Western Cascades Of Oregon Research Articles

Quantifying impacts of forest fire on soil carbon in a young, intensively managed tree farm in the western Oregon Cascades

AbstractForest soils of the Pacific Northwest contain immense amounts of carbon (C). Increasing acreage burned by severe wildfire in the western Oregon Cascades threatens belowground C stocks. The objective of this research was to quantify the changes in soil C stocks, nitrogen (N) stocks, and relevant chemical and physical parameters after a severe wildfire in a young, intensively managed Pseudotsuga menziesii (Douglas‐fir) tree farm in the western Oregon Cascades. This longitudinal study was originally established to detect soil C changes after a harvest; therefore, it offers insight into long‐term soil C dynamics after compounding disturbances. Forest floor and 0–30 cm depth soil samples were collected for comparison before and after the fire and were then split into size fractions to assess the fire's effect on different grain sizes and forest floor compositions. Overall, soil C was approximately 40 Mg C ha−1 lower after the fire, equivalent to approximately 30% of soil C stocks. Of these decreases, two‐thirds were in the forest floor and one‐third were in the mineral soil. C stock losses were driven by changes in mass in every composite level. C concentration was unchanged in most levels while N concentration increased in certain levels. Losses extended further belowground than most previously studied soil C decreases from severe wildfire. The effects of wildfire on soil C stocks in industrial tree farms should be further explored to determine long‐term trajectories of soil C and N.

Distribution of a Foliage Disease Fungus Within Canopies of Mature Douglas-Fir in Western Oregon.

Nothophaeocryptopus gaeumannii is a common native, endophytic fungus of Douglas-fir foliage, which causes Swiss needle cast, an important foliage disease that is considered a threat to Douglas-fir plantations in Oregon. Disease expression is influenced by fungal fruiting bodies (pseudothecia), which plug the stomata and inhibit gas exchange. Trees are impacted when pseudothecia plug stomates on 1-year-old and older needles resulting in early needle abscission. Mature (100 years+) trees appear to be less impacted from disease, and we hypothesize this is due to the greater emergence of pseudothecia on older than younger needles, which allows for more needle retention. We measured the density of pseudothecia occluding stomates across 2- to 5-year-old needles from upper, middle, and lower canopy positions of mature trees at three sites in the Oregon Coast Range and two sites in the western Oregon Cascade Mountains. Binomial generalized linear mixed model (GLMM) was used to test for the effects of canopy position (upper, middle, and lower), sites, needle age (2-5 years old), and years (2016 and 2017), and their interactions on the pseudothecia density. Pseudothecia density varied annually depending on sites, needle age and canopy positions. Pseudothecia density peaked on 3-, and 4-year-old needles, however, needles emerging from the same year, like 2-year-old needles in 2016 and 3-year-old needles in 2017 both emerged in 2014, had consistently similar patterns of pseudothecia density for both years, across site and canopy positions. Canopy position was important for 3-, and 4-year-old needles, showing less pseudothecia in the lower canopy. This research confirms that N. gaeumannii pseudothecia density is greatest in 3- and 4-year old needles in mature trees in contrast to plantations where pseudothecia density usually peaks on 2-year-old needles, and that pseudothecia density (disease severity) is generally lower in mature trees. Something about mature forest canopies and foliage appears to increase the time it takes for pseudothecia to emerge from the needles, in contrast to younger plantations, thus allowing the mature trees to have greater needle retention.

A land systems science approach to assessing forest governance and characterizing the emergence of social forestry in the Western Cascades of Oregon

