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This study was conducted to improve estimation of concomitant variables for implementation of a stand density management diagram (SDMD) for ponderosa pine (Pinus ponderosa Laws.) in northern California and Oregon. In traditional SDMD, isolines for variables such as stand volume are presented in such a way that uncertainty with estimation is not available. We developed the new top height and stand volume equations, as well as aboveground biomass and percent canopy cover, for building isolines in the SDMD using high-quality data collected from well-managed even-aged stands. The data were selected from the USDA Forest Service’s Pacific Southwest Research Station database. A total of 829 observations (from 113 plots across 15 sites in Oregon and California) were used for model construction. In addition, covariance-variance structures of all of the estimated parameters were provided so that users can evaluate the uncertainty associated with predictions. The model validation results indicated that the predictions made from fixed-effects model forms performed better than the current volume equation of SDMD, as well as those from mixed-effects model forms using the population average effect. The proposed equations provide enhanced predictions and additional useful information about managed ponderosa pine stands, including their uncertainty.

Natural regeneration cannot be effectively evaluated by tree density because of spatial heterogeneity typically observed. A proper interpretation of natural regeneration will consider some evaluation of area stocked. However, stocking estimates for natural regeneration are plot-size-dependent. Stocking at the 1-milacre scale is not generally comparable to that on a 4-milacre scale unless a generalized relation with stand density can be established. A generalized relation was first suggested to hold in a paper by Lynch and Schumacher (1941), but this has not been confirmed in subsequent studies. The Lynch and Schumacher hypothesis of a generalized regeneration density-stocking relation across plot size was tested using observations on 60 stands. Results were consistent with Lynch and Schumacher (1941). With evidence of a well-defined relation for plots ranging from 1 to 10 milacres, it appears possible to approximate, for ponderosa pine and associated species, the natural regeneration stocking percentage for a range of stocking standards based solely on observations of regeneration density. Confidence intervals were derived for a range of stocking standards in English units from 1 to 10 milacre and for metric units from 0.0005 hectares to 0.0040 hectares.

Stand density affects not only structure and growth, but also the health of forests and, subsequently, the functions of forest ecosystems. Here, we integrated dendrochronology and repeated inventories for ponderosa pine research plots to determine whether long-term growth and mortality responded to climate trends and how varying stand density influenced the responses. The plots were established prior to 1975 on existing stands throughout northern California. Although annual temperature increased consistently for the last 65 years, ring-width indices produced by eliminating age and thinning effects failed to detect radial trend regardless of site quality. However, interannual variation for the indices was substantial, reflecting a strong influence of climate on tree growth. Plot-level basal area increments were significantly affected by tree mortality. Stand density index explained most variation of mortality. Lowering stand density enhanced remaining tree growth, reduced mortality, and increased stand resiliency to disturbances and climate change. Besides higher climate moisture indices or lower vapor pressure deficits, any treatments that improve tree vigor and reduce stress will have a similar effect to reducing stand density. Although neither biotic disturbances nor abiotic conditions can be controlled, forest managers can manage stand density appropriately to enhance resilience to climate change and disturbances.

Quaking aspen (Populus tremuloides) is a valued, minor component on northeastern California landscapes. It provides a wide range of ecosystem services and has been in decline throughout the region for the last century. This decline may be explained partially by the lack of fire on the landscape due to heavier fire suppression, as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. However, there is little known about how aspen stand area changes in response to overlapping fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 52-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos and satellite imagery to delineate aspen stands and assess conifer cover percent. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We observed these same stands within the first period of fire exclusion for comparison (i.e., 1941–1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting expansion of aspen stand area. Stands with less edge:area ratio also expanded in area more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater loss of area and changes in location (movement) than in the return of fire period, highlighting their vulnerability to loss via succession to conifers in the absence of disturbances that provide adequate growing space for aspen over time.

Quaking aspen (Populus tremuloides) is a valued, minor component on western landscapes. It provides a wide range of ecosystem services and has been in decline throughout the arid west for the last century. This decline may be explained partially by the lack of fire on the landscape as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. Managers are interested in aspen restoration but there is a lack of knowledge about their spatial dynamics in response to fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 54-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos to delineate aspen stand size, location and succession to conifers. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We looked at these same stands within the first period of fire exclusion for comparison (i.e., 1941-1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting aspen recovery and expansion. Stands with less edge:area ratio also expanded more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater changes in area and location (movement), highlighting their vulnerability to loss in the absence of disturbances that provide adequate growing space for aspen over time.

