EEEEExtenxtenxtenxtenxtensssssionionionionion NoteNoteNoteNoteNote17

Ministry of Forests Research Program

Ministry contact:Allen Banner and Will MacKenzieB.C. Ministry of ForestsPrince Rupert Forest RegionBag 5000, 3726 Alfred Ave.Smithers, BC V0J 2N0(250) 847-7500

March 1998

Introduction

Riparian areas represent less than %of the provincial land base, but areoften considered the most dynamicof all landscape features. Natural dis-turbances and fluvial processes con-tinually work together in these areasto create distinctive ecosystems thatare crucial for biological habitat diver-sity. Because of their usually abundantsupplies of water and nutrients, mostriparian sites are highly productive fortimber. Riparian ecosystems also exerta great influence over animal andplant life, and many wildlife speciesdepend on riparian areas in some wayfor food, water, security, rest, travel,and reproduction.

However, because riparian areasusually occupy the lowest topographicpositions in landscapes and havenatural connections throughout thewatershed, they are particularly sensi-tive. Many of the known negativeeffects of historical land-use practiceson forested riparian areas resultedfrom a focus on the individual standor stream reach. Resource managersnow realize that a larger landscapeperspective and longer timeframes arenecessary when planning land-useactivities in riparian zones.

The Forest Practices Code acknowl-edges the importance of landscape

ecology concepts by enabling districtmanagers to designate planning areascalled landscape units, each withspecific landscape unit objectives.The Biodiversity Guidebook (B.C. Min-istry of Forests and B.C. Ministry ofEnvironment, Lands and Parks a),a component of the Code, recom-mends procedures to maintainbiodiversity at both the landscapeand the stand level. These procedures,which use principles of ecosystemmanagement tempered by social con-siderations, recognize that the ecologi-cal processes of riparian habitats mustbe sustained to maintain landscape-level biodiversity.

This extension note is the fifth ina series designed to raise awarenessof landscape ecology concepts andto provide background for the eco-logically based forest managementapproach recommended in theBiodiversity Guidebook. The focushere is on riparian areas. We firstdefine and describe riparian areas.We then discuss several ecologicalprinciples underlying the commonstructural and functional charac-teristics of riparian areas and reviewtheir implications for biodiversity.We also briefly examine some of thefunctions of healthy riparian areas

BiodiversityManagement Conceptsin Landscape Ecology

Riparian Areas: Providing LandscapeHabitat Diversity PART 5 of 71

January 2000. Policy direction for biodiversity is now represented by the Landscape Unit PlanningGuide. This Extension Note should be regarded as technical background only.

For those wanting a more in-depth understanding about riparian areas, refer to Voller’s chapter inConservation Biology for Forested Landscapes (Voller and Harrison ).

“ . . . the ecological

processes of riparian

habitats must be sustained

to maintain landscape-level

biodiversity . . .”

and cumulative harmful effects of poormanagement at the landscape level. Weconclude by suggesting how these con-cepts can be applied in landscape-levelplanning for biodiversity.

Riparian Areas: Definition

“Riparian” is derived from the Latinword ripa, which means bank orshore. Riparian areas are thereforeconsidered as the strips next tostreams and lakes that develop andsupport a typically rich and diverseflood-tolerant vegetation. While notall riparian areas are endowed withdistinctive vegetation, these ecosys-tems are nevertheless important be-cause of their proximity to water.

Landscape ecologists define ripar-ian strips in forested landscapes as“corridors” because they differ sub-stantially from the surrounding up-land matrix on both sides. Because oftheir linear character, these corridorsprovide important connectionsthroughout the forested landscape byjoining upper elevations and mid-slopes with valley bottoms.