National forests in the United States are undergoing a spatially and temporally uneven governance transition in response to Congressional policies, agency mandates, and social and economic pressures, with many moving from a wholly state-led ‘dominant federal’ model to a more collaborative networked governance model which we refer to as ‘social forestry’. While the broad contours of this transition have been observed and studied previously, there have been few attempts to characterize it using quantitative, qualitative, or geospatial methods. Here, we combine a novel remote sensing-based method with qualitative social science research to understand the emergence of social forestry and its implications for land use/land cover change associated with implementation of the Northwest Forest Plan (NWFP) in the Western Cascades of Oregon. We linked time-series satellite data with forest inventory data to track patterns of timber harvest at scales commensurate with timber management decision-making. We then compared these patterns to policy-based expectations. We found a significant disconnect between NWFP policy and actual timber harvest patterns, raising questions about the effectiveness of the NWFP land use allocation system and the ‘land sparing’ approach to managing tensions between conservation and production. Qualitative research, including semi-structured interviews with federal agency personnel and local stakeholders, shed light on the causal mechanisms and reciprocal relationships driving spatial patterns of timber harvesting, which we discuss in terms of the emergence of social forestry involving complex, place-based negotiations between the federal government and local veto actors advocating for conservation. Findings have implications for US Forest Service public engagement strategies and efforts to establish zones of agreement regarding timber harvesting, as well as broader discussions about the agency’s future.

How does tree regeneration respond to mixed‐severity fire in the western Oregon Cascades, USA?

AbstractDendroecological studies of historical tree recruitment patterns suggest mixed‐severity fire effects are common in Douglas‐fir/western hemlock forests of the Pacific Northwest (PNW), USA, but empirical studies linking observed fire severity to tree regeneration response are needed to expand our understanding into the functional role of fire in this forest type. Recent increases in mixed‐severity fires offered this opportunity, so we quantified the abundance, spatial distribution, species richness, and community composition of regenerating trees across a mixed‐severity fire gradient (unburned–high‐severity fire) 10 and 22 yr post‐fire, and use our results to inform a discussion of fire's functional role in western Oregon Cascades Douglas‐fir forests. Regeneration abundance was unimodal across the fire severity gradient such that the greatest mean abundance followed moderate‐severity fire (25–75% basal area mortality). Similarly, the greatest number of species was present within the most 25‐m2 regeneration quadrants (most extensive distribution) following moderate‐severity fire, relative to any other fire severity class. On average, species richness also exhibited a unimodal distribution across the severity gradient, increasing by 100% in stands that experienced moderate‐severity fire relative to unburned forests or following high‐severity fire, as predicted by the Intermediate Disturbance Hypothesis. Several distinct regeneration communities emerged across the fire severity gradient, including early seral tree communities indicative of those observed in initial and relay floristics successional models for this forest type. Most significantly, moderate‐severity fire alters successional trajectories and facilitates the establishment of a more diverse tree regeneration community than observed following low‐ or high‐severity fire. These communities are reflective of the diverse overstory communities commonly encountered throughout this forest type. The emergence of these diverse forests is unlikely to develop or persist in the absence of moderate‐severity fire effects, and may be perpetuated longer by recurring moderate‐severity fire relative to experiencing stand replacing fire. Therefore, moderate‐severity fire may be the most functionally important fire effect in Douglas‐fir forests and should be better represented in successional models and more prominent in ecologically based fire and forest management.

Tree traits influence response to fire severity in the western Oregon Cascades, USA

Wildfire is an important disturbance process in western North American conifer forests. To better understand forest response to fire, we used generalized additive models to analyze tree mortality and long-term (1 to 25 years post-fire) radial growth patterns of trees that survived fire across a burn severity gradient in the western Cascades of Oregon. We also used species-specific leaf-area models derived from sapwood estimates to investigate the linkage between photosynthetic capacity and growth response. Larger trees and shade intolerant trees had a higher probability of surviving fire. Trees that survived fire tended to experience a reduction in growth immediately following fire, with the most pronounced growth suppression found in trees within stands burned at high severity. Radial growth response to fire over time differed markedly as a function of tree size. Smaller trees that survived fire generally experienced enhanced radial growth relative to small trees in unburned stands. Conversely, larger trees that survived fire experienced significant and persistent reductions in growth relative to large trees in unburned stands. There was a linear relationship between diameter and tree leaf area in stands burned at low severity, but a non-linear relationship between diameter and leaf area in stand burned at high severity. Generalized additive models are well suited to modeling non-linear mortality and growth responses to fire. This research provides a better understanding of how fire severity influences tree-growth, forest succession, as well as the long-term resilience of forests to disturbances.