Forest inventories based on field surveys can provide quantitative measures of regeneration such as density and stocking proportion. Understanding regeneration dynamics is a key element that supports silvicultural decision-making processes in sustainable forest management. The objectives of this study were to: 1) describe historical regeneration in ponderosa pine dominated forests by species and height class, 2) find associations of regeneration with overstory, soil, and topography variables, 3) describe contemporary regeneration across various management treatments, and 4) compare differences in regeneration between historical and contemporary forests. The study area, a ponderosa pine (Pinus ponderosae Dougl. ex P. and C. Law) dominated forest, is located within the Blacks Mountain Experimental Forest (BMEF) in northeastern California, United States, which was designated as an experimental forest in 1934. We used 1935 and 2018 field surveyed regeneration data containing information about three species&mdash, ponderosa pine, incense-cedar (Calocedrus decurrens (Torr.) Florin) and white fir (Abies concolor (Grod. and Glend)&mdash, and four height classes: class 1: 0&ndash, 0.31 m, class 2: 0.31&ndash, 0.91 m, class 3: 0.91&ndash, 1.83 m, and class 4: &gt, 1.83 m and &lt, 8.9 cm diameter at breast height. We used stocking as proxy for regeneration density in this study. We found that historically, stocking in the BMEF was dominated by shade-intolerant ponderosa pine in height classes 2 and 3. Two variables&mdash, overstory basal area per hectare (m2 ha&minus, 1) and available water capacity at 150 cm, which is the amount of water that is available for plants up to a depth of 150 cm from the soil surface&mdash, were significantly associated with stocking, and a beta regression model fit was found to have a pseudo-R2 of 0.49. We identified significant differences in contemporary stocking among six management scenarios using a Kruskal&ndash, Wallis non-parametric one-way ANOVA. Control compartments had the highest stocking followed by burned compartments. In contemporary forest stands, recent treatments involving a combination of burning and thinning resulted in high stocking in height classes 2 and 3. Overall, the stocking in historical BMEF stands was higher than in contemporary stands and was dominated by ponderosa pine.

Quantifying shrub biomass can assist in natural resource management decision making. Nonlinear mixed effect models (NMEM) were developed to predict total aboveground biomass as well as biomass in leaves, 1-h, 10-h, and 100 or more hour fuel classes for seven species of shrubs common to the northeastern California. Using crown area as a predictor, an allometric (power) model was used as a base model. Coefficients varied by species, component, and by a nested combination of these random effects. The results showed that NMEM that used shrub species as random effect performed better than nonlinear fixed effect models in estimating total and component biomass in shrub species used in this study. Additionally, when fixed effect models were fitted by species, not all regression parameters were statistically significant at 0.05 level of significance. NMEM were able to account for within species variation very well. The largest variation was observed in total biomass while the smallest variation was observed in the biomass in 100 or more hour fuel class. The mean prediction bias and root mean square prediction errors for total shrub biomass was 0.0409 kg and 0.9249 kg respectively. While there were differences between the fixed effects models and mixed effects models, the mixed effects models would be preferred to the fixed effect models for future studies involving total biomass prediction for similar shrub species and regions.

Selected allometric equations and fitting strategies were evaluated for their predictive abilities for estimating above ground biomass for seven species of shrubs common to northeastern California. Size classes for woody biomass were categorized as 1-h fuels (0.1–0.6 cm), 10-h fuels (0.6–2.5 cm), 100-h fuels (2.5–7.6 cm), and 1000-h fuels (greater than 7.7 cm in diameter). Three fitting strategies were evaluated - weighted nonlinear least squares regression (WNLS), seemingly unrelated regression (SUR), and multinomial log-linear regression (MLR) - to estimate individual shrub biomass as a function of crown area. The inclusion of the shrub height as a covariate did not increase the accuracy of prediction for all species. When MLR was used, on the average, RMSE values were reduced by 23.1% for the 1-h component, by 23.9% for the 10-h component, and by 45.6% for the leaf component for serviceberry when compared to SUR. Based on the residual plots and cross-validation fit statistics, MLR is recommended for estimating AGB for seven major shrub species in California. The equation coefficients are documented for future use.

Historically, oak woodlands in western North America were maintained by frequent fire that killed competing conifers. Today, these woodlands are often in decline as competition from conifers intensifies. Among oak species affected is the ecologically important California black oak (Quercus kelloggii Newberry). Within its range, large high-severity wildfires have become more common. We examined responses of black oak to two mixed-severity wildfires 12 years apart (2000 Storrie Fire and 2012 Chips Fire reburn). Regeneration was examined in relation to fire severity as measured by the Relative differenced Normalized Burn Ratio (RdNBR). We found that the RdNBR of the Storrie Fire was a useful predictor of the RdNBR of the Chips Fire reburn, suggesting that effects of the Storrie Fire on vegetation influenced fire behavior in the Chips reburn (t 12 = 2.892, P = 0.014, n =14, r = 0.641). After experiencing a second top-kill (complete cambium mortality above the root collar) in the Chips reburn, 95 % (99 of 104) of black oak sprout clumps resprouted. Twelve years after the Storrie Fire, we found lower proportions of sprout clumps produced acorns in places where more overstory trees survived the fire (t 5 = −3.023, P = 0.029, n = 7, r = 0.804). After both fires, the crown volume of entire sprout clumps was lower in areas of higher live overstory tree basal area (Storrie Fire: t 5 = 2.527, P = 0.053, n = 7, r = 0.749; Chips reburn: t 5 = −3.597, P = 0.016, n = 7, r = 0.849). Our finding that most black oak survived successive top-kill from repeat fire suggested that repeated high-severity or mixed-severity fire is not an immediate threat to black oak presence on the landscape. Our findings also suggest that, if high-severity fire is followed by historically normal fire return intervals, rapidly regenerating black oak may be favored over conifers and recover from decline.