Riparian areas represent a dynamicinterface, or “ecotone,” between water-and land-based ecosystems, wherecomponents of both ecosystems inter-act. Natural disturbance events (e.g.,flooding, erosion, and sedimentation)are regular phenomena in these areas,causing fluctuations in the associatedmosaic of successional vegetationcommunities and in fish and wildlifepopulations. Indeed, the character of ariparian corridor can change continu-ally along its length, reflecting the soilmoisture and nutrient conditions,vegetation, or geomorphology of theadjacent upland area (Gregory andAshkenas ). However, while ripar-ian areas are greatly affected by thenature of the adjacent upland regions,

they in turn can also strongly controlhow the entire watershed functions.Therefore, the general condition ofriparian areas can have significant andwide-ranging economic and environ-mental consequences.

Riparian Areas and Biodiversity:Ecological Principles

Biologically, riparian areas arevaluable ecosystems in any forestedlandscape. Because of their high pro-ductivity and their inherent connec-tions with the rest of the watershed,riparian areas provide a crucial sourceof habitat diversity at the landscapelevel. The following ecological princi-ples explain some of the commonstructural and functional characteris-tics of riparian areas and their impor-tance for biological diversity.

. Riparian areas contain a widediversity of plant species.Riparian areas are usually transitionzones between different types of struc-turally complex vegetation communi-ties. This complexity exists because ofthe moisture gradient (the progressionfrom higher to lower moisture condi-tions) associated with these areas. Theproximity of water increases the yieldof plant biomass and provides theproper environment for plant speciesunable to grow in drier conditions.Flood-tolerant plants, includingmosses, sedges, and willows, occupypositions close to the water’s edge.Behind these species, a series of differ-ent understorey (herbaceous plantsand shrubs) and overstorey (decidu-ous and coniferous trees) canopylayers progressively develop towardthe upland boundary ( Figure ).Implications for biodiversity Manyanimal species are attracted to ripar-ian areas by the assortment of plant

Part of this Extension Note series (Spatial Patterns) contains more information about the matrix/patch/corridor model, and corridors are discussed more fully in Part (Connectivity).

This description of ecological processes focuses on a hypothetical riparian environment. Suchprocesses will be of greater or lesser importance in riparian areas, depending on the area’sbiogeoclimatic classification.

species in the multi-layered canopy andunderstorey. This structure is character-istic of transitional edge habitats.Riparian vegetation provides:

• excellent food resources (e.g., waterplants, herbaceous plants andshrubs producing berries and seeds,and leafy forage) for a wide rangeof species (e.g., invertebrates, fish,large and small mammals, andbirds);

• dense thickets for cover and shelter(e.g., deer hide in thick bushes;rodents make secure passageways,or “runs,” in the undergrowth);and

• habitats for the perching, nesting,and resting of aquatic and terres-trial bird species (e.g., snags pro-vide perches and cavities for nesting;shoreline vegetation provides nest-ing and refuge sites for waterfowl).

. Riparian vegetation influences thelocal aquatic and terrestrialenvironment.A distinctive microclimate is created forboth terrestrial and aquatic ecosystemsin riparian areas. Riparian vegetationshields the underlying soil from windand sunlight. This keeps soil tempera-tures cooler in summer, which decreasesmoisture losses and maintains the airtemperature at lower levels. Because of

these moister soil conditions, the spreadof ground fires is retarded. As a result,the plant communities in riparian areascan be older than those in neighbouringuplands where there is a more recenthistory of fire.

In winter, riparian vegetation mayprotect the zone against severeweather and reduce heat losses. Insummer, overhanging vegetation thatshades standing or flowing water helpsto regulate the amount of light reach-ing the water’s surface and, therefore,the water’s temperature. For instance,in smaller streams, incoming radiationmay be reduced up to % by canopyclosure (Wilzbach ).Implications for biodiversity Shadedheadwater streams contribute coolwater to riparian areas further down-stream (Stevens et al. ). This isimportant because, if water is cooler,levels of dissolved oxygen are higherand organic wastes can be brokendown more readily. Water temperatureand the amount of available lightalso determine whether the aquaticecosystem is dominated by primaryproduction or decomposition activi-ties. This in turn controls the type ofaquatic invertebrates present and,therefore, the type of prey availablefor the fish community.

