Relationships Within the Valley Floor Ecosystems in Western Olympic NationalPark: A Summary

Jerry F. Franklin, Frederick J. Swanson, and James R. Sedell

ABSTRACT

The major findings of the South Fork Hoh River research team emphasize interrelationships among componentsof the Olympic valley-bottom ecosystems. Geomorphic structures provide the basic template for both terres-trial and aquatic communities. Vegetation has significant reciprocal impacts on geomorphic processes, how-ever, and is a major element in formation of the most productive aquatic habitats. The South Fork pulseillustrates accomplishments possible with intense, short-term interdisciplinary research efforts and thevaluable functions National Parks can perform as benchmark areas to compare with exploited land systems.

Other papers in this report consider geomorphology, forest communities, Roosevelt elk, and aquatic habitatsand communities. There is some tendency to lose sight of the entire valley-bottom ecosystem in these morecomponent-oriented presentations, however.

The objective in this paper is to racapitulate the major findings of the South Fork research pulse with anemphasis on interrelationships among various components and processes. We also suggest broader implica-tions for Park management and point out how the Park is serving as a control or baseline site for inter-preting man's impacts on adjacent managed landscapes and establishing guidelines for improved management.National Parks provide the rare opportunities to study natural, undisturbed, valley-bottom forests andriver ecosystems.

Jerry F. Franklin and Frederick J. Swanson, U.S.Department of Agriculture, Forest Service, PacificNorthwest Forest and Range Experiment Station,Forestry Sciences Laboratory, 3200 Jefferson Way,Corvallis, Oregon 97331; and James R. Sedell,Weyerhaeuser Company, Forest Research Laboratory,505 N. Pearl Street, Centralia, Washington 98531.

43

GEOMORPHIC RESULTS

Landforms can be viewed as the template on whichthe terrestrial and aquatic communities of thevalley-bottom ecosystems develop. While geologi-cal processes determine the initial conditions,biological processes are significant modifiers.Vegetation-geomorphic interactions are particu-larly important in the cases of small streams andriver bars and terraces which are entirely the in-terplay between vegetation and fluvial processes.

Woody debris creates some of the most conspicuousvegetation influences on geomorphic processes.Fluvial processes mobilize large amounts of woodydebris, particularly by undercutting and uprootingtrees on forested alluvial flats and higher ter-races. Stabilized debris in the main river channelis important in setting up gravel bars, protectingpioneering vegetation from high flows and from buf-feting by floated organic debris, and regulatingflow into river side channels, thereby creating theespecially productive off-channel aquatic habitat.Woody debris in off-channel and tributary habitatsalso provides physical stability (Swanson 1980), adiversity of biological habitats, and an ecosystemenergy base both by retaining fine allochthonousmaterial and directly through decomposition (Cum-mins 1980).

Four major categories of aquatic habitat are iden-tifiable in river valleys: the main river channelwith fast, turbid, silty water; river off-channel,such as side channels partially isolated from themain stream; terrace tributary, which is low gra-dient and generally carries clear, slow-movingwater; and valley wall tributary, typically a highgradient stream with clear, fast water. Geomor-phic, hydrologic, and vegetation factors combineto determine the basic types and arrangements ofaquatic habitats.

AQUATIC RESULTS

Off-channel and terrace tributary habitats are ofoverwhelming importance for productivity of aquat-ic ecosystems of the South Fork and similar, broad,alluviated valleys in western Washington. Theserelatively protected sites have abundant, diversefood resources for both invertebrates and fish.Coho and cutthroat trout use these areas for rear-ing. Terrace tributaries provide important shelterwhen the main channel is in flood.

Glacial silt limits productivity of some parts ofthe main channel ecosystem, but not others. Pri-mary production in fast water areas of the channelis severely limited by the scouring action of siltand fine sand being transported in suspension muchof the year. Silt deposition in the few quiet watersites of the main channel prevents full utilizationby invertebrates of these potentially very produc-tive areas. Spawning is not greatly reduced by thefine sediment because hydraulic conditions preventexcessive accumulation in the major spawning siteswhere pools tail out into the heads of riffles.

Productivity of valley wall tributaries is limitedby the extremes of high and low flows and the denseconifer overstory which reduces primary productionby shading. Limited pool area and the difficultyof moving from pool to pool along these high gradi-ent channels constrain use of valley wall tribu-taries by fish.

Large organic debris is an important factor inshaping microhabitats in each of these types ofstream environments.

TERRESTRIAL RESULTS

The forest communities are strongly related tolandform or geomorphic surface. Alnus rubra stands dominate youthful fluvial deposits andmature Picea sitchensis-Tsuga heterophylla forestsoccupy older, higher surfaces. In the study area,different Picea-Tsuga communities are formed onupper and lower terraces, although dominant treeson both terraces are approximately the same ageand cannot be considered successionally related.The vegetation-landform model proposed for themain fork of the Hoh River (Fonda 1974) does notfit the South Fork, which probably reflects his-torical differences in timing and patterns offorest disturbances such as floods.