Estimating economic impact of black bear damage to western conifers at a landscape scale

Black bear (Ursus americanus) damage to trees in the Pacific Northwest is common, although volume and economic losses are unknown. Common measures to quantify bear damage to conifers at large scales rely solely on aerial estimates of red tree crowns (caused by complete girdling) and broad assumptions about stand characteristics. We surveyed 122 vulnerable stands in the Coast Range and western Cascades of Oregon using both aerial surveys and ground surveys. Then, we modeled 4 damage scenarios (Salvage; Total Loss; Root Disease; and Combined Damage) with the Forest Vegetation Simulator (FVS) growth and yield model and the Fuel Reduction Cost Simulator (FRCS). Damage polygons, digitized in real time from aerial surveys identifying red (dead or dying) tree crowns, overestimated bear damage by approximately 5-fold due to misclassification with root disease, and failed to detect partially peeled trees that contributed to economic loss. Damage polygons assessed from the air generally did not include red crowns, and were a mean distance of 58.8 m (SE = 8.8) from damage polygons’ outer edges to the nearest red crown. We accounted for mortality and volume losses from partially girdled trees that did not show red crowns in our Salvage scenario, whereas we assumed that all bear-peeled trees resulted in complete loss in the Total Loss scenario. At the landscape scale, economic loss was ≤0.35% of net present value under both damage scenarios, while processing bear damage trees (Salvage) was the most efficacious option. At the landscape scale, our worst-case scenario (Total Loss) resulted in an estimated loss of $56/ha to bear damage, 10-fold less than a previously reported estimate of $585/ha. Root disease was a more prevalent damage agent than bear damage but did not affect net present value at harvest. The majority (92%) of bear damage observed in ground surveys was older (>2 yrs) and existed at a low frequency (1.5 bear damaged trees/ha) and severity across the landscape. Our results suggest that black bear damage is not uniformly distributed and that perceived impact varies with spatial scale. On-the-ground monitoring of the status of bear damage across the western Oregon landscape will identify hot spots of severe peeling and provide an understanding of these changes over time.

Tree-Ring Carbon Isotope Records from the Western Oregon Cascade Mountains Primarily Record Summer Maximum Temperatures

Abstract Here we examine climatic influences on inter-annual variation in latewood tree growth (i.e. ring-width indices, RWILW) and stable-carbon isotope discrimination (Δ13CLW) from 1950 to 2013 at two SNOTEL snowpack monitoring sites in the Oregon Cascade Mountains. Douglas-fir and mountain hemlock trees were sampled at the lower and upper elevation sites where annual peak snow water equivalent (SWE) averaged 467 and 1128 mm, respectively. RWILW chronologies were poorly correlated among sites/species (r = 0.23, P = 0.063) and neither exhibited strong correlations with monthly or seasonal climate variables. By contrast, Δ13CLW chronologies were significantly correlated (r = 0.69, P < 0.001) and exhibited stronger climate responses. Multiple regression analyses identified summertime maximum temperature (Tmax) and/or vapor pressure deficit (VPD) as the primary drivers of Δ13CLW. Secondary influences included summertime precipitation, specific humidity, cloud cover, and SWE from the previous fall and winter...

Developing a representative snow-monitoring network in a forested mountain watershed

Abstract. A challenge in establishing new ground-based stations for monitoring snowpack accumulation and ablation is to locate the sites in areas that represent the key processes affecting snow accumulation and ablation. This is especially challenging in forested montane watersheds where the combined effects of terrain, climate, and land cover affect seasonal snowpack. We present a coupled modeling approach used to objectively identify representative snow-monitoring locations in a forested watershed in the western Oregon Cascades mountain range. We used a binary regression tree (BRT) non-parametric statistical model to classify peak snow water equivalent (SWE) based on physiographic landscape characteristics in an average snow year, an above-average snow year, and a below-average snow year. Training data for the BRT classification were derived using spatially distributed estimates of SWE from a validated physically based model of snow evolution. The optimal BRT model showed that elevation and land cover type were the most significant drivers of spatial variability in peak SWE across the watershed (R2 = 0.93, p value &lt; 0.01). Geospatial elevation and land cover data were used to map the BRT-derived snow classes across the watershed. Specific snow-monitoring sites were selected randomly within the dominant BRT-derived snow classes to capture the range of spatial variability in snowpack conditions in the McKenzie River basin. The Forest Elevational Snow Transect (ForEST) is a result of this coupled modeling approach and represents combinations of forested and open land cover types at low, mid-, and high elevations. After 5 years of snowpack monitoring, the ForEST network provides a valuable and detailed dataset of snow accumulation, snow ablation, and snowpack energy balance in forested and open sites from the rain–snow transition zone to the upper seasonal snow zone in the western Oregon Cascades.