Because fish and amphibians are

figure Illustration of the moisture gradient in a typical riparian ecosystem (fromStevens et al. 1995:2).

Emergents

Water

Aquatic Riparian area Upland

Sedges andrushes

Shrubs

Deciduoustrees

Coniferoustrees

Decreasing soil moisture

cold-blooded, air and water tempera-ture controls their body heat andmetabolic processes. Amphibianeggs and larvae and some species ofjuvenile fish are consequently verysensitive to the changes in water tem-perature brought about by vegetationremoval.

At Carnation Creek on westernVancouver Island, water temperaturesincreased by –°C after the removalof % of the forest cover includingstreamside vegetation in a clearcuttingtrial. This long-term study was initi-ated in and continues to examinethe effects of forestry activities onriparian areas. In creek areas affectedby logging and the related decrease inshade, the egg-to-fry survival rate ofcoho salmon has decreased, as has thenumber of spawning adults (Hartmanand Scrivener ).

Decreasing the amount of stream-side vegetation will therefore increasesummer water temperatures, whichcould:

• kill salmon and other fish species iftemperatures exceed tolerancelevels (over °C for some species);

• increase susceptibility to disease;

• increase competition from warm-water fish; and

• change the fish species and age com-position in streams (Voller ).

. Root systems provide bankstability and help reduce erosionand siltation.The root systems of herbaceous plantsand shrubs can stabilize lake, river,and stream banks by binding togethersoil, rock, and organic material, whichreduces erosion and prevents sedi-ment from entering the water system.This is particularly important instreams with relatively unstable banksand variable channels that can poten-tially transport sediment and cloudywater further downstream.

Tree roots withstand flood condi-tions more effectively than do shrubsand are therefore necessary for long-term bank stability (Gregory and

Ashkenas ). Undisturbed forestsadjacent to riparian areas can alsoprevent or reduce the effects of debrisavalanches, debris torrents, and debrisjams.Implications for biodiversity Sedi-ment, both suspended and deposited,can interfere drastically with the lifecycles of many aquatic creatures. Forexample, fish embryos may smother ifsilt settles on incubating eggs. Sedi-ment deposits may hinder the emer-gence of young fish hatching fromburied eggs. Cloudy, sediment-chokedstreams:

• clog fish gills;

• reduce the transmission of sunlightand therefore the growth of water-based vegetation; and

• imperil some amphibians, such asthe endangered Pacific giant sala-mander and tailed frog.

. Riparian zones are an extremelyimportant source of woody debris.

Streamside vegetation may becomeunstable during windstorms or whenstream banks are undercut duringperiodic flooding. Large pieces oforganic debris (trees, large branches,and roots) can fall into streams andcreate important habitats such aspools and protected backwater areas.By providing channel structure, thisdebris determines how water flowsthrough the watershed.

Large organic debris plays the fol-lowing important structural roles:

• creates and maintains stream struc-tures, such as islands, pools, gravelbars, riffles, and side channels;

• dissipates the energy of flowingwater, which slows currents, dropsgravel, and traps other sediment;and

• helps re-establish structuresin streams after floods, debristorrents, or landslides.

Implications for biodiversity Main-taining the natural abundance anddistribution of large organic debris inriparian areas:

• enriches riparian soil as it decays,

supplying a long-term source ofnitrogen and other essential nutri-ents to organisms;

• increases aquatic habitat diversity;

• creates rearing habitat (protectedgravel beds) for salmonid fishes;

• provides critical habitat for thereproduction of reptiles and am-phibians, such as the tailed frogand Pacific giant salamander; and

• supports a diverse assemblageof saprophytic fungi and wood-boring insects.

