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In recent years, large-scale tree mortality events linked to global change have occurred around the world. Current forest monitoring methods are crucial for identifying mortality hotspots, but systematic assessments of isolated or scattered dead trees over large areas are needed to reduce uncertainty on the actual extent of tree mortality. Here, we mapped individual dead trees in California using sub-meter resolution aerial photographs from 2020 and deep learning-based dead tree detection. We identified 91.4 million dead trees over 27.8 million hectares of vegetated areas (16.7-24.7% underestimation bias when compared to field data). Among these, a total of 19.5 million dead trees appeared isolated, and 60% of all dead trees occurred in small groups (≤ 3 dead trees within a 30 × 30 m grid), which is largely undetected by other state-level monitoring methods. The widespread mortality of individual trees impacts the carbon budget and sequestration capacity of California forests and can be considered a threat to forest health and a fuel source for future wildfires. Tree mortality due to climate change and other disturbances is on the rise. Here, the authors use high-resolution remote sensing data, ground observations and deep learning to quantify individual dead trees and potential drivers across California in the year 2020, encompassing 91.4 million dead trees. [ABSTRACT FROM AUTHOR]

Timber harvesting and related management practices associated with industrial timberlands have changed dramatically in the last two decades. Industrial timberlands are now more carefully assessed and mitigated. Recent studies of mass wasting in northern California included a review of historical aerial photographs from the early 1940s through 2016 and field measurements of nearly 3,000 shallow landslides on industrially managed timberlands. Significant improvements have been seen in management practices over time that include but are not limited to reduced harvest unit sizes, increased streamside tree retention, reduced road density, and improved road-building practices. These improvements are a result of a variety of sources such as evolving state regulations, voluntary conservation plans, and increased professional oversight. Subsequently, significant decreases in management-related erosion are being observed across the area included in this study. Observations show that improvements in management practices have positively affected regional mass wasting. In this investigation, significant changes have been noted in both causal mechanisms and landslide erosion rates. The study data shows that before the year 2000, nearly 85 percent of landslide-related erosion was determined to be the result of historical logging, either by harvesting or from roads (generally poor design and/or location). Shallow landslide erosion rates have varied over the duration of time reviewed for this study, peaking in the 1970s. Since 2000, erosion rates across the study area have decreased to 20 m3/km2/yr, which is a 92 percent reduction compared with the historical rate. [ABSTRACT FROM AUTHOR]

Drought contributed to extensive dieback of southern California chaparral, and normalized difference vegetation index before drought and near the end of the drought was used to estimate this dieback, after accounting for other disturbances recorded in aerial photographs. Within the perimeters of two megafires that occurred after the drought, the 2017 Thomas Fire and the 2018 Woolsey Fire, there had been extensive areas of dieback. Comparing dieback with Monitoring Trends in Burn Severity measures of fire severity, there was a highly significant negative relationship between drought‐caused shrub dieback and fire‐caused dieback as measured by fire severity. We interpret this as further support for our remote sensing methodology for prefire dieback. Models of fire behavior suggest that one means by which dieback contributes to fire size is through increasing the density and distance of spot fires, particularly under extreme wind conditions. Lower elevation chaparral associations appear to be most vulnerable and are closer to urban environments, which should be a concern to fire managers in regions subjected to extended droughts. [ABSTRACT FROM AUTHOR]

For each restoration project, it is essential to define a reference ecosystem towards which ecological restoration aims. Historical information may be useful in the construction of the reference model and in finding out about the type and degree of disturbances that have caused degradation on the site, as legacies of past human land-uses have been shown to be major determinants of vegetation and plant diversity even in the very long term. The aim of this paper is the retrace the history of three sites where restoration protocols were tested, to better apprehend the potential reference ecosystems as well as the disturbances that degraded them. To do so, we first compiled information on the reference ecosystems at the landscape scale. Then, we compiled historical and agricultural information at the scale of the sites from local historical documents, historical reviews and aerial photographs. The three sites most likely were grasslands or oak savannas before European settlement. Grasslands used to cover 8.9 million ha in California. They were species-rich grasslands managed with fire by the native people and grazed by native ungulates. Early settlers introduced cattle grazing and changed fire regimes. Later on, many grasslands were converted to cultivation. All three sites were used for ranching and sometimes overgrazed. At least two of them were cultivated, probably leading to restoration being harder there, as plowing eliminates perennial species, destroys the seedbank, changes soil characteristics. [ABSTRACT FROM AUTHOR]

