The Ecological Roots of New Approaches to Forestry by Fred Swanson and Dean Berg

uring the 1940s through the cepts of natural disturbance and suc- played a pivotal role in this transfor- 1980s, forest management cessional processes. Itwas commonly mation. In the broadest sense, we are and research in the Pacific argued, for example, that clearcutting moving from treating forest manage- Northwest focused largely mimics natural disturbance by wild- ment as a series of discreet operations on harvesting natural stands fire-but is not as wasteful because to viewing forests as ecological sys- and establishing Douglas fir the wood is harvested and used. tems. One of the central components plantations. This was accomplished But, forestry is in the midst of a ofthis emerging emphasis on integra- with relative efficiency by clearcutting, major transformation. A5HalSalwasser tive management is leaving residual burning woody residues, establishing of the u.s. Forest Service New Per- forest structures (e.g., trees, snags, dense stands of a single tree species, spectives Program has pointed out, down logs,) as biological legacies to hastening crown closure, suppressing we are involved in an evolution across be carried over from one stand to the competing vegetation, and other prac- three stages of natural resource man- next. tices. From an economic perspective, agement: from regulation of uses, to Although some of the techniques such intensive silvicultural practices sustained yield management, to sus- involved in managing biologicallega- provided a relatively high short-term tainable ecosystem management. Re- cies may be relatively new, the under- return on investment. Biologically, search within and at the interfaces lyingconcepts have evolved over more these practices seemed at least super- between wildlife biology, fisheries, than a decade. Concern for maintain- ficiallyconsistent with prevailing con- ecosystem ecology, and forestry has ing habitat and species in federal for-

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estland managed for timber produc- ... ment of many woody plants. These tion is reflected in federal laws, public surviving elements of the comments and litigation over forest In the broadest predisturbance system can strongly plans, and the continuing efforts of affect the rate and course ofecosystem many land managers to be good stew- recovery. Consequently, the design of ards of the land. Specifically, the con- sense, we are various ecosystem manipulations and cept of retaining structural and com- predictions of system response must positional diversity in managed stands moving from deal with nutrients, organisms, and to meet the objectives of multiple use structures both retained on and re- management is grounded in: 1) im- treating forest moved from a site as a result of distur- proved understanding of disturbance bance or management. processes in natural and managed for- ests, 2) a growing understanding of management as Ecological Functions ecosystem functions, and 3) experi- Parallel with disturbance ecology ence with managed forests, including a series of discreet research, there has been a great deal of the successes and failures of efforts to study focused on natural forest and implement intensive forestry practices. operations to stream systems during periods with- A major theme in leaving behind bio- out catastrophic disturbance. In the logical and physical legacies is main- viewing forests Pacific Northwest, much of this work taining future options-it is easier to began with the International Biologi- leave standing dead trees and large, cal Program in the 1970s and contin- rotting logs on land and in streams as ecological ued with the National Science Foun- than to generate them from an initially dation sponsored Long-Term Ecologi- clean clearcut. Although operational systems. cal Research Program in the 1980s, as testing of many of these alternative well as in a variety of other research prescriptions is in the early stages, it is programs. Findings from these and other studies include: imperative to work from results of is more complex than previously rec- ecosystem research and past forestry ognized. Recent studies in the central experience in designing new prescrip- Cascades Range of Oregon, based on ·Standing and down dead wood tions. detailed dendrochronologic analysis material is a significant element of of fire scar and total tree age records sustaining biological diversity (as habi- Disturbance Processes exposed in stumps, revealed that wild- tat for many species) and possibly Important changes in our under- fire was more frequent and involved a forest productivity. Traditional, inten- standing of natural systems have greater extent of low- and moderate- sive forest practices have the net effect emerged from analysis of the structure severity burning than expected. Large, of greatly reducing concentrations of and function of natural forest and wood debris in forests after the re- catastrophic fires were very heteroge- stream ecosystems and their responses neous, composed of patches of di- sidual woody debris from the previ- to disturbances. Studies in the Pacific verse sizes and bum severity. This ous natural stand decomposes. Northwest and elsewhere have re- complex wildfire regime left abun- vealed the dramatic importance of or- dant standing and down dead woody ·Coarse woody debris in streams ganisms surviving even extremely se- debris as well as highly variable densi- increases channel complexity, thereby vere disturbance. This was particu- ties of live trees. improving fish habitat quality and in- larly clear after the 1980 eruption of These studies ofdisturbance high- creasing retention ofnutrients in stream MountSt. Helens. Ourfirstimpression light the great importance of living systems. Stream cleanup practices em- was that previous ecosystems had been organisms and physical structures ployed in the 1970s, and splash dam- completely eradicated. However, which survive from one regime to the ming in earlier periods greatly reduced within days and weeks, surviving or- next. Examples of these "legacies" levels of coarse woody debris in ganisms of a great variety of life forms include: standing and down logs, soil streams, thereby reducing habitat qual- began the process of restoring terres- structure, high soil calcium contents ity. trial and aquatic systems. Survivors associated with cedar trees, reproduc- persisted below ground, in rotten logs, tive organs such as seeds and sprouts, ·Natural forest stands are very com- under snowpacks, and in lakes, and various vertebrate species (e.g., plex in early and late stages of succes- streams, and springs-some protected birds and mammals) as well as the sion-in contrast with the simpler under ice and snow cover. numerous invertebrates in the soil. structure and composition of stands Similarly, studies of wildfire his- Especially important are the hyphae managed intensively for wood fiber tory in Oregon revealed that this domi- and species of the mycorrhizal fungi production. Traditional practices nant disturbance process in the region which are essential to the re-establish- eliminate or reduce the duration of

