CHAPTER 4 - HISTORIC CONDITIONS Ecosystems are not static, but vary over space and time. This dynamic nature exemplifies the need for us to consider ranges of conditions under natural disturbance regimes, rather than single points in time. A key assumption of this concept is that when natural systems are "pushed" outside the range of natural variability, maintenance ofbiological diversity and ecological function is at substantial risk. The following narrative explains how ecological conditions have changed over time because of human influences and natural disturbances. This information is used to explain existing conditions and predict potential trends. Geologic History The LNSR, located on the west slope of the Cascade Range, is part of the North Santiam sub­ basin, which is a component of the WRB. The Cascade Range, which contributes the preponderance of drainage area for the Willamette River, extends for over 625 miles from northern California well into British Columbia in Canada. The general physiography of the Cascades is dominated by a string of potentially active volcanic peaks. These relatively recent craggy summits overlie a complex geologic sequence of older volcanic and sedimentary rocks. This plate commotion has modified the Cascades by basin and range faulting to the east and episodic mountain building and volcanism throughout their history and extent. The surface expression of these rock sequences has been altered through time by the numerous rivers that drain the wet western flanks and by intensive periods of mountain glaciation. Located within the Western Cascades physiographic region, the LNS watershed is composed of older Tertiary lava flows, tuff, and intrusive rocks. Dates on parts of this formation are mostly 17 to 32 million years old. The sedimentary portion of the assemblage forms a prominent escarpment along the north boundary of this watershed from Knob Rock east to Trappers Butte (Walker and Duncan 1989). Flow breccias of olivine andesite, basaltic andesite, and some basalt form a crescent-shaped cap on the higher elevation main ridges that extend northwest from Martin Buttes to Mount Beachie, then north to Silver King Mountain, and west towards Whetstone Mountain and along the ridge line to Henline Mountain and beyond. Erupted mostly from widespread, northwest-trending dikes and dike swarms and related plugs and lava cones, their dates range from about 10 to 17 million years ago or middle to late Miocene. The surface expression of these rock formations has been extensively modified by erosion with mountain glaciation. During the earliest and most extensive glacial periods, valley glaciers traveled down the LNS Canyon and some of its tributaries. The younger and more recent glaciations had smaller, coalescing valley glaciers occupying the predominant stream valleys. Ch. 4, Pg. 1 They formed cirques, bowl-shaped depressions with sheer rock headwalls, found in the higher elevations along the southern boundary of the watershed. Tams, small ponds that occupy cirque depressions, are found at Opal Lake and Elkhorn Lake. Large scale slump/earthflow instability has not been a significant factor in slope development or stream channel morphology in this area, except for a few localized reaches. This complex geologic history has produced a fairly uniform landscape ofU-shaped glaciated valleys with broad outwash filled bottoms that are separated by steep shallow-soiled headlands and sharp rocky ridges. Concentrations of gold, silver, copper, and lead minerals lay like widely spaced beads on an unclasped necklace that is strung down the western front of the Cascade Range. Historically, each bead has been the center for mineral exploration and mining activity since the late 1800s. This necklace extends from Mt. Hood into the Umpqua NF. The line ofthe chain crosses the LNS watershed in the north around Nasty Rock and Burnt Mountain and extends southward across the LNS to Phantom Natural Bridge and Dog Tooth Rock. The LNS lies at the heart of one of these beads with extensive gold prospecting activity around the tum of the century. The bead to the south is located in the Quartzville mining district. Disturbance Regimes and Ecological Effects There are many disturbance factors that operate within this watershed. These factors include wind, fire, floods, insects, disease, and humans. Today, humans are the agents of greatest disturbance in the landscape. When human population levels were low, frre was the primary disturbance force. It was used to manipulate the ecosystem for beneficial uses through planned ignitions and occurred naturally, primarily from lightning. Whether planned or not, frre affected a broad range of ecosystems from a few acres to many thousands. Native Americans recognized the benefits offrre and became accomplished practitioners of prescribed frre. The Kalapuya Indians burned the Willamette Valley for thousands of years prior to Euro-settlement. This use offrre to manipulate their environment extended up major river drainages such as the Santiam River and extended into the foothills of the Cascades and coast range (Boyd 1985). The