Context: Increases in tree cover at dry forest margins are a global phenomenon. Yet, how pre-existing tree cover interacts with terrain and water balance to influence tree cover change is not well-understood, nor whether subsequent disturbances restore prior tree cover patterns or create novel patterns. Objectives: To assess how terrain, water balance and pre-existing patterns of tree cover influenced late twentieth century tree cover change, and how subsequent wildfires altered tree cover patterns. Methods: We analyzed tree canopy cover at four sites at the forest-steppe ecotone on the eastern side of the Sierra Nevada, California, U.S.A., using aerial photographs from 1953/1955, 1999/2002 and 2016. Influences on tree cover change were assessed using statistical modeling, and tree cover in 1953/1955 was compared with post-wildfire tree cover in 2016. Results: From 1953 to 2002, area with > 25% canopy cover increased by 1.5 to 5-fold and treeless area decreased by 17–111%. Mesic areas and areas of sparse tree cover close to existing forest tended to gain more canopy cover. Subsequent wildfires caused a mix of net tree cover loss, little change and gain relative to 1953/1955, but at all sites areas with > 25% cover and < 10% cover in 1953/55 experienced net losses and gains respectively by 2016. Conclusions: Accounting for initial tree cover and its configuration are crucial to assessing water balance and terrain effects on tree cover change. Our work highlights how wildfires can generate novel patterns of tree cover relative to historical baselines, especially following decades of fire exclusion. [ABSTRACT FROM AUTHOR]

Summary: Currently, little is known about the impact of climate change on groundwater recharge in the Sierra Nevada and southern Cascade Range of California or other mountainous regions of the world. The purpose of this study was to determine whether small alpine peatlands called fens can be used as whole-ecosystem gauges of groundwater recharge through time. Fens are sustained by groundwater discharge and are highly sensitive to changes in groundwater flow due to hydrologic disturbance including climate change. Seven fens in the Sierra Nevada and southern Cascade Range were studied over a 50–80year period using historic aerial photography. In each aerial photograph, fen areas were identified as open lawn and partially treed areas that exhibited (1) dark brownish-green coloring or various shades of gray and black in black and white imagery and (2) mottling of colors and clustering of vegetation, which signified a distinct moss canopy with overlying clumped sedge vegetation. In addition to the aerial photography study, a climate analysis for the study sites was carried out using both measured data (U.S. Department of Agriculture Natural Resources Conservation Service SNOwpack TELemetry system) and modeled data (a downscaled version of the Parameter-elevation Regressions on Independent Slopes Model) for the period from 1951 to 2010. Over the study period, the five fens in the Sierra Nevada were found to be decreasing between 10% and 16% in delineated area. The climate analysis revealed significant increases through time in annual mean minimum temperature (T min) between 1951–1980 and 1981–2010. In addition, April 1 snow water equivalent and snowpack longevity also decreased between 1951–1980 and 1981–2010. For the fens in the Cascade Range, there were no discernible changes in delineated area. At these sites, increases in T min occurred only within the past 20–25years and decreases in snowpack longevity were more subtle. A conceptual model is presented, which illustrates that basic differences in hydrogeology of the Sierra Nevada vs. the Cascade Range may control the threshold at which changes in delineated fen areas are discernible. Overall, the results from this study show that fens in the Sierra Nevada have strong potential as whole-ecosystem gauges for determining long-term changes in groundwater recharge under climate change. Due to either more moderate climate change and/or hydrogeological differences, fens in the southern Cascade Range currently do not appear to have the same utility. A greater sample size of fens in the Sierra Nevada is needed to confirm the general applicability of this method. In addition, future work needs to focus on integrating fen monitoring with geochemical and/or isotopic process-level studies in order to quantify changes in groundwater recharge identified using this new approach. [Copyright &y& Elsevier]

Abstract: Aerial photographs and satellite images have been used to document the evolution of a small (<1km2) dunefield over the past 60–70years. Over this period, the dunefield has undergone significant changes, including development of well defined linear and crescentic dunes from an initial small area of partially vegetated dunes, resulting in an increase in the area of the dunes by a factor of 3 since 1944. The dune field continues to expand toward the southeast but its upwind margins are now experiencing significant erosion because the sand supply is now cut off by dust control measures in the source area and transport pathway. This study provides some information on the timescales of dune development in a high-energy aeolian environment, which formerly experienced an abundant supply of sand, with rapid development of crescentic dunes over a period of 20years. The complexity of dunefield development is also highlighted, even on decadal timescales, and the important role of episodic sediment supply in forming new generations of dunes. Periods of rapid dunefield change involving lagged input of additional sand from external sources appear to be linked to episodes of high flows in the Owens River, which is the main sediment source for the Keeler Dunes. [Copyright &y& Elsevier]