Uncertainty in carbon allocation strategy and ecophysiological parameterization influences on carbon and streamflow estimates for two western US forested watersheds

Increasingly sophisticated process-based ecosystem models account for the ability of plants to vary the proportion of net photosynthate that is allocated to individual organs – such as leaves, stems and roots. Because the governing mechanisms are still not well understood, models differ in the strategies used to represent carbon allocation processes. Allocation schemes may have important implications for ecosystem structure and biogeochemical cycling, thus there is a need to better understand how different carbon allocation strategies influence estimates of variables that are of interest to model users. At the same time, uncertainty in other ecophysiological parameters that are commonly used in carbon cycling models may influence these estimates and interact with different carbon allocation strategies. We use a coupled ecohydrologic model to understand how uncertainty in three relatively simple allocation strategies affects carbon (C) and streamflow estimates in two case study forested mountain watersheds in the western United States: a relatively wet site located in the western Oregon Cascades, and a drier site in California’s Sierra Nevada. Ecophysiological parameters controlling productivity rates, morphology, and nutrient requirements for growth are varied as well. The influence of specific ecophysiological parameters and allocation strategies on C sequestration and streamflow estimates differed between sites. At the wetter site, uncertainty in C cycling processes resulted in a three-fold difference in potential sequestered carbon, but had a negligible effect on annual and low monthly streamflow estimates. Conversely, at the drier site, C pool estimates showed limited sensitivity to ecophysiological parameter uncertainty, but considerable difference in annual and low monthly streamflow estimates across ecophysiological assumptions. At both sites, stemwood C pool estimates exceeded literature-derived field values when branch mortality—a surrogate for density thinning—was not included in addition to background mortality. Despite using site- and species-specific information, we are unable to invalidate any of the allocation strategies considered. Our results suggest that uncertainty in parameterization of ecophysiological parameters and assumptions about carbon allocation can strongly influence model estimates of both streamflow and forest carbon sequestration potential, but that influence is likely to vary with site bioclimatic characteristics.

Hydrologic and forest management controls on dissolved organic matter characteristics in headwater streams of old-growth forests in the Oregon Cascades

Dissolved organic matter (DOM) is a critical component of the carbon cycle linking terrestrial and aquatic ecosystems. Although many factors have been identified as influencing DOM fluxes and biochemical quality in rivers with varying land cover types, controls on DOM composition in forested headwater catchments of the western U.S. are poorly understood. This study examined the effect of hydrologic patterns and forest management history on stream DOM chemistry at watersheds located in the H.J. Andrews Experimental Forest of the Oregon Cascades. Specific UV absorbance at 254nm (SUVA254), generally indicative of aromaticity, increased in streams during storms with increasing surficial soil horizon and litter DOM inputs. Fluorescence excitation and emission matrices (EEMs) with Parallel Factor Analysis (PARAFAC) identified a protein-like DOM fluorescent component as well as several other components associated with terrestrial plant material. Correlation analysis between the protein-like DOM component and hydrologic patterns, SUVA254, and DOC concentrations suggest that DOM during dry seasons represents more microbially-processed sources, such as protein-rich, deeper soil or DOM with greater in-stream microbial processing, compared to more plant-like surface soil sources observed during high flow. The base flow index (the proportion of base flow to total flow) showed a high correlation with the relative proportion of protein-like DOM indicating that deep soil water is a source of the protein-like signal. The relative proportions of the protein-like DOM and humic DOM were also influenced by the abundance of coarse woody debris (CWD), but not live tree biomass, with the proportions of protein-like DOM highest in harvested watersheds with low surficial CWD. This study shows UV and fluorescent spectroscopy is a viable finger printing method to elucidate DOM sources in pristine headwater streams at the western Cascades of Oregon.