. Riparian vegetation providesimportant nutritional inputs foraquatic ecosystems.Organic litter, such as leaves, needles,twigs, mosses, and lichens, fallingfrom overhanging riparian vegetation,forms an important foundation in theaquatic food chain. This litter decom-poses or becomes a primary foodsource for aquatic invertebrates, whichin turn nourishes fish and a host ofother organisms in the riparian zone.In small- to medium-sized streams,for example, it is likely that –% ofthe food energy required by aquaticpopulations is supplied by leaf litter(Hollingsworth ).Implications for biodiversity Remov-ing vegetation in riparian areas elimi-nates an important source of food forboth aquatic and terrestrial organ-isms. For example, trials conductedfor the Carnation Creek study showedthat harvesting limited a stream’sability to retain leaf litter and alsoreduced the amount of leaf litter avail-able to % of pre-logging levels. De-ciduous leaf litter from unloggedtributaries was unable to compensatefor the loss of leaf litter in the mainchannel (Hartman and Scrivener).

. Riparian vegetation helpsmaintain water quality.Storm water runoff, which maycontain fertilizer residue, herbicides,pesticides, and other pollutants, canintroduce chemicals to riparian areas,

and reduce water quality. The rootsystems and microbes associated withriparian vegetation act as a naturalfilter, trapping chemical elementsfrom fertilizers (nitrogen and phos-phorus) and breaking them down intousable nutrients (Stevens et al. ).Vegetated riparian areas may thereforestore, cleanse, and slowly release waterand nutrients.Implications for biodiversity Cleanwater is essential for most livingorganisms. Adult amphibians, suchas salamanders and frogs, absorb thechemicals through their skin alongwith water (Stevens et al. ), whilefish may take up contaminantsthrough their gills during respiration.

When riparian vegetation is re-moved, the ability of the riparian zoneto filter deleterious substances and tostore water and nutrients is impeded(Bird and Rapport ).

• Excess nitrogen, in the form of ureaand ammonia from livestockwastes, dissolves in water and maycause fish kills.

• Phosphate fertilizers can also causefish mortality by producing algalblooms, which deplete dissolvedoxygen levels in the water.

• Herbicides and pesticides canthreaten all life stages of fish andamphibians.

Riparian Area Habitat Diversity:Landscape-level Concepts

Riparian corridors are important forpreserving biodiversity at the land-scape level (Harris ). In BritishColumbia, % of rare, threatened,and endangered species have all orpart of their habitat needs met byriparian areas (Stevens et al. )(Figure ). Part of the attraction is theproximity to free-flowing or standingwater. However, the greater diversityof plant species in these areas alsoprovides a wider range of habitatconditions and niches for wildlife.

In addition to containing diversehabitats for direct use, riparian corri-

Dysfunction in landscape:“cumulative effects” andriparian areasRiparian areas have impor-tant and positive connectionswith the rest of the water-shed that make themvaluable elements in thelandscape. However, theseconnections can be detri-mental if managementdisturbances at the headwa-ters are allowed to disruptthe continuity of the riparianecosystems furtherdownstream.

Some studies have shownlogging roads and clear-cutting can have thecumulative effect of increas-ing peak streamflows overthose experienced in forestedareas without roads or log-ging (Franklin 1992).Downstream effects can bemagnified when abnormallyhigh stream flows (due torapid rainfall runoff) occursimultaneously with snow-melt. During these dramaticrain-on-snow flood events,major landslides, debristorrents, and dam-breakfloods can be triggered,affecting aquatic envir-onments. Steep streamreaches can be scoured andsimplified; lower gradientreaches buried in debris andsediment; and plant, wildlife,and fish spawning habitatcan be damaged.

dors also function as important linkagesthat enable movements or flows to takeplace throughout the forested land-scape. For instance, within their chan-nels, creeks, streams, and riversdistribute water, soil, gravel, woodydebris, nutrients, and genetic material(e.g., plant seeds, spores, and water-borne organisms) to downstreamareas of the watershed. When theiradjacent floodplain or upland habitatsare also considered, riparian areas canlink several otherwise isolated forestpatches containing different wildlifehabitats. In this way, riparian corri-dors become natural routes for vari-ous travelling or migrating animalspecies. If their original habitatis disturbed by natural or humanagents, or if it deteriorates because ofpopulation pressures, forest-dwellingmammals may then use these corri-dors to disperse to new territory(Stevens et al. ).