use offrre maintained an oak-savannah ecosystem, which began changing back to a forested ecosystem (if not plowed) after settlers eliminated the Indian­ prescribed burning culture with their removal to reservations in the 1850s. Fire is the primary natural disturbance factor over the landscape and causes the greatest ecological effects over space and time. Understanding frre ecology terminology is helpful in understanding forest ecology from a historical perspective. Fire regime is a generalized description ofthe role frre plays in an ecosystem. It is the combination offrre frequency, predictability, intensity, seasonality, and extent characteristics offrre in an ecosystem. There are many descriptions, but the one used here is based on frre frequency and frre intensity (Agee 1981, Heinselman 1981). Fire frequency is the return interval offrre. Fire intensity/severity is the Ch. 4, Pg. 2 ecological impact of a frre, such as mortality of plant or animal species, changes in species composition, and other ecosystem characteristics. Wind also has the capacity to disturb large areas of the landscape and, on a historical basis, has done so approximately every 25 years (Teensma 1987). The last extensive large wind event in Oregon was the Columbus Day Storm of 1962, which blew down 11 billion board feet of timber in Oregon and Washington, 98 percent of which was west of the Cascade crest. Other major wind events occurred in December 1996, March 1963, February 1958, April1957, November 1953, January 1921, and January 1880 (Lynott and Cramer 1966, Hemstrom and Logan 1986). Wind has more influence on coastal forest dynamics than on the forests of the Cascades. Wind is also associated with patch-size disturbances over the landscape as are insects and disease. These three disturbance factors add small complex changes over large spatial and temporal scales and have direct and indirect influences on frre ecology. The LNS watershed occupies the dry to wet western hemlock plant association (73%), the Pacific silver frr plant association (26%), and mountain hemlock plant association (1 %). There are multiple frre regimes in these zones based on the physical factors of elevation, aspect, orientation ofland forms on the landscape, climate and weather patterns. These factors have significant effects on frre behavior (frre regimes) and, therefore, frre history (Teensma 1987). The multiple frre regimes are: (1) infrequent severe surface frres (more than 25-year intervals); (2) long return interval crown frres and severe surface frres in combination (100-300 year return intervals); and (3) very long interval crown frres and severe surface frres in combination (over 300-year rotation return intervals). The source of fire ignitions comes from lightning and humans. Occurrence or patterns of lightning fires are mainly d.etermined by regional climate, land forms, elevation, aspect, and fuel type. Map A gives a reference to regional annual lightning fire patterns. Lightning is the primary source ofwildfrre ignitions in the Pacific Northwest. Human-caused ignitions are a result of industrial activities (logging, welding, road building, etc.), arson, carelessness (debris burning, escaped prescribed bums, campfrres ), and structural frres in the forested landscape. In the LNS watershed, lightning starts occur primarily in the higher elevation east portion (low occurrence) and human-caused ignitions occur in the lower elevation west portion of the watershed. Ch. 4, Pg. 3 Ch. 4, Pg. 4 Map A. Regional Annual Lightning Patterns on National Forests of Oregon and Washington. These patterns are an index to lightning fire activity and show number of storms per 40,000 ha per year. (From Morris 1934) .I. WaminpOD Oreaon 0 50 JOO 150 Km 3ad4 ~ lllld2 ~ l):c:'liONI Ch. 4, Pg. 4 Fire effects resulting from these fire sources are varied. An infrequent severe smface fire bums Qn the soil surface. and active burning does not involve the tree crowns. This fire rej,time wouJd slopes). The effect could include maintaining Douglas-fir as primary tree species by removing thin barked trees and promoting thick barked trees, maintaining low amounts of downed wood due to fuel oonswnption with more frequent burning, and maintaining brush species that sprout and can live under a tree canopy. This fire regime is less dependent on changes in weather patterns (drought) than other fire regimes. Crown fires and severe surface fires every 100.300 years are more dependent on changes in weather patterns. In this instance, the forest ecosystem accumulates fuel over time. Wind and disease interact more often and contribute to patch dynamics. Legacy trees from the previous disturbance and natural mortality help create a multi-storied canopy. Intolerant tree species dominate the lower canopy. As the stand ages, more sunlight reaches the forest floor, and the shrub and herb layer diversifies. Under normal conditions, fire starts cannot develop enough energy to do extensive: damage to the landscape. This is due to the energy required to evaporate the high amounts of internal water in the combustion phase of burning carbon-based fuels.