Mature valley-bottom Picea sitchensis-Tsuga hetero-phylla forests contrast with those found elsewherein the coastal P. sitchensis zone of the PacificNorthwest (Franklin and Dyrness 1973). Stands,especially those on lower terraces, are open withrelatively low density of above-ground biomass andnumerous openings of up to a hectare or more.Picea is reproducing successfully, earning recog-nition as a climax tree species on these sites.While the relative success of Picea and Tsuga re-production appear to have oscillated over the pastcentury, there is no evidence that either is goingto be replaced successionally. Grazing by Roose-velt elk is a factor that may favor survival ofPicea reproduction over that of Tsuga, but grazingis almost certainly not the sole cause of variationin reproductive success. Wind and floods appear tobe the major environmental factors disrupting thesevalley-bottom forests, whi7a wildfire appears tobe inconsequential.

Coarse woody debris is an extremely importantstructural feature of the terrace forests. Woodydebris occupies much of the forest floor and con-tains large masses of carbon and nutrients. Re-production of trees on older terrace surfaces isconfined almost exclusively to rotten logs andassociated stumps and root wads. Logs vary sig-nificantly in their value as nurseries dependingupon log species, decay state, and terrace level.Forest renewal is dependent on seedbeds of coarsewoody debris.

44

APPLICATIONS

The South Fork of the Hoh River appears to be thearchetype of the western Olympic Mountain rivervalley ecosystem. Fluvial landforms and pro-cesses, mature Picea-Tsuga terrace forests, andvalley-bottom aquatic habitats are well repre-sented. The valley habitats have undergone mini-mal modification from adjacent mountain sideslopesand river tributaries in comparison with the otherfour major river valleys of the western OlympicMountains. It therefore seems appropriate tomanage and utilize the South Fork valley as aprimary site for research on Olympic rainforestsand associated streams.

Recognition that off-channel and terrace tributaryhabitats are aquatic hotspots and essential toanadromous fish in the Olympic river valleys hasimplications for managers inside and outside thePark. Park managers should locate trails, roads,and other developments so as to have minimum impacton these features. Resource managers outside thePark should appreciate the importance of providingoff-channel and terrace tributary habitats with atleast as much protection as the main channel. Re-habilitation of such habitats may be essential inareas where they have been destroyed by logging orroad construction activities.

The significance of woody debris is further docu-mented for both scientists and resource managers.Debris can now be seen to play important roles inlarger streams and rivers, roles which must beaccounted for by land managers in programs of ri-parian management and stream cleanup. The role ofwoody debris as critical seed bed in coastal foresttypes has implications on lands managed for timberproduction as well as on lands reserved from devel-opment.

CONCLUSIONS

The South Fork study demonstrates the use of a Na-tional Park and Biosphere Reserve as a benchmarksite for scientific research and a control area foradjacent manipulated landscapes. The only remain-ing natural examples of river valleys in the coast-al region are within Olympic National Park. Theknowledge gained in the pulse study has extendedour understanding of northwestern ecosystems to adistinctive variant (the rain forest) and a largerscale (river drainage).

Finally, the pulse in the South Fork of the HohRiver demonstrates the numbers and types of datathat can be gathered by an interdisciplinary re-search team in a short time span. A successfulproject is based on substantial logistical plan-ning and a balance between careful definition ofobjectives and ample opportunity to pursue prom-ising leads and for serendipitous discoveries.

LITERATURE CITED

Cummins, Kenneth.1980. The multiple linkages of forests tostreams. In Richard Waring, ed. Proceedings,20th Annual Biology Colloquium. Oregon StateUniv. Press. Corvallis, OR. In Press.

Fonda, R. W.1974. Forest succession in relation to riverterrace development in Olympic National Park,Washington. Ecology 55(5):927-942, illus.

Franklin, Jerry F., and C. T. Dyrness.1973. Natural vegetation of Oregon and Washing-ton. USDA For. Serv. Gen. Tech. Rep. PNW-8,417 p., illus. Pac. Northwest For. and RangeExp. Stn., Portland, OR.

Swanson, Frederick J.1980. Erosion as an ecosystem process. InRichard Waring, ed. Proceedings, 20th AnnualBiology Colloquium. Oregon State Univ. Press.Corvallis, OR. In Press.

In: Starkey, Edward E.; Franklin, Jerry F.;Matthews, Jean W., tech. coords. Ecologicalresearch in National Parks of the PacificNorthwest: Proceedings, 2d conference onscientific research in the National Parks;1979 November; San Francisco, CA. Corvallis,OR: Oregon State University Forest ResearchLaboratory; 1982.

Reproduced by USDA ForestService, for official use.

45