Controlling competing vegetation is vital for early plantation establishment and growth. Aboveground biomass (AGB) response to manual grubbing release from shrub competition was compared with no release control in a twelve-year-old ponderosa pine (Pinus ponderosa Lawson &amp, C. Lawson) plantation established after a wildfire in northeastern California. In addition, response to chemical release followed by precommercial thinning in an adjacent plantation was also examined as a growth potential from a more intensively managed regime, where shrub competition was virtually eliminated. We measured AGB in both planted trees and competing woody shrubs to partition the biomass pools in the plantation. The results showed a significant grubbing treatment effect on basal diameter (BD) at 10 cm aboveground (p = 0.02), but not on tree height (p = 0.055). Height and BD were 2.0 m and 7.4 cm in the manual release, respectively, compared to 1.7 m and 5.6 cm in the control. However, chemical release produced much greater rates of tree growth with a height of 3.6 m and BD of 14.7 cm, respectively. Tree AGB was 60% higher with the manual release of shrubs (1.2 Mg ha&minus, 1) than with control (0.7 Mg ha&minus, 1) (p &lt, 0.05). The planted area without shrub competition yielded a much higher green tree biomass (16.0 Mg ha&minus, 1). When woody shrub biomass was included, the total AGB (trees and woody shrubs) appeared slightly higher, but non-significant in the no release control (13.3 Mg ha&minus, 1) than in the manual release (11.9 Mg ha&minus, 1) (p = 0.66), the chemical release had 17.1 Mg ha&minus, 1. Clearly, shrub biomass dominated this young plantation when understory shrubs were not completely controlled. Although the manual release did increase targeted tree growth to some degree, the cost may limit this practice to a smaller scale and the remaining shrub dominance may create long-term reductions in growth and a persistent fuels problem in these fire-prone ecosystems.

Accurate estimates of growth and structural changes are key for forest management tasks such as determination of optimal rotation times, optimal rotation times, site indices and for identifying areas experiencing difficulties to regenerate. Estimation of structural changes, especially for biomass, is also key to quantify greenhouse gas (GHG) emissions/sequestration. We compared two different modeling strategies to estimate changes in V, BA and B, at three different spatial aggregation levels using auxiliary information from two light detection and ranging (LiDAR) flights. The study area is Blacks Mountains Experimental Forest, a ponderosa pine dominated forest in Northern California for which two LiDAR acquisitions separated by six years were available. Analyzed strategies consisted of (1) directly modeling the observed changes as a function of the LiDAR auxiliary information ( δ -modeling method) and (2) modeling V, BA and B at two different points in time, including a term to account for the temporal correlation, and then computing the changes as the difference between the predicted values of V, BA and B for time two and time one. We analyzed predictions and measures of uncertainty at three different level of aggregation (i.e., pixels, stands or compartments and the entire study area). Results showed that changes were very weakly correlated with the LiDAR auxiliary information. Both modeling alternatives provided similar results with a better performance of the δ -modeling for the entire study area; however, this method also showed some inconsistencies and seemed to be very prone to extrapolation problems. The y -modeling method, which seems to be less prone to extrapolation problems, allows obtaining more outputs that are flexible and can outperform the δ -modeling method at the stand level. The weak correlation between changes in structural attributes and LiDAR auxiliary information indicates that pixel-level maps have very large uncertainties and estimation of change clearly requires some degree of spatial aggregation; additionally, in similar environments, it might be necessary to increase the time lapse between LiDAR acquisitions to obtain reliable estimates of change.