Complex mountain terrain and disturbance history drive variation in forest aboveground live carbon density in the western Oregon Cascades, USA

Forest carbon (C) density varies tremendously across space due to the inherent heterogeneity of forest ecosystems. Variation of forest C density is especially pronounced in mountainous terrain, where environmental gradients are compressed and vary at multiple spatial scales. Additionally, the influence of environmental gradients may vary with forest age and developmental stage, an important consideration as forest landscapes often have a diversity of stand ages from past management and other disturbance agents. Quantifying forest C density and its underlying environmental determinants in mountain terrain has remained challenging because many available data sources lack the spatial grain and ecological resolution needed at both stand and landscape scales. The objective of this study was to determine if environmental factors influencing aboveground live carbon (ALC) density differed between young versus old forests. We integrated aerial light detection and ranging (lidar) data with 702 field plots to map forest ALC density at a grain of 25m across the H.J. Andrews Experimental Forest, a 6369ha watershed in the Cascade Mountains of Oregon, USA. We used linear regressions, random forest ensemble learning (RF) and sequential autoregressive modeling (SAR) to reveal how mapped forest ALC density was related to climate, topography, soils, and past disturbance history (timber harvesting and wildfires). ALC increased with stand age in young managed forests, with much greater variation of ALC in relation to years since wildfire in old unmanaged forests. Timber harvesting was the most important driver of ALC across the entire watershed, despite occurring on only 23% of the landscape. More variation in forest ALC density was explained in models of young managed forests than in models of old unmanaged forests. Besides stand age, ALC density in young managed forests was driven by factors influencing site productivity, whereas variation in ALC density in old unmanaged forests was also affected by finer scale topographic conditions associated with sheltered sites. Past wildfires only had a small influence on current ALC density, which may be a result of long times since fire and/or prevalence of non-stand replacing fire. Our results indicate that forest ALC density depends on a suite of multi-scale environmental drivers mediated by complex mountain topography, and that these relationships are dependent on stand age. The high and context-dependent spatial variability of forest ALC density has implications for quantifying forest carbon stores, establishing upper bounds of potential carbon sequestration, and scaling field data to landscape and regional scales.

Disturbance legacies increase the resilience of forest ecosystem structure, composition, and functioning.

Disturbances are key drivers of forest ecosystem dynamics, and forests are well adapted to their natural disturbance regimes. However, as a result of climate change, disturbance frequency is expected to increase in the future in many regions. It is not yet clear how such changes might affect forest ecosystems, and which mechanisms contribute to (current and future) disturbance resilience. We studied a 6364-ha landscape in the western Cascades of Oregon, USA, to investigate how patches of remnant old-growth trees (as one important class of biological legacies) affect the resilience of forest ecosystems to disturbance. Using the spatially explicit, individual-based, forest landscape model iLand, we analyzed the effect of three different levels of remnant patches (0%, 12%, and 24% of the landscape) on 500-year recovery trajectories after a large, high-severity wildfire. In addition, we evaluated how three different levels of fire frequency modulate the effects of initial legacies. We found that remnant live trees enhanced the recovery of total ecosystem carbon (TEC) stocks after disturbance, increased structural complexity of forest canopies, and facilitated the recolonization of late-seral species (LSS). Legacy effects were most persistent for indicators of species composition (still significant 500 years after disturbance), while TEC (i.e., a measure of ecosystem functioning) was least affected, with no significant differences among legacy scenarios after 236 years. Compounding disturbances were found to dampen legacy effects on all indicators, and higher initial legacy levels resulted in elevated fire severity in the second half of the study period. Overall, disturbance frequency had a stronger effect on ecosystem properties than the initial level of remnant old-growth trees. A doubling of the historically observed fire frequency to a mean fire return interval of 131 years reduced TEC by 10.5% and lowered the presence of LSS on the landscape by 18.1% on average, demonstrating that an increase in disturbance frequency (a potential climate change effect) may considerably alter the structure, composition, and functioning of forest landscapes. Our results indicate that live tree legacies are an important component of disturbance resilience, underlining the potential of retention forestry to address challenges in ecosystem management.