Surface traces of the Quaternary active Kern Canyon and Breckenridge faults were mapped via aerial reconnaissance, analysis of light detection and ranging (LiDAR) elevation data, review and interpretation of aerial photography, field reconnaissance, and detailed field mapping. This effort specifically targeted evidence of late Quaternary surface deformation and, combined with separate paleoseismic investigations, identified and characterized the North Kern Canyon, South Kern Canyon, and Lake Isabella sections of the Kern Canyon fault and the Breckenridge fault. The mapping presented here provides definitive evidence for previously unrecognized Holocene and late Pleisto cene east-down displacement along the Kern Canyon and Breckenridge faults. Our results indicate that much of the Kern Canyon fault has undergone Quaternary reactivation to accommodate internal deformation of the otherwise rigid Sierra Nevada block. This deformation reflects ongoing, seismogenic crustal thinning in the southern Sierra Nevada, and highlights the effects of localized tectonic forces operating in this part of the Sierra Nevada. [ABSTRACT FROM AUTHOR]

The article discusses a study on the regional earthflow activity and sediment flux across 226-square kilometers of eroding Franciscan Complex rocks of the Eel River catchment in northern California. The researchers used a combination of airborne light detection and ranging and orthorectified historical aerial photographs to map earthflow movement between 1944 and 2006. They found a similarity between the slope distribution (SD) of the earthflows and the SD of the site.

This study focused on a spatial and temporal analysis of the active channel and associated floodplain lakes using aerial photographs spanning five decades (1942, 1962, 1985, 1999) over a 140 km long reach of the Sacramento. Planimetric changes were analysed longitudinally and temporally to highlight the spatial structures and their evolution through time. The results underline complex changes and space-time pattern in bank erosion, channel length and active channel width. The bank erosion and also channel lengthening were higher between 1962 and 1985 than in the two periods studied before and after. Active channel width significantly decreased from 1942 to 1999; partly progressively from upstream to downstream with local widening whatever the studied periods. Similarly the floodplain lakes observed before 1942-1962 were significantly different in size and geometry from those which appeared during the most recent period. The creation of lakes is less frequent after the 1940s, with a secondary peak of occurrence during the 1962-1985 period. The interpretation of these changes is complex because of various human pressures acting over different time scales (bank protection, flow diversion, sediment starvation, land-use changes) and various natural influences (flood sequences through out the period, geological setting). The findings are discussed by comparison with previous work, and highlight the important effect of dam impact on peak flow and sediment starvation modifying longitudinally hydraulic conditions within the channel, but also the increase in riprap protection which induced change in bank erosion, channel planimetry and floodplain lake characters (geometry, frequency of renewal). Variation in flood intensities is also observed as having positive effects on the bank erosion pattern. Secondarily, land-use changes also controlled bank erosion intensity. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The Million Trees LA initiative intends to improve Los Angeles''s environment through planting and stewardship of 1 million trees. The purpose of this study was to measure Los Angeles''s existing tree canopy cover (TCC), determine if space exists for 1 million additional trees, and estimate future benefits from the planting. High-resolution QuickBird remote sensing data, aerial photographs, and geographic information systems were used to classify land cover types, measure TCC, and identify potential tree planting sites. Benefits were forecast for planting of 1 million trees between 2006 and 2010, and their growth and mortality were projected until 2040. Two scenarios reflected low (17%) and high (56%) mortality rates. Numerical models were used with geographic data and tree size information for coastal and inland climate zones to calculate annual benefits and their monetary value. Los Angeles''s existing TCC was 21%, and ranged from 7 to 37% by council district. There was potential to add 2.5 million additional trees to the existing population of approximately 10.8 million, but only 1.3 million of the potential tree sites are deemed realistic to plant. Benefits for the 1-million-tree planting for the 35-year period were $1.33 billion and $1.95 billion for the high- and low-mortality scenarios, respectively. Average annual benefits were $38 and $56 per tree planted. Eighty-one percent of total benefits were aesthetic/other, 8% were stormwater runoff reduction, 6% energy savings, 4% air quality improvement, and less than 1% atmospheric carbon reduction. [Copyright &y& Elsevier]