A plot-based census was conducted of trees >8.9 cm in breast height diameter in a 4000 ha forest in northeastern California in 1933 and 1934, prior to any harvest activity. The trees were tallied by size class and species on contiguous plots specified to be 1.01 ha in size, although some plots had a forested area less than this specification due to natural openings in the forest. In general, variability in all metrics declined as scale increased across a range from 1 ha to 244 ha, although much of this variability was in the tails; the inner quartile range appeared to be more stable, particularly so for crown area. Although metrics were derived at a smaller scale (

The ability to estimate and monitor standing dead trees (snags) has been difficult due to their irregular and sparse distribution, often requiring intensive sampling methods to obtain statistically significant estimates. This study presents a new method for estimating and monitoring snags using neighborhood attribute filtered airborne discrete-return lidar data. The method first develops and then applies an automated filtering algorithm that utilizes three dimensional neighborhood lidar point-based intensity and density statistics to remove lidar points associated with live trees and retain lidar points associated with snags. A traditional airborne lidar individual-tree detection procedure is then applied to the snag-filtered lidar point cloud, resulting in stem map of identified snags with height estimates. The filtering algorithm was developed using training datasets comprised of four different forest types in wide range of stand conditions, and then applied to independent data to determine successful snag detection rates. Detection rates ranged from 43 to 100%, increasing as the size of snags increased. The overall detection rate for snags with DBH ≥ 25 cm was 56% (± 2.9%) with low commission error rates. The method provides the ability to estimate snag density and stem map a large proportion of snags across the landscape. The resulting information can be used to analyze the spatial distribution of snags, provide a better understanding of wildlife snag use dynamics, assess achievement of stocking standard requirements, and bring more clarity to snag stocking standards.

The Blacks Mountain Experimental Research Project created two distinct overstory structural classes (highstructural diversity [HiD]; low-structural diversity [LoD]) across 12 stands and subsequently burned half of each stand. We analyzed stand-level growth 10 years after treatment and then modeled individual tree growth to forecast stand-level growth 10 –20 years after treatment. Net stand growth was compared between treatments and with adjacent Research Natural Areas (RNAs). An analysis of variance of growth in total aboveground tree biomass suggested that growth was greatest in unburned stands (P 0.001) and in LoD stands (P 0.039). We formed iteratively annualized nonlinear models to forecast individual tree growth. Modeled diameter growth, height growth, and mortality were used exclusively for forecasting and highlighting growth and mortality trends in the data (i.e., not testing effects). Forecasts of stand board foot volume suggested that HiD and LoD stands may be no different in net growth in the second decade since treatment (P 0.355). Differences between logged and unlogged stands appeared to be much greater: we predict that RNA stands will net 136 board feet ac 1 in the forecast period, whereas HiD and LoD stands are expected to net 627 and 485 board feet of volume per acre. We also tracked the large tree (dbh 23.5 in.) component stand density index (SDI) over the measurement and forecast periods. We found that the unburned HiD treatment had a net positive effect (13% increase over 20 years) on relative density, whereas the burned HiD was not expected to change (P 0.803), and unlogged stands tended to exhibit a declining SDI over time ( 16%).

An experiment designed to evaluate the treatment effects of salvaging merchantable fire-killed trees on surface fuels and regeneration was established after a wildfire in northeastern California. The study was then monitored for 10 years. Surface fuel accumulations were rapid, corresponding with a high rate of snag decay and subsequent breakage or windthrow. Pine snags retained exhibited the fastest rates of breakage and transition to surface fuels, while white fir and incense-cedar were much more stable for the duration of this study. Natural regeneration observed following salvage was scarce and did not appear to be related to treatment. Similarly, artificial regeneration, although highly variable between treatment units, both in terms of growth and survival, was not related to salvage treatment.

We analyzed 45 years of data collected from three ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) levels-of-growing-stock installations in Oregon (OR) and northern California (CA), USA, to determine the effect of stand density regimes on stand productivity and mortality. We found that periodic annual increment (PAI) of diameter, basal area (BA), volume, and aboveground dry mass were significantly related to stand density index (SDI) and stand age at start of the period; the quadratic trends varied among sites. Precipitation departure from the normal for each period explained a significant amount of residual variation in all PAI variables except diameter. BA production did not change significantly as SDI exceeded 270 trees·ha−1 at the OR sites and 320 trees·ha−1 at the CA site. Stand productivity was the highest at Elliot Ranch (CA) and the least at Blue Mountains (OR). A similar trend held in growth efficiency under lower stand densities (SDI < 600). Most of the mortality was caused by Dendroctonus bark beetles in stands that exceeded SDI of 500 trees·ha−1. Limiting SDI was about 900 trees·ha−1, although plots at Elliot Ranch reached much higher than that. The results demonstrate that silvicultural control of stand density can be a powerful tool for reducing bark beetle caused mortality without sacrificing stand productivity. Resume : Nous avons analyse les donnees de 45 ans provenant de trois dispositifs de densite de peuplements de pin ponderosa (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) etablis en Oregon (OR) et au nord de la Californie (CA), aux Etats-Unis, dans le but de determiner l'effet du regime de densite des peuplements sur leur production et leur mortalite. Nous avons trouve que les accroissements annuels periodiques (AAP) en diametre, en surface terriere (ST), en volume et en biomasse aerienne anhydre etaient significativement relies al'indice de densite des peuplements (IDP) et al'âge du peuplement au debut de la periode; les tendances quadratiques variaient selon la station. Les ecarts de precipitation par rapport ala normale de chaque periode expliquaient une partie importante de la variation des residus de tous les AAP, al'exception de celui du diametre. La production en ST ne changeait pas de facon significative lorsque l'IDP excedait 270 arbres·ha−1 sur les stations de l'OR et 320 arbres·ha−1 sur

