gene pools, communities, ecosystems, and ecosystemprocesses have evolved.Applying Disturbance EcologyConceptsManagement activities can be successfully integrated into the naturallandscape by paying attention to thepatterns that result from natural disturbances and by anticipating futuredisturbances. To aid this integrationprocess, the Biodiversity Guidebookgroups the biogeoclimatic units ofBritish Columbia into five naturaldisturbance types characterized bysimilar disturbance regimes. Theseregimes were responsible for the composition, size, age, and distribution ofspecific forest types on the landscape,as well as the structural characteristicsof forest stands.To conserve biodiversity and maintain more natural landscapes,landscape-level management activitiesshould be kept within the historicalrange of variability that existed as thecurrent ecosystems and landscapesdeveloped. This concept is central todesigning management prescriptionsbecause it provides a reference pointfrom which to evaluate the success ofecosystem management. It can helpto: describe the dynamics of ecosystems that undergo continualchange, identify the range of sustainablefuture conditions, and establish the limits of acceptablechange (Morgan et al. ).Several current landscape designmethods incorporate important elements of the historical range ofvariability, such as site history, naturaldisturbance regimes, and successionalprocesses. (See, for example, Diaz andApostol ; Bell ; RegionalInteragency Executive Committee ; Diaz and Bell .) British Columbia’s biogeoclimatic ecosystemclassification system provides a framework that can be used to study howthe historical roles of natural disturbances have affected differentecosystems, and how disturbanceregimes interact with resource management activities.New management practices shouldconsciously focus on the effects ofnatural disturbances and the value ofbiological legacies, rather than on the
particular disturbance agent responsible. Larger-scale disturbances, such asmore extensive wildfire and windthrow, are emulated at the landscapelevel by designing similarly sized andshaped cutblocks, and leaving remnant patches of live and dead trees, aswell as residual coarse woody debris.Several adjacent cutblocks may beneeded to mimic larger natural disturbances, especially wildfires insub-boreal and boreal ecosystems(DeLong ). At a landscape scale,the choice of rotation age, rate of cut,and cutblock layout will determinethe future age-class distribution andlandscape pattern. The long-termconsequences of these new management regimes should be evaluatedover several cutting cycles.No single silvicultural system willprecisely reproduce the inherent natural variability because forests arecreated by a variety of disturbances.Some of this natural variation can beintroduced into managed landscapesby using a variety of silvicultural systems, but the choice will ultimatelydepend on the biological, social, andeconomic objectives for the landscape.The basic premise asserts that whenan ecosystem is managed within itshistorical range of variability, it willremain diverse, resilient, productive,and healthy.Text by Susan Bannerman
ReferencesBell, S. . Total resource design. InVisual landscape design trainingmanual. B.C. Min. For., Rec.Branch, Victoria, B.C. Rec. Br. Publ.No. - . App. . pp. – .British Columbia Ministry of Forestsand B.C. Ministry of Environment,Lands and Parks. . Biodiversityguidebook. B.C. Forest PracticesCode. Victoria, B.C. ix p.Cissel, J.H., F.J. Swanson, W.A. McKee,and A.L. Burditt. . Using thepast to plan the future in the PacificNorthwest. Journal of Forestry ( ): – , .DeLong, C. . Lessons from wildfire: managing the pattern of forestharvest. B.C. Min. For., PrinceGeorge For. Region, Prince George,B.C. Res. Note PG- . p.Diaz, N. and D. Apostol. . Forestlandscape analysis and design: aprocess for developing and implementing land managementobjectives for landscape patterns.U.S. Dep. Agric. For. Serv., Portland, Oreg. R -ECO-TP- - .Diaz, N. and S. Bell. . Landscapeanalysis and design. In Creating anew forestry for the twenty-firstcentury. K. Kohm (compiler).Island Press, Covelo, Calif.Franklin, J.F. . Preservingbiodiversity: species, ecosystems, orlandscapes? Ecological Applications ( ): – .Hansen, A.J., T.A. Spies, F.J. Swanson,and J.L. Ohmann. . Conservingbiodiversity in managed forests:lessons from natural forests.BioScience ( ): – .Morgan, P., G.H. Aplet, J.B. Haufler,H.C. Humphries, M.M. Moore, andW.D. Wilson. . Historical rangeof variability: a useful tool forevaluating ecosystem change. Journal of Sustainable Forestry ( / ): – .Parminter, J. [ ]. Natural disturbance ecology. In Conservationbiology principles for forestedlandscapes. J. Voller and S. Harrison(editors). B.C. Min. For., Res.Program, Victoria, B.C. In prep.Regional Interagency Executive Committee. . Ecosystem analysis atthe watershed scale: federal guideto watershed analysis, Version . .Regional Ecosystem Office, Portland, Oreg.Rogers, P. . Disturbance ecologyand forest management: a review ofthe literature. U.S. Dep. Agric. For.Serv., Ogden, Utah. Gen. Tech. Rep.INT-GTR- . p.White, P.S. . Natural disturbance,patch dynamics, and landscapepattern in natural areas. NaturalAreas Journal ( ): – .
ecological types across a landscape, the dispersal and movement of plant and animal species, and the flow of energy and nutrients. The Forest Prac-tices Code explicitly recognizes landscape ecology by designating planning areas called Landscape Units, each with specific Landscape Unit Objectives. The Biodiversity Guide-book (B.C. Ministry of .
The high stiffness of the optical bench readily transmits disturbances through the structure. To attenuate high frequency disturbances to the Earth-observing instruments, including reaction wheel disturbances, gimbal disturbances, and disturbances from the sun-pointed instruments, the . force and torque
population ecology) and then subsequently covering interactions between species in a community (i.e., community ecology). However, to facilitate completion of the final paper, I have recently switched to covering community ecology and ecosystem ecology before population ecology. As both ecology and evolution have to be covered in the same .
Taguchi divide disturbances into three categories - External disturbances: variations in the environment where the product is used - Internal disturbances: ware and tare inside a specific unit - Disturbances in the production process: deviation from target values A three step method for achieving robust design (Taguchi) 1. Concept .
Ecology therefore means the study of an organism in its natural home. Odum (1963) defined ecology as the study of structure and function of nature or the study of inter-relationships between organisms and their environment. ECOLOGY AS A COURSE: Ecology is part of Biology because it dea
campus locations' Conceptual Landscape Master Plan (CLMP) . The framework consists of the Bases of Design: Landscape Concepts and Landscape Elements. The TP/SS-CLMP, the RV-CLMP and the GT-CLMP define the landscape concepts and elements which must be followed when site and building landscape projects are designed for each campus.
LANDMAP is a complete All-Wales GIS based landscape resource where landscape characteristics, qualities and influences on the landscape are recorded and evaluated into a nationally consistent data set. LANDMAP comprises five spatially related datasets known as the Geological Landscape, Landscape Habitats, Landscape Habitats, the Historic
aquatic, coastal, and marine systems. For these reasons, there is great demand for training in spatial analysis tools accessible to a wide audience. The first edition of this book, Learning Landscape Ecology: A Practical Guide to Concepts and Techniques, was the first "hands-on" teaching guide for landscape ecology.
approaches to the subject of reconstruction in archaeological illustration, and other media i.e. films. Method(s) of teaching: The module comprises: A weekly practical session (2hrs) where tutor will introduce different materials and recorded graphic data to be drawn. 1 x lecture Visit and meet with archaeological illustrators and graphic designers in their workplace Method of assessment: The .
