55 



ability constrains the set of species that can inhabit a particiilar environment, and 

 disturbances, such as fire, windstorms, and floods, interact with the physical factors 

 and the species to determine the character of the vegetation. For example, in some 

 parts of the West, on cool, wet, north-facing slopes, fire mav bum infi^uently, al- 

 lowing enough time for forests to develop. On warm, dry slopes across the valley, 

 fi-equent burning results in the formation of grassland vegetation. Disturbance pro- 

 duces two very different habitats, despite the fact that regional climate, sod parent 

 material, and species availability may be the same in both places. Furthermore, the 

 cool, moist vegetation of the forest understory discourages fire in the forest, while 

 grasses encourage fire spread, thus reinforcing the disturbance cycle. 



Humans tend to have their greatest influence on vegetation through theu" influ- 

 ence on disturbance pattern, fii^quency, and intensity. While some spectacular cases 

 of human alteration of species availability have occurred, such as the disappearance 

 of chestnut fit)m the Eastern forest as a result of the introduction of a Ei^asian 

 blight fiingus, ovir most pervasive influence has been on disturbance, through both 

 harvest practices and fire management. In the Pacific Northwest, the disappearance 

 of old-growth Douglas-fir forest is essentially the result of increasing the ft-equency 

 and intensity of catastrophic disturbance in the form of clearcutting. On the east 

 side of the Cascades, fire suppression has resulted in the growth of insect-ridden 

 firs and Douglas-firs suppression has resulted in the growth of insect-ridden firs and 

 Douglas-firs into forests fi-om which fu-e once excluded them. Their presence now 

 threatens to alter the fire regime fi-om one of fi-equent, low-intensify fires, easily en- 

 dured -by Fire resistant pines and larches, to one susceptible to high-intensity, cata- 

 strophic fires, which no species will survive. The Blue Mountains Forest Health Re- 

 port described the situation this way: ". . . when human activities and processes fail 

 to mimic the natural events that shape and define the vegetation conditions and 

 character of stands, nature may intervene on its own behalf, through pest epidemics 

 and catastrophic wildfires, to correct the unnatural state." 



It is now clear that in order to avoid catastrophe and restore to the landscape the 

 natural ecological systems upon which biodiversity depends, we must restore to the 

 landscape those disturbance regimes with which the native biota evolved. In most 

 places, this will require dramatically reducing the amount of wood we can expect 

 to produce fi-om a site. It also likely will require increased use of prescribed fire, 



Kazing reductions, and Umitations on visitor use. In some places, it will require al- 

 wing what have traditionally been considered catastrophes, such as fire and floods, 

 the space they need to run their course. None of this excludes humans from the eco- 

 system, but it will require a dramatic change in the way we view our relationship 



with it. , , J • 1 • -i. 



Unfortunately, our understanding of exactly what needs to be done is only in its 

 infancy. Appreciation for the important role of disturbance in ecosystems has only 

 been hilly embraced by the ecological profession in the last decade or so. Natural 

 distuii)ance patterns and processes are under investigation in many forest types, 

 but much more work must be done before this knowledge can be turned into rec- 

 ommendations for management. 



One of the best understood regions of the country, in terms of natural disturb- 

 ances, is the Pacific Northwest. Many management problems are now understood 

 in terms of human alteration of natural disturbance processes. Westside endangered 

 species problems are understood as resulting from large-scale, catastrophic harvest- 

 ing. The short term solution requires protecting the remaining older forest from fur- 

 ther disruption. On the Eastside, forest health problems are known to result from 

 disruption of fu-e cycles and now threaten to catastrophically alter the forest. 



This appreciation for the role of distrubance has prompted scientists to explore 

 means of mimicking the effects of natural disturbance in Northwest ecosystems. 

 'Vew Forestry", which relies on leaving large quantities of wood following harvest- 

 ing, is a direct attempt to mimic the post-disturbance environment. Experimentation 

 with prescribed fire has shown that fire cycles can be restored. Further improve- 

 ment in these methods promises to allow society to benefit from the products of the 

 forest without destroying its means to produce. Federal investment in these meth- 

 ods will allow us to continue to rehabilitate and reforest long into the future. I con- 

 clude this discussion with a short list of recommendations for rehabihtating North- 



(1) Save the blueprints. The first priority for federal land management agencies 

 in the Pacific Northwest should be to identify and protect those functioning 

 ecosystems that will provide the information essential to intelligent management. 

 In forests, these are l5iely to be roadless areas and watersheds containing function- 

 ing old-growth communities. These areas will be essential in the future both for the 

 information they provide and as standards against which to compare management 