Abstract: Natural landscapes are increasingly subjected to impacts associated with urbanization, resulting in loss and degradation of native ecosystems and biodiversity. Traditional classification approaches to the characterization of urbanization may prove inadequate in some human-modified landscapes where complex and unique combinations of conditions can make classification and delineation of patches difficult. We describe a model that depicts existing human development as a fine-grained continuous variable using parcel-based land use data and transportation networks. We derived percent development values across our 88000-ha study area, the Lake Tahoe basin. Our modeled values were highly correlated with observed levels of development based on high-resolution aerial photographs. We demonstrate how our model of development can be used to address practical conservation questions by evaluating the potential effects of highly interspersed urban land development and wildland conditions on the amount and availability of habitat suitable for the resident California spotted owl (Strix occidentalis occidentalis) at two points in time (current and 40 years in the future). The results indicated that assessments not accounting for the indirect effects of development may overestimate the amount of available habitat by 19–83%. Portraying urbanization as a continuum across entire landscapes captured fine-grained landscape complexity at scales that were relevant to the habitat needs and environmental sensitivities of a species of conservation interest. This relatively simple approach should aid ecologists and landscape planners in evaluating the current or future effects of urbanization on ecological elements and processes. [Copyright &y& Elsevier]

We studied the 1941 diversion of Furnace Creek Wash (drainage area 439 km²) into Gower Gulch (5.8 km²) as an experiment in the transient response of a channel to a large change in water and sediment discharge. We measured sequential changes in valley width using a time series of aerial photographs (1948-1995), airborne laser elevation data from 2005, and a field survey. We found that the response of the system varied depending on the prediversion channel morphology and bedrock geology. In two steep knickzone segments, narrowing, knickpoint retreat and bedrock incision dominated, indicating a detachment-limited response. In the relatively low-gradient main part of Gower Gulch, widening dominated as the coarse postdiversion sediment load covered the channel bed. This transport-limited part of the system has undergone only modest incision and adjustments in gradient. Over long periods, the lowering rate of Gower Gulch probably depends on knickpoint retreat, but the present-day response of this non-steady-state system is a hybrid of incision and narrowing in detachment-limited reaches and widening in transport-limited reaches. This system demonstrates the importance of evolving channel geometry in setting the transient response of rivers to changes in forcing parameters. [ABSTRACT FROM AUTHOR]

The land-use history of an ecosystem influences current structure and possibly response to modern disturbances and stresses. In semiarid systems the nature of land-use legacies is poorly understood, confounding efforts to establish sustainable management approaches. We compare previously cultivated and non-cultivated lands in Owens Valley, California, where cultivation once extended to 34% of the valley floor but was largely discontinued by 1940, to measure the influence of past disturbance on modern vegetation. We combined historic maps of cultivated and non-cultivated land with an extensive vegetation survey, historic aerial photographs, and satellite measurements of vegetation response to precipitation variability to examine the importance of land-use history in determining the sensitivity of vegetation to annual variations in precipitation. Remote sensing analysis showed that total plant cover on previously cultivated lands was lower and fluctuations in cover were marginally more dependent on precipitation compared with plant cover on non-cultivated lands. We then compared modern plant assemblages within cultivated and non-cultivated land to determine if compositional differences could explain the current patterns of vegetation cover. We found lower species richness on previously cultivated parcels, and higher frequency and cover of perennial grasses on non-cultivated lands. Therefore, we showed differences in land-cover patterns, isolated a mechanism that could account for the differences (species differences), and developed a method for remotely analyzing land regions that have experienced historic anthropogenic disturbance. [ABSTRACT FROM AUTHOR]

Natural color photographs were used to detect the coverage of saltcedar, Tamarix parviflora, along a 40 km portion of Cache Creek near Woodland, California. Historical aerial photographs from 2001 were retrospectively evaluated and compared with actual ground-based information to assess accuracy of the assessment process. The color aerial photos were sequentially digitized, georeferenced, classified using color and texture methods, and mosaiced into maps for field use. Eight types of ground cover ( Tamarix, agricultural crops, roads, rocks, water bodies, evergreen trees, non-evergreen trees and shrubs (excluding Tamarix)) were selected from the digitized photos for separability analysis and supervised classification. Due to color similarities among the eight cover types, the average separability, based originally only on color, was very low. The separability was improved significantly through the inclusion of texture analysis. Six types of texture measures with various window sizes were evaluated. The best texture was used as an additional feature along with the color, for identifying Tamarix. A total of 29 color photographs were processed to detect Tamarix infestations using a combination of the original digital images and optimal texture features. It was found that the saltcedar covered a total of 3.96 km2 (396 hectares) within the study area. For the accuracy assessment, 95 classified samples from the resulting map were checked in the field with a global position system (GPS) unit to verify Tamarix presence. The producer's accuracy was 77.89%. In addition, 157 independently located ground sites containing saltcedar were compared with the classified maps, producing a user's accuracy of 71.33%. [ABSTRACT FROM AUTHOR]