Inter-annual variability and spatial coherence of net primary productivity across a western Oregon Cascades landscape

Inter-annual variability (IAV) of forest Net Primary Productivity (NPP) is a function of both extrinsic (e.g., climate) and intrinsic (e.g., stand dynamics) drivers. As estimates of NPP in forests are scaled from trees to stands to the landscape, an understanding of the relative effects of these factors on spatial and temporal behavior of NPP is important. Although a high degree of spatial coherence (i.e., the degree of spatial synchrony over time) is often assumed, this inherent behavior is rarely examined. Quantifying this term may improve future predictions as site-level estimates are scaled up spatially. We quantified the spatial coherence of bole biomass production (BBP) within and between trees, and bole-related NPP (NPPB) between sites of varying age, elevation, moisture, and species composition across a forested landscape in the western Cascade Range of Oregon. Within sites, individual trees with lower than average BBP were the most coherent. IAV of BBP increased as average tree BBP increased and spatial coherence was reduced. Among sites, NPPB was the most spatially coherent (r=0.92) between young sites, while older sites and comparisons between age classes revealed a much larger range in spatial coherence (r=−0.18 to 0.85). Our findings indicate climate variability may be of greater importance for spatial coherence between young sites, and that intrinsic factors could be decreasing spatial coherence between older sites or sites not in close proximity. The wide range in spatial coherence between sites found in this study, coupled with the complex land use history patterns across forested landscapes, has significant implications for modeling and scaling of NPP.

Post‐fire tree establishment and early cohort development in conifer forests of the western Cascades of Oregon, USA

Early‐seral ecosystems make important contributions to regional biodiversity by supporting high abundance and diversity of many plant and animal species that are otherwise rare or absent from closed‐canopy forests. Therefore, the period of post‐fire tree establishment is a key stage in forest stand and ecosystem development that can be viewed in the context of competing management interests in diverse early‐seral ecosystems vs. rapid forest development for ecological or commercial objectives. Previous work in Douglas‐fir/western hemlock forests of the Pacific Northwest suggests stands initiate either with abrupt establishment (&lt;20 years) or by protracted establishment with low tree density persisting &gt;100 years. To improve understanding of how post‐fire tree establishment and early cohort development have varied in space and over time and elucidate some of the factors contributing to that variation, we analyzed forest structure, tree ages, and Douglas‐fir growth across the central western Cascades of Oregon where cohort ages span nearly eight centuries. The number of post‐fire cohorts was estimated per stand, and establishment trajectories were evaluated by cohort. On average, it took 43.5 years to reach establishment of 90% of the trees per cohort. The rate and duration of establishment were surprisingly consistent across variation in topography (elevation, slope position, and aspect), among cohorts initiated from the late 12th to the early 20th century, and regardless of the severity of the cohort‐initiating fire or the timing of establishment by shade‐tolerant species. Only 8% of cohorts completed establishment within 20 years and 12% had establishment lasting &gt;80 years. Douglas‐fir growth (basal area increment) exhibits high plasticity in relation to different competitive interactions within uni‐specific and multi‐species cohorts and between cohorts of different age, suggesting wide variation in the structure and dynamics of early‐seral ecosystems and an ability to tolerate moderate competition when young. This study illustrates that post‐fire establishment in Douglas‐fir/western hemlock forests of the central western Cascades historically was a multi‐decadal process. Limited regeneration in a short window did not necessarily lead to persistent shrublands. In fact, post‐fire forest development appears resilient to considerable variation in the fire regime and climatic and biotic constraints on tree establishment.