Riparian ecosystems and undis-turbed riparian populations can alsofunction as reservoirs of genetic mate-rial. Because they are so biologicallyproductive, these areas help to main-tain a “storehouse” for genetic diver-sity. For example, when adjacent areasare disturbed by fire, logging, orfloods, animal species can use connec-tive riparian corridors to colonize orrepopulate the disturbed areas. Intact

vegetation in adjacent riparian areasalso acts as a seed source to revegetateseverely disturbed upland or stream-side areas (Bunnell et al. ).

Applying the Concepts:Managing Riparian Areas toProtect Habitat Diversity

The principles of ecosystem manage-ment provide a solid conceptualframework for:

• identifying riparian managementobjectives;

• evaluating current land-use prac-tices; and

• developing future resource alterna-tives (Gregory et al. ).

For example, one of ecosystemmanagement’s central tenets is thatdeviating from the natural range ofan ecosystem’s historical variabilitycan increase the potential for unfore-seen consequences. Therefore, ifbiodiversity is to be maintained inriparian zones, planning effortsshould recognize the ecosystem’shistoric structure and functions, andits connections with the rest of thelandscape.

The Forest Practices Code requiresthat Riparian Management Areas(rmas) be designated along bothsides of streams and around lakes andwetlands (B.C. Ministry of Forests andB.C. Ministry of Environment, Landsand Parks b). These managementareas, because of their linear natureand ecological linkages across forestlandscapes, are often pivotal elementsof the Forest Ecosystem Networks(fens) outlined in the BiodiversityGuidebook (B.C. Ministry of Forestsand B.C. Ministry of Environment,Lands and Parks a).

As a buffer against upslopeactivities, rmas are intended to pre-serve the diversity and productivity offish, wildlife, and riparian ecosystems.These areas can fulfill several func-tions, such as:

• serve as a trap, or sink, to decrease

figure Percentage of species at riskthat use riparian areas andproportion of users that show astrong or some dependence onthese ecosystems (from Stevenset al. 1995:9).

Terrestrial vertebrate classTa

xa a

t ris

k (%

) u

sing

rip

aria

n ar

eas

the rate at which upslope sediment,nutrient, or other chemical runoffenters and contaminates the waterbody;

• regulate flows of surface orsubsurface water by diffusing itand reducing its velocity;

• maintain bank stability and limiterosion potential;

• control water temperature by sup-plying shade;

• provide vegetation debris and ter-restrial invertebrates as a foodsource for aquatic organisms;

• supply coarse woody debris forstream channel stability; and

• provide habitat for a diverse arrayof animal and plant species(Voller ).

The optimal width of riparianmanagement areas will depend on theriparian classification and the natureof the surrounding watershed. As acoarse-filter approach, watershedanalysis helps to identify past andpresent riparian ecosystem elements.It also organizes this informationso that the direct, indirect, andcumulative effects of managementactions can be estimated and theirconsequences understood beforethese activities take place (Regional

Interagency Executive Committee). This sort of analysis is impor-tant because it shifts our focus fromspecies and sites to the ecosystems andlandscapes that support them.

Because of the dynamic nature ofriparian ecosystems, managers areoften faced with limited knowledgeabout their historic processes andconditions. Therefore, decision-making must often occur within anatmosphere of uncertainty. In thesecases, managers should refine theirplans by adopting a flexible, adaptivemanagement approach that allows forfeedback and adjustment as new in-formation becomes available.