On 28 August 2002, a visually striking sequence of events appeared in satellite imagery showing a coastally trapped disturbance (CTD) propagating northward along the coast of California against a northerly background flow. As a narrow tongue of coastal stratus indicative of the CTD propagated northward, a long, linear set of wave clouds developed ahead of the advancing CTD and angled away from the coast. The CTD and cloud lines moved northward over the next ∼6 h and, as they approached Cape Mendocino (CM), the leading edge of the CTD clouds rolled up into a cyclonic mesoscale eddy—with the wave clouds being wrapped into the eddy. The CTD abruptly stalled and failed to round CM. Further, a second cyclonic mesoscale eddy formed southwest of Point Arena (PA). Although there has been extensive study of the propagation phase of CTDs, relatively little attention has been paid to the cessation of their propagation wherein mesoscale eddy development is not uncommon. Using the U.S. Navy's Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS), run in an operational manner, numerous observed features of this case are forecast, including: (i) the cold, shallow, cloud-filled, northward-propagating CTD; (ii) the development, linear structure, orientation, and movement of an oblique hydraulic jump–like (“shock”) feature; (iii) a southerly wind shift associated with the CTD that precedes the advancing cloud tongue by several hours in both the observations and the model; (iv) the modeled CTD that rounds PA, but fails to round CM; and (v) the formation of modeled cyclonic mesoscale eddies near both CM and PA. North of PA, however, a phase error develops in which the modeled CTD propagation is too slow. The model forecast cloud tongue behaves as a gravity current, and similar to earlier observational and modeling studies of CTDs, the model forecasts a bore propagating in the stratified atmosphere immediately above the marine boundary layer. Supercritical flow is forecast in the accelerating northerly flow rounding CM, and when the advancing bore interacts with this high Froude number region a pronounced oblique shock develops and the CTD stalls. Vorticity is enhanced along this shock due to vertical stretching and potential vorticity is generated within the shock. Additionally, juxtaposition of the CTD's southerly flow with the background northerly flow creates a vortex sheet–like shear zone along the offshore flank of the CTD, with the horizontal gradient of absolute vorticity changing signs, which is a necessary condition for classic barotropic instability. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to evaluate spatial resolution effects on image classification. Classification maps were generated with a maximum likelihood (ML) classifier applied to three multi-spectral bands and variance texture images. A total of eight urban land use/cover classes were obtained at six spatial resolution levels based on a series of aggregated Colour Infrared Digital Orthophoto Quarter Quadrangle (DOQQ) subsets in urban and rural fringe areas of the San Diego metropolitan area. The classification results were compared using overall and individual classification accuracies. Classification accuracies were shown to be influenced by image spatial resolution, window size used in texture extraction and differences in spatial structure within and between categories. The more heterogeneous are the land use/cover units and the more fragmented are the landscapes, the finer the resolution required. Texture was more effective for improving the classification accuracy of land use classes at finer resolution levels. For spectrally homogeneous classes, a small window is preferable. But for spectrally heterogeneous classes, a large window size is required. [ABSTRACT FROM AUTHOR]

Abstract: Tree canopy cover data from aerial photographs and building energy simulations were applied to estimate energy savings from existing trees and new plantings in California. There are approximately 177.3 million energy-conserving trees in California communities and 241.6 million empty planting sites. Existing trees are projected to reduce annual air conditioning energy use by 2.5% with a wholesale value of $ 485.8 million. Peak load reduction by existing trees saves utilities 10% valued at approximately $778.5 million annually, or $ 4.39/tree. Planting 50 million trees to shade east and west walls of residential buildings is projected to reduce cooling by 1.1% and peak load demand by 4.5% over a 15-year period. The present wholesale value of annual cooling reductions for the 15-year period is $ 3.6 billion ($ 71/tree planted). Assuming total planting and stewardship costs of $ 2.5 billion ($ 50/tree), the cost of peak load reduction is $ 63/kW, considerably less than the $ 150/kW benchmark for cost-effectiveness. Influences of tree location near buildings and regional climate differences on potential energy savings are discussed. [ABSTRACT FROM AUTHOR]