Fire‐mediated pathways of stand development in Douglas‐fir/western hemlock forests of the Pacific Northwest, USA

Forests dominated by Douglas-fir and western hemlock in the Pacific Northwest of the United States have strongly influenced concepts and policy concerning old-growth forest conservation. Despite the attention to their old-growth characteristics, a tendency remains to view their disturbance ecology in relatively simple terms, emphasizing infrequent, stand-replacing (SR) fire and an associated linear pathway toward development of those old-growth characteristics. This study uses forest stand- and age-structure data from 124 stands in the central western Cascades of Oregon to construct a conceptual model of stand development under the mixed-severity fire regime that has operated extensively in this region. Hierarchical clustering of variables describing the age distributions of shade-intolerant and shade-tolerant species identified six groups, representing different influences of fire frequency and severity on stand development. Douglas-fir trees > 400 years old were found in 84% of stands, yet only 18% of these stands (15% overall) lack evidence of fire since the establishment of these old trees, whereas 73% of all stands show evidence of at least one non-stand-replacing (NSR) fire. Differences in fire frequency and severity have contributed to multiple development pathways and associated variation in contemporary stand structure and the successional roles of the major tree species. Shade-intolerant species form a single cohort following SR fire, or up to four cohorts per stand in response to recurring NSR fires that left living trees at densities up to 45 trees/ha. Where the surviving trees persist at densities of 60-65 trees/ha, the postfire cohort is composed only of shade-tolerant species. This study reveals that fire history and the development of old-growth forests in this region are more complex than characterized in current stand-development models, with important implications for maintaining existing old-growth forests and restoring stands subject to timber management.

Effects of disturbance scale on soil microbial communities in the Western Cascades of Oregon

To gain a better understanding of how rapidly microbial communities respond to different magnitudes of perturbation that mimic minor or catastrophic disturbances. Two montane sites in the western Cascade Mountains of Oregon with adjacent areas of forest and meadow vegetation were studied. A reciprocal transplant experiment evaluated both minor (soil cores remaining in the same vegetation type) or more severe disturbance (soil cores transferred to a different vegetation type). The biomass and composition of the bacterial and fungal communities were measured for 2 years following the establishment of the experiment. Minor disturbance (coring) had little impact on microbial biomass but transferring between vegetation type showed greater fungal biomass in soil incubated in the forest environment. The composition of bacterial communities was not influenced by coring but responded strongly to transfers between vegetation sites, changing to reflect their new environment after 2 years. Fungal community composition responded somewhat to coring, probably from disrupting mycorrhizal fungal hyphae, but more strongly to being transferred to a new environment. The response of the microbial community to major disturbance was rapid, showing shifts reflective of their new environment within 2 years, suggesting that microbial communities have the capacity to quickly adjust to catastrophic disturbances.

Influence of spatial temperature estimation method in ecohydrologic modeling in the Western Oregon Cascades

Key Points Surface temperature interpolation method effects ecohydrologic modeling Temperature interpolation strategy influences soil parameter calibration Improved temperature lapse rates increase estimates of net primary productivity

An individual-based process model to simulate landscape-scale forest ecosystem dynamics

Forest ecosystem dynamics emerges from nonlinear interactions between adaptive biotic agents (i.e., individual trees) and their relationship with a spatially and temporally heterogeneous abiotic environment. Understanding and predicting the dynamics resulting from these complex interactions is crucial for the sustainable stewardship of ecosystems, particularly in the context of rapidly changing environmental conditions. Here we present iLand (the individual-based forest landscape and disturbance model), a novel approach to simulating forest dynamics as an emergent property of environmental drivers, ecosystem processes and dynamic interactions across scales. Our specific objectives were (i) to describe the model, in particular its novel approach to simulate spatially explicit individual-tree competition for resources over large scales within a process-based framework of physiological resource use, and (ii) to present a suite of evaluation experiments assessing iLands ability to simulate tree growth and mortality for a wide range of forest ecosystems. Adopting an approach rooted in ecological field theory, iLand calculates a continuous field of light availability over the landscape, with every tree represented by a mechanistically derived, size- and species-dependent pattern of light interference. Within a hierarchical multi-scale framework productivity is derived at stand-level by means of a light-use efficiency approach, and downscaled to individuals via local light availability. Allocation (based on allometric ratios) and mortality (resulting from carbon starvation) are modeled at the individual-tree level, accounting for adaptive behavior of trees in response to their environment. To evaluate the model we conducted simulations over the extended environmental gradient of a longitudinal transect in Oregon, USA, and successfully compared results against independently observed productivity estimates (63.4% of variation explained) and mortality patterns in even-aged stands. This transect experiment was furthermore replicated for a different set of species and ecosystems in the Austrian Alps, documenting the robustness and generality of our approach. Model performance was also successfully evaluated for structurally and compositionally complex old-growth forests in the western Cascades of Oregon. Finally, the ability of our approach to address forest ecosystem dynamics at landscape scales was demonstrated by a computational scaling experiment. In simulating the emergence of ecosystem patterns and dynamics as a result of complex process interactions across scales our approach has the potential to contribute crucial capacities to understanding and fostering forest ecosystem resilience under changing climatic conditions.