Text by Susan Bannerman

References

Bird, P.M. and D.J. Rapport. .State of the environment forCanada. Environ. Can., Ottawa,Ont.

British Columbia Ministry of Forestsand B.C. Ministry of Environment,Lands and Parks. a. Bio-diversity guidebook. B.C. ForestPractices Code. Victoria, B.C.

British Columbia Ministry of Forests

Watershed analysis: somekey historical questionsThe watershed’s historicalrange of variability (thevariations in ecosystemconditions and processesover a period of time) pro-vides an important referencepoint for riparian area plan-ning. Some key questions(Regional Interagency Execu-tive Committee 1995) to askabout historic watershedconditions include:1. What erosion processes

occurred and where didthey take place? (e.g.,consider surface erosionand mass wasting)

2. What were the character-istics of the historichydrologic regime? (e.g.,consider total discharge,peak and minimum flows,sources of cold waterseepage and ground-water recharge)

3. What plant communitiesand seral stages werepresent? What deter-mined their compositionand pattern? (e.g., con-sider natural disturbanceregimes)

4. How were stream chan-nels structured and howwas sediment transportedand deposited in thewatershed?

5. How would the water-shed’s water quality becharacterized in the past?

6. What species and habitatswere historically present;how were they distributedand how abundant werethey?

7. What were the majorhistorical human uses inthe watershed, includingaboriginal and othercultural uses?

and B.C. Ministry of Environment,Lands and Parks. b. Riparianmanagement areas guidebook. B.C.Forest Practices Code. Victoria,B.C.

Bunnell, P., S. Rautio, C. Fletcher, andA. Van Woudenberg. . Problemanalysis of integrated resourcemanagement of riparian areas inBritish Columbia. B.C. Min. For.and B.C. Min. Environ., Lands andParks, Victoria, B.C. Work. Pap. /.

Franklin, J.F. . Scientific basis fornew perspectives in forests andstreams. In Watershed manage-ment: balancing sustainability andenvironmental change. R.J. Naiman(editor). Springer-Verlag, NewYork, N.Y. pp. –.

Gregory, S. and L. Ashkenas. .Riparian management guide.Willamette National Forest, U.S.Dep. Agric. For. Serv., Eugene,Oreg.

Gregory, S., F.J. Swanson, W.A. McKee,and K.W. Cummins. . An eco-system perspective of riparianzones. BioScience ():–.

Harris, L.D. . The fragmentedforest: island biogeography theoryand the preservation of biotic di-versity. University of Chicago Press,Chicago, Ill.

Hartman, G.F. and J.C. Scrivener. .Impacts of forestry practices on acoastal stream ecosystem, Carna-tion Creek, British Columbia. Can.Bull. fish. and Aquatic Sci. .

Hollingsworth, R.W. . fish habitat

and forest fragmentation. In Con-vention of the Society of AmericanForesters. Soc. Am. For., Rochester,N.Y. pp. –.

Regional Interagency Executive Com-mittee. . Ecosystem analysis atthe watershed scale: federal guideto watershed analysis, Version ..Regional Ecosystem Office, Port-land, Oreg.

Stevens, V., F. Backhouse, and A.Eriksson. . Riparian manage-ment in British Columbia: an im-portant step towards maintainingbiodiversity. B.C. Min. For. andB.C. Min. Environ., Lands andParks, Victoria, B.C. Work. Pap. /.

Voller, J. . Riparian areas andwetlands. In Conservation biologyprinciples for forested landscapes.J. Voller and S. Harrison (editors).B.C. Min. For., Res. Br., Victoria,B.C.

Wilzbach, M.A. . How tight is thelinkage between trees and trout?In California Riparian SystemsConference. U.S. Dep. Agric. For.Serv., Berkeley, Calif. Gen. Tech.Rep. GTR-PSW-, pp. –.