Prediction of the area of possible inundation is critical for debris-flow hazard management. This is typically done with inundation modeling programs, but many of these models are not specific to predict post-wildfire debris flows, a particularly dangerous subset. For this research, deposition patterns from flows triggered by the 2003 Christmas Day storm in areas burned by the Old and Grand Prix Fires in southern California were used to develop runout parameters specific to post-wildfire debris flows that can be incorporated into the LAHARZ inundation modeling program. Detailed mapping using aerial photographs, confirmed by field mapping, was used to document the cross-sectional area of the debris flows in drainages (A), the planimetric area of the flows (B), the volume of the flows (V), and the location of onset of deposition. These data were used to modify the power law equations required by the model, where the equations A = 0.26 V0.40 and B = 7.4 V0.81 are the best estimates for the post-wildfire data. These are statistically the 50th percentile values. More conservative values are also calculated as: A = 0.54 V0.40 (80% prediction interval), A = 0.82 V0.40 (95% prediction interval), B = 32 V0.81 (80% prediction interval), and B = 73 V0.81 (95% prediction interval). These values are expected to apply post-wildfire debris flows in the volume range of 102 to 105 m3 in the mountain ranges in Southern California. • Debris flow runout modeling programs do not account for post wildfire events. • Calibrated parameters developed for post wildfire debris flows for LAHARZ program. • Equations also provided for more conservative 80% and 95% prediction internals. [ABSTRACT FROM AUTHOR]

A sequence of aerial photographs of Mendel Glacier, a debris-covered glacier in the central Sierra Nevada, California, suggests that at least one outburst flood originated from a subglacial reservoir beneath a prominent mid-glacier surface depression. By 1962, a ring of crevasses 250 m in diameter was centered within the depression, implying recent ice collapse. In 1972, the crevasses had almost disappeared, and by 1987, a lake of similar area had replaced the crevasse ring. No lake was present in 1995/6. Theoretical examination of ice overburden and hydrostatic pressure at the glacier bed indicate that a subglacial water reservoir may have formed beneath the surface depression prior to 1962. According to theory, as water accumulates within the reservoir, the hydrostatic pressure increases until it is equal to the ice overburden pressure down-glacier from the reservoir, at which point an outburst flood initiates. Cesium-137 measurements from the Mendel Glacier outwash plain indicate the post-bomb-testing deposition of approximately 20 cm of sand, lending support to the flood hypothesis. The supraglacial lake is ephemeral, and likely reflects relatively high inflow rates or low outflow rates. This sequence of events is possible because the debris cover reduces local ablation rates, forming a depression up-glacier of the debriscover, which in turn forces water to flow into a subglacial reservoir. As long as the debris content is relatively low (<13% by weight), the reservoir water will eventually float the glacier and initiate an outburst flood. Debris-covered glaciers should be recognized as potential sources of outburst floods in alpine regions. [ABSTRACT FROM AUTHOR]

A two-stage system for selecting stream reaches and riparian communities for restoration was applied to the 80-km San Luis Rey River below the Lake Hen-shaw dam in southern California. In the first stage, data from topographic quadrangles and aerial photographs were analyzed to define and classify reaches. These analyses concluded that (1) 28 km of the river and adjacent floodplain were suitable for second-stage evaluation of restoration needs and (2) 32 km met criteria for reference conditions at the stream reach scale and should be protected from further impacts. The remaining 20 km of the river and flood-plain were considered unsuitable for restoration to reach-scale reference conditions; individual sites may be restored under existing regulatory review. Second-stage field sampling provided data on vegetation and floodplain landforms and substrate from more than 3000 plots within the 28 km of river and 1120 ha of floodplain selected for further study. Classification of floristic samples stratified by landform/substrate class indicated six primary riparian communities on the floodplain, some associated with particular floodplain landform/substrate classes and others ubiquitous. Reference conditions for these communities were interpreted from the data. There were two major departures from reference conditions: free-dominated communities were less extensive than historic levels and exotic plants had significantly invaded some landforms and communities, displacing natural communities. General goals would include restoration of tree communities and removal of exotics, with further consideration of site-specific objectives. The results included estimates of the areas by community type requiring restoration. The approach was developed for streams in the semi-arid western United States, but it may be adapted for use elsewhere. [ABSTRACT FROM AUTHOR]