How soil moisture mediates the influence of transpiration on streamflow at hourly to interannual scales in a forested catchment

AbstractThe water balance equation dictates that streamflow may be reduced by transpiration. Yet temporal disequilibrium weakens the relationship between transpiration and streamflow in many cases where inputs and outputs are unbalanced. We address two critical knowledge barriers in ecohydrology with respect to time, scale dependence and lags. Study objectives were to correlate components of the water balance equation at hourly to annual scales, quantify time lags, and simplify critical components of the water budget during wet and dry conditions. We tested interrelationships among precipitation, vapour pressure deficit, transpiration, soil moisture, and streamflow within the confines of a 60‐hectare forested watershed in the western Cascades of Oregon. The Pacific Northwest is an ideal location to compare wet and dry seasons because of its Mediterranean climate. Soil moisture explained more than 80% of the variation in streamflow at all temporal scales investigated. Streamflow was most strongly coupled to soil moisture in the wet season because of gravitational drainage patterns; strong coupling of transpiration to vapour pressure deficit was dominant in the dry season and driven by low humidity. We observed progressively longer hourly time lags between soil moisture and streamflow in the dry season, which relates to an increasing soil moisture deficit that took an average of 48 days to refill after the onset of winter rains. We propose that transpiration drives seasonal patterns in soil moisture that relate to patterns in streamflow only after long time lags. In other words, soil moisture mediates the influence of transpiration on streamflow. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Extreme flood sensitivity to snow and forest harvest, western Cascades, Oregon, United States

We examined the effects of snow, event size, basin size, and forest harvest on floods using &gt;1000 peak discharge events from 1953 to 2006 from three small (&lt;1 km2), paired‐watershed forest‐harvest experiments and six large (60–600 km2) basins spanning the transient (400–800 m) and seasonal (&gt;800 m) snow zones in the western Cascades of Oregon. Retrospectively classified rain‐on‐snow events delivered 75% more water to soils than rain events. Peak discharges of &gt;10 year rain‐on‐snow events were almost twice as high as rain peaks in large basins but only slightly higher in small basins. Peak discharges of &gt;1 year rain‐on‐snow events increased slightly (10%–20%) after logging in small basins, but small basin peaks do not account for the magnitudes of large basin rain‐on‐snow peak discharges during &gt;1 year floods. In extreme floods, despite very high infiltration capacity, high soil porosity, and steep hillslope gradients, prolonged precipitation and synchronous snowmelt produce rapid, synchronized hydrograph responses to small variations in maximum precipitation intensity. At the large basin scale, forest harvest may increase the area of snowpack and simultaneous snowmelt, especially in elevation zones normally dominated by rain and transient snow, thereby increasing large basin peaks without producing very large percent increases in small basin peaks. Further work is needed to describe water flow paths in melting snowpack, snow cover and the area experiencing snowmelt, synoptic peak discharges, and routing of flood peaks through the stream network during extreme rain‐on‐snow floods. The evolving structure of the forest on the landscape is a potentially very important factor influencing extreme rain‐on‐snow floods.