Large scale, high-severity fires are increasing in the western United States. Despite this trend, there have been few studies investigating post-fire tree regeneration. We established a study in the footprint of the 2000 Storrie Fire, a 23,000 ha wildfire that occurred in northern California, USA. We used a stratified sampling design to quantify post-fire vegetation dynamics across four levels of burn severity and three forest types on the Lassen National Forest nine and ten years following fire. Within each sampled stand, we recorded tree seedlings, forest overstory, shrub cover, and abiotic factors hypothesized to influence growth and establishment. Median conifer seedling densities varied substantially by burn severity: 1918 seedlings ha −1 in the Unchanged units; 4838 seedlings ha −1 in the Low-severity units; 6484 seedlings ha −1 in the Medium-severity units; and 710 seedlings ha −1 in the High-severity units. Increased burn severity was associated with greater shrub coverage: shrub cover in High-severity burns was more than three times those of lower burn severities. We calculated Shannon’s Species Diversity ( H ′) and Pielou’s Evenness ( E H ) indices to examine woody shrub and tree diversity. Abies spp. were by far the most abundant regenerating conifer species, which may be a concern for land managers; shrub cover after High-severity burns was dominated by Ceanothus spp. Although fir regeneration was prolific, the Storrie Fire generated diverse vegetative responses, potentially aiding in the reintroduction of the diverse landscape mosaic homogenized by a century of landscape-scale fire exclusion.

In a study of post-fire logging effects over an 8 year period at Blacks Mountain Experimental Forest, salvage logging was conducted at varying levels of intensity after a 2002 wildfire event. In a designed experiment, harvest prescriptions with snag retention levels ranging from 0% to 100% in 15 experimental units were installed. Observations of standing snags and surface fuels were made 2, 4, 6, and 8 years after the fire. Fire-killed snags fell rapidly over time, leading to elevated surface fuel levels in areas where no salvage logging was done. The 1000 h and larger surface fuels were strongly related with basal area retention level, with values ranging from 0–60 Mg ha-1 by year eight. However, when expressed as a percent of standing retained biomass, surface fuel accumulation was not related to treatment. In year 8, surface fuel was 81% of retained bole biomass. The retention of snags after this wildfire event provided snags for wildlife foraging and nesting habitat, however most of these snags were lost within 8 years after the fire. White fir snags were more stable than pine and appeared to be used with greater frequency than pine for cavity excavation

Forest understory communities are important components in forest ecosystems providing wildlife habitat and influencing nutrient cycling, fuel loadings, fire behavior and tree species composition over time. One of the most widely utilized understory component metrics is understory vegetation cover, often used as a measure of vegetation abundance. To date, understory vegetation cover estimation and prediction has proven to be inherently difficult using traditional explanatory variables such as: leaf area index, basal area, slope, and aspect. We introduce airborne lidar-derived metrics into the modeling framework for understory vegetation cover. A new airborne lidar metric, understory lidar cover density, created by filtering understory lidar points using intensity values increased traditional explanatory power from non-lidar understory vegetation cover estimation models (non-lidar R 2 -values: 0.2–0.45 vs. lidar R 2 -values: 0.7–0.8). Beta regression, a relatively new modeling technique for this type of data, was compared with a traditional weighted linear regression model using a leave-one-out cross‐validation procedure. Both models provided similar understory vegetation cover accuracies (± 22%) and biases (~ 0%) using 40.5 m 2 circular plots (n = 154). The method presented in this paper provides the ability to accurately obtain census understory vegetation cover information at fine spatial resolutions over a broad range of stand conditions for the interior ponderosa pine forest type. Additional model enhancement and the extension of the method into other forest types warrant further investigation.

The purpose of this article was to determine whether natural regeneration or planted seedlings should be used in group-selection openings. The answer depends on the survival and growth rate of both types of seedlings, and that could depend on the size of the openings and the effect of trees on their edge. In this side-by-side study, the natural pine seedlings originated from the 1988 seed crop and the 1–0 nursery-grown seedlings were outplanted in spring 1989. Openings ranged from 0.01 to 0.65 ha. The plant community consisted of many species of shrubs, forbs, and grasses with manzanita having the highest density and greatest development. After 9 years, manzanita had an average density of 13,870 plants/ha, 2,050 m2/ha of foliar cover, and was 125 cm tall. From 1990 to 1997, planted ponderosa pine seedlings were taller (P < 0.05) than natural seedlings, and from 1995 to 1997, mean stem diameter at 30 cm of planted seedlings was larger than natural counterparts (P < 0.05). Development for 1 year in the nursery apparently gave the planted seedlings a growth advantage over the natural seedlings. For natural seedlings, distance from opening edge had little effect on pine height or diameter growth regardless of opening size. Planted seedlings, however, appeared to increase in height and diameter growth with both opening size and distance from edge.

Ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) stands with late-seral features are found infre- quently, owing to past management activities throughout western North America. Thus, management objectives often focus on maintaining existing late-seral stands. Observations over a 65 year period of stands with no past history of harvest showed substantial ingrowth in the smaller diameter classes and elevated rates of mortality among the largest mature trees in the stand. Adjacent stands, with combinations of thinning and prescribed fire, had far fewer high-risk mature trees and generally lower rates of mortality after treatment. Forecasts using individual-tree diameter growth and mortality models suggest that observed declines in these stands with remaining old trees and a dense understory will continue in the absence of any treatment. Increased vigor in thinned stands appeared to be offset by an increase in mortality of large trees when thinning was followed by prescribed fire. Resume´ : Partout dans l'ouest de l'Amerique du Nord, il est peu frequent de rencontrer des peuplements de pin ponderosa (Pinus ponderosa Dougl. ex P. & C. Laws.) aux derniers stades de succession ecologique acause du type d'amenagement pratiquedans le passe´. Par consequent, les objectifs d'amenagement sont souvent axes sur le maintien des peuplements aux derniers stades de succession ecologique qui existent encore. Des observations s'etalant sur une periode de plus de 65 ans dans des peuplements qui n'ont pas eterecoltes dans le passemontrent que le recrutement est elevedans les classes inferieures de diametre et que le taux de mortaliteest eleveparmi les plus gros arbres matures. Il y a beaucoup moins d'arbres matures ahaut risque et le taux de mortaliteest generalement plus faible dans les peuplements adjacents apres qu'ils aient etesoumis adiverses combinaisons d'eclaircie et de brulage dirige´. Des previsions basees sur la croissance en diametre des arbres et des modeles de mortaliteindiquent que le declin va se poursuivre en l'absence de traitements dans les peuplements oude vieux arbres persistent et dont le sous-etage est dense. Dans les peuplements eclaircis, l'augmen- tation de la vigueur semble contrebalancee par un accroissement de la mortalitechez les gros arbres lorsque l'eclaircie est suivie d'un brulage dirige´. (Traduit par la Redaction)

A common, but largely untested, strategy for maintaining forest biodiversity is to enhance stand structural complexity. A silvicultural experiment was implemented from 1996 to 1998 at Blacks Mountain Experimental Forest, California, to test the efficacy of two levels of structural diversity (high versus low) and two levels of prescribed underburning (burn versus no burn) for maintaining or restoring biodiversity. Small mammals were trapped and tagged in experimental units for 2 noncontiguous weeks in fall 2003 and 2004. Total number of captures and number of captured individuals varied by year (P < 0.002). No treatment effects were detected for all species lumped together or for the three most frequent species analyzed separately ( Tamias amoenus J.A. Allen, 1890, Peromyscus maniculatus (Wagner, 1845), and Spermophilus lateralis (Say, 1823)), with the exception that T. amoenus was captured more often in burned units in 2004 (P = 0.004 for year × burn interaction). Mixed-effects regression models indicated that the number of captures and captured individuals of T. amoenus and P. maniculatus decreased with increasing residual basal area of overstory trees, but opposite results were obtained for S. lateralis. After accounting for residual stand density differences, T. amoenus was captured more frequently in units of low structural diversity and S. lateralis in units of high structural diversity.

A large-scale interior ponderosa pine ( Pinus ponderosa Dougl. ex P. & C. Laws.) study was conducted at the Blacks Mountain Experimental Forest in northeastern California. The primary purpose of the study was to determine the influence of structural diversity on the dynamics of interior pine forests at the landscape scale. High structural diversity (HiD) and low structural diversity (LoD) treatments were created with mechanical thinning on 12 main plots. Each plot was then split in half with one-half treated with prescribed fire. During the 5 year period after the treatments, the LoD treatments showed slightly higher periodic annual increments for basal area (BA) and significantly higher diameter increments than did the HiD treatments, although HiD carried twice as much BA as LoD did immediately after the treatments. Prescribed fire did not affect growth, but killed and (or) weakened some trees. No interaction between treatments was found for any variable. Stand density was reduced from the stands before treatments, but species composition did not change. Old dominant trees still grew and large snags were stable during the 5 year period. Treatments had minor impacts on shrub cover and numbers. These results suggest that ponderosa pine forest can be silviculturally treated to improve stand growth and health without sacrificing understory shrub diversity.