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complex early and late seral forest ... acre), experience with shelterwood stages, possibly eliminating ecologi- cuts may provide a strong basis for cal processes and species that are de- anticipating effects on regeneration. pendent upon them. Input of nitrogen Tbe concept of Growth and yield potential of sites to Pacific Northwest conifer forests, where green trees are retained may be for example, occurs by nitrogen-fIX- retaining maintained by paying close attention ing organisms particuTarlyevident in to stand density, and thinning to con- early and late successional stages of biological legacies trol crown competition for light. In forest development. The presence of some cases, traditional and these nitrogen-fIXingspecies isgreatly through nontraditional practices may overlap. reduced in stands managed on short Forexample, regeneration on low den- cutting cycles, and in which compet- sity retention units may be achieved ing vegetation is suppressed. The net timber cutting is by using stocking levels and geneti- t i effect may be a reduction in long-term cally improved stock similar to that nitrogen input to these forest systems neither a return to used for intensive plantation forestry. where nitrogen availabilitycommonly Finally, when considering where limits productivity. Furthermore, sup- any early period of we are in terms ofunderstanding com- pression of biological legacies and plex forest ecosystems, it is useful to early seral vegetation, combined with consider the historical context of in- unsuccessful efforts to reestablish tree poor practices nor tensive plantation and multiple use plantations on clearcut harsh sites, may an abandonment forestry. Plantation forestry has been disrupt the belowground ecosystem developed over the past three decades to the point that the site isconverted to through the concerted efforts of in- nonforest vegetation. of the important dustry, universities, and Forest Service research and development programs. ·Insectivorous birds and canopy lessonsfrom The total research and development invertebrates, such asspiders and ants, investment in plantation forestry prob- can be important predators of forest ably exceeds several hundred million insect pests. Retention ofhabitat struc- decades of dollars directed at the rather singular ture, such as large, live trees and mul- objective of maximizing wood fiber tiple canopy layers, may maintain ben- intensive forestry production. Multiple use forestry is eficial predator-prey relations in man- only beginning to develop and is do- aged forest stands and landscapes. research. ing so in a much more piece-meal fashion, perhaps in keeping with its .Tree root systems help anchor soil more complex objectives. In both on hillslopes. Timber harvesting on poor practices nor an abandonment of cases, there has been a great deal of marginally stable slopes can lead to the important lessons from decades of learning as we go-always building increased incidence of landslides and intensive forestry research. on past experience. debris flows in downslope and down- Some contend that the practice of The extent to which alternative stream areas. retaining green trees and snags is a forestry practices meet the biological return to the "high grading" logging objectives for which they were de- We could cite many additional ex- practices used at various times in the signed has yet to be determined in amples of ecosystem elements which 1930s and '40s. However, new prac- detail by research and monitoring. We contrast between natural forests and tices have very different objectives and have not learned everything about for- stands managed intensively for wood strategies. Retaining trees of high value ests. We will always be managing fiber production. Considered indi- provides habitat, maintains the pro- with less than complete information. vidually, perhaps none of these eco- ductive capacity of the site, and sus- Hence, we need flexibility in our silvi- system functions justifies revamping tains a supply of large, high quality cultural systems such that we can con- traditional forestry practices. But,con- logs. The biological features of the tinue to adapt based on new informa- sidered in aggregate, the need to resulting stands are quite different from tion. iii modify forestry to maintain future op- those that were left after high grading. tions and minimize risks is clear. Many techniques explored in the Fred Swanson is leader for the ecosystem development of intensive plantation management team of the U.S.Forest Ser- Experience with Managed Forests forestry will be important in the design vice Pacific Northwest Research Station in The concept of retaining biologi- of more multiple use forestry prac- COn/allis,Oregon. Dean Berg is the silvi- culturistfor the Olympic Natural Resources callegacies through timber cutting is tices. For example, in denser green Center at the University of Washington. neither a return to any early period of tree retention units 00+ trees left per

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