This work presents the results from the initial model development of a simulator to predict vegetation dynamics in young plantations growing in a Mediterranean environment. The simulator can predict growth dynamics for coniferous crop trees as well as competing hardwoods and shrubs. Model specification included conifer, shrub, and hardwood competition expressed at the plot-level. The system employs water-holding capacity as an indicator of productivity. Growth data were obtained from 109 plantations, ranging in age from 3 to 25, in southern Oregon and northern California. Douglas-fir (Pseudotsuga menziesii Mirb. Franco), the most common conifer species, was observed in 80 of the sampled stands. These observations were used for model development of the primary driving functions, which forecast 2-year basal diameter increment, height increment, and crown width increment. Parameters for all three dynamic expressions for growth were estimated using weighted, nonlinear three-stage least squares. This estimation method provided a predictive model with slight improvements in standard errors for two of the three equations (an average of 3% for height and diameter growth) and no improvement for crown width, when compared with two-stage least squares. The system includes competition from shrubs and hardwoods in predictions of height growth, diameter growth and crown width increment. This allows individual-tree/distance-independent simulator architecture to be extended to young plantations in southern Oregon and northern California.

Awildfire at Blacks Mountain Experimental Forest provided the opportunity to observe fire severity at the point of transition between treated and untreated stands. At several locations in the forest, the wildfire burned from a dense stand of largely pole-size trees, into an area that had been recently treated with combinations of thinning and prescribed fire. These treatment areas are part of a large-scale experiment designed to evaluate stand structure, grazing and prescribed fire in an interior ponderosa pine (Pinus ponderosa P.&C. Lawson) forest. Tree survival and damage were sampled on strip plots arranged perpendicular to the treatment plot boundary. Logistic regression was used to develop a model relating the probability of initial mortality (within 9 months after the fire) to distance from treatment plot boundary, and treatment history (thinning and prescribed fire). Fire behavior simulation was used to evaluate the effectiveness of the pre-fire stand treatments. The model shows that probability of survival was greatest in those areas that had both thinning and prescribed fire prior to the wildfire event. Survival was near zero for the untreated areas. Survival in thinned-only areas was greater than untreated areas but substantially less than the areas with both treatments.

Six white fir trials were established during the last half-century to develop guidelines for managing the existing natural stands across northeastern California. We analyzed data collected from these trials at about 5-year intervals since their installation. Because these trials were independent of each other, the design and treatments varied among the sites. Targeted density treatments were selected based on 40, 55, and 70% of normal basal area from early yield tables at three of the sites. More density treatments were included at the remaining three sites. We found a significant response in growth to different stand densities regardless of site qualities, ages, and stand histories. Periodic annual increment for basal area and volume varied significantly by periods for all sites except the basal area at one site. Regardless of site quality, thinning from below leaving about 64% of the original measure of basal area did not significantly reduce productivity. If performed early in the life of the stand, such a thinning will reduce the accumulation of flammable materials due to natural self-thinning. A logistic function of periodic annual increment for basal area to relative stand density fits the data well and can be a useful tool for forest manager.

This paper describes the development of growth equations for competing vegetation in young conifer plantations, consistent with an individual-tree growth model architecture. Response variables were height increment, basal diameter increment, and change in crown width for a 2-year growth interval. The results for three common competing shrub and three competing hardwood species are presented. Fit statistics for hardwoods were generally much better than those obtained for shrub species. Crown width growth equations generally had very poor fit statistics. Static crown equations also relate crown area to plant height. The equations were developed for use in an individual-tree plant growth model for young plantations.

We evaluated the relationship between crown cover measured with a vertical sight tube and stand basal area per acre in treated (thinned, burned, and thinned and burned) and untreated interior ponderosa pine (Pinus ponderosa P. & C. Lawson) stands in northeastern California. Crown cover was significantly related to basal area at the plot level and stand level. In addition, the relationship was not affected by two extremely different thinning regimes. However, the predicted crown cover was generally lower, for a given level of basal area, in a recently thinned stand than in a stand that had not been recently thinned. Prescribed fire had no detectable effect on the relationship. The maximum measured value of stand level crown cover in untreated stands in this study was about 60 percent. West. J. Appl. For. 20(4): 240–246.

The US Department of Agriculture (USDA) Forest Service Blacks Mountain Experimental Forest is a 4,000 ha, pine-dominated tract in northeastern California, in the Lassen National Forest. Between 1934 and 1960, research at Blacks Mountain focused on various methods of harvest and bark beetle activity. These studies demonstrated the effectiveness of harvesting on increasing tree growth and reducing widespread mortality from bark beetles.

Three solutions are presented for estimating stems per acre when trees are tallied by diameter class with horizontal point sampling. The first solution is based on the arithmetic mean of the diameter-class limits. The second is based on the geometric mean of the diameter-class limits and is unbiased for uniform within-class diameter distributions. The third is a harmonic mean solution; it is derived from the ratio of the geometric mean squared and the arithmetic mean. If the within-class distribution is linear, then the solution based on the geometric mean is preferable. Any of these solutions may be adequate provided diameter-class widths are minimized, particularly for small trees. The geometric-mean solution is the recommended solution in instances where uniformity can be assumed within diameter classes. Observed frequencies in two stands, however, provided inconsistent results. In estimating tree frequency, errors resulting from grouping become smaller as tree diameter increases. For large trees, estimation of frequency can be obtained with much wider diameter limits than with small trees for a fixed level of grouping error. Rather than fixing diameter-class width, it may be advantageous to consider a narrower class width or exact measurement for trees in smaller diameter classes. West. J. Appl. For. 12(4):108-114.

Forest managers need accurate biomass equations to plan thinning for fuel reduction or energy production. Estimates of carbon sequestration also rely upon such equations. The current allometric equations for ponderosa pine (Pinus ponderosa) commonly employed for California forests were developed elsewhere, and are often applied without consideration potential for spatial or temporal variability. Individual-tree aboveground biomass allometric equations are presented from an analysis of 79 felled trees from four separate management units at Blacks Mountain Experimental Forest: one unthinned and three separate thinned units. A simultaneous set of allometric equations for foliage, branch and bole biomass were developed as well as branch-level equations for wood and foliage. Foliage biomass relationships varied substantially between units while branch and bole biomass estimates were more stable across a range of stand conditions. Trees of a given breast height diameter and crown ratio in thinned stands had more foliage biomass, but slightly less branch biomass than those in an unthinned stand. The observed variability in biomass relationships within Blacks Mountain Experimental Forest suggests that users should consider how well the data used to develop a selected model relate to the conditions in any given application.

In the past, researchers from the Pacific Southwest Research Station (PSW) undertook forest growth studies to evaluate how best to manage timber resources. However, historical and future data collected at PSW growth plots also have the potential to increase our understanding of the ecological processes occurring in our forests and shed light on national issues of importance. This report provides information on the history, geography, plant species studied, installation, and measurement interval of each plot along with a list of publications arising from data gathered at these plots. This will enable current and future researchers to reidentify these plots and continue research at these locations.

In 2008, Forest Service Research and Development celebrated the Centennial Anniversary of these Experimental Forests and Ranges. This publication celebrates the many scientists who over the course of decades conducted the long-term studies that began and are continuing to shed light on important natural resource issues. Story suggestions were solicited from the Experimental Forest and Range Working Group and were selected to demonstrate the array of research issues being addressed on these living laboratories. Gathering a wealth of information from her interviews with scientists, Gail Wells proceeded to write these “…wonderful success stories from 100 years of research.” Studies established decades ago on many of these sites are still going strong. Experimental forests and ranges provide a valuable, long-term stream of information about the land and its resources. Over the years, researchers have built an impressive body of science to support good land management and further understanding of natural processes. Their research sheds light on many important questions. These experimental forests serve as living laboratories that help us connect the future to the past.

Six modeles qui decomposent la croissance du peuplement et deux modeles de croissance d'arbre sont evalues pour leur capacite a predire l'accroissement quinquennal en surface terriere des peuplements de Douglas taxifolie (Pseudotsuga menziesii (Mirb.) Franco) dans l'Ouest de l'Oregon. Les modeles d'arbre predisent directement l'accroissement de l'arbre en diametre alors que les modeles de croissance du peuplement predisent directement l'accroissement brut du peuplement en surface terrie et len accriametrarbre llemen de prsive et active sont evalues pour le double niveau de l'arbre et du peuplement. En general, l'approche par arbre est superieure a celle du peuplement pour predire la croissance de l'arbre et du peuplement. Neanmoins, cette superiorite s'attenue lorsque la longueur relative du houppier est eliminee des modeles d'arbre. Ce resultat suggere que certaines disparites entre les deux approches sont dues a la presence de la longueur relative du houppier dans les modeles d'arbre a recomposition passive. L'approche de decomposition additive semble la plus adequate pour les peuplements juveniles (âges de moins de 50 ans). L'hypothese de linearite requise par cette approche de decomposition ne semble pas aussi valable dans les peuplements plus âges avec des arbres plus gros. Les deux modeles de peuplement analyses qui font appel a la croissance brute sont inferieurs au modele d'arbre pour predire la croissance brute en surface terriere sur une periode de temps.

Using a sample of 866 Douglas-firs, a predictive model is presented which expresses 5-year height growth as a nonlinear function of potential height growth, crown ratio and height of the subject tree divided by dominant stand height. The adjusted coefficient of multiple determination ( R 2 ) of this model exceeded 0.70, which was superior to four alternative models derived from previous studies. The final model also fit well to the data from each crown class. A number of different techniques for expressing competitive effects were also studied. The most influential variables in the height growth analysis were related to tree position, crown competition factor in larger trees and height divided by dominant stand height. Crown ratio, considered an index of tree vigor, was statistically significant but only accounted for about 8% of the residual variation in height growth.